63 galaxie xl, 390 crusiematic 300 hp. rebuilt engine in may at local machine shop, everything new and bored .060 over. has pertronic ignition and 2 yr old holley 670 street avenger. ran fine until about october 1rst. when starting cold engine got serious backfire and smoke. since that day it will not start or run corectly. thought it might be ignition wires, new set, no change. had to advance the timing about 20 degrees to start without serious backfire. even then it has no power but spark knocks stuters and skips alot. switched to holley no change. installed old ignition point system into distributor, no change. switched distributor (pertronics also) from my brothers galaxie, no change. checked compression early on, it was low at 170 but consistant. checked it again yesterday it was even lower at 150 but consistant. the fact that i can somewhat compensate with advanced timing and get it to run(sounds fairly good idling, but no power for driving) keeps leading me to slow valve timing. i know that if this is true crank gear or cam sprocket would have to slip or shear a key then slip. I guess it is possible that the rebuild tech left the key out and it ran on friction for a while. I really hate to open up the front of engine without hearing what you guys think or have experienced. please advise any thoughts or experience. thanks
Hi, I think you are on the right track. Symtoms of valve timing or slipped chain, are low but even compression. Usually the compression goes to something like 70 lbs; But I think, like you said, a missing or broken crank pin/key could be your problem.
Well, I just completed the timing investigation. The key is in place on both the crank gear and the timing sprocket. No sign of any problem there. I am going to reassemble the timing cover and peripheael equipment. I dont know where to go next. Maybe someone has an idea or similar experience.
Hi, another thought. How long ago was this engine rebuilt and how many miles are on it? My rebuilt 292 died a slow death because of the use of unleaded gas. I had to have my heads rebuilt. [sunken valves] New valves, new valve guides, hardened valve seats, new cam, and lifters.
Thanks Bob, engine only has about 1,000-1,500 miles. I switched out the distributor using my brothers 1963 galaxie 390. Same problem continued. Yesterday 11/5/10 I did a cylinder leakdown test. Every cylinder is good. Oh btw I found my compression guage is 30 lbs low therefore my earlier compression test was actually 180 lbs. So!!! I have eliminated a "stuck open valve". My next move is to remove intake and check for a damaged cam. Will advise once it is complete. Thanks
Problem solved, finally. It was the coil. Installed pertonix igniter with blaster coil about 2 yrs. ago. During all my trials I never supected a new coil gone bad. I had noticed what i thought was weak fire. Finally had an experience local mechanic check the car. He immediately thought the fire was weak and subsequently replaced the coil, retime the engine and all is well.
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