I am in the process of building a 355. I am using a forged crank, Eagle h beam rods, forged pistons and a host of aftermarket parts. I was hoping to use my CC 230/236XE with 2,000 miles on it but the builder showed my something very interesting. He checked the cam and it is bent. He put in his lath and with a caliper turned the cam slowly and 3 out of 5 cam journals were at least 6 thousands out of round. He said that if it was reinstalled it would take the cam bearings out in no time. The motor it was in spun three rod bearings. It did not lockup but began to chirp and squeel. I have not run it since. What would cause this. I have never seen a bent cam. I have seen wiped cam lobes but? Any ideas.
HVY SS

 

Heat from losing the rod bearings is possible

 

Please go into greater detail and explain how that would be possible if you don't mind.

 

Rod bearing partially spins, friction creates IMMENSE amounts of localized heat. Heat warps cam (among other possible things) a few thousandths. Just an idea

 

All I can tell you is that It was on a stock rebuilt rotating assemby with ported AFR heads and the 230/236 XE cam with 4.10 gears and a built 4L60E and a yank 3500 stall. I got aprox 2,000 miles out of it and it blew. The oil pressure went from 25psi at idle to 8 psi idle and at that point I knew I had ether spun a bearing or the oil pump was bad.Within a matter of seconds after the oil pressure dropped the squeeling began. That is the last time the motor was ran.
HVY SS

 

Check some out of the box sometime. Found that to be the case on about 1 out of 15. Not sure if it's a manufacturing problem or handling problem after they are made.

 

Cams can be bent by dropping, or perhaps even in shipping.

FWIW, if you want to check a cam for straightness, place it in precision V-blocks located on the end journals and then use a dial indicator to indicate runout of the three inner journals. Chucking it in a lathe, even on the centers and then checking a journal doesn't really tell you how the cam will run in the bearings.

Some (most?) cam companies purchase semi-finished cam cores with bearing journals already ground. They check for straightness and correct it if necessary before they grind the lobe profiles. Checking after grind is also a good idea. If when you install you cam it doesn't turn freely you should remove it and check it for straightness. If it's good, look at the cam bearings or cam bores in the block.

BTW, if the journals were actually "out of round" or egg-shaped by .006, I doubt if the cam would even go into the block. Some folks call the variation they see on the non-supported journals "out of round". It's really eccentricity of the journals or a bowed (bent) cam causing the runout readings.

I'd recheck the cam per the above before I scrapped it.

My $.02

 

I agree.

And here's a picture to put with the description.

Camshaft straightness check

A camshaft can be straightened just like a crank. I'd say that .001 or less TIR is good.

-Mindgame

 

Thanks for the pic. If I didn't explain it too well, that's just what I meant.

What is that cam from, BTW?

.001 TIR would be just fine. It probably flexes more than that in use.

 

While the cam is showing say .005 inch bow in it at the center bearing, put your thumb on the cam and push. You'll move at least .003 or .004 out of the bow.....no big deal. Sometimes it helps to see just what it takes to move something so little. So spring loads through the lifters will straigten it in the bearings anyways.
Now out of round, as mentioned, .006 would be bad. That you measure with a micrometer, just like crankshaft journals, and not in a lathe or in v-blocks.

 

I question the use of that particular pic. AFAIC, that pic doesn't display well, the setup used to check a camshaft for straightness. I find the pic somewhat misleading, cuz the indicator appears to be on a cam lobe. It would appear to be displaying one setup/procedure used for checking lobe lift. I understand the intent, but this could confuse some that view this thread. For the pic to be more helpful, it should have the indicator on an inner bearing journal. Then it would more aptly display a/the setup needed to expose a bent cam. At the risk of nit picking, my 3¢ worth.

 

Some cast cores cannot take the spring pressure and the load of severe ramps. They don't "bend" they twist like a pigs tail,which may show "bent" in a lathe because the journals are on a different plane from the "twist". Nothing twists in a streight line.
A billet core should be used with a large or severe ramp cam,weather hyd or mech.

 

All things, no matter how stiff, will flex. Camshafts, cranks... if they have to run in a line of bearings you're better off with them being as straight as possible.

As for the cam in the pic.. I have no idea where it's from other than to say it's most likely a motorcycle cam. I just found it with an "image" search and it fit the criteria so there it is.

Arnie,
I'd hope that common sense would win out in situations like this but maybe I give people more credit than they deserve? Yes, you would want to check the journal, not the lobe. Seems that'd be obvious after the first .010-.020 of travel on your indicator...

-Mindgame