Yanmar SB12 Using Oil

[Compass790]

Forgot to add: Have you checked crankcase breather is not blocked? Don't know SB12 setup but that could possibly cause your oil consumption problem

[Homer Shannon]

I checked it earlier and it seemed OK. While I have the valve cover off, I will disassemble it and clean it. (Everything under the cover is nice and clean, no gunk at all.) I did see a post indicating that the breather could be installed wrong and cause an issue, but I doubt that is my problem. At any rate, I'll double check it.

My best guess is that the rings have just not worn into the bore properly. I have no explanation for this, but I don't think the bore looks as smooth as it should be at over 2,000 hours. The bore will get a good honing and new rings will go in. The head will be repaired and then we wait to see how it does.

[Compass790]

Originally Posted by Homer Shannon

I checked it earlier and it seemed OK. While I have the valve cover off, I will disassemble it and clean it. (Everything under the cover is nice and clean, no gunk at all.) I did see a post indicating that the breather could be installed wrong and cause an issue, but I doubt that is my problem. At any rate, I'll double check it.

My best guess is that the rings have just not worn into the bore properly. I have no explanation for this, but I don't think the bore looks as smooth as it should be at over 2,000 hours. The bore will get a good honing and new rings will go in. The head will be repaired and then we wait to see how it does.

Sounds like a plan. Yea your breather unlikely to be the problem if it's nice & clean & hose isn't kinked. On our ysm8 engine it's possible to install vent cover upside down but yours may be different. Suggested it as running outa ideas. Rings never properly bedded is a possibility I guess but unusual. If no cracks in head not much else left afaik
Good luck

[a64pilot]

Of course a piston head is less diameter than the skirt, and a bore wears in a taper, you have to measure in a couple of places but usually in the upper third is where the wear is worst.
You can get a real good idea of bore taper by using a new ring and pushing it down the bore with the piston turned upside down, the ring gap will tell you if the bore is greater or not as of course it will open up in a worn area and close up where there isn’t wear.
You have to do this anyway to set ring gap.
Just to give an idea, you need an inside mike to know, you may can borrow one at an auto parts place, they rent all kinds of tools.

[Wotname]

Originally Posted by Homer Shannon

.......

My best guess is that the rings have just not worn into the bore properly. I have no explanation for this, but I don't think the bore looks as smooth as it should be at over 2,000 hours. The bore will get a good honing and new rings will go in. The head will be repaired and then we wait to see how it does.

Please let us know how you are going to approach the honing process.

In situ, DIY?
In situ, professionally?
Remove liner, DIY?
Remove liner and take to engine shop?

If DIY, could you post photos as well?

My very limited understanding is that there are many wrong ways and only a one (few?) right way(s) so I am keen to hear of a first hand account!

[Homer Shannon]

I got the head back from the machine shop yesterday. Greg, the machinist, said that he put a small weld on the most damaged area of the head then shaved it 0.010" and it now looks much better: before https://1drv.ms/u/s!AiR9KzpBmPls1i4wrevMWCJlyjV3, after https://1drv.ms/u/s!AiR9KzpBmPls1jX4Y8V2qJafffvB.

I removed the injector, which came right out, and will be taking that to a place in Bow NH that can check the spray pattern and the pop pressure. How important is it to replace the O rings and thermal gasket in the pre-combustion chamber? These do not seem to want to come out. I did order the new parts to refresh these. https://1drv.ms/u/s!AiR9KzpBmPls1jYx8L0l3gxbqsD4

[Compass790]

Greg the machinist: looks like he did a good job. Do you know how he welded the head? Cant comment on pre-combustion chamber parts as I never removed ours. I didn't replace stuff that lies under the injector either, just re-annealed copperwasher & used 518 flange sealant on injector face with no problems. Good idea to replace & follow w/shop manual instructions tho. Wotname did pre-combustion chamber so he mite chime in.

[Wotname]

Homer, the head looks nice! I'm surprised the machinist didn't remove the pre-com chamber before doing any work but perhaps that isn't normal practice (???).

My concern would be swarf inside the pre-com chamber, sure most could be flushed / blown out but would all of it be removed - and does it matter? It would matter to me but again it might not really matter in the real world.

I'm surprised that Compass790 had copper washer against the injector insulator washer, this is not shown in the YSE parts book / manual but I do recall other Yanmar injectors having that arrangement.

However at the end of the day, if the pre-com chamber doesn't exact easily maybe the sealing doesn't need replacing but best practice would suggest removing it, inspecting and replacing copper seals and heat insulator.

[Compass790]

Interestingly yr btm right cooling passage looks much smaller than top right. Guess they 'sposed to be symmetrical. I assume that's a casting fault.

[Wotname]

Originally Posted by Compass790

Interestingly yr btm right cooling passage looks much smaller than top right. Guess they 'sposed to be symmetrical. I assume that's a casting fault.

Well spotted

[Homer Shannon]

I thought Greg did a nice job. He would have had to take off about 0.020" before he started carving into the pre-combustion chamber, so there was no need to remove it. I did get the fiber washer out - that was pretty easy. I've got some penetrating oil in the head now and in a few days I'll see if I can get the chamber out. If I can't, I'll replace the fiber washer and leave it at that. Can'be be worse than it was!

[Homer Shannon]

I’d like to thank all the contributors to this thread. You have been very helpful assisting me with this engine rebuild.

At this time I am waiting on parts. I had the head inspected and the machinist recommended a small weld over the worst area (only about ¼” square) and then took off 0.010”, which cleaned it right up. The valves have been cleaned, lapped and reinstalled. I took the injector to Diesel’s Fuel Injection in Bow, NH for a free pop test, which showed the spray pattern and valve pressure to be good. I’ve honed the bore with a Flex-Hone and I’m ready to put the piston back in when the parts show up.

Some listers expressed concern about honing the bore in place. Here’s how I did it. I rotated the crankshaft until the crankshaft throw was to port. This gave me a bit more room to work and it put the oil feed hole on the crankshaft facing down. I then covered the entire crankshaft with three layers of heavy paper wiping rags. In then put a piece of folded towel material down the bore, stuffing it tightly around the remaining area between the crankshaft and the cylinder liner. Lastly, I slid down a 1” high plastic cup cut from the bottom of an old cottage cheese container. This was nearly the same diameter as the bore and fit tightly. The plastic cup was not so much to catch anything as to keep the hone from grabbing the rags and pulling them out of position. I then gave the bore sixty strokes with the Flex-Hone.

I wiped out the bore and then cleaned it with soapy water. When doing the washing part, I removed the plastic cup and replaced it with a folded wad of paper toweling. I probably didn’t wash as thoroughly as I might like, but I got it clean and all the stray liquid ended up in the paper toweling. The crankshaft and bearings stayed dry and clean.

When the parts show up, it shouldn’t take long to do the reassembly. Then I’ll fire it up and see how it runs.

[Wotname]

^^ thanks for the update; any chance of a high res photo of the honed bore?

[Homer Shannon]

I received my parts today from TOAD. I can't start work until the weather clears a bit - Tuesday, I hope. It looks like I will need some help with the rings.

In the existing set and the work shop instructions, there are three types of rings: top ring, distinguishable by being shinier, two following compression rings, and the oil ring, which is a dual lip ring. All are identical top and bottom and do not need to be oriented up/down.

In the new set, pn 105400-22500, there are four unique rings: one, green with a yellow mark and labeled "Tp"; one with a unique non-square edge labeled "Tp 3" and a yellow mark; one silver ring marked with a "T" and a red mark; and the oil ring, which is obvious.

I do not know what the order for the rings (other than the oiler) are with this new configuration and I do not know which way they need to be oriented. Is anyone aware of the correct placement or able to interpret the markings on the rings?

I am pleased to see that there are significant changes to the rings. I suspect that in the past forty years there has been a lot of improvement in the ring technology and some of that can now be incorporated into my old engine.

[Wotname]

Originally Posted by Homer Shannon

I received my parts today from TOAD. I can't start work until the weather clears a bit - Tuesday, I hope. It looks like I will need some help with the rings.

In the existing set and the work shop instructions, there are three types of rings: top ring, distinguishable by being shinier, two following compression rings, and the oil ring, which is a dual lip ring. All are identical top and bottom and do not need to be oriented up/down.

In the new set, pn 105400-22500, there are four unique rings: one, green with a yellow mark and labeled "Tp"; one with a unique non-square edge labeled "Tp 3" and a yellow mark; one silver ring marked with a "T" and a red mark; and the oil ring, which is obvious.

I do not know what the order for the rings (other than the oiler) are with this new configuration and I do not know which way they need to be oriented. Is anyone aware of the correct placement or able to interpret the markings on the rings?

I am pleased to see that there are significant changes to the rings. I suspect that in the past forty years there has been a lot of improvement in the ring technology and some of that can now be incorporated into my old engine.

FWIW, my limited ring experience suggests any manufacturers identification marks on a ring face towards the head.

The YSE/YSB rings have a chromed top ring that is barrel (or D) shaped outer face. The next two rings have a very slight tapered face.