The 1GM10

Since I've had this engine for ten years in the boat - I thought I would do a few pages on its servicing peculiarities. Altough I did quite a lot of stuff on the restoration pages - the actual things that start to go amiss while in use are slightly different.

If you want a good parts source - register with RibMarineParts - and you can access the EPC ( electronic parts catalogue ) that all the dealers use. If using IE and download Isoview - you can buy online and view the part drawings. Very useful site.- | see here |

Very interesting to see what is available as parts. Don't take it for gosple though. Oversized pistons are not on there - but they ARE available for the 1gm10 - just are not listed in this elecronic catalogue ?

That said - I have found French Marine - to be the best to deal with on parts ( genuine ) Watch out for sites saying - 'replaces Yanmar**** ' - these are not yanmar parts.

If I can see a maker on the part - ie water pump bearings were Koyo 6000 - then ok go buy it from an industrial source for far cheaper - and smaller gaskets etc hardly matter. But head gasket - non genuine, forget it ! - thats my feeling anyway.

I know Yanmar do not make this stuff - but they source good parts.

There is some absolute crap around. Buy aftermarket - very cheap- at your peril. I recently heard of someone who was trying to torque seagull head bolts - Stainless - ebay - BSF - they were stretching at only 40 ft lb !

Shop around - most full gasket sets are asking £75 for non genuine - yet I found a place selling Genuine full gasket set for just £85.

Something else to sort out if I ever consider a rebuild. Some rebuild thoughts | here |

Piston and Rings

As stated above - there are oversized piston and rings available for the 1gm10 - despite what you read eleswhere. | here |

The three exposed oil pipes.

These are two at the lower front - sort of running from the oil filter, across the drain plug and past the water pump - one long one and one very short thing. Big banjo head bolts 19mm bolts head. Fit new copper washers. Old ones can be anealed ( softened) by heating to bright cherry - then cooling, either quenching in water or left to cool. But for important oil pipes buy new ones. Good quality ones are a nice deep copper colour - 100% copper.

They can corrrode badly if much water is flying about down there, It shouldn't be - but a slightly leaking water pump will toast them pretty soon.

My stuffing box does not leak much at all - so if I see any much water in the engine bilge - more than 1/2 a teacup - I'm looking for where its coming from.

When I got Lena she had a tide mark all around the engine bilge about five inches deep ! Someone had been running with loads of water in the bulge there. As soon as I fired up the engine for real on the water - the pump was shooting it out at the front seal. I think they had been running like this and just letting the bilge pump pump it out. Both lower pipes were severely corroded.

They are very expensive pipes from Yanmar. But you can get standard oil/hydraulic type banjo ended hoses to fit easily - and much cheaper Better too - as they can't rust.

The other is not so obvious but worth looking at. It connects to the back of the head, just by the air filter mount - and runs down the engine casing, around the starter motor mount bolts to a banjo lower down. Take off the starter and the air filter housing and mounting plate - you can then remove it easily ( no need to drain oil ) This pipe is smaller than the others ( it feeds the rocker gear ) - and maybe a hose type would not run exactly the same route. Check it.

Water pump

Ha - now this can be a pig if you go about it the wrong way.

It sits just next to the lower pulley wheel. It is bolted to the timing case with three bolts - no gasket, has a rubber o ring on it. It backs into a slot at the end of the oil pump shaft.

Once it is out - its easy to put your finger in the hole and feel whether the slot is level/upright etc.

When you replace it - make sure the lug on the pump and the slot on the shaft are similar - ie both LEVEL and it slips in easily. Its quite a loose fit. No problem - so long as you know how its mating up.

Two main things to go wrong with the water pump. Impeller - and seals on the front shaft leaking water.

Impellor should last a season - and change it with the water pump out. The paper gasket is expensive for what it is - but treat it carefully or renew it. The cap is too tight I think without it. Its also a very subtle 'cam shape' ie - not quite round - so make sure it sits on the pump chamber the right way.

They say do not use grease on the impellor. One source says Glycerine - one says washing up soap.

Silicone grease would not harm it - but I think they do not want 'sticky' - ie its raw water being pumped and it has grit etc in it. What does wear quite a bit is the back of the front cover. If excessive you really should get a new cover plate - about £12 - I think. They are dead flat - so you coulld maybe reverse them, cleaning off the paint. Its solid bronze. If the holes are not exactly equidistant though - it may not work, or may be 'awkward' to refit the small cap screws.

The impellor just presses on the shaft. If it 'really' won't come off - remove the pump and you can remove the circlip at the rear - then the bearings and the shaft will knock backwards out of the housing. After that - you may find your seals start leaking ! They needed changing anyway if they do.

The water pump rotates ANTI clockwise as looking from the front - so the impellor lugs all bend to the right when fitted. The engine crank turns CLOCKWISE - from the front, so the camshaft and the oil pump shaft rotate the opposite way (gear driven) The older belt driven pump went the same way as the engine crank.

To remove it.

Take off all the hoses - check them anyway. Also check for scale build up in the outlet pipes( they are quite narrow bore internally )

Be careful with the bolt heads - they can be rusty down there. You do not want to round one over ! There are three bolts equally spaced. The two to the right are ok - but the one to the left is tucked a bit behind the pulley flange. There's plenty of space but difficult to see. With my front panel removed I can just see the bolt head - but it will be more by feel than sight. Try to take them out - and replace them with new stainless bolts of the same size if you want to do yourself a favour ! The originals are flange bolts, which are prone to running round if you attack them a little hamfisted. Its dark and awkward down there !

It is so much easier to work on the impellor with the pump off. Once removed once - new bolts and well copper greased, no problem in future.

I think I recorded the saga on one of the sailing pages. Ilfracombe, 2am, trying to change the impellor. Rounded over bolt on the pump housing. Had to fight to change it in situ. Ended up 'inventing' the method with the ring of plastic tube - much swearing, and trying to see the cover plate using the back of a spoon as a mirror !

Once back on the mooring - with major access panels removed, I had to resort to filing both flats off the bolt head to take smaller spanner. It was 10, tried nine would not hold - filed it to 8mm, hammered on spanner, just got it. Very awkward - one bolt I was glad to see out. Be careful with these fixings where access is poor. Renew them if slightly marred - do yourself some favours. We are supposed to be enjoing this stuff !!!


To strip the pump you just remove the large circlip and the two bearings and the shaft slides out.

The seals really need replacing once a year ( read on ) They are not expensive from Yanmar - about £6 and £8 each - or you can get the same seals from somewhere like Simply Bearings for a few pounds. The types and sizes I have listed | here |

Similarly with the bearings - Simply Bearings sell the same make ( toyo 6000 ) @ £2 each !

What genarally happens is once the seals actually start to leak - often un-noticed for a while - then with all the grit and crud in the water - the shaft starts getting marked up. A new pump is now £240 - and just a new shaft is £80 - not cheap so look after it. Best way to do that is change out the seals every year. These pumps take a bashing.

Once the shaft is slid out - you can knock out the seals from the Impellor side. You have to change both as you have to knock out the rear first - and whacking them out wrecks them. Clean up the housing and press them back in. Just need a light tap with a suitable sized socket or similar. Easy.

Check the way they go around. If you have the manual, you can see from the engineering drawings. The open lip + spring goes to impellor - same with the rear, lip to engine. Flat faces, face each other together in the middle gap. This middle gap - with its drain holes - is where water leaks from if your front seal goes.

With new seals even a visibly marked shaft will not leak. But for how long - who knows. If your shaft is clean and sweet - keep it that way by changing the seals every year. Change the impellor, strip the pump - new seals.

To press the bearings is not hard. BUT - between them is a small ( hidden) 10mm circlip in a groove. Best to knock this out sideways with a piece of thin metal ( about 1mm max ) Find the open jaw - and press it out from between the two bearings with the metal pressed sideways in a vice.

Then - you can press the bearings off with a suitable tube/socket - either up or down the shaft. I did mine in a vice - with some old seagull bronze bushes. Just get a new circlip - then press them back on, and press them tight together either side of the circlip. Obviously - do not damage the end lug or the impellor end machined flat. Hardly need changing though - maybe once in the life of an engine. But - if you are fitting a new shaft - then press on new bearings anyways.

Worn bearings will wear out seals more often as well.

If you ever have to fit an impellor in situ - with the pump in try this. Get a short piece of plastic tube - about an inch long and the same diam as the housing in the pump. Get the cam on the shaft end 'at the top'. Then fit the impellor into the tube, flaps bent the right way, cam flat at the top, lubricated. You can then locate the tube against the front casing - and push the impellor onto the shaft and the flaps slide straight in. Have fun...!

Its fiddly with the pump on the bench !


I had trouble with mine - scuffing up the belt to a load of black dust. Someone in Cardiff yacht club said check the pulleys are in line. You can get shims for the lower pully but to do that you have to have access to pull it !

I see my pulley has four m8 threaded holes through it - at 90 deg spacings. So would take a simple puller maybe. Also note - these holes are vertical/horizontal at TDC - useful for reference if you mark the top one.

Actually - what was amiss with mine was the bolt was wrong.The alternator was pulling sideways out of line. It was a 7mm 120 - and should be 8mm 120. This bolt is avalable as a Yanmar part no - cheap too - about £ 2. Any 120 M8 bolt would do - part threaded.

Actually, a 130mm M8 bolt with 10mm cut off works better - as there is solid bar under part of the inner alternator lug - as opposed to thread.

The connections at the back are fairly straight foward - if difficult to see. There is a 2 pin push on plastic plug - only goes on one way. The pos 12v is a stud - and the neg feed is a Bolt that comes out - so watch it does not fall. My Pos had two wire attached - so when removed - link them together with an electrical tie - so you don't forget one on the way back.

To remove the belt

Loosen the top bolt - m8 x 120mm . This is a straight through bolt - you need to hold both ends. Then loosen the lower arm bolt.

This bolt on the lower adjuster bracket - which can be difficult to see - is through a slot in the adjuster arm. This adjuster arm connects to the engine block low down on the front. The alternator lug is threaded ! - the outer nut is a lock nut.

So - determine which side is the bolt head and which is the 'nut'. Once the nut is loose - you still have to loosen the Bolt - then it will slide to get the belt off. You wont move the bolt - until the nut is loose !

To remove completely

Remove the lower bolt entirely. Remove the leads. Support the unit - its heavy - and remove the top through bolt, Wiggle it out !

Whipping off the alternator makes for good access to things at times. I like to be able to have these things off easily. You get used to where the bolts are, the spanner sizes and their foibles - so when you may have to do it in less than ideal circumstances, its easier.

I know nothing of it internally - I'm not too up on electronics !

Lift pump

Easy to overlook - but I think seldom seem to give problems.

Two bolts to remove - a bit fiddly, small and easily dropped. (easier with a small socket and a bit of grease) I've never had a problem with replacing it. Just insert it fairly level and without any force. The nuts sometimes need to pull the unit in snug if the cam was up a bit - pressing on the arm. A new washer is hardly needed - so long as the old one is intact.

You can test it in two ways (as spec in the manual )

Firstly - It should pull fuel up a tube on the inlet side to a head of 0.8m - operating the cam.

Secondly - with both pipes off - submerge it in deisel, block the outlet and pump the lever. There should be no bubbles escaping ( this shows the diaphram is seating ok at the cover) joint. ie - the body is not leaking air.

They are fairly cheap new £90 - and now no parts available for internals.

Something to check if things are amiss.

You can take off the cover. Check the diaphram obviously for breaks or cracks. In the bottom housing are two non return vlaves - which are held in place with a small screw and a plate. Take them out and take them apart - check for crap and bits a debris blocking the seat/rubbers etc. They are both the same - but one goes in upside down to the other, to become flow and non return etc. They come apart and clean easily. If there are bits in there it will not suck. So - if you do give the pump a test - use 'clean' diesel !!!

The Yanmar Lift Pump specs - quote Suction Pressure 60mm HG ( 2.362 in HG roughly )

I checked my Cav primer bulb - Its pulling approx 0.5 in HG ( max approx ) Hard to be precise as its barely on the scale of 0 - 30 in !

By comparison - the Racor 200 series has a flow restriction of 0.254 in HG.

The Racor 500 turbine ( no primer, 10 micron filter ) - and the 400 series (with primer bulb) are 0.509 in HG approx each.

Fine fuel filter

Can be a sod if its tight - if so just take it off ! Its only two bolts - and split the banjos.

Bear in mind - the outlet banjo and pipe needs to stay VERY CLEAN. Its beyond the fine filter - so will pass any crap to the injector pump ! Its the one which is the hard pipe. Inlet is the braided one.

Clean of and loosen the outlet banjo - leave hand tight.

Remove the braided inlet banjo lower connection - leave the top on. Then the two top mounting bolts. As soon as you remove the outlet banjo - cover the pipe end with something clean. Wash and clean the outlet banjo bolt before refitting and fit new copper washers. (12mm )

You can now work on and clean out the entire filter housing. You should use a new o ring seal. Yes - I know they are extra to the cost of the filter ! only a few quid. You can get aftermarket filters complete with new o ring from places like SSL diesel parts ( not hugely cheaper though ) They also have good price for aftermarket oil filters ( Baldwin )

Make sure, if you take it right off, that the head section gets thoroughly cleaned - ie beyond the filter - well washed through. NO BITS should be getting into that injector pump.

The copper washers are 12mm. Either fit new ones ( best) or heat the old to BRIGHT cherry and quench in water. This anneals and softens them again ( apparently it matters little if you let them cool - or qench in water ) Make sure if using old ones they have no bad digs on dents. New are cheap enough - but not always to hand !

You can easily get Dowty type aluminium/nitrile seals - both in metric 12mm - and, if you search a bit in actual Imperial - ie 1/2", not 1/2 BSP - for CAV filter connections. I see the Yanmar washer on the bleed screw on the injector pump is a 6mm dowty.

They do say dowty type washers should only be used where there is a 'thread gap' at the base of the fitting ?

A 10 dowty fits the bleed screw on the CAV quite well - which appears to be 3/8 unf - or 3/8 something ?

If you buy new washers get them from somewhere decent. HAlfrauds packs are crap copper ( like you get with cheap water pipe) whereas good copper washers are a deep copper colour.

When in situ - even with the sealing ring off - the bowl will not remove until the filter is off the spigot - and there is not much space for fat fingers, to pull it off. Can be awkward if its a tight fit. Poor design - most engines now are spin on fuel filters.

The bleed screw is not a normal type bleed screw - ie tapered seat. Its just a screw with a washer, which can go bad if overtightened. The screw as a slot ground in it. Why not a proper bleed screw as on brake line ? New ones are available as a part no. For some reason the filter one is nylon - and the injector one is rubber ? Same screws - same size, same function ?

Also - be very careful if you take one right out. The slot in the thread is sharp and the housing is alloy - VERY easy to cross thread. I bought new bleed screws, as the heads were getting a little rubbed up.

Bleeding ( useless ) :-)

One thing here to get sorted first - and that is what and where is your pre-filter unit, if you have one. ?

The head of a cav type prefilter has a bleed screw - but - if this head is higher than the level of fuel in your tank - then sucking from the lift pump you can't open it. Also - if your tank is top feed ( like Vetus polythene ) - then the same applies. You cannot 'suck' fuel from the lift pump primer, from the tank with an open vent on the CAV.

For a tank below the CAV - or a top feed tank, a primer bulb helps greatly.

ASAP ( and I see Norris Marine ) sell primer bulbs designed to fit to the inlet or outlet of CAV filter units. They work very well - and are very cheap to buy. You can get Cav filters with a bulb built in - and some Racor filter units have them.

Using the lift pump to fill the CAV filter from emtpy is difficult. You can fill the unit using the top plug and a small funnel. I used to fill it by taking the hose off the lift pump - and press in a rubber type outboard primer bulb and suck it through until I'm pumping fuel out - then whip it onto the lift pump. Then use the lift pump lever from there.

Once the line is filled to the CAV - if the filter unit is below the fuel level, then one should be able to bleed the top of the cav with the screw. The fuel should siphon down to it. They can be a problem - prefilters.

A primer bulb avoids all this. It will fill the cav - pressurise the line all the way through to the injector pump bleed screw. All I don't really like is there is some suction needed to pull fuel through the primer non return - so I wonder about strain on the lift pump ?

The suction for the lift pump is specified - so I suppose I could test the fuel line with my Mityvac gauge and see what suction it is needing to pull through the primer bulb. I can suck through it easily - so its not much.

( I have now checked this and its approx 0.5 in HG - the Yanmar spec for its suction pressure is 2.362 in HG )

These primer bulbs are metal connections - ie banjo and cav style washers.( no hose clips )

Once the fuel is through to the lift pump - just open the screw ( cross head) on the top of the filter housing - and pump the primer lever until clear fuel flows. The primer lever will not feel right if the engine cam is right on the top of its profile - turn it a bit and the lever will work ok.

Pump until clear fuel runs out.

Do the same with the bleed screw on the Injector pump front fuel inlet pipe nut ( cross head screw in centre of the banjo bolt )

Use a spanner on these screws - not a pozi ( they are hex head )

If you have a primer bulb - use that, not the lift pump. You will push past the lift pump seals no problem. You dont need to use the lift pump arm at all with a primer bulb.

Then crack the nut a half turn or so at the injector - give it half throttle, lift the decompression lever and hold it up ( tie it up - easier ) and turn over the engine on the starter about ten to fifteen times. Put a wad of cloth or a pad under the injector nut - so you can see that diesel is getting out there. Saves mess too.

Turn off the water intake while doing this ( but if the engine was drained - fill it beforehand to get some water in the impellor and pump)

Go to normal starting set up and she should fire up.

If major stuff has been off - ie main injector pipe, injector pump - it may fire and splutter to a stop agian. Just repeat the injector line bleed. If it does not start in two turns or so - bleed it again right through. Its quite quick to bleed these things.

Check the banjos for tight every now and again - lift pump, fuel filter and injector pump. They are all on a vibrating engine and can work loose.

Only known to Yanmar - they make their inlet spigot on the lift pump banjo 7mm !

Its almost impossible to get 7mm hose ( it is available in the cotton braided type fuel hose see SSL dieselparts )

8mm just is a bit loose. There is no type of 8mm banjo unit that has 8mm spigot. You can get an 8mm banjo to a 6mm spigot - and can get a 6mm spigot to a CAV unf 1/2" fitting - so one could use 6mm hose to the lift pump ( maybe too small ? )

I have at present gone with 7.5mm cotton braided fuel hose - which will go onto an 8mm cav spigot - and is better on the lift pump. But this stuff is not the best fuel hose out there.

Starter motor

Know how to take this off - is very easy but can be awkward to get the bolts loose if its not been off for a while. Its impotant - it does not just start the engine - it has the main high amp battery connectons attached.

If you ever have the alternator off, then take the starter off as well.

You can then decide how is best to attach the earth lead ( mine is to the upper starter motor mount bolt)

Make sure the Pos leads are good and sound and clean. Fit locking washers. Make sure the earth lead mates to clean metal - fit a good split locking washer. The easist way to do the bolts is from the engine front - with a socket and an extension bar. Thats ok - if you keep that stuff on the boat at all times.

I carry a tool kit which is not very big - but was put together when doing up the boat. So everything I replaced - if I need something it went in the tool kit.

Sometimes though, getting something off the first time, or when bolt heads are gruffy - you need something more. Why these things must come off - so you know they are freed up - and any bad bolts can be replaced - or stupid cross head screws in daft places ( temp sender unit wire) can be changed to a hex head bolt !

I've just had the starter off - to treat and spray up the engine casing - and to check injector timing. I got it ok with a ring spanner - both bolts. But I have good access to the right engine side ( removable panel ) Its easier with an extension bar and socket.

It gives great access to the right side of the engine - zinc anode etc - and for a clean up. Also to check the oil pipe from the rocker ( above)


Hiding behind the alternator - difficult to see. ( why couldn't they have put this somewhere else ! )

It is a flat plate - same gasket as the thermostat - two bolts. On the back is a zinc anode. It has its own captive stud through the zinc - and screws into the plate with a rubber washer under it. The outside nut then locks it. Removing the outside nut will not loosen the zinc - it has to screw off the plate ! ( duhh - spent a while fighting with that one - before deciding to go buy the workshop manual.)

Easy to do with some access - again a job to do with Alt off. Seal it well with red hermetite and a new paper gasket ( same as thermostat gasket ). If the zinc is half gone scrap it. They are quite cheap. A new one is about 25mm long and 20mm thick.


Strange how people don't seem to understand thermostats - I read all sorts of crap about them.

If you have any doubts about a thermostat not working right - in an emergency take it out, better than leaving it in and it sticking shut.

So - what does it do ? Basically, it stops the raw water flow from going through the block when the engine water temp is under 42 deg C. Once the water heats up past there - it opens, allowing water to flow through the engine block.

I suppose - if the water was freezing cold and the engine lightly loaded, it may partially close while the engine was operational - if it was running too cold. Raw water can be very cold.

Generally - in summer and warm climes, the thermostat is going to open and stay open at normal running temps.

What it cannot do is cool an engine. It can only make the engine temp warmer by blocking the flow through it.

Its sole function is to stop the engine running cold.

The water after the pump splits two ways - this is at the T-junction where the hoses connect above the water pump. One is in to engine block and the other up to the thermostat housing - via the lower hose. The thermostat housing is also where water leaves the engine to go on to exhaust ( when the thermostat is open )

So - there are two routes for the water after the pump - either into the engine block or up to the thermostat housing.

When you fill an engine - cold, the thermostat is closed. Water can flow up the outer hose, through the housing and out the exhaust. Water cannot flow out of the top of the engine - as the thermostat closes it off. BUT - there is a small hole in the thermostat ( 2mm ) this small vent does allow the engine block and head to fill with water ( vents off the air ) - even with the thermostat closed. Make sure that little hole is clear.

So - when you start the engine - the water in the block and head is static - it can't flow out of the thermostat housing because the thermo is closed, blocking any major flow. The water being pumped flows up to the housing, past the thermostat and out to exhaust.

The thermo opens at 42 deg C - and should be fully open at 52 deg C.

So - the engine just heats up stationary water, raw water intake is going straight out of the exhaust - until that water reaches 42 deg C. Then the thermo opens. Water can now start flowing out of the thermo housing, setting up a flow through the engine and head. When open, it closes off the flow from the lower hose. As it partly opens - it allows more or less flow through the block, diverting it through the bypass hose. This would only happen though - if the engine was running at UNDER 52 deg C - which is to be blunt, very cool.

So - if its sticks shut - you will fry the engine.

If it sticks open - thats normal hot running conditions - fully open.

There is a big difference between the two !

So what happens with it out ?

There is a straight flow through the engine and block - but also the bypass hose has the capabilty to take some flow as well - so one would lessen the amount of water potentially flowing through the engine. Technically - if you blocked the bypass hose, and left it out - then it would be normal hot running.

Many sources say running with out a thermostat means a cooler engine - yes, on start-up. But once to temp, it would run hotter - unless the bypass hose was blocked off in some way, giving a full flow through the engine block of all the water being pumped.

Most of my old ones have tested bad by opening way too late. Stick them in a water bath - with a decent thermometer and see the opening temps. When corroded up they are slow to open.

I tried an old one in hot kettle de-scaler ( they are now £35 new ! ) and they come up sparkling in a flash.

Kettle descaler works well when very hot ( formic acid ) but I'm not sure these low temp termo's like to get too hot. So don't take them over 62 C or so.

The descaler certainly cleans all the white salts off them and they seem to then take on a new life.

You want to see them opening at that 42 deg C mark.

On the 1GM10 - the housing for the thermostat can be replaced upside down - which is a no no. It means that when the thermostat opens - it blocks off the outlet hose to the exhaust ! You will not get far with a reversed housing. They are marked with an arrow somewhere.

If you do remove it entirely for a clean up bear in mind there is a right way and its impotant ! Its very clear which way in the drawing in the manual.

The Head and injector

Since I have mine off at the moment - a few remarks.

Be careful of the shop manual - if you look at one. Their drawings are wrong | see here | See the link for the right way.

Be careful in the manual over tightening torques. They say tighten the studs to 44 ft lb - but the head is tightened to 55 ft lb ! ( why not tighten studs to 55 ft lbs ? ) easy to read this casually as head torques.

If removing the injector familiarise yourself with the set up below it - precombustion parts | here |

The injector just slides down the hole - so should come out easily. If it went in without its protective O ring to stop water getting down the sleeve hole - you need to give it some persuasion.

I did remove mine with the head on earlier this season. I removed everything I could around it - ie the lifting eye, alternator etc. I then took off the top clamp and pipes etc. Then removed the fixing studs with doubled nuts. They are not too tight.

I could then get an adjustable on the very bottom flange - not the one above it. A bit of a twist and it came out ok. Mine had no O ring on and had been in there 20 years.

Look again at the above link ( pic ) of the precombustion chamber parts.

You then have to pick out the copper top shim ( easyish ) and the heat washer below it ( difficult ! ) Thats what the book says anyways.

Ideally the copper washer needs to be renewed - but it takes a bit of the heat washer with it it seems. Maybe just removing the injector and relacing you may be ok back onto the top copper washer. But the injector base makes a deep ring impression in it so needs to reseat exactly the same. It should do - but who knows ?

The way this precom chamber is set up does not lend itself too well to removing the injector with the head on - some how ? See the page on the pre com unit for more.

Lifting the top unit off can unseat the lower slightly - and that to me seems a pig to get out with the head in situ !

Let put it this way - with the head off and laid on my bench in good light - once I had the top and the lower halves of the precombustion chamber out - I still had to make a wire hook, then flatten the bitter end, to enable me to get the thin copper shim out of the bottom of the injector sleeve bore. So - in situ, trying not to drop bits down the centre hole directly into the combustion chamber ?

To take the head off is quite easy. Have a good solid bar and socket for the head nuts. The two outside of the rocker box are often corroded - and they are tight. I need a bar 2 foot long to get them.

Once off - be careful of the pot. Best leave the piston tdc if its going to be a while off - cover it well and temporarily grease the top surface of the block.

With the head on the bench most things have been said on the precom page.

I had to make a tool to pull up the upper half the chamber. Maybe it would have knocked up from below along with the lower half - but I was being very careful with it. Bit of an unknown quantity - but now I've seen it out its pretty solidly made. It wouldn't bend or distort easily - but by knock it upwards I mean tap it gently !

It just slides up the sleeve hole for the injector. The lower half has a lug which slides in the machined groove. Make sure the groove is cleaned out low down when you replace it.

There is a copper shim under the lower half - and between the two. On top is the heat washer and on top of that is the wide 'penny washer' thin copper shim. This part is not shown on most of the exploded drawings - but its listed as a part no ? ( it is shown on the EPC - but not in my 2002 manual drawing ? )

Again - I think this has been added - to stop the heat washer welding itself to the base of the injector. These heat washers have all been changed to non-asbestos - and I think the new ones stick to things a bit ?

There have been various superceeded versions of the valve guides and seals.

The seals I have just bought fit ok - but are different to the old. The old have a spring around - like most seals. The new have no visible sign of a spring ?

I may be buying new guides - so will see what they are. They are now two the same - but mine are different ( eng no 11165 c 1993 ) Inlet extends more into the chamber. I wonder if they are now both long or both short.

Somehow the inside of a head is a good sign of what shape the engine is in. This was clean, little carbon at all - top of piston hardly a thing to clean off - valve heads clean. It surprised me really - but somehow I think my recent engine 'out of sorts' maybe have been either the gasket blowing a bit or the exhaust leaking ( carboned and pitted seat - just about caught it with some lapping. Any longer the wear would have required a reseat )

Its a quick job - I had it off in an hour or so.

Check it for flat - the max run off is quoted as 0.07mm ( head) which is pretty generous on a head this size. ( 0.05mm block ) See the other head pages for more on this.

The specified sealant for the gasket is Three bond - which is apparently still available from Yanmar.

As far as I can gather after much searching online - the manual, even the older one before 2002 - was out of date and never modified. No sealer is needed on the current gaskets - they are coated and seal themselves on pressure. The Threebond quoted seems to have been a high temp rated RTV ( room temperature vaulcanising) - acid free etc.

I have tried to make contact with Yanmar to get a definitive answer ( no reply ) I have spoken with French Marine - who are in the business of rebuilding yanmar engines - and the answer is as above - no sealant on the new gaskets. !

You have ro realise with these 1gm10 head gaskets - there is no pressured oil way. The tappet chamber holes are just drip holes open to the rocker assembly chamber. The oil feed to the head is external by pipe.

Of the 6 waterway castings in the head and block only two are used - on the side opposite to the thermostat. All the rest are blocked off by the gasket metal face. The water in the block is under no pressure - not like a car engine with radiator etc. It flows straight in and out again.

Essentially all the head gasket is doing is holding outward pressure on the bore for compresion and combustion. Its main seal is the metal ring around the bore hole of the gasket.

Make sure the block and head are well cleaned and free from grease.

Wash with white spirit, then meths then acetone. White spirit seems to get to grease more than Meths, Meths takes the white spirit - then acetone has little to do to finish up. Watch Carb cleaner, it sometimes has lubricants in it. Brake cleaner should be ok.

Exhaust Elbow

see separate page | here |

Injector Pump

I ended up having mine rebuilt ( by DTM in Bristol - on the recommendation of Rollo, Yanmar agents ). I'm not really sure it needed it - but when tested the they came back to me saying it needed rebuilding ? How can one argue ?

I was troubleshooting a distinct lack of power - and maybe a very good hard run would have sorted things out. But boats are not like cars - I can belt a car up the open road and its no great shakes if it conks out on me. Its different in a very tidal Bristol Channel - I do not want to be out there, on my own with no power. The river Axe is no better - in fact its worse !

While running on the mooring - at least for 20 mins at various loads in gear - it suddenly made loud tapping 'row' - enough for me to leap for the engine stop, it was loud and sounded nasty. Before I got there it stopped of its own accord - with a huge blast of pure white smoke, the like of which I have never seen before. It seemed horribly terminal, actually - and I was in no good mood ! It was then I had the injector pump out for testing. I did check the tappets valves etc - and turn it over for any audible rattle. It would not restart - except to run 'slower than tickover', despite what throttle one gave it.

After the rebuild I did a 6 day cruise around Ilfracombe and S Wales - and although it was smoking to start with, it quickly cleared up. We had some overheating problems - which appears to have been a clogged intake grill ( and a blocked waterway in the head near the temp sender unit.) Maybe it was just gummed up - and a good run and heat up might have cleared it up - who knows.

I also worry about these places - like DTM. I have to trust them - and I don't like that much. Is the stoke on the pump 'exactly 7mm to spec', does it fire at the right psi, does it meet all the specs as listed in the workshop manual ???

Yanmar do make replacement parts for the pumps - Marine Power is actually listing them online ! The piston and Barrel come as an assembly - about £160 - and the delivery valve is about £60-80.

The main barrel assembly is a very specialised unit and need extreme care to work on ( very clean ) - but the delivery valve is servicable with care. It can get crud in it - and you can clean it out. One thing to watch out for.

When re-set, the top unit is torqued to a very acurate torque against a spring ( about 36 ft lbs ). Onto this unit screws the outlet pipe union.

If you ever take the outlet pipe off - make sure you HOLD THE LOWER NUT when undoing it. Otherwise there is a risk of upsetting the lower unit torque setting. If that torque setting is wrong - the engine will race away on you - which is not good !

So I have removed one recently - and put one back in. They are easy to remove - but - are very severely ( from new ) stuck down with grey Yanmar glue ! You need to see the manual as to where the fuel lever sits in the slot of the governer arm. It literally sits loose in a slot - ie it just lifts out and upwards. See it through the oil filler hole.

The fuel lever is a sliding fit and loose - in the barrel of the pump - and does not want to be banged or bent about. It has to be a smooth sliding action. Be careful of it when lifting out the pump. The pump it quite heavy - and the lever quite delicate ! When tilted, it should glide along under its own weight, either way.

Take off the three nuts and you will probably have to tap it a bit firmly. Once free - try to not disturb the packing - as thats stuck down as well.

I have yet to check the timing - as I thought I ought to, with the pump being rebuilt. If its looking out at all - I will remove the pump, and all the shims - check their thickness etc. Then buy the Yamar shim pack - its an ok price ( £10 for thee shims - 0.1, 0.2, 0.3 ) and set it from there.

As far as I can work out from the badly worded 2002 Yanmar manual ( and wrong info as well - ie if 'slow' add shims !!! ) - and from looking at the older Yanmar manual ( which is much clearer and has the info right ) -

To check the timing -

Remove the HP pipe from the injector pump to the injector. Ideally - attach a 'spill pipe' to the top of the injector pump outlet. If 'no spill pipe' - just watch the flow from the top of the injector outlet nipple ( this is as stated in the Yanmar manual ) Afik - a spill pipe is just a dummy bit of pipe with a cut end that more acuarately shows when fuel is 'spilling' ?

Easiest to remove the alt - and starter, then check the timing marks on the flywheel. There is a single line @ 15 deg tdc - and a line plus T @ tdc.

Make sure the syatem is bleed through to the injector pump. Lift the decom lever - half throttle - turn engine over by hand, right way - check when fuel comes out of the injector pump oultet. Should be 15 deg before tdc.

I deg = 0.1mm on the shims. Adding shims retards - ie + 0.1mm = 14 deg tdc. Removing advances - minus 0.1mm = 16 deg before tdc.

Stands to reason - the pump is operated upwards from a cam at the bottom. When at a certain height it will fire the delivery valve. Raise the pump unit - it will fire later. Sink it down a bit - fire earlier.

I've yet to see what sort of spurt of fuel comes out - or how easy it is to see it anything is amiss. I shall only change it if it seems 'way off'. The engine is starting ok and running fine - just a bit black at full power.

When replacing - just be careful with the fuel lever. It has to drop into the 'fork' of the governer lever. Its a very slack fit. Its quite easy to see and do.

As stated above - the crank pulley has four threaded holes through it - and these are exactly vertical/horizontal at TDC. The flywheel marks are easiest to line up with a torch shone 90 deg on - it casts a shadow from the lug pointer - onto to flywheel face. I couldn't get my head in position to line them up !

Its probably esier to set at TDC - then mark the crank pulley somehow at 15 deg before. The crankpulley and the injector pump are then close together to get a visual synch.

Some good sources - Dec 2013

Rib Marine parts - online EPC illustrated parts catalogue - & online sales ( good - but goes a bit wonky at times, especially on the stock check. Great for checking parts nos - and for the part drawings ! )

ProRib marine - worth checking out.( oversized piston and rings )

SSLDsiesel parts - good for CAV parts, fuel hose etc.

French Marine - good service, very knowlegable on phone.

Keyparts - cheap and free postage, but check if the parts are Yanmar Genuine ( important with things like head gaskets,

Marine Power

PDF download - old style 1gm10 full workshop manual - ( GM/HM 60Mb is the old full version ) This is actually clearer to use than the 2002 version - as it has separate section for single cylinder engines.

The 2002 Manual is online somewhere - I downloaded it ! but can't find it now. I do have a copy of it - but its 64 Mb. Contact me if you are stuck.

If you are in the Bristol area Rollo have an outlet nr the Gordano juction - and can get any part for Yanmar on a weekly basis, whenever the bulk order comes in. Handy for me as its on the way to the boat - and no cariage charges - or waiting around for deliveries.

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