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Author Topic:   main bearing clearence
Dirt Full Roller

Total posts: 42
posted May 15, 2002 02:16 PM
can someone tell me what the correct clearence on my stock 350 main bearings.and the correct way to do it?
thanks in advance

Dirt Freak

Total posts: 353
posted May 15, 2002 02:40 PM
.002-.003 is acceptable. We shoot for .0025-.003. If you are using a high volume pump you can run them on the loose side. Keep them on the tight side if you are using standard pump.

[This message has been edited by dirtbuster (edited May 15, 2002).]

Dirt Full Roller

Total posts: 42
posted May 15, 2002 03:19 PM
i am getting .006 on all the mains, do you all think this is o.k.

Dirt Freak

Total posts: 458
posted May 15, 2002 04:14 PM
It will NEVER live with .006 of clearance.
You need to be .0025 to .0030 A little more in a Aluminum block.....Because Aluminum expands more than steel with the heat......

If you are checking with a plastic stip (plastigauge) you are only checking one direction......... A rod or main needs to be checked in 3 different directions to make sure it's round. you could have .002 one way and have .005 the other......this must be checked with the proper gauges. Most people don't have them.........You need to bring this block and crank and rods to a GOOD machine shop and have them measured.

.002 to .0025 on the rods

.0025 to .0030 on the mains.

measure straight up and down, then 60 degrees on either side to make sure they are round..........that's what works. If they aren't right spend the money NOW......if you don't you will bolt it together and spin or burn a bearing then you will spend MORE money next week...........


Dirt Maniac

Total posts: 135
posted May 15, 2002 05:16 PM
new8.. Something is wrong here. You need to recheck things, because .006 is too much, and is actually hard to get unless something is worn out, or has been machined or assembled wrong. You are measuring clearance in the vertical direction aren't you? An installed bearing is not round, and will show more clearance at the parting line. This is called eccentricity, and is part of the design of the bearing, and will vary according to what purpose the bearing is intended for. The main(and rod) bearing BORE should be deadnutz round, but the installed bearing is not.

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