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00transamnh 
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Joined: 15 Sep 2016
Location: Maine
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 Topic: How to measure bearing crush
Posted: 12 Oct 2016 at 12:05pm |
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Need some help folks.
I am rebuilding a Model B engine and could use some tips on how to properly measure the required .0015 bearing crush required on the main crank bearings. The crank has been turned down .010 and I have a set of .010 oversized bearings.
Unfortunately my selection of at home measurement instruments is very limited. The one solid instrument that I trust is a set of dial calipers.
Can anyone provide some insight into how I can verify that I am getting the appropriate crush? I fundamentally understand how the shims work and how to measure for the .002 bearing clearance.. but measuring for the .0015 crush is stumping me.
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steve(ill)
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Joined: 11 Sep 2009
Location: illinois
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Posted: 12 Oct 2016 at 12:10pm |
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you set the bearing insert into the cap. The bearing must sick up past the cap 1.5 thousands of an inch on one side so that when you install the cap, the bearing is crunched and not allowed to rotate or move in the bearing cap. .. you have to take the number of shims to be installed into account...the bearing half inside the block cavity could be flush with the face. ... with new bearings, you might have to file the end of the bearing insert as it may be too long and have too much crunch.
Edited by steve(ill) - 12 Oct 2016 at 12:13pm
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Like them all, but love the "B"s.
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Tbone95
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Posted: 12 Oct 2016 at 12:14pm |
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You can probably do it good enough to make it work, but realistically, you're not measuring .0015 accurately with dial calipers.
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00transamnh
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Location: Maine
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Posted: 12 Oct 2016 at 12:29pm |
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Thanks guys.
Hypothetical here... if I have .008 of shims on each side of the cap I should reasonably be measuring .008+.0015 beyond the cap. Meaning the bearing shell should stick out .0095 beyond the cap (or each bearing should protrude .00475 if I grind them evenly).
Between feeler gages and dial calipers I should be able to get close.
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DrAllis
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Posted: 12 Oct 2016 at 3:08pm |
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If you have just had the crankshaft reground to -.010", and you have new -.010" bearing shells, you need to use new shims that measure .010". You shouldn't really need to do anything else. You can plastigauge for the oil clearance, but if everything is correct, the clearance will be correct and within spec.
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Dick L
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Location: Edon Ohio
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Posted: 12 Oct 2016 at 3:31pm |
With a fresh ground crankshaft with bearings matched to the grind you should only need to be concerned with the bearing to crankshaft journal clearance. When installing new bearings to a used in spec under sized crankshaft is when you need to check for crush along with clearance. I shoot for .002 measured clearance between the two adding 1.5 thousands for crush. I file the bearing half in a bearing cap to get a proper filing.
Something has changed somewhere and I can no longer post pictures the old way. I can only post a link how I fit and file bearings(when needed).
Edited by Dick L - 12 Oct 2016 at 3:34pm
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00transamnh
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Posted: 12 Oct 2016 at 6:22pm |
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Thanks Gents. So, Dick are you saying I should need no shims at all or do you agree with Dr Allis that a .010 shim stack is what I should need?
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DiyDave
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Posted: 12 Oct 2016 at 7:31pm |
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Plastigage is what you need, just pop a stick in, tighten the cap in question, remove cap, and compare to the chart that comes with the plastigage kit, and you will know...
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Dick L
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Posted: 12 Oct 2016 at 7:42pm |
 Dick L wrote:
With a fresh ground crankshaft with bearings matched to the grind you should only need to be concerned with the bearing to crankshaft journal clearance. When installing new bearings to a used in spec under sized crankshaft is when you need to check for crush along with clearance. I shoot for .002 measured clearance between the two adding 1.5 thousands for crush. I file the bearing half in a bearing cap to get a proper filing.
Something has changed somewhere and I can no longer post pictures the old way. I can only post a link how I fit and file bearings(when needed).
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Yes I agree! I was trying to expand on where to be concerned. People get mixed up on where and how when it comes to fitting bearings for clearance and crush. Crush being how tight you squeeze the two haves together. You always have to shim these rods and mains (if) you have not had them machined to do away with the shims.
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