Mechanical roller lifters on a hydraulic roller cam!
As many of you know I'm working on my 502 66 roadster this winter, upgrading the heads, cam, and exhaust. Today I got the cam out and ...
The cam is a "6543" (stamped on one end) roller -- so it's the 502/502 standard GM Gen VI hydraulic roller cam (GM #1236 6543).
The lifters on the cam, on the other hand, are solid rollers -- they look a whole lot like the solid lifters on the comp cams site but don't have any markers. The lifters look good. The engine has comp cams magnum pushrods and comp cams pro magnum roller rockers.
When I spoke to the prior owner (who built the engine) he said he had swapped in mech roller cam and swapped it back out but he swore up and down that the car had hydraulic roller lifters when he sold it. Oops.
NO WONDER I HAD SO MUCH TROUBLE SETTING THE VALVE LASH! Assuming I had hydraulic rollers (as he had said), I tried the "zero lash plus 1/4 turn" method and (duh) got no compression. So I went to 0.020" and it ran great.
So for those of you who were wondering -- yes you can run a hydraulic roller cam with solid roller lifters. Or, I was very lucky. But the thing ran great for 3+ years of street use (summers only, probably 4-5k miles).
I'm researching cam options now -- thinking a big hydraulic roller such as the crane 139741, 234/242 duration at 0.050, .610-.632" lift.
Re: Mechanical roller lifters on a hydraulic roller cam! (Hank)
The reason it worked pretty well, is that you ahve a very mild hyd roller there. When you get into more aggressive cams, things change.
A solid roller or flat tappet has "clearance ramps" built into the first and last part of the lobe to gradually take up the slack and easily let it close. As the cam becomes more aggressive, these ramps become more important to keep the valvetrain from beating itself to death.
You can usually get by with hyd's on a flat tappet, but it doesn't work as well as it could. The lift starts earlier than it would with solid lifters and acts "bigger". If it was a cam designed for hyd's they would take advantage of not needing to take up the clearance and make the cam even more aggressive in the first and last few degrees off opening and closing to increase performance.
Of course right up to a point where the hyd's float or pump up. There are many race guys running solid cams with hyd. lifters and setting them as solids to meet rules requirements. Of course, they tear them down and replace parts a lot too.
Clem's way of setting them at .003 or so will work, but still doesn't address the performance potential loss of having the right cam combo. I wouldn't select a new Hyd, roller cam and plan to run it that way.
I'd take this as a perfect opportunity to put in a good street roller SOLID cam and be happy about it!!
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Mechanical roller lifters on a hydraulic roller cam!
