Greetings Fellow Builders, I have a situation that I need help with. I have a '79 GM 292 inline six that has been completely rebuilt. Bored .06 over with 10.5 : 1 pistons. Patrick headers, Ofy 3 single carbs, HEI ignition, Comp Cams cam and lifter kit, new valve springs and valves. coupled to an S10 5 gear. All f this is installed in a '50 Chevy Coupe. So far all this sounds good right? Now comes the situation. We gave this set up an easy break in period with NO hammer down runs. After about 20 hours (tops) of run time the engine started hammerin' and we shut it down and disassembled it. The cause of the hammer was-- the cam had walked back in the engine far enough for the crank throw to strike the cam lobe. Removed cam, cam gears, lifters and replaced with NEW cam, lifters, and gear set, all from Comp Cams. Started over with break in procedure. After about 10 hours of careful run time, BOOM. We have not disassembled the engine yet, BUT after removing the side cover and removing #1 lifter, found the whole bottom of the lifter gone and it appears that the cam has again walked backward in the engine. The cam lobe is not centered in the lifter hole by approx 1/4". WTF is going on? Is there a rear thrust bearing missing in the cam journal? We are lost on this. ANY BODY got some info for us? Rog aka 66Ragman
Hi Rog, what cam gear are you using (material). Is it the fiber with a steel insert (hub) or an aluminum piece?? If it's aluminum you cannot "press" it on the cam, it needs to be heated and installed! Been down this road years ago when building performance 6 cyl Chev's! The steel hubbed pieces can be pressed, not the aluminum's! Thanks, Gary in N.Y. P.S. We use to fabricate a cam bolt and washer setup on all these units to guarantee the gear stayed in place.
Verify that the camshaft is indeed walking excessively. The cam lobes are not suppossed to be centered with the cam bores but off center, that is what helps make the lifters spin as well as a tapered angle ground into the lobes. The lifter bottoms are also radiused, so really, only a small cross section of the lobe and lifter are actually making contact with each other. Cam endplay should only be as much as the crank endplay.
You do have the cam retainer in place? The one that goes behind the timing gear and acts as a thrust washer. I've got the Leo Santucci 2nd edition Chevrolet inline six power manual out an I don't see any specific instructions for installing the timing gear that would differ from what GOSFAST posted above. Usually you heat the aluminum gear and slip it on the cam.
Thanks for the reply GOSFAST, I am using the alum gear and the installation was , heat the gear to approx 450 degree F and place the cam end in ice for one hour then press in place. IE "shrink fit". What type of bolt on did you use? Rog
Mr48chev, Yes Sir, the retainer is right where it's podda be.. I just wondered if there was a thrust bearing behind the cam that I didn't know about. Rog
CNC-Dude, I have not pulled the gear cover off yet to verify the walk. I hope you are correct and that the cam has NOT moved. If so it means that Comp Cams sold me a defective lifter/cam set. (IMHO). I will post results when the cover gets removed. Not sure how soon that will happen, HOPEFULLY with in 7 to 10 days. Rog
Also, drilling and tapping the end of the cam for a bolt is a good remedy as well, and added security for a cam that just has a pressed gear.
I had the same trouble on a 250 Chevy, the aluminum gear was moving on the cam. I ended up with a steel gear which worked out fine.
did you have the thrust washer in place behind gear when you put on gear? it has to cface a certain way aswell. i don't mean to ask a dumb question because any of the shop manuals give the max thrust movement so you prob checked it. with out the thrust washer it way too much and would be noticable.
I bet you could find some help on the Inliners International hi-po forum or contact Tom Langdon at Stovebolt Engine Co. Also get Leo's book - he covers EVERYTHING! Good Luck, Tim
The Jalopy Journal
