VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Bearing Clearances on 27' truck

Does anyone know what the correct tolerances should be for main and rod bearings on a 27' engine? :confused:

The bearings clearance should be between 0.001"-0.002". The best way to check is the roll test on the crank bearings and hammer tap test on the rods. Plastigage is an alternative but suggest bluing the bearings to check for high spots.

Tryed using plastigage on mains and at .002" was getting a high spot. Please forgive my ignorance, but how do I 'blue' the bearings for high spots? Once found, how do I correct the high spots?

Get some bearing bluing at the auto parts store. You may need to check several as the high volume places might not carry it. Put a thin even coat on the bearing or shaft then assemble the part. Rotate 1 revolution and take apart. Check to see if there is an even coat or thin and thick places. If all the bluing is removed then there is metal to metal contact. Using a bearing scraper (a curved, triangular shaped, sharp-edged tool that looks sorta like a soldering iron) to remove a little material from the high spot. If careful a sharp knife blade can be used but it is easier to remove too much with anything but a scraper.

There are some articles on the web on the process. You will need to use a search engine to find them.