Scored Crankshaft Question (Yanmar)

[model 10]

Look at the bottom shell, it has metal piled up. It's about as gross as the digits holding it. Wear gloves man. There is no need to make sailing look so distasteful.

[Compass790]

Wotname I have been thru this process & can tell you what not to do. You cannot buy crankshafts any more. I couldnt find oversize bearings. I got the crankpin ground & machined up an LG2 bronze bearing to use temporarily till we could find a second hand crankshaft. Guy who ground the crankpin told me the hardness went way in & I could do it again ( Over 1mm less in dia). Just pulled it apart again ( as have got good used crank) & found the LG2 bearing is surviving good ( 200 hrs) but crankpin is scored because LG2 is too hard & any particles wont sink into it like white metal. I'd be tempted just to polish your crankpin & put new bearings in but I'm not an engine rebuilder by trade. If you want a cheaper aftermarket std bearing or other parts PM me. YSE, YSB, & YSM8 crankshafts are the same FYI

[Wotname]

Originally Posted by Bill Seal

I would polish the journal with crocus cloth, put a .002 shim between the cap and insert, check out the clearance with Plastigage, and go for it while trying to find another engine in a year or so.

Never thought of that!

Is this a serious suggestion or are you pulling leg?

If it is serious, I understand it would be a "field repair" but it could work...

[Wotname]

Originally Posted by Guy

Look at the bottom shell, it has metal piled up. It's about as gross as the digits holding it. Wear gloves man. There is no need to make sailing look so distasteful.

Hey, I resemble that remark!
Gloves are for re-assembling clean engine so your hands don't make them dirty...

And it is for a mobo anyway...

[Compass790]

Originally Posted by Wotname

Picture of bearing shells.
Now that I have had a better look, it is clear that the scoring matches the journal lube passage and so I am assuming the hard stuff has scored the softer bearing metal down to the backing shell material and then started working on the hardened crank journal.

At this stage, I need to get the crank right out and check the mains.

Have found one second hand crank, supposedly still within limits for around $450 (USD) - work in progress!

I gotta short block for $55 but ya but ya have to keep yr eye out on Ebay or whatever yr local sites are.Cant be in a hurry. Amazing how t...a....d some people are moaning about yr hands WTF???

[Pizzazz]

Well, if it is the crank pin, then I know Yanmar makes -50 bearings (20/1000") for the YS so you are all set. Get the -50, polish the journal and measure the gap with plastigauge. If you have room then grind the journal a little bit. In any case, you are at the limit, so it would be a short term repair. For the crank pin, the stresses are very high, so you want a machine shop to polish/grind it, so that it is a perfect circle. Yanmar states the tolerance is only 1/1000 for the oval and I do not think you can achieve that by polishing by hand.

[Lepke]

The crank still has most of its bearing surface. The engine will never know the difference. If you do proper maintenance in the future it should last a normal life.
In the olden days we polished much worse journals with crocus cloth. When the journal was slightly undersized, we added shim stock under the bearing to get the required clearance. And the engines ran fine.

[jimbunyard]

Now that's an interesting picture.

I take it that the bottom is the rod and the top is the rod cap?

While depth is notoriously hard to judge in pictures, it certainly appears to me that the groove in the worn shell (the one that is showing copper) is shallower than the groove in the bearing in the top of the picture, or indeed even than the groove further up the sides of the worn bearing. Which would leave me to believe that the trash passed through rather earlier in the life of the engine, and it ran quite a while with the scored crank, at least long enough to wear the aluminum (or whatever it is) off the bearing.

Could just be an optical illusion though...

Other than the groove, the bearing shows normal wear; would expect the bottom of the mains to be similarly worn.

450.00 seems steep for a used crank, especially if your crank is within spec except for those 2 little scratches...

By the way, what happened to the existing engine?

[Wotname]

UPDATE.

I've gone off half cocked (again ). As some of you have indicated, there are undersized bearings available for the crank pin; both 0.25 and 0.50 (mm) so the pressure is off for a moment. It was undersized mains that are no longer available.

Next excitement will be seeing what the mains look like.

[Wotname]

Originally Posted by jimbunyard

...........

450.00 seems steep for a used crank, especially if your crank is within spec except for those 2 little scratches...

By the way, what happened to the existing engine?

Don't really know, it was removed from the boat before I got it and AFAIK, it was removed because of no compression. I believe that sea water had got back into the exhaust port and sat there for weeks (and perhaps months). I do know that the crank had been removed from it and sold sometime after that.

[Compass790]

No the excitement will be if they are knackered as from memory ( not to be trusted) I think the flanged main bearing ( flywheel end) was $400+ US when I tried Toad marine supply. I'm just going to machine new main bearings to suit slightly worn crank. Sorry if I put you crook I couldnt get any aftermarket undersize big-end bearings, we never buy genuine Yanmar if we can avoid it. To grind the crank-pin only cost me $40.
It says not to shim or machine big-end bearing but I'd certainly try shimming but I already said about machining big-end bearing

[Compass790]

Common problem for seawater to get in exhaust v/v end on these engines due to poor design/material of exhaust elbow.I sell a few aftermarket exhaust v/v's because of this prbblem & recommend making a stainless elbow if you can weld.

[Wotname]

Originally Posted by Compass790

No the excitement will be if they are knackered as from memory ( not to be trusted) I think the flanged main bearing ( flywheel end) was $400+ US when I tried Toad marine supply. I'm just going to machine new main bearings to suit slightly worn crank. Sorry if I put you crook I couldnt get any aftermarket undersize big-end bearings, we never buy genuine Yanmar if we can avoid it. To grind the crank-pin only cost me $40.
It says not to shim or machine big-end bearing but I'd certainly try shimming but I already said about machining big-end bearing

Hmm... well the Yanmar parts are expensive...

I have some current prices (in AUD). The main on the flywheel side $480, the other main $100, the thrust washer $70

[shakey doug]

These engines are about as crude and tough as any engine ever made. Over built to run on very poor quality fuels, 80% of the those still running would have cranks in this condition or worse. Give it a light rub & box up.

[Elie]

Originally Posted by four winds

I wouldnt attempt to remove the scoring. The engine will never know it's there.

Only you will have to work at forgetting about it.

That the good idea!. As long as there is no barbs or rough area on the bearing(a light sanding would take care of that). the oil pressure will be ok, and you will notice nothing as the engine will run perfectly. The good bearing surface is large enough to permit to ignore that little scratch...