Crankshaft main bearing clearance help

[peteshack]

Replacing seals/gaskets on my 77 Spider with the 1765cc engine, 75K miles.
Definitely been worked on by PO - Thrust washer was laying in the case banged up.
Inspected the main crankshaft bearings and seemed a bit worn, so I decided to replace them.



The bearings were oversized .01
I that's guess because journals measure 2.0765 - 2.0775, and spec is 2.0860 - 2.0868

I installed new .01 bearings, plastigaug-ed, and the clearance was only .0015. Spec for the 1765 is .0020 - .0037
Pistons removed, I couldn't turn crank by hand, but I could with a wrench.

Not sure what to do.

Engine seemed to run fine before, so should I not worry about the tight clearance or should I get the journals reduced by 0.0005 to get my clearance up to 0.002?

Or do the bearings look OK?

Thanks!

[18Fiatsandcounting]

A few thoughts:

1) Don't reuse the old bearings. In addition to scoring, the black marks are kinda odd, like the oil was overheating and baked itself into the bearing surface.

2) How accurate are your measurements on the crankshaft journals? Are they round all the way around, and from one side to the other? No high spots or egg-shape? Maybe the 0.010" regrind wasn't done all that well?

3) The crankshaft should easily spin by hand, even with the pistons if you have the crankshaft pulley on the end. As you note, the minimum journal clearance is about 0.002", and if the clearance is 0.0015", the crank should still turn fairly easily. The fact that it doesn't means that something is wrong. I'm hoping the crankshaft isn't bent.

4) I wouldn't trust Plastigauge in this situation. To get a firm read on the bearing/journal clearance, you'd need a high quality micrometer and a dial bore gauge.

-Bryan

[peteshack]

Thanks for all the info Bryan.

I'll admit, the measuring may not have been the best. I measured with a digital micrometer (slide kind) and didn't really measure all the way around. Just took a few readings on some of the journals.

Sounds like I better take it to a machinist and have them really check it out for me.

[18Fiatsandcounting]

Sounds like I better take it to a machinist and have them really check it out for me.

Definitely. The more I look at your bearings, the more I think there was either oil starvation, overheating, or too close a tolerance.

There's a good summary of bearing failure by Mahle. Just google "mahle engine bearing failure" and the pdf document should be the first hit. Lots of pictures of scary looking bearings....

-Bryan

[1976spyd]

so, what would the best bearing be for a rebuild ?

[peteshack]

Having a tough time finding a reliable engine shop here in Memphis area.
But I can find someone who will simply grind the crank to what I ask for.

So I'm purchasing an outer micrometer, and a bore gauge to try to get the precise measurements so I can get the .0022 -.0037 clearance with a .01 bearing.

I'll also try to measure for any crank bend using a dial indicator.

I'll post my measurements back here in a couple of days.

[18Fiatsandcounting]

The general rule of thumb for bearing clearance is about 0.001" per inch of journal diameter, which for your 2.08" journals, would be about 0.0021" clearance. Fiat chose to specify clearances slightly larger than this for likely good reasons, such as oil viscosity, oil volume flow, higher revving engine, longevity, etc.

My suggestion is to very accurately go over this crankshaft journals and figure out what's going on (why you can't rotate it by hand). Check for high spots, taper, egg-shaped, bent, etc. If you don't have a good crank, there's not much reason to proceed down that path.

If you need a regrind or even just a good polishing, your crankshaft shop should be able to help with that.

As for bearings? I'm not particular to any brand, but rather just buy what the vendors sell.

Oh, and I keep forgetting to ask: I'm assuming the engine is out of the car, yes? Given that the thrust washer was laying in the oil pan, the block should be carefully gone over as well.

-Bryan

[peteshack]

So I purchased an outer micrometer, bore gauge, and dial indicator to measure everything correctly.

I measured the main journals left and right edges, and again at 90deg.
They all measure 2.0770 - 2.0780
Spec is 2.0860 - 2.0868, and at .01 under it would be 2.0760 - 2.0768

I set the bore gauge to the outer micrometer and checked bearing clearance.
All measured 0.0014 - .0015
Spec is .0020 - .0037

I set the crank in the block with only top bearings (oiled), no caps, and positioned dial indicator on each main journal as I rotated the crank.
No real variances noted.

Without the caps, I can turn the crank by hand although it's pretty tight. Definitely doesn't spin freely.

Do you think the under-spec clearance is the real cause for not being able to turn by hand?
Would I ask a machinist to grind the crank down by .001 or just tell them to get it in range of 2.0760 - 2.0768?

[18Fiatsandcounting]

Do you think the under-spec clearance is the real cause for not being able to turn by hand?

With a clearance of 0.0015" or thereabouts, the crank should still turn easily in the bearing saddles, even with the main caps installed and torqued down. The crank shouldn't "spin" in the sense that you can spin it up by hand and then have it keep spinning when you release it, but it should rotate freely and smoothly. Have you bought a new set of 0.01" oversize bearings, or are you using the old bearings? If the old bearings, maybe these are out of round or otherwise goofed up.

Can you tell where the crank is locking up? Are the thrust washers OK?

-Bryan

[peteshack]

OK, knowing it should turn at .0015 helps.
Yes I'm using new. 01 bearings.

With the caps off it does seem to bind up a bit when I turn it.

I think at this point it's time to send it to an engine shop. The challenge now is to find a good one near Memphis, or maybe ship off to Allison in California?

Thanks for all of your feedback!

Pete

[18Fiatsandcounting]

Diagnosing a crankshaft issue is not Fiat specific, so any machine shop should be able to do this. It's one of the most basic of operations, and your engine is no different than a small block Chevy in this regard.

Just one thought: If you do want to send the engine out, look up Jon Logan at Midwest-Bayless in Ohio. Much closer to Memphis.

-Bryan

[peteshack]

Bryan, thanks for Jon's contact!
Driving the engine up to him on Monday.

[18Fiatsandcounting]

Awesome! I've never used Jon's services as I do my own work, but he has a lot of good recommendations. Let us know what you find out.

-Bryan