Amazing Yanmar 2 GM

[Nelsonhow]

If any of you follow this site you'll know I posted last fall About whitish smoke and a loss of power from my 1983 Yanmar 2gm in my hunter. Well this winter I stripped down the top end expecting to do a valve job. When I got the top end apart the head and cylinders looked GREAT. I did clean out the exhaust manifold , reamed the cooling passages with a wire rod in both the block and head and cleaned out the temperature manifold. After all this I noted that the thermostat appeared to be stuck closed. (It would not open in a pot of boiling water. ). I replaced the thermostat and all the various gaskets and bushings. Polished the cylinders of a very small amount of carbon. The valves looked so clean I didn't even bother checking the specks. I put it all back together with no extra parts. Other than a small problem with the water pump! I replaced the impeller and I think I had the impeller vanes flipped backwards, which I fixed by opening it up and making sure the we're flipped correctly , and the standard bleeding for air. She started right up and purrs like a kitten.

I also replaced the alternator because I broke off one of the electrical studs while removing it.

So the problem might have been a minor overheating issue causing steam. (. I backed off on the rpms as soon as I saw smoke last year.)

I am very impressed with the engineering of this motor. If after almost 30 years of hard use she seem to have very little wear! Wish I were the same.....

I think I may descale the old girl next season but it doesn't seem to be necessary.

Anyway, we splash on Monday and I'm looking forward to a good sailing season.

Thanks to all you out there for your advice last fall.

 

[Benny17441]

Good job, but a faulty thermostat should have been identified early in a diagnostic routine of the cooling system. The causes of overheating conditions are usually independent of other problems that may be present and can be addressed independently. The old engines are very hardy indeed and if well taken care off should see 40+ years in service.

 

[kloudie1]

I agree that the Yanmar folks really did a fine job with the old GM series.. I worked with a friend on one that had not been run in 5 years.. We changed the impeller, bled the fuel. Then we decompressed and spun it until the oil pressure light went off.. then threw the lever to get compression and she fired immediately... A fine little jewel.

 

[Sailm8]

Could you elaborate on the impeller problem? My understanding was that it makes no difference how the blades are facing when you install it, it will flip the right way with the first rotation. Right or wrong?

 

[Lost]

Book says make sure that it's going the correct way when I did it it would turn them depending on the direction you turned the pully but that was with the cover off