The Stovebolt Site Forums The Shop Area Engine Shop lifter to bore relationship (bad cam?)

Hi all,
I have a chevy 327 in my truck, and I recently pulled my intake off to change the gaskets.
As I was adjusting my rockers, I noticed tht the top edge of one lifter was not lining up with the top edge of the bore cast into the block. I thought as long as the travel appeared to be the same as the others, I should be ok.
My thinking was that maybe the upper surface of the bores (lifter valley area) was cast a little off for just that one bore, but I find that unlikely.


Is this a common thing? (casting defect?)

Harmless.

I think I'm going to pull the valve cover to actually measure the travel. I've been chasing a sporadic hesitation, and I've gone through everything else (ignition, gasket, power valve).

Just to give you an idea, all the other lifters line up with the top edge of the bore when at the cam heel (valves closed), and they rise up to what appears to be just about 1/4".
That one lifter "appears" to be just under 1/4" below the top edge of the bore at the heel of the cam, and then it rises up to maybe 1/8" above the top edge of the bore when the valve opens.

I guess what I should be asking is, how small does the movement of the valve have to be to start causing problems?

Late 60s early 70s SBC are known to have bad cams that wore excessively. I have a 68 327 that had 100k + miles on it when I got it. When I went to adjust the valves, I noticed that some were barely moving 1/4 inch if that. Ran a lot better with a new cam. I also have a 72 350, that I picked up used. Having had problems with the 327 I checked the 350. The 350 cam was not as bad as the 327, but showed wear of 10-25% on all lobes. My experience.

Larry

That could be due to the phase out of zinc phospahte in our engine oils. All the new cars are coming with roller lifters, so the tyranical powers that be decided to screw the rest of us who prefer classic cars and trucks.

I've actually been using ZDDP additive along with Valvolines VR-1, but I didnt hear about this until 5 years after my engine rebuild, so the damage could have already been done.

If I do end up having to replace my cam and lifters, I'll be using Rhoads "Super Lube" lifters in combination with the zinc oil and additives I've been using.

Well, it turns out the travel at the rocker arms are in fact the same. I did discover one (not the one in question) that was about 1/16" shy of the others, but I don't think that would be enough to cause a difference, and it could be due to the head casting.

This is good, in that I don't have to go through the ordeal of cam replacement (radiator, water pump. cover, manifold, on so on).

Thanks for your perspective and experience.

Unless you're measuring the lift at the outside shell of the lifter with a dial indicator, you're not likely to get an accurate reading. The inside plunger of a lifter can leak down as the engine is rolled over by hand, and yes, if there is actually a 1/16" difference in valve lift, that's far too much variation. When I'm degreeing a cam on a race engine, I substitute a solid lifter for a hydraulic while checking cam timing and lift.
Jerry

Yeah, I realize that, but the lifters bleed down pretty quick, because these Rhoads lifters bleed down more than conventional lifters.

I thought I would try replacing my HEI module, and it "seems" to be doing ok. If this doesn't cure the hesitation, I only have the in-cap coil to replace. After this, I will consider tearing it apart to replace the cam and lifters.

So you think that the 1/16" discrepancy is enough to cause what I'm experiencing?

1/16" is .0625", and I'm unhappy with a .005" difference in lift from one valve to another. I don't know if that would cause the problem you're having, but before considering a cam change, I'd want to run some very accurate measurements with as little variation as possible. Am I correct in hearing you're running Rhoades lifters on a street-driven 327? WHY? Those things are supposed to be used to make an extremely radical cam more able to be driven on the street. If you're running a cam that needs those lifters, you're WAAAAAAY over-cammed, and the engine is going to run lousy anywhere except wide-open throttle.
Jerry

Yes I know. Thats why I'm up in the air about it. The Rhoads lifters for example reduce the cam lift by .20 to .30 at idle, and the duration by 10 to 15 degrees, and this of course is consistent amongst all the valves. Just one valve deviating might cause the hesitation I'm experiencing...maybe.

What I have in there now is a kit I purchased some time ago, and has since been discontinued. It was designed for good mid range and towing power, but because of the variable lifters, it also has excellent off idle power.

To add to this, it is sporadic. Most of the time she purrs like the vixen she is. I'm going to see how she does with the new module.

I've never seen a lifter that changes valve lift by over 1/4". Maybe you mean .020" to .030"?
Jerry

Whoops, yeah, thats what I meant.

Well, I thought I would update the board on what resulted.

It turns out that it was the holley carbs causing the hesitation, though it could be a combination of Holley's Quality Control having issues lately (from what I've read), in conjunction with the alcohol in our gas.

I changed the carb twice, both times curing the problem of hesitation. It got so bad with both carbs, that I had to rebuild each carb once, and changed the power valve on one twice.
Each time it got to the point they just wouldnt idle, and I had to resort to turning in the idle screw a lot, but it still ran really bad.

I think that the design of the Holley makes it highly susceptible to alcohol. I replaced it with a quadrajet from SMI just last week, and its never ran so good.
FYI, I also have one of these SMI quadrajets on my Chevelle (well over a year now), and it experiences no problems at all.

So there it is. Thanks again all.