cracked main bearing

[art ebeling]

This is the rear main bearing cap o a 29 I am working on. Is there anyway to save this or is it new babbit time?

[ModelA29]

Those flaws look like they have been there since it was poured.

[nkaminar]

The prudent thing to do is to find a good cap and then fit it to the crankshaft using Timesaver. You could put it back in but you are taking a chance. If you only drive the car occasionally down to the local ice cream store then you could chance it. Don't put it back in if you plan on doing any tours or extended trips.

It looks like you have the engine out of the car and have it mostly apart. If you haven't already done so, take the crankshaft out and look at the Babbett in the block.

[Bob Bidonde]

The crack is likely due to the Babbitt rear thrust face not adhering to the cap when it was poured, so there is a small gap between the Babbitt and the cap. Continuous on-off pressure from the crankshaft bends the Babbitt and it eventually cracks. This is a common malady with the Model A's rear main bearing.

[Gene F]

These responses look spot-on to me.

[SAJ]

Sponsored Links (Register now to hide all advertisements)

I am thinking it may be possible to affix the thrust face with tiny countersunk screws much as is done to retain aftermarket bronze thrust washers. A simple drill and tap job. A screw could even be countersunk into the bearing face for more security. The rest of the babbitt looks good enough to try and save this bearing.
SAJ in NZ

[Bob Bidonde]

The repair thrust face available from Syner's (A-6334) is my choice. I have an engine that needs it. I plan to secure the repair thrust face with JB Weld.

[Terry Burtz, Calif]

Originally Posted by Bob Bidonde

The repair thrust face available from Syner's (A-6334) is my choice. I have an engine that needs it. I plan to secure the repair thrust face with JB Weld.

Art Ebling's forward thrust bearing is bad. The part you show is for the rear thrust bearing.

The rear thrust bearing is loaded by timing gear thrust and when the clutch pedal is depressed. The forward thrust bearing is not loaded and simply keeps the crankshaft from moving.

My suggestion is to do nothing because there is a forward thrust bearing in the cylinder block that will keep the crankshaft from moving.