stew's94z

Gentlemen,
I recently helped a friend complete the buildup of a 489 BBC and after the 20 minute initial break-in the oil was changed and none too soon. The oil was black with cast iron dust and shavings...not a good sign.
The teardown revealed the cam sprocket had worn into the block a full .100 in only 20 minutes. After I checked timing gear squareness and found the cam sprocket to be out almost .030 I reasoned either the cam nose or the cam sprocket was out.
The dial indicator on the nose told the story.
Total runout on the cam face was .007. The high spot was marked and the cam sprocket installed. Runout on the sprocket was .022 at the same spot.
Clearance on the cam button was set at .005-.007 for the solid roller but no one spun the cam sprocket to check for runout so a small oversight on something that should not have to be checked turned out costing a motor. The block, pistons, rings, bearings, and cam are dead, the crank is wounded.
It actually appears that the cam was never finish cut on the face. It does not have the feed lines of being faced on a lathe but rather the chatter marks of a roughing cutter being plunge cut across half the face.
Has anyone else seen this or heard about this happening before?

Thanks, Stew

OldSStroker

It's a first for me, but your analysis sounds right on. I am surprised that the sprocket surface wasn't ground when the sprocket diameter was finished because in an automated grind cycle which I suspect the major cam blank makers use, this is part of the cycle.

Many cam companies purchase cam blanks from cam blank manufacturers which are complete except for the grind on the lobes. Incoming inspection at the cam company is probably a sampling plan, and inspection after lobe grinding is most likely concentrated on the lobes.

I think it is important that you contact the cam company ASAP and describe the problem just as you did here. (You probably already have. ) They should immediately replace the cam, and want you to send back the bad one. It should alert them to check their stock of cores for this problem and contact their core manufacturer.

You didn't say if this was a cam from one of the major cam companies. If it was, it is very important that they be informed. If it was from a smaller company that grinds not only the lobes, but the bearings and nose themselves, they have an in-house quality problem. They should be happy you discovered it for them, and replace the cam.

Again, good analysis of the problem, Stew. I'm also impressed that you didn't "rant" against the manufacturer.

My $.02

stew's94z

Thanks for your reply Old.
The cam came from a major player in the cam industry and I can't rant too much because I have one of their grinds in my 383 lt1.
I just feel sick for my friend that invested several thou in this motor and now has to spend a couple more to try and save it.
Actually the first thing I checked was the crank to cam centerline squareness. After that was verified I moved on to the nose and the problem was found. I'm a cnc machinist by trade and part of my job title is to not take anything for granted but I let this one slip by and I feel partially responsible.

Later,Stew