Thrust bearing chucking motor...post mortem

carl

carl

True Classic
Took the motor all apart. I must admit, in the area where the crank and block are next to the thrust washers, nothing jumped out at me. Both washers had fallen out again and both were mangled up. I'm going to chuck the block (the 5th crank bearing block had been all chewed up. The crank I would not mind saving and there is a shop here that does nothing but crankshafts so I may take it to him for an opinion on whether to get rid of it.

This is all very sad as this ex-ITC race motor was otherwise in great shape. Pistons and rings look brand new, rod and crank bearings look perfect. The motor always had really nice oil pressure.

I'll keep all the ancillaries and actually a lot of those parts are needed to finish up the replacement motor.

If there are any measurements or pictures wanted in regard to the thrust washer issue, let me know.
 
Not the greatest news for me Carl and makes me a bit nervous. I was hoping you would find something obvious
 
I wonder if the block and/or crank had possibly been machined in the past, perhaps as part of the race engine prep, including the surfaces where the thrust bearings ride....causing them to have greater clearance/tolerance or reducing the size of the ridge that retains them.

It might be too late to check, but out of curiosity it would be interesting to know what the crank's total end play is (preferably with a dial gauge) without the thrust washers in place. Then what the thickness of both thrust bearings were. To compare the two dimensions.
 
Easy enough to drop the crank back in the block but the thrust washers are pretty beat up.
 
MWB gives a new std size spec, that would substitute for a measurement.
bearings.jpg
 
carl said:
the thrust washers are pretty beat up
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If they were new when you assembled the engine then you can just go by what their size was when new. As I recall they were not in place long enough to have any significant wear. As Jefco points out, standard = 2.37mm, or whatever oversize they were. The whole thought here is to try and determine if the block or crank had more than normal clearance that allowed them to fall out again.
 
post some pictures of the thrust washers and the crank thrust face / block recesses ... they can't just fall out if clearance was in spec.

SteveC
 
carl said:
IMG_0971[2][1].JPG
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I don't like the bevel on the inner face of the rear flange, it should be at a right angle to the crank's axis; my crank was much less worn there.
That looks like it would push the TW up and out, bending the inner part in.
Block looks OK, how is the bearing cap?
 
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From the pics I would venture that the crankshaft is the problem.

The thrust surface on the rear of the crankshaft looks like it's been ground or worn quite a bit. It should not have a sharp edge, it should look more like this one.
20190610_141255.jpg

The block looks good, and of course the thrust bearings are toast. How does the cap look?
If you had some good thrust bearings you could install them and see how much play you get when you shift the crankshaft "forward" - as if you were depressing the clutch. My guess is that you'll see more play in that direction than the other.
Good news, a good crankshaft should fix you up. Bad news, you probably need a good crankshaft.

FWIW
Notice the nice fillets on the Fiat crankshaft. Also, note the size of that bearing journal, way big for such a small engine. Also note the quality of the machining on all of the engine components, Fiat did a really good job manufacturing these SOHC jewels!
 
I certainly do not know much about the engineering or design, but I have to agree the others - the wear on at least one part of the crank looks very suspicious. Compare the angles on the two sample pictures from earlier posts; your crank and Mike's crank:

IMG_0971[2].JPG
20190610_141255.jpg


Seems like that angle would not allow the thrust washer on that side to be securely held in place. And once it fell out, the crank could move over and let the other one out.

Seeing your picture reminds me of another example we saw awhile back. His crank had the same "pointed" wear at that place and he had issues with the thrust washers as well. But I don't recall who it was.
 
This is the bearing cap.

IMG_0921[2].JPG


You can see the obvious groove machined in it. My buddy did put a spot of weld at the top of each end of the groove (after this pic was taken).

I'll pull the bearing cap off the motor I'm rebuilding and compare the crank shoulders to the "bad" crank.

Even if the block is good I'm not going to keep it, not looking for a third strike on this issue. If anyone wants the block with bearing caps free, obviously, let me know......and you have to come get it, not shipping!
 
that crank and block are basically trashed. there is no way you will keep thrust washers in that. I totally agree toss that one not worth the machining to repair. the crank and block would both have to be built up and re machined. There are no over sizes that wold take up that much once it is trued.
 
I pulled the bearing cap off the motor I'm rebuilding and we can definitely say the crank is trashed. As noted in Doc's, post with the side by side pics, the surface that the rear thrust bearing rides on should be perpendicular to the crank axis and on my bad crank it's angled. On my good crank it's clearly perpendicular. I will never know what started the deformation process, but I sure as hell know what to inspect when I have a crank exposed by removing a bearing cap.

Case closed.
 
carl said:
I sure as hell know what to inspect when I have a crank exposed by removing a bearing cap.
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And that has been the value of this unfortunate event for me as well. I've never experienced a problem like this, so had nothing to base my impressions on. In a earlier comment someone mentioned how damage to the crank or block surfaces could cause a problem. That made perfect sense to me, but until I saw those pictures and heard the description of events it really wasn't as meaningful. Perhaps this has helped others as well; hopefully Cliff will be more at ease knowing what to look for in his situation. So as much as I wish it hadn't happened to you, it has provided a benefit in some way. Plus now you know that your efforts to build the other engine will result in no such problems.
 
crank thrust face is U/S (That's Un-Serviceable for the people who haven't read the other thread...)

As several have noted it should be a nice right angle to the journal face (with a nice even radius between the two)

That's the reason the thrust washers dropped out.

If you had the crank thrust face ground back flat, it might come good with some oversized thrust washers .... I've seen 20 and 30 thou oversize, so as long as your not having to remove more material than the available thrust washers your golden. I wouldn't even think of having the crank welded, not a used cast iron crank, you'd never get a decent weld.

SteveC
 
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