tolerances and such
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Senior User
Joined: Nov 2002
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From: ca
tolerances and such
I am working on my first build up of a 400m and i've came to something which I have had no prior experience tolerances.
I was told to use something called plastigage to measure the gap between the crank and bearings when I put the crankshaft in.
Is it necessary to check this? And if so how would I go about doing it?
I was told to use something called plastigage to measure the gap between the crank and bearings when I put the crankshaft in.
Is it necessary to check this? And if so how would I go about doing it?
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Joined: Feb 2001
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From: Porterfield
tolerances and such
Well go to your auto parts store and ask for the plastigage for cranks and rods, I think it comes in a few differant colors the green is what I use .
Then you will take a Small piece of it place it on your crank journal and put on the main cap and torque to spec. DO NOT MOVE CRANK.... Now remove main caps and use the gage on the paper to measure the gap... Should be between .001 to .002 ... Now do the same to all your rods ...Make notes to all your readings in a not pad for future referances.
Then you will take a Small piece of it place it on your crank journal and put on the main cap and torque to spec. DO NOT MOVE CRANK.... Now remove main caps and use the gage on the paper to measure the gap... Should be between .001 to .002 ... Now do the same to all your rods ...Make notes to all your readings in a not pad for future referances.
Posting Guru
Joined: Aug 2000
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From: PacNW
tolerances and such
Originally posted by dustinleavitt2000
they had like thre colors and thats all the could tell what color or colors should I get and how much???
they had like thre colors and thats all the could tell what color or colors should I get and how much???
Laughing Gas
Joined: Nov 2002
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From: Fairmont
tolerances and such
Also don't have any oil on the crank journals when you do this, you'll get a bad reading. Like stated befor put the plastigage between the crank and the bearing, not the block and the bearing. Sounds dumb but I know someone who did this.
Also when you are done getting your readings leave the plastigage alone. It will dissolve in oil. You can do more damage trying to remove it.
Plastigage keeps alot longer if you keep it in the refrigerator.
Also when you are done getting your readings leave the plastigage alone. It will dissolve in oil. You can do more damage trying to remove it.
Plastigage keeps alot longer if you keep it in the refrigerator.
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Laughing Gas
Joined: Nov 2002
Posts: 1,198
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From: Fairmont
tolerances and such
If it's for the street, .001-.0015, Racing applications we have studied and found .002"-.00225" is perfect. I will not let a race engine go over .0025" (Very few exceptions)
Street I'd hate to see .002". Keep in mind the difference between .001" clearence and .002" clearence is not .001", but twice the clearence. Catch that? Not trying to be tricky here.
On some occations we have split bearing sets to get or proper clearence. In other words used (1) std bearing half and use (1) .001" bearing half to tighten it up .0005". You get the idea.
Street I'd hate to see .002". Keep in mind the difference between .001" clearence and .002" clearence is not .001", but twice the clearence. Catch that? Not trying to be tricky here.
On some occations we have split bearing sets to get or proper clearence. In other words used (1) std bearing half and use (1) .001" bearing half to tighten it up .0005". You get the idea.
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Senior User
Joined: Mar 2001
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From: Maryland
tolerances and such
TMI, thanks for the info. I am gathering this info to fix my blonder listed as "rebuilt 351m I think its shot" I will be pulling the eng out next week to check what I messed up. Thanks Art
