I have a '54 Chevy 235 block with a mild Chet Herbert cam I installed 30+ years ago. Everything was running fine but the rear main seal was leaking. I decided to replace the seal during the winter, which I did. Also decided to plastigage the main bearings, while it was apart, AOK. Never touched the cam, valve lifters etc. Put it all back together, turned it over with the starter and clunk. Somehow a tooth on the cam timing gear had a sliver sliced off. Replaced the timing gear. Now the #2 cylinder rod is interfering with the #2 exhaust valve cam lobe, about 1/8”. The cam lobe seems to have the high spot exactly facing down when the piston is at the top. It would seem to me that something had to move at least 1/4” but I can't find anything with that big of a space. The timing marks are right on, facing each other, and the timing mark on the new gear matches exactly with the old gear. I thought maybe when I re-installed the vibration damper I drove the crank back but it doesn't look like it. It has got me stumped. Any ideas?

PS. the cam is flush with the timing gear and both timing gears are in line

How did you install the damper? Is the crank snout drilled and tapped? How are the cam lobes aligned with the lifters? How much end play do the crank and cam have?

The crank is not drilled and tapped, so you drive on the damper. looking down thru the lifter bore virtually all you see is lobe, its not off center. The crank will move fore and aft but only about half the thickness of a dime. Thanks for giving it some thought.

Did you remove the cam to change the gear? Did you heat the gear to slip it on? Did you remove the cam thrust plate? Could you have reversed the ring? That may be excessive end play on the crank. If you pound on the end you can harm the thrust bushing in the main bearing. Just trying to think of what moved and why. If the cam is where it should be then the crank must have moved. This is puzzling.

If you replaced the gear in the car, that is without taking the cam out, it is possible that you have the cam, retainer and spacer ring either jammed on or not on completely spacer ring seated and sandwiched between the crank and cam gear. Then, when you tightened the two cam retaining screws, because of the excess clearance, you pulled the cam further into the block then is permissible, pushing the rear cam plug back.

What cam and crank set did you use? Part number?

Been out of town and contact. The cam is flush with the face of the timing gear, had it pressed on at the machine shop. The cam retainer has .026in clearance to the gear. The depth of the cam in the block is set by the cam retainer, when you bolt it down the cam can't move more than the .026in fore or aft. so I'm relative sure the cam is in the right place. The fore and aft clearance at the thrust bearing is .016in. Doesn't leave much room for the crank to be out of place. The timing mark on the new cam gear is in the same place as the old, relative to the woodruff key slot. The cam gear and crank gear are lined up with each other. I seem to remember the same problem when I assembled the engine 30yrs ago but can't remember what it was. I'm sure it's a slap your forehead/duh thing.

I found this. Your end play may be too much.

CAM

"Before installing the pistons and rods, check the end play in the crankshaft by forcing the crankshaft all the way forward or aft, then slipping a feeler gauge between the bearing end cap and the base of the crankshaft counterweight. The reading should be between .003-inch and .009-inch. If it is not within tolerances, replace the rear intermediate main shells and check again. Also, on the Chevy, check the lash between the timing gears with a feeler gauge. It should read between .004-inch and .006-inch. "