Re: Bad news from my compression test I think....how can car STILL refuse to start?

Posted by JWL On 2012/9/11 10:04:45

Refacing the valves is commonly known as grinding them. You will need to take them to a machine shop or other shop that has the equipment to do this job. You can get the angle specs from the shop manual. I believe Packard used two angles: 30 and 45 deg., but I don't know which angle is for the exhaust and intake. Looking at the valves will quickly tell you the angle for each. If the valves have been ground before they may be too thin to do another grinding. If this is the case, then you will need new or good used valves.

Lapping is a way to improve the surface on the valve seat. It is a simple procedure using lapping compound and a suction cup tool. This can be done only if the seats are in good condition and do not need to be ground. Grinding the seats also takes a special tool and grinding stones. This was a common job "back in the day", but is a lost art now as all the engines have their valves in the head and not the block. Folks just take the head to the shop for a valve job. If the seats need grinding you will need to find someone who has the tool and stones and is willing to come to your house to do the job in the car; or, tow the car to the garage or shop.

Lapping is the final step in a valve grind job. It mates the valves and the seats and serves as a check (with the pattern left on the valve and seat) to make sure the valve-seat contact is at the proper place on each.

Years ago I did a valve job on a 1939 Cadillac V-8. An L-head engine. The exhaust valves were all replaced because they were too thin from previous jobs, and one had cracked. Also, one of the valve guides was replaced. The valve seats in the block were in great shape and lapping the newly refaced intake valves and the new exhaust valves worked as I did not have to have the seats ground. Measuring and getting the valve stems to the correct length to set the pistons in the hydraulic lifters at the right setting was the most difficult part, but you do not have to worry about this as you have mechanical tappets.

Good luck,

(o[]o)