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Finding a lot of F20s with main bearing damage -

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Finding a lot of F20s with main bearing damage -

 
Old 02-19-2018, 06:55 PM
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Default Finding a lot of F20s with main bearing damage -

I've got 3 blocks in the shop 2 F20s and 1 F22. One had lost all oil pressure and beat the crank so badly on the center main that it is not salvageable. The other two were caught before it got too bad and both the cranks were fine.

Does anyone know what the out-of-round spec of the ENGINE JOURNAL bore is? (not the crankshaft) The engine that saw the worst shows .0004" difference from one side of the journal to the other on the Y axis and as much as .001" on the X axis
On the other two blocks im getting no difference on the Y axis but still around .0004"-.0008" on the X axis

The only general spec I can find is one that KINGS bearings offers which is .001" on the X axis as long as the X is larger than the Y.
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Old 02-21-2018, 10:19 AM
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I'd think the specs should be no worse (and probably better) than the crank journals. For the F20, Helm spec (F20C) for both out-of-round and taper for the crank journals is 0.2mil (4um new, 6um limit). If it the engine journals were significantly worse, the crank journals would quickly wear past their limits.
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Old 02-21-2018, 01:28 PM
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The bearing shells do not make a perfect circle in this engine. That's why the instructions say to measure bearing clearance, and crank journal runout. The circle is made by the oil film in in the clearance.
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Old 02-22-2018, 12:42 PM
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Originally Posted by Slowcrash_101 View Post
The bearing shells do not make a perfect circle in this engine. That's why the instructions say to measure bearing clearance, and crank journal runout. The circle is made by the oil film in in the clearance.
I know this. But to say just measure the bearing clearance and runout of the crank would not be a bright idea in an engine that has seen use. If the mains are worn you could see significant variations in measurement from the X to Y axis. I agree that they should not be perfectly round, but there should also be a spec for how much out of round is acceptable. There is a reason why line boring the mains is a thing. Trying to get some information out of inline pro now. Will report back if I get an answer.
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Old 02-22-2018, 02:44 PM
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Think they can scrape material off the back of the bearings to match journal out of round.and also peg the bearing.
Just got to find a o/s bearing that is suitable though !!
I gave up and got another engine
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