Yanmar engine

IMHO Yanmar’s are generally good boat engines. I would buy one tomorrow. This forum has identified a few weak spots which you can keep on to of. Those which come to mind are
Hour meters become impossible to read (perhaps your engine has had a new one).
Exhaust mixer manifold needs changing for a stainless aftermarket one - get a couple of gaskets and have a gander.
Raw water pumps are weak - carry a spare
Make sure you change engine oil regularly using mineral oil (best is typically cheapest available at supermarkets)
Don’t let them idle for more than a couple of minutes
Get a proper “c” or hook spanner for fuel filter changes
 
Nudge said:
It's possible that your cones may have become "glazed" and have stopped gripping. You can check to see if your shaft is not turning evenly and that will be a clue. BEWARE!! Many mechanics who aren't conversant with the engine (and actually some who should be...) look at the ridges on the cones and tell you that you need new ones. This is not so!! Gentle lapping in will cure this. Diagnosis is not cut and dried and the only true way of telling is to strip the box and force the cones together and twist by hand, If they don't lock together and grip each other, get out the lapping paste and a slow turning lathe and lap by hand. Good luck!
Click to expand...
Thanks for your advice, sadly that is beyond my technical abilities.
The mechanic confirms your diagnosis and will take off the gearbox and strip it. I will have to trust he knows what he’s doing, but so far I have had good service from them.
 
Halo said:
IMHO Yanmar’s are generally good boat engines. This forum has identified a few weak spots which you can keep on to of.
Exhaust mixer manifold needs changing for a stainless aftermarket one - get a couple of gaskets and have a gander.
Click to expand...
Corrosion occurs inside and is hard to spot without taking off the manifold, but thats an easy task. A stainless replacement will probably be cheaper than a Yanmar part even with shipping costs from USA.
http://exhaustelbow.com
 
Nudge said:
It's possible that your cones may have become "glazed" and have stopped gripping. You can check to see if your shaft is not turning evenly and that will be a clue. BEWARE!! Many mechanics who aren't conversant with the engine (and actually some who should be...) look at the ridges on the cones and tell you that you need new ones. This is not so!! Gentle lapping in will cure this. Diagnosis is not cut and dried and the only true way of telling is to strip the box and force the cones together and twist by hand, If they don't lock together and grip each other, get out the lapping paste and a slow turning lathe and lap by hand. Good luck!
Click to expand...
A quick update on my slipping gearbox and opening/closing of the folding prop.
I finally lost forward drive one day when I reversd out of my berth and upon engaging forward nothing happened.
It turns out now that the cones are still allright, but the torque limiter is bust. The rings inside it are distorted and their teeth bent/damaged. They have been replaced, and as often with spare parts, they are not cheap.
I did not know there was a torque limiter, but I can understand it must have taken the brunt of the impact when we got a fishing net in the prop in July.
 
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