Thread: Unknown cam?

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Superdave asked a question, he did not ask for an opinion.

I tried to answer his question in a simple and direct manner.

I didn't express my opinion on the feasability of what he was doing because that's not what he asked!!

I know yjere are a lot of very knowledgeable people on this board, that's why stop by. BUT, sometimes just answering the question asked may be the way to go.

By the way, I'm NOT trying to start trouble or get anybody riled up, just giving my opinion (which nobody asked for).

Originally Posted by Geezer2

Superdave asked a question, he did not ask for an opinion.

I tried to answer his question in a simple and direct manner.

I didn't express my opinion on the feasability of what he was doing because that's not what he asked!!

I know yjere are a lot of very knowledgeable people on this board, that's why stop by. BUT, sometimes just answering the question asked may be the way to go.

By the way, I'm NOT trying to start trouble or get anybody riled up, just giving my opinion (which nobody asked for).

Thank You! Right or wrong, I'm just trying to learn more.

PLease read the captions and look at the picture as it describes in generic form the differences by looking at the cam. note there is type above and below picture. The type below the picture is most impotant, I hope this helps you out some.

1, After break in, a flat tappet cam is married to its lifters. You cannot move lifters between different bores, and you cannot use those lifters on a different cam. The lifters either stay with that lobe, or get thrown out, period.

2, The following picture shows a flat tappet camshaft in the front, and a roller camshaft in the rear.

You cannot visibly tell if it is a solid lifter cam or a hydraulic lifter cam. The rate of lift (not the lift) is one factor in the solid/hydraulic design. Measuring such and then analyzing the data is not something you can do...plus you have no "specification" for this cam to compare your data with. That's the problem with unknown equipment. For all you know, it's a stock 2bbl cam that someone removed in order to install a high performance cam. The visible difference between cams is so small, it is a game of chance.

Look closely again at the nose of the cam where the timing gear mounts....like several others have said, there should be a couple of digits stamped there. For all you know, you have a 307 2bbl powerglide cam.

For the expense of tearing an engine down to change parts, it appears risky to use an unknown part. If the lift is too high, you risk coil binding the springs. Perhaps some of the guys here know if you can run hydraulic lifters on a solid cam....you cant do the opposite.

Most of us who have raced have had to reuse parts out of necessity. When you are strapped for cash but are still in the points hunt you are forced or tempted to do things you shouldn't. That being said I have run used cams a time or two with some results for a short until I could afford to change it out. The problem I think you might be facing is that (I assume) this is going into a street motor for which you hope will be a long time. Chances are better than 50% it won't work for you. But it is something dictated by your current circumstances.

I dont know why you could'nt, but I am almost sure you are not supposed to. It could be maybe because the short duration on a hydraulic cam is too steep of a climb and rapid step down for a solid lifter. The hydraulic spring might compensate for this quick action. I am only speculating now though, just letting my common sence work a bit, and sometimes thats a stretch. That is a good question I think. I am thinking with my solid roller for example, lash is set at .018 and .022, thats not much play for the quick and rapid lobe to lifter movement required especialy at 7000 RPM. remember just talking out my azz at this point.

You may have a Comp Cams XE268H. Follow this link and then call/email these guys for some more help in identification.

http://www.compcams.com/Cam_Specs/Ca...x?csid=93&sb=2

While I have never used this cam, specifications look pretty good for a TPI small block.

A solid lifter cam has a take-up ramp that slowly eases the lifter up until the clearance is gone. If you put hydraulic lifters on one, the valve starts opening way too soon, and since it only opens the amount that the clearance is supposed to be, the valves will burn out prematurely and the engine will run poorly at idle due to the too-long duration.

FWIW, you can run solid lifters with a hydraulic cam but not the other way around. If you do run solid lifters with a hydraulic cam, you set the tappets at .003-.004. I know, because back in the 1960's I did it on the 283 I built for my '59 Impala. This was on the advice of the machinist that worked with me on the engine. I never had any problems with it.