Main Bearing Clearance issue

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Jrama403
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Main Bearing Clearance issue

Post by Jrama403 »

Just in the process of installing our crank and noticed it was pretty hard to turn over by hand.

Tightened Main Caps to 80 ft/lbs

Plasti Guaged the bearings and looks like we are sitting at .0015 clearance (we tested 2 different bearings with the same results.

Spec is .001 to .0025

I have some pictures attached.

The crank has decent resistance when trying to turn it with one hand (best done with 2 hands) Further to the point check out the attached pictures of the wear marks left by turning the crank over by hand a dozen times.

Thoughts?

Image

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Russ Pottenger
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Re: Main Bearing Clearance issue

Post by Russ Pottenger »

Plastic gauge isn't the most accurate way to measure. Double check and make sure you have thrust clearance but it looks like you might have to line bore the block.
If your machine shop has V blocks they can check your crankshaft for straightness to eliminate that as a potential problem
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Re: Main Bearing Clearance issue

Post by Cheromaniac »

Russ Pottenger wrote:Plastic gauge isn't the most accurate way to measure. Double check and make sure you have thrust clearance but it looks like you might have to line bore the block.
My thoughts exactly.
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Re: Main Bearing Clearance issue

Post by gonridnu »

It appears from your pics the radius on the crank may be interfering with the bearings based on the "shiny" on both sides of the bearing. It could also be that you have not properly set the thrust bearing which would push the crank into an improper position.

First things first though. You need to leave the thrust cap slightly loose. Tap the crank towards the back of the engine with a dead blow or block of wood, then tap it forward to align the thrust surfaces, then tighten the thrust cap down. With an indicator attached to the block you can now measure crankshaft endplay

This will put the crank in the proper position relative to the rest of the bearing saddles. .0015" is a decent clearance and you should be able to easily rotate the crank with one hand (depending on assembly lube). It will still have a little drag, but should not require a lot of effort to turn it.
Jrama403
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Re: Main Bearing Clearance issue

Post by Jrama403 »

gonridnu - You have the correct answer! Turns out it needed to be tapped (set thrust) and everything fit just fine. Engine is all togther and I have it in the jeep, trans is on, manifold is on (PITA), should be smooth sailing hooking up the easy stuff.
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Re: Main Bearing Clearance issue

Post by Jrama403 »

gonridnu - You have the correct answer! Turns out it needed to be tapped (set thrust) and everything fit just fine. Engine is all together and I have it in the jeep, trans is on, manifold is on (PITA), should be smooth sailing hooking up the easy stuff.
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