Crankshaft Wear Question - YSE 8.

[Wotname]

Please help me to work out the best way to deal with wear of the thrust face of a crankshaft main journal. The engine is a Yanmar YSE-8 that I'm currently rebuilding.

The rough sketch (not to scale) shows the issue better than I can describe. The forward thrust face and it's associated thrust washer shows almost zero wear. However the aft (flywheel end) thrust face on the main journal has ~10 thou wear and the aft combined main / thrust bearing is (of course) also worn. This bearing is getting replaced but should I be concerned with the wear on the actual crankshaft. If so, what are my options. FWIW, getting another crank is not an option.

1. Build up the wear with metal spray and and regrind the aft thrust face
2. Polish out the wear marks and not worry
3. Polish out the wear and remove the paper gasket between the crankcase and flywheel housing in order to move the aft main bearing thrust face towards the aft crank main journal. Use a chemical sealant in lieu of the paper gasket.
4. Have the forward thrust washer built up with white metal so it is 10 thou thicker thus moving the crankshaft towards the flywheel end and taking up the "slack".
5. ?????

Does it matter if the crankshaft has an extra 10 thou between it's front and rear thrust limits?

Why is all the wear on the aft end only? Is it because of the weight of the flywheel / clutch assembly and the incline of the engine in the boat or for some other reason(s)?

If the longitudinal movement is not critical, then 2 is certainly the cheapest option but if it critical, then 1 is probably the best but dearest while 3 is a cheap solution and achieves almost the same result. If so some reason, 3 proves impracticable, 4 remains a cheapish option.

Thoughts???

[jimbunyard]

If you're replacing the rear main bearing/thrust washer, measure the amount you need to make up after polishing the thrust journal and make a shim of the appropriately-sized thickness of shim stock and put it under the thrust flange before installing the brg/tw. If I understand correctly...



Don't know for sure, but it seems likely that a bearing supply house would be able to get pre-cut shims with varying od/id dimensions and thicknesses. Worth a shot to ask.

Don't know why, but it is common for the thrust to be worn more at the rear, in the manner you describe.

[DougR]

Most engine manufacturers that use thrust bearings which are separate from the main bearing shell offer oversize thrust bearings to compensate for crankshaft wear. Those that have thrust faces built into the main bearings shells offer main bearing shells that are undersize on the main bearing portion while over thickness on the thrust surface.

If these aren't available for your engine, then I think I would clean up the crankshaft thrust surface and shim behind the thrust flange on the bearing insert, same as mentioned by Jim.

I think most of the wear that you see on thrust bearings is the result of end thrust produced by helical drive gears on the timing gears.

DougR

[model 10]

I would shim the rear main fwd and enlarge the oil hole to match if necessary. If there is an end play spec, I would go as loose as possible. You may need to dress the bearing shells to fit further fwd.

[Cheechako]

Originally Posted by jimbunyard

If you're replacing the rear main bearing/thrust washer, measure the amount you need to make up after polishing the thrust journal and make a shim of the appropriately-sized thickness of shim stock and put it under the thrust flange before installing the brg/tw. If I understand correctly...



Don't know for sure, but it seems likely that a bearing supply house would be able to get pre-cut shims with varying od/id dimensions and thicknesses. Worth a shot to ask.

Don't know why, but it is common for the thrust to be worn more at the rear, in the manner you describe.

That's what I was thinking. Have that worn face properly smoothed and flat. Then shim the bearing to make up. BTW, you can cut thin brass shim with good scissors.

[Wotname]

Interesting... so far everyone is suggesting to shim the rear main brg/tw forward. This was also my first thought but it was discarded for the following reasons.

It would be difficult (but not impossible) to get the thickness of the shim exact. The engine shop is not keen on pressing in the bearing more than once. They are concerned that it is possible to damage the bearing by fitting, removing, refitting etc. Keep in mind the bearing is outrageously expensive (~$500) and the next one will have to be imported. So unless I'm convinced that this option is less risky than I currently believe, I am not too keen to shim.

I suppose I could shim and if it proves not enough, live with the result and if too much, then regrind the crank surface some more.

I am thinking that option 3 (in post 1) would achieve the same result but maybe I am missing something.

I did forget to say that under/over size main bearings are not available.

Another option which I also discarded was to turn up a new bearing from LG bronze. It was discarded because I wasn't sure how well this would last or if it would damage the crank. The Yanmar bearing (according to their literature is made from Kelmet metal which has a high(ish) Pb content (24%). I couldn't source any bearing stock that came close. Also it would not have the steel backing and so may be difficult to press in properly. Anyhow, I have shelled out the dollars for the Yanmar part now .

[Cheechako]

Originally Posted by Wotname

Interesting... so far everyone is suggesting to shim the rear main brg/tw forward. This was also my first thought but it was discarded for the following reasons.

It would be difficult (but not impossible) to get the thickness of the shim exact. The engine shop is not keen on pressing in the bearing more than once. They are concerned that it is possible to damage the bearing by fitting, removing, refitting etc. Keep in mind the bearing is outrageously expensive (~$500) and the next one will have to be imported. So unless I'm convinced that this option is less risky than I currently believe, I am not too keen to shim.

I suppose I could shim and if it proves not enough, live with the result and if too much, then regrind the crank surface some more.

I am thinking that option 3 (in post 1) would achieve the same result but maybe I am missing something.

I did forget to say that under/over size main bearings are not available.

Another option which I also discarded was to turn up a new bearing from LG bronze. It was discarded because I wasn't sure how well this would last or if it would damage the crank. The Yanmar bearing (according to their literature is made from Kelmet metal which has a high(ish) Pb content (24%). I couldn't source any bearing stock that came close. Also it would not have the steel backing and so may be difficult to press in properly. Anyhow, I have shelled out the dollars for the Yanmar part now .

Measure before you clean up the crank. Measure after. Use that thickness of material removed for the shim.

[Lepke]

If the engine always had oil, the wear on the crank should be minimal. The bearing naturally wears. If the bearing is down to the copper, I'd suspect dirty oil first.
The paper gasket makes up for slight machining differences so I'd keep it and shim the bearing to achieve oem clearance. Shimming is a common practice for experienced mechanics. Mechanics that are only parts changers usually cringe. Racing engines, if not align bored, often have shims under bearing shells to make an exact clearance that off the shelf replacement bearings can't do.
Most auto parts stores should have shim material in varying thicknesses. It comes in sheets. Nobody, even Yanmar is going to have custom cut shims. They can best be cut with a small, sharp blade on a cork or rubber pad. In engines with separate thrust bearings, depending on the design, have the shim glued in place with something like locktite.

[shakey doug]

Check crank web deflection the cause may be found there. The shim option as mentioned by others would be the way to go if no deflection problem found. The chances of finding thicker thrust washers would be slim.

[Compass790]

Wotname , If you have cleaned up crank thrust face you can measure thickness of old bearing flange if you have already removed it or in place if there is enuff flat beside it. Then dummy assemble it using old bearing if u have access to press ,measure side play & make shim to suit. I did it this way to work out how thick to get my flange machined to & it worked out according to calc. ( Miracles do happen!) Tolerance for crank sideplay is 0.155mm-).315 so it shouldnt be too difficult to land in that range.
Then you dont risk damaging yr new overpriced bearing .

[Wotname]

Originally Posted by shakey doug

Check crank web deflection the cause may be found there. The shim option as mentioned by others would be the way to go if no deflection problem found. The chances of finding thicker thrust washers would be slim.

Thanks, I hadn't considered crank web deflection - worth looking into!

[Wotname]

Originally Posted by Compass790

Wotname , If you have cleaned up crank thrust face you can measure thickness of old bearing flange if you have already removed it or in place if there is enuff flat beside it. Then dummy assemble it using old bearing if u have access to press ,measure side play & make shim to suit. I did it this way to work out how thick to get my flange machined to & it worked out according to calc. ( Miracles do happen!) Tolerance for crank sideplay is 0.155mm-).315 so it shouldnt be too difficult to land in that range.
Then you dont risk damaging yr new overpriced bearing .

Yes, this might work OK.
Get the crank cleaned up, dummy fit with old bearing still in place, measure end play, remove old bearing and compare the thrust thickness with the old one and the new one. Do the maths and add a shim of the required thickness.

What could go wrong.

[model 10]

[QUOTE=Wotname; What could go wrong. [/QUOTE]


The shims could fall out and cause the engine to blow up?

[jimbunyard]

Originally Posted by Wotname

Interesting... so far everyone is suggesting to shim the rear main brg/tw forward. This was also my first thought but it was discarded for the following reasons.

It would be difficult (but not impossible) to get the thickness of the shim exact. The engine shop is not keen on pressing in the bearing more than once. They are concerned that it is possible to damage the bearing by fitting, removing, refitting etc. Keep in mind the bearing is outrageously expensive (~$500) and the next one will have to be imported. So unless I'm convinced that this option is less risky than I currently believe, I am not too keen to shim.

I suppose I could shim and if it proves not enough, live with the result and if too much, then regrind the crank surface some more.

I am thinking that option 3 (in post 1) would achieve the same result but maybe I am missing something.

I did forget to say that under/over size main bearings are not available.

Another option which I also discarded was to turn up a new bearing from LG bronze. It was discarded because I wasn't sure how well this would last or if it would damage the crank. The Yanmar bearing (according to their literature is made from Kelmet metal which has a high(ish) Pb content (24%). I couldn't source any bearing stock that came close. Also it would not have the steel backing and so may be difficult to press in properly. Anyhow, I have shelled out the dollars for the Yanmar part now .

One of the beauties of working with metal is its' ability to be reliably measured and fitted.

There is no reason a good machine shop can't measure the existing relationships between the crank and old brg, measure the new brg and work out the desired shim thickness based on how much metal is removed from the crank.

If the crank endplay max is .45 mm (.0177") and the standard is .155 - .315mm, as stated in this manual,

http://www.google.com/url?sa=t&rct=j...Gt7n-2LyHj51FR

you've got a lot to work with.

Without being there, my approach would be to install the new front bearing, thrust washer and unpolished-thrust-journal crank, install the end plate with the old brg/tw and new gasket, and measure. Then grind the thrust journal 'X' amount and make up the differences between the amount taken off the crank and the difference in the new thrust bearing and the old thrust bearing to meet the desired end play (.230mm?) with a shim of the calculated thickness.

You'd still have the option to make adjustments via the end plate gasket thickness...

Agree with your shop, that rear main/thrust brg is a one-time installation thing...

How bad is the rear thrust journal?

Can you get or have made a thicker front thrust washer? Is there clearance at the back if you do?

[Wotname]

Originally Posted by jimbunyard

One of the beauties of working with metal is its' ability to be reliably measured and fitted.

There is no reason a good machine shop can't measure the existing relationships between the crank and old brg, measure the new brg and work out the desired shim thickness based on how much metal is removed from the crank.

The amount of metal already removed by the wear can only be estimated but it can be estimated reasonably well. Of course the amount removed by regrinding can be accurate so the total removed will be sorta close.


If the crank endplay max is .45 mm (.0177") and the standard is .155 - .315mm, as stated in this manual,

http://www.google.com/url?sa=t&rct=j...Gt7n-2LyHj51FR

you've got a lot to work with.

Very true

Without being there, my approach would be to install the new front bearing, thrust washer and unpolished-thrust-journal crank, install the end plate with the old brg/tw and new gasket, and measure. Then grind the thrust journal 'X' amount and make up the differences between the amount taken off the crank and the difference in the new thrust bearing and the old thrust bearing to meet the desired end play (.230mm?) with a shim of the calculated thickness.

Sounds reasonable

You'd still have the option to make adjustments via the end plate gasket thickness...

Agree with your shop, that rear main/thrust brg is a one-time installation thing...

How bad is the rear thrust journal?

It is the rear thrust journal that has the all the wear. It has a groove on it that is similar size of thrust brg face and that groove is ~10 thou deep. The front thrust journal is unworn and as is the front thrust washer.

Can you get or have made a thicker front thrust washer? Is there clearance at the back if you do?

The machine shop can add white metal to the front thrust washer if necessary.

So a combined approach might be best. Do as you and/or Compass 790 have described and if necessary, make the final adjustments by working on the front thrust washer. At least it is easy to get to and rework if required.