main bearings
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main bearings
just disassembled my 460. i have never used plastigage before.almost embarrassed to ask this but, do i need to buy new main bearings to check oil clearance or do i check the clearance with the old main bearings and then decide what size bearings to buy?
Fleet Mechanic
Joined: Mar 2004
Posts: 1,529
Likes: 35
From: Kansas
Originally Posted by burge743
just disassembled my 460. i have never used plastigage before.almost embarrassed to ask this but, do i need to buy new main bearings to check oil clearance or do i check the clearance with the old main bearings and then decide what size bearings to buy?
until they used it. Actually, you can use plastigage on new or used bearings.
It would be nice to know what you are doing to the engine. Are you completely overhauling it, re-ringing it or what? If you completely have the engine disassembled, I would have the crank freshened up, but that's just me.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
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From: Lake Tahoe, Nevada
The plastigauge will tell you the clearance betweent the bearing and the crank. It won't tell you what size bearings to buy. To determine that, look on the back of the bearing for any markings. If there is nothing there, you will have to measure the crank journal diameter. If you are not equipped to do that, pull the crank and take it to an automotive machine shop and let them evaluate it for you. If there is any scoring or ridges on the journals, you will need to get it turned.
Hotshot
Joined: Dec 2003
Posts: 18,423
Likes: 9
From: iowa
You should have the crank measured anyway if your going through it, that will tell you if you need to have it ground or just polished, and rather there is any taper to the journals.
You can use plastigauge to determine how much clearence you have though to determine if just putting new bearings in would be enough.
Just remember plasitigauge is a pretty rough measurement, so if this is a hi performance application using GOOD mics, and inside mics to measure the exact difference between teh bearings and the actual journal is the only way to get a precise measurement but most street builds don't need that type of accuracy.
You can use plastigauge to determine how much clearence you have though to determine if just putting new bearings in would be enough.
Just remember plasitigauge is a pretty rough measurement, so if this is a hi performance application using GOOD mics, and inside mics to measure the exact difference between teh bearings and the actual journal is the only way to get a precise measurement but most street builds don't need that type of accuracy.
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