YSE12 Engine Rebuild

[Scaffi S28]

I have a Yanmar YSE12 engine which needs new rings and a valve grind etc. I'm reluctant to get involved in taking the engine out altogether, and I was wondering whether anyone knows whether the work can be done with the engine still in the boat. It's a wet-sleeve design, so thats a start, and the big issue will be whether the rod/piston can be removed by accessing the conrod bolts from behind the pressed tin plate on the other end of the crankcase.

Any thoughts ?

Thanks,

Nitram

[John Brewer]

I have just re-engined my boat after nursing a very tired and worn engine for the last 10 years. During that time I had the head off twice and found that it was quite feasable to work on the top end with the motor in the boat.

You will find that the engine oil will be very sooty and dirty! It will get every where.

I have rebuilt many motors over the years. You may find that a "top end de-coke" and head service will restore considerable performance. It is feasable to do this work with the engine in the boat.

The problem you have is that if the rings need replacing there will be considerable wear in the bore and probably the main and big end bearings. Wear in the bore will involve a lip at the top of the cylinder which must be removed or the new rings will break when arriving at the top of the stroke.
Also if replacing the rings the bore should be "honed" so that the new rings will "bed in". I would recomend that if work on the rings is to be carried out the engine should be removed from the boat so that it can be fully cleaned. Also if working to the motor to this extent it is worth replacing all the oil seals.

I think you will find that it is a lot easier to remove the engine if work on the bottom end is to be undertaken. Certainly the end result will be a lot better.

Good luck with the rebuild

[Chief Engineer]

Two guys and a strong boom and you can suck that engie right out

[Scaffi S28]

Yeah, it'd certainly be better to have the engine out and on the bench to do an overhaul, but access into the back of the gearbox and the shaft join is just appalling and it freaks me out a bit. So I thought there might be a way to get at the top end without disturbing the bottom.

I remember replacing the rings on a Renault when I was about 17, by removing the sump and taking the rod/piston out the top, together with the wet sleeve. Has anyone ever done this with a YSE engine ?
Cheers,
Nitram

[Chief Engineer]

Can you post a picture or two of your engine?

You say it is difficult to get to the shaft coupling, fortunately (for me) I am the perfect size for getting into those tight spots.

At this point, I would endeavour to try to remove the engine, that way you can do a complete rebuild and be done with it. Plus it gives you a chance to clean up the engine compartment.