I am installing a TPIS ZZ-9 Camshaft in an 88 GTA 5.7L. The engine was rebuilt about three years ago. The motor is apart now and to my dismay I discovered that the block did not come w/ a roller cam and roller lifters. I figure that the engine shop tried to save some money on the rebuild considering that I only paid $1,800 for the replacement long block. This block though was originally made for a roller cam. I have already installed the lifter valley spider, tappet link bars, hydraulic roller lifters, and shorter pushrods from GM. Everything fit and bolted right in. The ZZ-9 Camshaft and valve springs are also installed. The only problem I have now is that the thrust plate for the cam doesn't fit the block. This is installed in front of the cam onto the block right behind the cam timing gear to keep it from walking forward. The bolt pattern is further apart on the block than it is on the thrust plate. I would like to know if there is another thrust plate that I could order from GM. Were there two types of thrust plates used? I thought of drilling out the present thrust plate but I am hesitant. I am worried that that the center of the thrust plate might not be centered with the new camshaft. I would rather have something bolt right in. Has anyone had a situation like this? Any help will be truly thankful.

Joe

 

You could use a Comp or equivalent roller "button"... about $18, problem solved the way it always was before the factory "discovered" rollers and made all their weird adaptations...

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"So many Mustangs, so little time..."

 

If you're unable to use the bolt on thrust plate you'll need two additional parts.

Here's the reason. A flat tappet cam, either mechanical or solid lifter, has ground into the cam lobes a slight taper that keeps the cam centered and prevents it from walking back in forth in the block.

A roller cam doesn't have this, so you'll need a thrust bearing that will go between the timing chain gear and block and you'll also need a needle bearing thrust bumper that fits directly in the center of the cam gear.

The thrust bearing comes in different varieties. There's a brass version, there's a 3 piece Torrington bearing set and there's a timing chain set which comes with the thrust bearing built in.

You'll need to move to one of them because the cam will walk backwards and cause the cam gear to eat away at the block putting lots of metal in the engine.

Of the three the best ones to use have the bearing which consist of two large diameter washer which has the bearing sandwiched between them.

Crane and CompCams (and probably others) sell a timing chain set that has the bearing made into the cam gear.

Be aware though, that the 3 piece Torrington bearing set is NOT a direct bolt on. Because of its thickness, it will cause the cam gear to stick out slightly so that the gear won't be in direct alignment with the crank gear. If run this way it will cause excessive and premature wear to the chain.

You can either take your cam gear to a machine shop, have them measure the thickness of the 3 piece Torrington bearing set and them machine that amount of the block face of the gear OR you can opt to by one of the timing chain sets that are already modified to account for that thickenss.

The forward thrust bearing limits forward movement of the cam. There should be about .006 clearance between the thrust bearing and the inside of the timing chain cover.

Hope this helps.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

 

JA,

I'd vote for modifying the existing retainer plate and/or the cam button.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

Joseph, see your other post. GM makes 2 different thrust plates with different mounting spacing. If you need a roller timing chain then look at GM's single roller. It comes with the thrust plates and all bolts. Part number is in the other post.

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Bob '89 Formula CC350
Last(lost)Member of the Elusive Great Lakes Crew
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