Off with Her Head - Off with Her Head !
Something that came up when I was searching for various online info on rebuilding 1Gm10's - many posts on forums of confusion over which way the head gasket goes, up or down.
It only has two holes in it for water - despite the head having 6 open ports. I think this is a hang over from the old YS series - which seemed to have all these ports present in the head gasket. Probably still the same old castings !
Having just removed the old one - and knowing fairly certain that this head has never been off - it was not an issue really to me. But it got me looking at the workshop manual to see where the confusion was - and there I found the confusion !
Its wrong !
The drawings of the head are upside down, for the 1GM10/2GM20 and 3GM30 drawings. see below -
If this is the top of the gasket as it is on the block - and the tappet chamber holes are away from you - then the flywheel, prop side is to the right. The push rods are right between the exhaust port - the exhaust port is on the left of the engine when facing the front gear side. See my old gasket that came off - below
This is the UP side - as it sits on the block. It has been established that the latest Yanmar gaskets do not have a TOP mark - only a stanped A - and also this Pat No.This is a genuine Yanmar gasket
This is looking from the 'starter motor' side - pushrod chambers away from you, flywheel and prop on right - gearcase on left.
This is the way it goes. Small hole over the open port near the temp sender. Graphite type material with 6 port holes showing DOWN
Metal side, just showing the SMALL HOLE - and ONE OVAL opening - UP.
The two holes are on the flywheel side - ie the opposite side to the thermostat.
It stands to reason, that if you only have two holes for the block water to flow into the head - and then out of the thermostat to the wet exhaust - they are going to be on the OPPOSITE side to the thermostat, so water flows through the head. The thermostat is on the gearcase side.
Below - side by side to the first drawing in the manual - is the torque setting, which is right !
Tappet chamber toward you, flywheel on left, gearcase on right - exhaust port between 4 and 2 studs. AS it should be
No wonder people were in some confusion. I sort of know my head has never been off - but it can well be the case you might think its been done wrong in the past !
Vey bad - for an important - and costly - item.
Geoff - 23rd Dec, 2013 ( just made some upside down mince pies ! )