My starter will not disengage

Question:

I bought a 1980 El Camino from a guy at the place where I work. He had put a new 350 cid engine in it that he got from a parts house. After going through three starters and two starter rings he gave up and sold me the truck. Now I have the engine on a stand. I’ve tried every shim combination and new starter and ring combination and the starter still will not disengage all the way. I need help! I’ve never had any trouble with a Chevy starter before. The front right side of the engine is stamped V1027CUB and there’s also a hand-stamped number of 61394. The back of the engine block has GM 3970010 cast into it.

Answer:

In the stamped-in engine code V1027CUB the V represents the Flint, Michigan, engine plant, 1027 indicates that the engine was originally assembled January 27th, and CUB is the application code, which indicates that the engine was configured for a 1975 Corvette with a base L48 engine and 4-speed manual transmission, or a 1977 or 1980 full-size, rear-wheel drive GM car.

What you called the “hand stamped” number 61394 is probably a job number or date code stamped into the block by a machine shop or rebuilder. The casting number 3970010 was the same for a family of 350 cid blocks that were very widely used in a large variety of different GM cars and trucks.

Your engine can use either of the two different diameter flywheels utilized on Chevrolet V-8 engines. The larger diameter flywheel measures 14 inches and has 168 teeth and the smaller one measures 12.75 inches and has 153 teeth. If you’re using a larger, 168-teeth flywheel you need a starter motor with a staggered bolt pattern. If you’re using a smaller, 153-teeth flywheel you need a starter motor with a straight across bolt pattern.

If your engine is mated to an automatic transmission, the starter nose needs to be the aluminum version. If your engine is mated to a manual transmission, the starter has to have the cast iron style nose. If you have a correct flywheel, starter motor, and motor nose combination, and the motor and solenoid are working properly, the motor should engage and disengage the flywheel smoothly and consistently.

Once in a while slight shimming between the motor and engine block is required. If you have a correct combination of parts and can’t get the motor and flywheel to disengage even after shimming the motor then something is probably wrong with the relative positioning of the starter motor on the block. I’ve never seen it, but I suppose it’s possible that the starter motor mount holes in the block are located in the wrong place.

If you make very careful measurements of the bolt holes relative to other important points, such as main bearing cap bolt holes, in your block and in another 3970010 cast block and compare the measurements you can determine whether your starter mount holes somehow got drilled incorrectly.