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Join Date: Apr 2002
Location: Omaha, NE
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Playing with plastigage
After several failed attempts to get a clean run with the plastigage (and not smearing it), I finally was able to torque up a rod to the crank using the stretch method to .001-.00105 (M9 ARP bolts). Interestingly it took about 45 ft-lbs of torque to get them there and this was using ARP lube. ARP instructions specified 40 ft-lbs.
The crankwork was done by Armando at CCR and the rod journals were sized to .0027-.0028" per his recommendation but I wanted to try the plastigage to learn how to use it to confirm clearances. I'm using my old ARP rod bolts for practice. I suppose the correct way to do this would be to mount the rod in its final location on the crank, not just any of the journals. I don't know where they will be located yet Im still weighing the piston assemblies. Plastigage seems more like an eyeball check than a highly accurate method of verifying clearances. 
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1980 911SC Targa 3.6L |
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12-19-2015, 12:55 PM
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Plastigage - Indicator
Agree - plastigage is good for confirming your journals are in spec, but not for a precise measurement.
Here's my observations from using it during my rebuild: Checking Connecting Rod Bearing Clearances With Plastigage Nice work - measure twice (or as many times as you can stand) and assemble once...  Gordo
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Don "Gordo" Gordon '83 911SC Targa |
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12-19-2015, 03:12 PM
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It looks like there's oil on the journal? Plastigauge gets used dry, no oil anywhere, that will give inaccurate results.
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12-19-2015, 03:21 PM
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I did use a tiny dab of assembly lube to get the plastigage to stick to the journal. Not sure how else to do it. I discovered this from researching plastigage in this thread:
Checking Connecting Rod Bearing Clearances With Plastigage
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1980 911SC Targa 3.6L |
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12-20-2015, 04:47 AM
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Are those scores in the journal or is that from the assembly lube? Did they grind it or just polish it? Are you using standard or undersize bearings?
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12-20-2015, 06:11 AM
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No scores on the journals its from the lube. The journals were sized to match the rods with the bearings installed with .0027-.0028 oil clearance. Crank rec'd full treatment magnefluxed, cross drilled, new plugs, polished.
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1980 911SC Targa 3.6L |
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12-20-2015, 07:38 AM
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Chain fence eating turbo
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I'd argue that Plastigauge when done right is more accurate, as folks generally do not know how to use micrometers properly. Not saying everyone, but you have to get the feel and take lots of readings for accuracy.
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12-20-2015, 09:15 AM
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Join Date: Jul 2003
Location: cross roads
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The plasti stuff has saved my butt more than once.
I always use it as a last QC check. Somehow the wrong bearings got in the box one time , or was marked wrong....the green stuff is a good final quality control check. The guys that are pure machinist laugh at it .., but for us who do a engine once in a while , plasti gage is a asset for me.
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D troop 3/5 Air Cav,( Bastard CAV) and 162 Assult Helicopter Co- (Vultures) South of Saigon, U Minh Forest, Delta, and all parts in between |
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12-21-2015, 08:29 AM
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x 10. Assume nothing, measure everything.
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12-22-2015, 04:32 AM
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