65 352 Heads...burnt #7 valve
 

I did some searching on this forum and came up with some clues but need some help. I just purchased a 65 galaxie 352 with 72,000 original miles. The engine has never been apart. It is dropping a cylinder at idle. Compression test show 110 on number 7 with 150 on the rest. A vacuum guage needle swings back and forth at idle so I suspect a burnt exhaust valve. I did install an MSD ignition system (coil, cap, rotor, wires, petronix, and MSD box) but my luck wasn't good. I have heard that #7 and #8 cylinders are prone to this. I am going to pull the heads for repair and have hardened exhaust valve seats installed. Is there something I can do to keep this from happening again. I read a post describing the difficulty installing a new seat on this cylinder because of the thin area around it. This is going to be a daily driver with lots of miles. Also, does anyone know of a top quality machine shop in the SF Bay Area that is familiar with FE heads? I appreciate any help here. Thanks.

Mark

Hi an' good score on your galaxie.burnt valves can be from running lean from an air leak or ..in my case over revving and bending the valve..have you tried doing a wet test ..a little oil in the cylinder if the commpression comes up the it might be a broken ring..and if you have ajustable rockers ..a 352 should have. check you clearances.it might just be not closeing compleatly..good luck..

A burnt valve usually reads very low compression #'s. 0-40 if truly burnt. I'd do a po-boy leak down if you don't have a leak down tester. What your speaking of could be a weak valve spring,bent valve(weak seal), stuck rings on a cyl, etc.. Using the hose from your comp tester and removing the valve stem you can set the #1 piston at TDC and use a compressor to fill the cylinder with air with the pressure set to about 50psi. Make damn sure your at TDC and then follow the firing order 90º at a time and fill the next cyl and see what you get. A bad exh valve will show easily. But with 110psi I dont think that is your issue. I'd almost vote look into the ignition/sticking valve travel for cylinder.
JMO cheers

Thanks for both replies. Time for a second look at the head. Went to the GoodGuys Summer Get Together today and low and behold my old Snap On dealer had his truck there. He is getting the 18mm hose for my leak-down tester which turned up missing from my kit for me next week. Meanwhile, I will pull the valve cover and look at the valve lash and valve stem. Thanks again.

Mark

Burnt Valve...missing cylinder at idle Update
 

Couldn't wait until next week, so I pulled the valve cover off the left head. It had never been off, original gasket, etc. Non-adjustable rockers. Valve springs, pushrods, and valve stem looked okay. Cranked it over watching the rockers and springs and saw nothing abnormal. Put it back together and started from the beginning looking for the simple answer. Got out a aresol can of carb cleaner and started spraying around the intake looking for a vacuum leak while it was idling. Found the vacuum hose that T's off the intake and feeds the coffee can vacuum reservoir for the heat/ac system cracked under the carb. Replaced it and all is well. Idle is smooth and runs great. Thanks for the help.