The Stovebolt Site Forums The Shop Area Engine Shop 216 Cam timing . . . I think I have a problem.

I Rebuilt the carb . . . now it runs a little better, but still pops back through the carburetor. I decided to check the cam timing and followed instructions in the 48..51 manual.

They say to remove all lash from the exhaust valve.

Rotate engine to the Triangle on the flywheel right after the exhaust valve is starting to close.

Line up the triangle and measure height of lash adjuster relative to the head.

Then rotate the crank till the rocker stops moving and it should travel .044 +/- .004 inches.

Well, I did this a couple of times and I get .085" consistently. This is .041 too much according to the manual. This would mean my cam/ignition timing is delayed relative to the pistons. Heck . . .the way it runs, sounds like the timing might be bouncing all over the place.

How does the cam gear slip? Can't imagine it would jump a tooth . . . and it must be keyed isn't it? Am I going to have to pull the motor or can I fix it in the truck? :confused:

Pop back through the intake?? leaking or bent intake valve or exhaust cam lobe gone. Your timing gear may have gone to lunch, and jumped out of time.The piston struck an intake valve bending the head.The exhaust valves on Stovebolts are recessed, no interference posssible, but the intakes are almost flush with the head face.The fiber cam gear with a metal insert is keyed to the cam shaft.Perhaps the fiber is weakened with age and has slipped on the insert.Or the slip in cam timing may be enough to cause popping without valve train damage.The bent intake push rod is the clue to the mystery.
One the other hand I think the engine wouldn't run at all if the timing jumped due to a broken tooth.. What happens when the missing tooth comes around again while the engine is running?Maybe the variance in the cam timing you noted is just worn parts.Does 40 thou affect the timing enough to make a low power engine like a 216 run lousy?Gotta pull the pan to get off the timing cover.Do you have access to one of those mini cameras to have a look into the spark plug hole?

i'm not familar with this engine but before i took anything apart i would make sure that the base timing is ok and mechanical advance/vacuum advance if equipt is in good working order. the engine runs so i don't think your timing components are the problem.

I got the bright idea of running a compression check after reading Tony's post. 95-100 on 1-4&6, 40 on #5. I looked at the intake valve on #5 to see if it was sticking and it didn't look like it. I checked the lash and I couldn't get a feeler guage in it - so I imagine it was too tight. I loosened it up and then ran comression test again, 90 psi with a fast leak down. I started it up again and it ran better . . . centered up the distributor adjustment by loosening the vac advance bracket clamp on the dist body and set timing at around 8 deg BTDC w/vac advance disconnected. Warmed it up for 30 minutes and then shut it down and adjusted all valves. . . now it runs smooth and quiet Engine needs a slight bit of choke to run really well on the road, but all in all MUCH MUCH BETTER! No more popping through the carb. Drove the truck into town and topped off with premium unleaded and some gas treatment. Actually drove pretty nice - I am a happy camper! I think I might actually start liking this truck again