yanmar 1gm10 re bore?or skip???

Niander

Niander

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Hi is it possible to re bore this engine ?...can you get plus size pistons because the compression is low the bore is marked and if i put oil in the injector hole then i can feel the increase in compression using the hand starter so thats the problem!.....can i rebore it???or is for the skip???
 
It depends on how much of the work you can do yourself. I would dismantle it, take the head, block and piston to your local engine reconditioner and get them to measure it up, and test the head & block for cracks.
If the head/block is unservicable (cracked) - then its new engine time.
If the they are ok, armed with the dimensions see your yanmar dealer for prices on oversized pistons/rings. You will also need a gasket set, possibly main bearings, valves, etc (rebuild kit is £300 for a volvo single cylinder) Cost it all up, and you will find the rebuild cost is much less than a new engine, but it will be still an old engine. It cost around £1k to rebuild my 2001, but I was able to use my current piston, and just got the bores honed. Most boat engines are deratives of automotive or industrial engines, so remember to check out a specialist piston/ring supplier who will match it dimensionally
 
Yes, it can be rebored. However low compression could equally be valves or a porous head, so take the head off and have a look. Any bore damage or wear will be immediately obvious. All the dimensions and wear limits are in the workshop manual including reboring for oversize pistons.
 
I had low compression on mine, it was sorted with new rings and the bore honed <sic>, my next tool purchase will be a honing tool so I can do it myself next time.

Far cheaper to go this way than to fit sleeves, I don't think there is enough meat on the 1GM to consider a rebore, but will be interested for future reference to know how you get on with this.

Have you changed the rings yet?

EDIT>> Actually, tarona corrects me on the bore situation. But I agree with him, get the head recut, mine cost about £65 I think, new valves (bedded) and a minute skim. The exhaust valve is known to fail and leak on these engines.

Mine now runs sweet as new again. It would have been much cheaper had I done more myself, but I had time constraints and lack of a few specialist tools.
 
hi ive lapped in the valves already...they are ok ...and as compression got better when i put some oil in bore ...this temperoraly sealed piston seal...proves problem is bore[especially as i know it is marked due to being stood with water in....:([previous owner]....
 
If you pm me with an email address I will send you a scan of the relevant pages of the manual with the bore, piston and ring dimensions.
 
yanmar can supply oversize pistons for your engine upto +40 however i would go with an engine rebuilder as they can supply bog standard pistons and rings at half the price.
The block is good to +40 on the rebore but its the head thats the weak link.


steve
 
bog standard pistons and rings at half the price

are these yanmar or pattern pistons?

as i said the head is in good cond...its the bore...as it has water damage and i have seen it but tried to get away with it but not enough compression to run...am starting dismantle now...
 
There are a few weak points with these engines but I expect that you know about the exhaust elbow problem. If this is neglected for long enough it can ruin the head as the exhaust port gets rust holes that go into the pushrod tunnels. I've got a bad head like this in my collection of bits and if I ever get around to it I might try threading the exhaust port with a thread-tap and letting-in a piece of threaded pipe coated with "Heldtite". A fine thread would be needed, possibly BSP or conduit thread. Hours of amusement but it could save hundreds of pounds. Welding of cast iron is not really a good idea as first the casting needs to be shotblasted. Avoid the use of Nickel rods but instead practice what the Americans call "Furnace Welding" i.e. use vast amounts of preheat and cast iron rods. It is a hot and horrible way to do the job so metal surgery is probably the best way forward unless one has a spare £600 burning a hole in one's pocket!
 
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