Yanmar SB12 Using Oil

[Compass790]

Originally Posted by Wotname

Homer, as an aside, do you always leave the engine with the piston raised to almost TDC on the compression stroke after shut down?

If not, I believe it is a good practice as it ensures the valves are tightly closed and more importantly, the bore is only left open to the oil rich crankcase rather than the cabin atmosphere (via a open inlet/exhaust valve). This should reduce possible rusting on the honed bore surface.

I don't know if this called up in the SB operation manual but Yanmar does call it up in the YSE manual as part of the shutdown procedure. Possibly more important in a horizontal cylinder but it can't hurt and is probably beneficial.

Although i thought the suggestion of leaving the piston at TDC on shutdown is a great idea after thinking on it some more there is still the crankcase breather to expose the sump to cabin air. Still think it a better idea coz it leaves oil on cylinder walls rather than having the rings scrape it off tho it sounds like Homers' engine isn't doing that too effectively.I'll try to remember to do it.

[Homer Shannon]

My logic for not doing this procedure (other than laziness) is that no one bothers to do this on a multi-cylinder engine as some of the pistons would always be out of the ideal closed position. And, those engines don't wear out because they are not left at TDC. Other than "because you can" how is this habit more beneficial to a one cylinder engine than any other engine?

[Wotname]

Originally Posted by Homer Shannon

My logic for not doing this procedure (other than laziness) is that no one bothers to do this on a multi-cylinder engine as some of the pistons would always be out of the ideal closed position. And, those engines don't wear out because they are not left at TDC. Other than "because you can" how is this habit more beneficial to a one cylinder engine than any other engine?

Well they do wear out by having the bore rust ever so slightly if left for a month or more (or so the theory goes) and this rust is rubbed off at the next start and they suffer from valve seat pitting. As you say, it can't be done with a multi cylinder engine and almost everyone these days has multi cylinder engines so the question never arises.

Having the valves tightly shut must be a good thing - not possible to get water (or moisture) inadvertently introduced into the cylinder.

No space in the cylinder for condensation to occur must be a good thing. Even if there isn't any upside, there certainly isn't any downside.

Yanmar thought it a good enough to include in the operations manual back in the day.

But I sure the few of us still with singles don't do it in general.

[pmagistro]

Hey, I had a similar issue with my SB12. It was burning about a quart of oil per day. I replaced the valve guides, cleaned up the head and replaced the head gasket to no avail.

The next season I replaced the cylinder liner, piston, and rings. It was a relatively easy job and the engine runs perfectly now without burning a drop of oil. I was able to torque the bolts to spec through the side case without removing the engine.

I have some photos of the process and am happy to answer any questions you have.

[pmagistro]

Originally Posted by a64pilot

You can get a leak down tester for less than $50. I’m sure they can be rented too, you will need a compressor, doesn’t have to be a huge one but a bicycle pump won’t work.
The trick is going to be how to connect it to the engine, usually it’s remove a spark plug, we have injectors and your likely going to have to fab something up, but you have to do that for a regular compression test too.
I haven’t read this article, but bet it’s a good guide.
Just google engine leak down tester and you’ll get hits.
https://mobiloil.com/en/article/car-...-leakdown-test

Couple of thoughts: the SB12 fires on compression alone. There are no spark or glow plugs. So you can't test compression as you would on a gasoline engine. Simply the fact that it starts indicated adequate compression. However, it can still burn significant oil if the oil scraping ring is worn.

Also, there are no valve seals on the SB12, just guides.

[pmagistro]

Last but not least, I forgot to mention that I have a cylinder liner puller and a bunch of other esoteric tools specific to this fix on this engine. I would be happy to sell/lend them to you.

[Homer Shannon]

Pmagistro, that's for that information and the tools offer. If I need to pull the cylinder, I'll probably take you up on the offer.

More progress today. I took off the oil pan and I think this is the way I am going to have to work on the crankshaft cap bolts. Side access is difficult and could cause a stripped bolt head or bad torque reading on reassembly. Lying on my back and working over my head, I think I can reach in and do the work OK, if painfully. I have not taken the piston out yet - still a bit nervous about that step - no turning back from there. I took photos of the bore which are posted at https://1drv.ms/f/s!AiR9KzpBmPls1ir6MmvonE1GHj9f. These are pretty high res, you can zoom in on them. The ring that you see at the top is not a lip. If anything, the opening of the cylinder is slightly larger than the bore itself. You can feel something when you run your finger over this, but it is not enough to catch your nail.

Any suggestions on how to remove the head studs? I gave it a half-hearted try with two nuts, but the one I attempted did not budge. I don't know that I have to remove them but it would make honing easier.

[pmagistro]

Sounds good. I won't be back to the boat until Nov 8. FWIW Tanager is a '78 B29.9, hull #113. I've done a ton of projects over the last two years, including the HD joint, solar, propane, full plumbing overhaul including seacocks, electronics, some rigging, etc and am happy to answer any questions. Planning on installing a windvane and fridge next month.

Replacing the cylinder liner was nice, because I cleaned a mountain of crud out of the block and it wasn't all that hard to do. I had to manufacture a piece to pull the old liner out of a plate of sheet metal because the old parts are unavailable, and it worked just fine. I figured the cost was so much less than a new engine, and then I could count on the crankcase being as good as it will ever be in a 40+ y/o engine. Same story for the piston; I considered reusing the old one but in the end just replaced it. I was able to do all the work crouched in the starboard lazarette through the side case.

If you want to replace the studs you might just buy a stud extractor.

Good luck!
Phil

PS. Photos posted at https://photos.app.goo.gl/Vevx5JDKMnnDp4FXA

PPS. Here's a list of the parts I used along with some prices:

Head gasket 104564-01332
thermostat gasket 105582-13201
bonnet gasket 105582-11310
side case gasket 105582-01810
Cyliner Liner assembly 704500-01900
includes:
cylinder liner 104500-01100
Rubber packing 103338-01300 x 2
Piston/Ring 104511-22090 qty. 1 $116.59
Piston Pin 105500-22300 qty. 1 $23.33
Circlip 124250-22400 qty. 2 $1.56 ea.
Bushing 104200-23910 qty. 1 $10.11
Pipe 105582-59800 qty. 1 $18.15
Pipe 105584-59070 qty. 1 $19.61
Bolt 104200-54080 qty. 2 $2.91 ea.

[pmagistro]

As an aside, you might want to check out your exhaust system while working on things. After I did my overhaul, the d*mn engine started to overheat. Turns out that the mixing elbow had corroded through. Might be nice to have it blasted while you have everything torn apart, because if the tiny little passage to the thermostat corrodes shut the engine will heat up SIGNIFICANTLY beyond the "not too hot" you alluded to earlier.

[Homer Shannon]

Pmagestro, that's interesting. My boat is a Bristol 29.9, too. 1978, hull 46. They must have made a bunch of them that year! The engine has been a good soldier for a long time and I suppose it is due some refreshing. Even now, other than the oil consumption, it runs well. People complain that the SB12 vibrates and is noisy, but I think it's not too bad and it will move the boat at 5.5kn. the boat wouldn't cruise at much better than that with a V8!

[Compass790]

Originally Posted by Homer Shannon

Pmagistro, that's for that information and the tools offer. If I need to pull the cylinder, I'll probably take you up on the offer.

More progress today. I took off the oil pan and I think this is the way I am going to have to work on the crankshaft cap bolts. Side access is difficult and could cause a stripped bolt head or bad torque reading on reassembly. Lying on my back and working over my head, I think I can reach in and do the work OK, if painfully. I have not taken the piston out yet - still a bit nervous about that step - no turning back from there. I took photos of the bore which are posted at https://1drv.ms/f/s!AiR9KzpBmPls1ir6MmvonE1GHj9f. These are pretty high res, you can zoom in on them. The ring that you see at the top is not a lip. If anything, the opening of the cylinder is slightly larger than the bore itself. You can feel something when you run your finger over this, but it is not enough to catch your nail.

Any suggestions on how to remove the head studs? I gave it a half-hearted try with two nuts, but the one I attempted did not budge. I don't know that I have to remove them but it would make honing easier.

Seen a lot worse bores. My guess,just from photo, is that you'd probably get away with a hone & new rings. Looks like a tiny bit of water damage tho but not bad. Personally i would measure the bore & piston & compare to factory specs & wear limits instead of guessing. Dont be scared of getting the piston out you can always put it back. Now you have gone this far actually a hone, new rings & big-end bearing should be a minimum. But I can understand if you are working in situ it's a bit problematical.
If you try to pull the liner you can fill the block with crc rust eliminator & let sit overnite. Take out thermostat & anode first, block hole. It's very hard to do with a rusty salts caked liner

[Wotname]

Originally Posted by Homer Shannon

......

Any suggestions on how to remove the head studs? I gave it a half-hearted try with two nuts, but the one I attempted did not budge. I don't know that I have to remove them but it would make honing easier.

The two nut method has always worked for me but it does require a full hearted approach .

[Wotname]

Originally Posted by Compass790

....
If you try to pull the liner you can fill the block with crc rust eliminator & let sit overnite. Take out thermostat & anode first, block hole. It's very hard to do with a rusty salts caked liner

I used hydrochloric acid (muriatic acid in USA). Filled the water jacket in the block and left it sit for 30 minutes - it fizzes a lot - but it cleans years of salt and crud very fast. Got to rinse well and I suggest neutralise with bicarb soda afterwards.

[Wotname]

Originally Posted by Homer Shannon

Well, I confess to being of the "if it ain't broke, don't fix it" mentality. So, in the 20 years I've owned the boat I've never had the head or even the valve cover off. Of course, I usually only put about 50 hours on the motor a season, so 1,000 hours is a lot of years. mmm - like 20!

The motor USED to start easily. Lately, when really cold and unrun for a few days, it's become more difficult to start. It was run last Thursday when I hauled out (it started fairly easily), but today it was difficult to start. It does seem to be getting worse. It does not seem to matter how much throttle I give the engine for it to start as long as it's not fully stopped - the engine will not idle at zero throttle - it shuts down.

As for the lip, I'll know more when I clean up the bore a bit. I may find one buried in the carbon.

Far be it for me to suggest how someone should maintain their engine but I am very curious to know if you have been replacing the engine anode over the years.

My experience has been that the cast iron Yanmar raw water cooled engines last forever if the anodes are keep up to them but I would like to know how yours is looking if you haven't replaced the anode during this time - I am assuming salt water operation.

Most things left unmaintained can be fixed or replaced when the time comes but replacing a corroded out cast iron block is not normally done

And for other readers, the injection pump used on this engine does not have a seperate fuel shutoff lever, the engine is shut down by moving the throttle lever back past idle to a "stop" position.

[a64pilot]

I don’t understand the reluctance to remove the engine?
Remove it, then you can do a proper overhaul clean and paint it etc, and while you can hone the cylinder, if you replace it and maybe a piston, and have the head done, you have essentially a brand new engine, and will likely never have to do anything serious to it again.