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 Cam Thrust plate thickness
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chuckies76ta
Cochise

Canada
334 Posts

Posted - 09 Jan 2007 :  9:02:46 PM  Show Profile  Visit chuckies76ta's Homepage  Reply with Quote
I bought a new cam thrust plate and it is .114 thick. The stock one is .122, a difference of .008

With end play somewhere around .003" to .oo7" will the new plate cause too much end play?

Thank you Charles

Mr. P-Body
Running Bear

USA
2258 Posts

Posted - 10 Jan 2007 :  08:16:17 AM  Show Profile  Visit Mr. P-Body's Homepage  Reply with Quote
Charles,

If running a flat tappet cam, no, everything should be fine (lifter rotation forces the cam to the rear). A roller, it could go either way. If you have an original that's still in good shape, use that one. They're a bit harder and seem to last longer than the repros.

Jim
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chuckies76ta
Cochise

Canada
334 Posts

Posted - 10 Jan 2007 :  08:36:23 AM  Show Profile  Visit chuckies76ta's Homepage  Reply with Quote
Thanks Jim: Running a Comp Roller this time. The originals I have, do have a little wear on them. I remember somewhere reading that if you hook your finger nail on the wear area to replace the thrust plate.

Thanks again. Charles
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Brian Baker
Mongo

USA
1050 Posts

Posted - 11 Jan 2007 :  12:38:04 AM  Show Profile  Reply with Quote
Jim,

I thought from the way the lobes are ground on a flat tappet cam that it forces the cam toward the front of the block (hence the reason they call it a thrust plate)?

Will Rogers never met a liberal.
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Mr. P-Body
Running Bear

USA
2258 Posts

Posted - 11 Jan 2007 :  08:33:05 AM  Show Profile  Visit Mr. P-Body's Homepage  Reply with Quote
Brian,

The "rake" on the lobe is there to force the lifter to spin in the lifter bore, allowing long life from the tappet. The direction of "thrust" is toward the rear, but Pontiacs, Fords, and precious few others actually USE a thrust plate to maintain "end play".

Chevy and larger MOPAR engines rely strictly on the rake to push the cam towards the rear. I've seen a BBC race engine spit the cam right through the water pump! (I have no idea why, it was over 30 years ago, and I was hardly qualified to change spark plugs, much less analyze failure...)

Because the Pontiac oil pump and distributor turn CCW, the cam can oscilate, which is where the plate comes into play.

Hope this is helpful...

Jim
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chuckies76ta
Cochise

Canada
334 Posts

Posted - 11 Jan 2007 :  10:06:53 PM  Show Profile  Visit chuckies76ta's Homepage  Reply with Quote
Jim: I just pulled out my cam and tried the new and old thrust plates with the cam gear and the thickness of the plate does affect end play..

With the new one the end play is .011". The old gm one end play is around .004" to .005"

Jim: What's a good spec for end play on a roller cam?

Thanks Charles

Edited by - chuckies76ta on 11 Jan 2007 10:11:04 PM
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Mr. P-Body
Running Bear

USA
2258 Posts

Posted - 12 Jan 2007 :  08:37:53 AM  Show Profile  Visit Mr. P-Body's Homepage  Reply with Quote
Charles,

We've seen them anywhere from .003" (too tight, caused distributor gear wear in a 351M) to .020" (too loose, causes too much oscilation). Ideal would be in the .005-.010" range.

Jim
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chuckies76ta
Cochise

Canada
334 Posts

Posted - 12 Jan 2007 :  6:27:10 PM  Show Profile  Visit chuckies76ta's Homepage  Reply with Quote
Thanks Jim, I appreciate the info..

Charles
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wakesupremo
Crazy Horse

United Kingdom
745 Posts

Posted - 03 Jul 2013 :  5:35:51 PM  Show Profile  Reply with Quote
Thanks for the replies. I don't understand how the wear, and therefore the rattle, began in the first place then as the cam thrust plate isn't worn, just gummed up with softer cam gear metal rubbed off onto it.
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cortcomp
Coyote

USA
5459 Posts

Posted - 03 Jul 2013 :  5:37:50 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I think you meant to reply over here:

http://psp.aquacomp.net/topic.asp?TOPIC_ID=6885

maybe just bad cam gear?
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Raleigh251
Tribal Scout

USA
1 Posts

Posted - 12 Apr 2019 :  11:07:32 PM  Show Profile  Reply with Quote
There should be a trust plate on the 389. There is a guy that makes a Pontiac Cam trust plate with roller Torrington bearings. These are great for all cams but are a must for roller cams. His name is Scott Sims he does the work for $285 his contact info: 812-350-8637 or simsb53@gmail.com. Or you could pick up a cheap stock one for $50.

R.Sutherland
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