Yanmar SB12 Using Oil

[Wotname]

Originally Posted by Homer Shannon

I started putting together a list of the parts I would need if I go ahead and rebuild my engine's head and put in new rings. In this process I have noticed that no valve guide seals are shown or listed in the parts diagram. (Item 33/34 in the attached diagram is a retainer.) https://1drv.ms/u/s!AiR9KzpBmPls1hfnrR3o8rBWZFZi

Is it possible that this design does not have valve guide seals, and if so, wouldn't wear on the valve guides themselves, therefore, create more oil consumption than usual?

Am I right in my conclusion about the seals not being used?

Probably, the YSE doesn't have valve guide seals and this engine is of similar vintage and share most of it's design features.

As to the oil consumption, I will leave it to others with more knowledge of these things to comment except to say I think any increase in oil consumption would be minimal.

[a64pilot]

Oil consumption would be very minimal, what guide seals do more than anything else is prevent oil from creeping down another shut down so you don’t get a smoky start, but it would only be a smoky start.
I know building race motors years ago we never bothered with valve seals, don’t know why, they didn’t cause a problem, just we didn’t fit them.

If they aren’t called for, I wouldn’t fit them.

[Homer Shannon]

The YSE and YSB are identical in this area, so if the YSE does not have them, the YSB does not either, which was what I was surmising. Thanks for confirming it.

[Compass790]

I deal a bit with YS8/12 series aftermarket parts & can tell you as Lepke says valve guides are rarely a problem. Almost sure your problem will be in the piston/rings & cylinder liner area. A bloke (guy in N.America english) i know is currently using a piston & rings out of an SB12 in his YSE12 so they must be compatible.
Before i sourced aftermarket liners I used to have similar oil consumption to yours in our YSM8 but putting new Piston & rings in slowed it right down even with a badly worn liner at least once it wore in. Took about 50 hrs to wear in as i didnt hone as was intending to put new liner in. Previous to putting new piston & rings in i had to squirt oil in air intake to get compression high enough to start it.
Now it has new liner in hardly use any oil btwn oil changes.
Wotname has given you good advice particularly concerning oil pump, rotor seems to wear down into case messing up the clearances.

[Compass790]

Forgot to say changing the oil viscosity from 15w-40 to straight 30 will not solve your oil consumption problem. Try it & see. However you definitely can run a while like that if you wish to put up with it as you have been doing for years. Doubt very much that you have seals on yr v/v guides,not in that era.
If you do up the cylinder area you will get more power as well I'd hazard a guess

[Wotname]

Originally Posted by Compass790

...........
Wotname has given you good advice particularly concerning oil pump, rotor seems to wear down into case messing up the clearances.

Maybe I'm not as smart as I thought I was

Had another look at the parts breakdown and the SB differs from the YSE/YSB in that it has a discrete oil pump housing that is replaceable unlike the Y series where it is just milled into the front PTO case.

FWIW to any reader!

[Homer Shannon]

I pulled the head off of this motor this morning. It was a lot easier than anticipated. Everything looks pretty normal, but I am concerned that one of the three head bolts (studs, actually) had a lot of oil on it and there was a lot of oil in this area on the head gasket. I think most of this oil got on the head gasket during disassembly, but in the attached photo of the head, it does look like some of that oil may have been finding its way into the combustion chamber. It is possible that my oil consumption issue is due to a failing head gasket? Seems a bit far fetched to me as I don't know why oil, that is not under pressure, would be getting sucked into the combustion chamber. Still, I'd like to hear from more experienced mechanics before moving forward.

I have also confirmed that I can remove the piston rod cap through the side panel. It is not necessary to remove the motor to get the piston out. I'm not going to take that next step, however, until I hear from others about what I have found so far.

Photos are posted at [URL="https://1drv.ms/f/s!AiR9KzpBmPls1ibkpMIJGuPEN15Z"]/URL]

[a64pilot]

Very unlikely oil consumption is from head gasket.
I’ve never seen it, but then I suppose I haven’t seen everything. It is possible, but I think very unlikely.

[Wotname]

^^ I concur.

At this point, I would be looking for any lip at the top of the liner and give the bore a good clean (very good clean) and look to see if there are any hone marks left.

If any lip or no hone marks, I would pull the piston, measure the various aspects (ring gap, land size etc) and probably pull the liner and measure. All can be done is situ although the liner might fight you a little.

Depending on measurements, hone and new rings OR new piston (& rings) and liner.

[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.

[Compass790]

Originally Posted by Homer Shannon

I pulled the head off of this motor this morning. It was a lot easier than anticipated. Everything looks pretty normal, but I am concerned that one of the three head bolts (studs, actually) had a lot of oil on it and there was a lot of oil in this area on the head gasket. I think most of this oil got on the head gasket during disassembly, but in the attached photo of the head, it does look like some of that oil may have been finding its way into the combustion chamber. It is possible that my oil consumption issue is due to a failing head gasket? Seems a bit far fetched to me as I don't know why oil, that is not under pressure, would be getting sucked into the combustion chamber. Still, I'd like to hear from more experienced mechanics before moving forward.

I have also confirmed that I can remove the piston rod cap through the side panel. It is not necessary to remove the motor to get the piston out. I'm not going to take that next step, however, until I hear from others about what I have found so far.

Photos are posted at [URL="https://1drv.ms/f/s!AiR9KzpBmPls1ibkpMIJGuPEN15Z"]/URL]

What wotname & A64 says but I'd add that from your pic it looks like you have way too big clearance between piston & bore so gud chance that everything in there is worn out. It could be just the photo or my eyes but you need to check.
The way your piston looks I doubt the head gasket is the problem

[Homer Shannon]

Wotname:

When I bought the boat, twenty years ago, the previous owner instructed me about topping the cylinder after shutdown. I confess that I did it for a while but have stopped the practice for a long time.

I guess my next step is going to be to clean the cylinder and get a better look at it. What do you recommend to clean it with? BTW, the cylinder does not seem to have a significant lip. There is a build up of carbon in the top ~5/16" but I think that can be taken right off and the bore would be smooth.

From there, I'll have to pull the piston. I don't think that will be difficult, though replacement may be complicated by the lack of space to swing a proper torque wrench. I'll take some measurements and make sure I can get a proper tool before I disassemble.

[Compass790]

I'm surprised you dont have a significant lip. Btw how long has it been since the valves have been ground? Manual says every 1000 hrs for our YSM8. When you said it starts easy how much throttle do you need to use? For example when we had low compression we needed full throttle, now the engine has had a birthday it needs no throttle even at 5oC

[Homer Shannon]

Originally Posted by Compass790

I'm surprised you dont have a significant lip. Btw how long has it been since the valves have been ground? Manual says every 1000 hrs for our YSM8. When you said it starts easy how much throttle do you need to use? For example when we had low compression we needed full throttle, now the engine has had a birthday it needs no throttle even at 5oC

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.

[Compass790]

Aaah well if the rocker cover hasnt been off I can assume that means tappet clearances were never adjusted either. Now you have the head off you can check the valves & their seats. What about oil & fuel/oil filter changes ? Probably time to clean injector or replace nozzle too. There are youtube vids on doing that