After removing the valve covers on my running 289, I noticed the number 5 valve springs/lifter did not travel the same length or height as the others on the bank. Both intake and exhaust seem to be coming up short. Oddly, I have weak compression in that cylinder...go figure. What could this be??? Collapsed lifters? Valve not seating? I do not think the cam is wiped but I don't know about these things. I had the heads off and everything seemed fine. I put in new seals and I have no leaks, smoke, or anything like that. The timing is good...no fluctuations. Idle is a little rough but smooths out under acceleration. I need to rebuild my leaking carb which should help that...I hope. It sems like it is running on 7 cyl until you tromp on it. No hesitation, good rev., but pulsing or throbbing at idle. I need some help here. When I pull the plug wire, not much change either. I have about 90lbs compression in all cyl and 50 in this one. What could it be???

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Assuming hydraulic lifters, its either the lifter or flat cam lobe

 

If your intake valve is not opening very much that will explain your low compression reading on that cylinder. You need air to compress in order to have compression lol

You're saying intake AND exhaust just on that one cylinder seem to have low movement compared to the rest? That is kinda weird. I'd suspect a flat lobe, because even a colapsed lifter should still be giving you full range of motion, accompanied by a lot of noise lol. Over time, that could be what flattened the lobe...

 

oh ya what cam is it? Comp? Those are and were notorious for flats

 

Thanks. It is a stock cam...stock "C" code 289, 1966 Coupe W/C-4. If the cam were flat, would I get any erratic timing issues? And, there may be a bit of noise. I had so much chatter in the beginning I re-adjusted the valves a second time. They are hydraulic of course and I was surprised I would have to adjust them again, but I did them in a series according to some other advice. After all the noise, I went cyl. to cyl, in order, snug and about 1/2 turn after. The engine had not been run for awhile so I wondered too if a lifter might be sticking. I've only put about 150 miles on it since I got it going again. Still in break in mode. New crank and bearings. Very responsive with no hesitation. I'm hoping it's a lifter or lifters. Better yet it would work itself free or whatever. Hey, one can hope!

Thanks again and keep the info coming.

 

How was the cam and lifters broke in? Thats key

 

OK...say it with me...STUPID. I did not replace the cam or lifters. The engine has been rebuilt but I don't know when. It has .040 on the pistons so it has been bored. The rod numbers were random. A couple with 5, a couple with 2, you get the idea. All in the correct location as far as piston to rod to crank, just different. I done more of an inspection and thougough cleaning with new lower end bearings, crank and rods. New oil pump to be sure of good flow. Everything was heavily doused with Permatex Engine Build Lube. The thick red kind. I put it on everything that moved before starting it up. Nothing was froze up or overly tight, just sitting. Thanks again.