15-20 years ago we used to do quite a few of some 350sbc oval track motors.
There were two classes, and we did several for each class.
The milder class were 8.5cr, ex manifolds, stock 2bbl intake, and heads with 1.72 intake valves.
We had done a pile of cam testing on those things, and had it narrowed down to 2 different ones.
One was a Comp, the other was a white box special.
The Comp was about 5hp better, but cost twice as much.
If it was for a customer that wanted the “good stuff” and was okay with paying for it....... it got the Comp.
I wasn’t doing assemblies, but checking for lifter rotation wasn’t part of the normal assy...... and cam failures were very very rare.
So, I’ve got one of them on the dyno and fairly quickly into the cam break in I start hearing some clatter.
We ran these with zero preload, so if there was any clearance in the valvetrain, you’d hear it.
Pull the covers, find one rocker is just barely loose.
I reset it, start it back up....... a few minutes later, the clatter starts to come back.
Pull the cover...... it’s the same one loose again.
Okay....... didn’t make it through break in.
Pull motor off the dyno, put another one on.... and carry on.
They pull the cam out........ one lobe and lifter are starting to go away.
The others are perfect.
Stick another cam in the motor, new lifter in that hole, install pushrod and rocker...... turn the cam round and round...... no rotation.
Decent rotation in any other hole.
Okay, it’s a lifter bore problem.
Checked lobe taper on cam, it’s basically right at .002.
I order a cam and have them add a thou of taper..... so, .003.
Get new cam, check taper....... it’s .003.
Checking for rotation in the offending bore.......lifter starts to move...... barely....... then goes back the other way.
The lifter still won’t go round and round.
The others all really whip around good now with .003 taper.
What to do, what to do? Really don’t want to pull it all apart and get the lifter bores done.
Well, at that point in time it was easy to get Schubek lifters..... especially for a Chevy.
We bought one lifter and put it in that hole.
Buttoned it up and it was good to go.
Worked like a champ.
