Yanmar 1gm10 replacement

David N.

New member
I've been dealing with a good running 29 year old engine, with a bad soot problem.  I installed a new injector, pulled and cleaned exhaust elbow, new fuel, etc.  No help.  Mechanic ran a compression test and it's just below spec @ 390 psi, saying 395 psi is the minimum spec.

My plan was to slowly work into a replacement in the next year or so, but then I noticed a drip @ the raw water pump housing and found the block has eroded away @ a bolt thread.  1 drip every 5 seconds or so.

Stepping up my replacement timeframe to immediately and I'm finding a few Indonesia sites offering new motors. 

Any opinions on this particular site/business listed below?  For an otherwise good looking site, that price can't be right. 

Anyone in the US known to have new motor stock?

Do you think I can fill that void with something to buy me some time, like get me through the summer?  I did clean the area best I could and ran some 6000 adhesive up in there, but really don't expect it to stop the drip.  But maybe.  I'm away from the boat now for 3 weeks so can't go check it.  


Yanmar 1gm10.jpg

Last edited by a moderator:


So. Cal
had one just like that, was like that when i bought it and the other two bolts were holding the pump fine.  removed the pump cleaned the surface with solvent and used JB weld for steel to build it back. re taped the hole and filed the surface flat. still going strong 6 years later. repaired a mini engine/transmission case Rod Came through the case,  40 years ago with the same JB weld and the engine is still going to this day. not saying it is the best way but it was worth a try and it worked for me.



Super Anarchist
Soot problem with my 1GM10 was due to the alternator load when the engine was cold.  It's only a 35A alternator but it's also only an 8hp engine.

I had the alternator's field wire brought outside the case and installed an external regulator.  The programmed delay in charging allowed the 1GM enough time to warm up before the alternator load kicked in.  No more smoking/soot when cold.  It also charged the batteries properly.

But if you insist, another J92 owner had his 1GM replaced with a two cylinder Beta.  It was expensive but done very well by H&M in Sausalito:



David N.

New member
I thought about the JB Weld but was unsure about its ability to hold while tapped and then bolted again.  Glad that worked for you because I'll be giving it a shot.  New motors are twice the price I thought...and twice the backorder timeline.

Did you at all drill/tap further into the casing?  I assume it's crankcase not too much further from original OEM threads.

That Beta repower is interesting.  I'm going to throw out $13K to do that job...and I may be soft.  



Toledo, OH
I happen to know someone who just pulled a well-maintained engine (fresh water) from his J-29 that is for sale. I believe it to be a 1gm 10. PM me and I can put you in contact with him.



New member
heavy soot is almost always caused by cold running your engine...how many guys run the engine to get out of the slip or whatever and shut her down without ever letting her feel a good load and warm up fully-FYI-it's MOST guys ruining their own engines-usually the same guys who only get a year or two out of their batteries



Super Anarchist
Boston, MA
New motors are twice the price I thought...and twice the backorder timeline.
David, are you saying that the site you posted actually wants $4k for the 1gm10? that makes more sense to me, since it cost me nearly that to get mine rebuilt last year (cracked head).


David N.

New member
The link above is too good to be true, plus other scam red flags on an email I got back from them.   Pretty good website IMO, but it just can't be legit.  

Turns out I was wrong about the location of the water pump rusted out threads.  They are in the timing case cover, not the block.  I found a Yanmar dealer that does up front rebuilds, so to speak.  He'll get me a rebuild in 3-4 weeks then I mail back my core.  All up around $4k with shipping.  Once I receive the motor and feel the shop is worthy of press, I'll post contact info. 

FYI From Yanmar, a new 1gm10 without transmission is around $8k.  With transmission over $10K and a 4-7 month wait time.  And, that motor doesn't meet US emissions so you have to jump through some hoops before they will actually sell you one.

I'll be on the boat this weekend and will post a pic of the soot issue, as well as the smoke I get above 2800 rpms.  Even though I already pulled the trigger on another motor, I think the soot problem is more of a fuel delivery issue than a slightly low compression and want to understand the issue. 

Thanks for the comments about the alternator loading early and running the motor cold.  I feel I've got both of those items under control.    


Latest posts