Main Bearing Clearance

AA Ford Discussion Group relating to the repair and restoration of your AA Ford.
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NZAA
Posts: 9
Joined: March 21st, 2017, 11:13 am
Body Type: Cousins & Atkin
Model Year: 1928

Main Bearing Clearance

Post by NZAA » August 21st, 2017, 1:07 am

Hi There,
my father and I had the A engine from our truck rebuilt and after approximately 1500 miles it developed a deep knock. I have since found that the rear main bearing had too much clearance (more than .006") i am in the process of shaving down the caps to try to get a bit more life out of it and am wondering what the recommended clearance is????

Bob C
Posts: 1071
Joined: April 24th, 2003, 11:50 am
Body Type: Mail truck, Stake tr
Model Year: 1931
Location: SO CAL

Re: Main Bearing Clearance

Post by Bob C » August 21st, 2017, 8:42 am

.0015-.002 should do it. With only 1500 miles on the rebuild why are there no shims left??

Bob

NZAA
Posts: 9
Joined: March 21st, 2017, 11:13 am
Body Type: Cousins & Atkin
Model Year: 1928

Re: Main Bearing Clearance

Post by NZAA » August 21st, 2017, 12:16 pm

The person that Rebuilt the engine along with many others that I've talked to was against installing shims at the lineboring stage for reasons i'm unsure about as they would have made this process much easier and would have saved me from shaving the caps down resulting in oval holes for next time it is rebuilt. The other thing he was against and i'm sure it has also contributed to the increased clearance in such a short time was peining the babbitt. When we were assembling the engine we found that by pushing our thumbs on the sides of any of the bearings in the block or rear main cap (the untinned ones) oil could be seen squishing out between the babbitt and block/cap.

Bob C
Posts: 1071
Joined: April 24th, 2003, 11:50 am
Body Type: Mail truck, Stake tr
Model Year: 1931
Location: SO CAL

Re: Main Bearing Clearance

Post by Bob C » August 21st, 2017, 1:07 pm

Sounds like that engine in not long for this world.

Bob

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