new main bearings problems
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Senior User
Joined: Jan 2005
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new main bearings problems
i'm currently rebuilding my 74 351w. i had the crank ground so that it's .020 under and when i put the main bearings in and torqued them down, i only turned the engine over by hand 30 times and it scratched the inserts. the rear main is the worst but i'm just wondering how much scraping is accectable on a fresh rebild. how long could it possibly run if it's scratching allready???
Posting Guru
Joined: Sep 2005
Posts: 2,238
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From: Kiefer, Northeastern Okla
Don't go any farther with your rebuild. Get new bearings, and make sure everything is absolutely clean before reassembly. Check the crank for scratches also. Did you clean the crank after machining? When you consider bearing tolerances, dust and dirt smaller than a human hair can have disasterous results in a hurry. Use only lint-free shop rags, NOT paper towels. Scrub well using hot soapy water and rinse well. Dry with compressed air. Clean again using brake cleaner and dry w/ air again, making sure you get the oil holes. Most shops will do a decent clean-up, but since you're doing the assembly, it's your responsibility to make sure it's absolutely clean, and it's a lot easier (and cheaper) than another rebuild. P.S. ALWAYS use Platiguage to check bearing tolerances before final assembly, on rods And mains.
FTE *******
Joined: Jan 2004
Posts: 791
Likes: 1
From: Pittsburgh, PA
Were you turning by HAND or by hand with a ratchet? Big differance. It should be coated with a nice assebly lube, and after TQ'ing it down you should be able to spin the crank with a nice steady drag on it from the oil. If you set there and spin it 50 times, your going to push the oil out also. The idea is to assemble with the good prelube, get er together, and get er started. If you wait 3 months before starting....I really would consider taking her back apart and re lubing the mains and rods, and the lifters as well.
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Post Fiend
Joined: Dec 2003
Posts: 6,658
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From: "Islander"
I would be easy to just pull the dizzy and pre oil the motor before firing it up than tear down again.
On cranks that have been ground and oil holes chamfered it's a must to micro polish across the oil holes as small burs can stick up and scratch bearings.
.....=o&o>.....
On cranks that have been ground and oil holes chamfered it's a must to micro polish across the oil holes as small burs can stick up and scratch bearings.
.....=o&o>.....
Last edited by "Beemer Nut"; Mar 23, 2006 at 12:18 AM.
