rod bearing plastigage help?
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Originally Posted by joecar
Bad assumption. 
Either way, assuming a clearance is correct and finding out later it wasn't takes the longest and costs the most!
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Joined: Apr 2006
Posts: 40
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From: Madison CT
Originally Posted by ezrollin
assuming I got the right bearings for my engine, i shouldnt need to check clearance
the measurements that are used are the ones coming from the factory, on a used engine there is wear and when there is wear those numbers are not correct. my engines teacher made us plastiguage even if you had a brand new crank and bearing. he said has seen a few bearings be in the wrong box or just cut wrong. its cheap enough / easy enough and verry accurate. Even if you do it and find everything is perfect, its better to know then guess
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Joined: May 2006
Posts: 34
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From: New Smyrna Beach
yea, you definetly should check everythings clearance, to much or to little clearance on start-up could be very damaging. Also, remember to clean the plastigage very good from the area you checked before reassembly.
ezrollin... a nice thing about gauging the clearance is that if you find one rod too close and another too loose, you can swap bearings, whole or half and get all the clearances exactly where you want them. This will ensure longevity. GL
Charlie
Charlie
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Joined: Mar 2006
Posts: 49
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From: Northwest Indiana
I am going to plastigage my mains and rods as well and I was wondering if you are suppose to torque all the new bolts completely and reuse them upon final assembly or should I use the old bolts for measuring purposes. I am using all ARP fasteners with clevite 77 bearings and an eagle crank. Also when you set the plastigage on the bearing surface is it more accurate to lay it parallel or perpendicular to the bearing. Thanks in advance.
If I were you, I would install the bolts per ARP's instructions. Pay particular attention to the burnishing process. Usually they have you fully torque and then loosen the bolts a few times to reduce the friction in the fastener. Also, use whatever lubricant they recommend when installing.
When I've used plastigage, I laid a strip perpendicular to the bearing so that one end points to the front of the engine, and the other towards the rear.
When I've used plastigage, I laid a strip perpendicular to the bearing so that one end points to the front of the engine, and the other towards the rear.
I recently took some pictures while checking the bearings on my 406 SBC. With the rod cap off, set a short piece of the plastigage on the crank.
Install the rod cap and torque to spec. Remove the cap and compare the flattened thickness to the gauge on the plastigauge wrapper. You are looking for .0015" to .003" clearance.
Install the rod cap and torque to spec. Remove the cap and compare the flattened thickness to the gauge on the plastigauge wrapper. You are looking for .0015" to .003" clearance.
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Joined: Feb 2008
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just like the other ppl said how to use it, it is very straight forward and easy (as i just used it today) but you can only figure plastigage is a true measurement if the crank or rod bearing journels are not out of round or tapperd... i would check for out of round and tappers before i plastigaged it....
0015, 77, bbc, bearing, bearings, crank, gage, high, instructions, plastigage, plastigauge, plastiguage, reads, rod, sbc, tolerances
