Roughly four minutes or so into a cam break-in the engine suddenly began backfiring. Shut it down and pulled the distributor to find this mess:
http://www.colorado4x4.org/uploads/cam_gear.jpg
http://www.colorado4x4.org/uploads/cam_and_dist_gears.jpg

Cam gear was used but showed minimal wear at best (IMO), distributor gear was new (HEI conversion). Both were lubed prior to startup and both were coated in oil upon removal. No unusual noises accompanied the failure until it finally wore thru a tooth and went out of time. Up until then the 401 was purrin' oh so nicely :D

Any thoughts? What the heck would cause such a failure? Notice the distributor gear came out of the deal with barely a scratch on it :confused: You'd think that cam gear was made of aluminum the way it shredded like that.

How tight is the oil pump?

Yours is the 3rd amc cam gear failure that I have heard of in the last 6months.

3 of us built 360's 1 had this problem over and over....I fixed it:) It's been a while so verify but heres what we did.his cam was walking,on a buick v-6 it has a cam button and spring(I believe it's the older 231 .ci close if not right) went to the buick dealer an bought em.Funny thing is the inside of the timing cover has a flat spot machined on it like there is supposed to be 1 there ? problem solved...this is excactly what we went through...big headache for a while.

Eric, I agree looks like an end play issue.. one that a button would solve. You running one?

Not running a button at the moment (never needed to before), but it's looking like I might need to with this cam. It's been suggested that I spin the engine with the starter while the timing cover is off and observe the cam. If it moves around during that test I have a cam walk problem. It's an Edelbrock Performer cam btw.

Originally posted by Eric Ruhl
Any thoughts? What the heck would cause such a failure?

Installer error? :flipoff2: Seriously, i dont know much about it, but sounds like end play to me.

If the cam gear was used and you never had this problem before I would definetly look into the cam walking or the new distruibutor gear. Could it have the wrong pitch somehow or be the wrong gear? Could have lined up enough to fit but also enough to eat the cam gear.

Just thinking out loud :flipoff2:

I agree with the cam walk issue as well.

A few other things, is the Chev dist gear the same pitch as the AMC one?

What is the AMC cam gear made of and what type of gear is on the dist?

Just a thought but a bronze dist gear may be what you need but I would try a cam button first

The distributor uses a stock AMC V-8 gear so the pitch should be correct. Going to check for cam walk this weekend and when the new gear arrives I'll check clearance between the cam bolt and the timing cover. I'll then install a button if required. Just one of those things I never really thought about or experienced. Sucker goes out in a hurry though when it's wrong :rolleyes: Distributor and mangled cam gear are on their way to the distributor manufacturer for their review. Another possible issue that was pointed out is the clearance gap between the distibutor housing and the gear. Apparantly this alone won't cause a failure, but if cam walk is present it aggravates the problem. Hope to have the issue solved in time to try again March 1st :D

Thanks for the help everyone! I'll keep you posted on what I discover.

:beer:

What distributor is that? Is it a converted HEI? If so they may have a problem with not contacting the cam gear properly. The Team Rush guy had some good info before he got foot in mouth disease and got banned. Check out ORC they put up with his crap over there. Mo did a search on ORCand found the info not too long ago.

Eric, I have a couple AMC V-8's and whichever is running at the time runs the same Mallory distributor and the same cam gear. I have heard that AMC cam gears/ distributor gears are like ring and pinions, buy 'em new, run 'em in and keep 'em together. One new part deserves another.
You shouldn't have a problem with cam walk since new cams are ground with a taper on the lobes so the lifters thrust the cam towards the back of the block. But, who knows... it's a possibility that the 4.0 cam bolt, which has a spring pin/ thrust setup might work with the AMC 8's? I can check for you if interested- I was gonna do this with one of my 401's but it doesn't seem to care.

I assume from your posts on CO4x4 that you're familiar with PAS's dizzy gear oiling kit? My last 401 ran this, also the internal main bearing oil bypass kit. 6400 RPM redline, 12.5 second 1/4 CJ-5, no problems...:D