Quick question about cam thrust

[LIL6cyl]

I’m setting up my front cover and have a question. I am running a cast roller 218-218 and have set the thrust at just above 3 thousandths. I’ve seen discussion where some like to run around 8 to 10. I can remove a 5 thousandths shim and be very close to 9. Any recommendations? Stock spec?

 

[750H.P.V6]

There isn't really a stock spec as the OEM flat tappet cam just had a spring loaded thrust button to control thrust loads. .003" is a little tight, .005- .010" is where you should shoot for.

Neal

 

[BEATAV8]

.003 is definitely tight.
I’m happy with .010 to .015
Also put the lifters in their bores and rotate the cam, check for any possible contact between a lifter and the cam lobe next to it.

 

[TireFryer]

Curious, why can’t you run a spring tensioner button with a roller cam? Why do you need a shim style?

 

[BEATAV8]

Curious, why can’t you run a spring tensioner button with a roller cam? Why do you need a shim style?

Shims force the cam to stay in a certain place. A spring permits movement which might allow the lobes to crash into an adjacent lifter. Such a crash can’t happen with a typical flat tappet because the lobes are much narrower, there’s lots of room.

 

[TireFryer]

Thank you for the explanation

 

[LIL6cyl]

I think I will open it up to .005. I know the cam was clearanced a lil over .010 for the lifters and lobes.

 

[LIL6cyl]

Got everything installed tonight. I opened it it to .0065.

 

[Turbo6inKY]

There isn't really a stock spec as the OEM flat tappet cam just had a spring loaded thrust button to control thrust loads. .003" is a little tight, .005- .010" is where you should shoot for.

Neal

Minor correction: The stock spring is there to keep the cam in place when the engine isn't running.

Flat tappet cams are ground to produce a thrust towards the rear of the block while spinning, which is what keeps them in place. Rollers are ground "flat" so they don't side-load the bearings in the lifters and need a thrust surface at the front of the engine to keep them from walking out.

 

[750H.P.V6]

Minor correction: The stock spring is there to keep the cam in place when the engine isn't running.

Flat tappet cams are ground to produce a thrust towards the rear of the block while spinning, which is what keeps them in place. Rollers are ground "flat" so they don't side-load the bearings in the lifters and need a thrust surface at the front of the engine to keep them from walking out.

We did a pretty big investigation into flat tappet cam failures back in the day. My recollection is that one bank of lobes are ground with taper in one direction and the other bank is ground with taper in opposite direction to minimize the thrust loads. At some point the lobe taper on the #3 exhaust lobe was reversed in an effort to reduce lobe/lifter wear. It didn't really work as the problem is more a function of the lifter bore placement in the block vs the lobe position on the cam. Sorry, I think I got off track.

Neal