Comp Roller Lifter Max Lift Pressure Dump?

I also posted this one over on the other big Ford forum:

Right now I have an engine on the stand that has a Competition Cams XR 286 solid roller cam with Comp lifters. I was just turning the oil pump by hand getting up pressure and having a look when I noticed that when I rotate the engine to where a lifter is at or near max lift it DUMPS oil pressure. It's as if the relieved portion of the lifter body that's down by the roller gets pushed all the way up into the lifter galley. This isn't going to work... It take the oil pressure from about 85lbs to around 20!

I think what it is is that this is a very mild cam and it's been ground with the base circle too large which is causing the problem. Has anybody else seen this one?
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This is a COMMON happening when using roller lifters with Mopar big blocks and some Mopar small blocks on one side.

SOME big block Fords and Cleveland's can have this same problem once in a while, especially with a larger bearing core camshaft. It has nothing to do with the base circle dimension but, how far the lifter goes UP the bore at maximum lobe lift and exposes a slight amount of the oil gallery at the lifter roller cut-out.

The base circle diameter shouldn't matter because the lifter should stop in about the same spot irregardless of it's dimension or the cam lift.  But if this cam could be reground to a smaller base circle and smaller overall lobe size and it would probably fix the problem.

What I found today is that the roller lifter from Competition Cams measures about .800 from the bottom of the roller where it sits on the cam to the top of the relief above the roller wheel.  If I turn the engine so that a lobe is at about max lift, set a dial caliper to .800 and stick it down into the lifter bore so that the tip touches the cam lobe the butt of the caliper is above the oil galley opening.  I'm going have some Morel lifters in hand tomorrow to measure and try in the engine.  

I just wonder how many people have struggled with low oil pressure problems despite building the engine with the correct clearances etc because this causes a hell of a leak.

This cam was ground by Comp and no there's no heads or valvetrain on the engine yet. I was just cranking up some oil pressure by hand to see how things looked like they were going to oil.

Dave ... you caught it on this one, (probably because something just wasn't right with this in your mind), and it does happen with other engines from time to time.

BUT ... everybody's an Engine Builder; just ask 'em.  An experienced Engine Builder building other than OEM type rebuilds figures out this kind of stuff and later knows what to look for when something "just isn't right".

"Good judgement comes from experience and, well: experience ... that comes from bad judgement", Ben Franklin

Thanks for posting Dave,info like this is good to know.

Yesterday I swapped in a set of Morel lifters that I got through PBM/Erson Cams. They worked without trouble and the difference in the height of the cutout on the side of the body is about .100 less. I then polished the bodies very slightly using a cratex wheel right around the oil hole to reduce that area about .001 so that they will oil the top end of the engine properly.

I'd say that if you measure the height of the cutout on the lifter from the bottom of the wheel and it's .700 or less it should work without any trouble. .800 as with the Competition Cams lifters and you might run into problems.