Big Block enthusiasts, I own a 66 Chevelle that I recently installed a 73 Model 454 truck block. In my initial Piecing together of this hoss, I ran into a problem that i think is the cause of my new problem. When I bought this block, it was already assembled and ready to go. I pulled out the Comp. 280 cam and installed a Lunati 292. With the intake off, i noticed that when i was setting my valves my cam was "walking" towards the rear of the motor a great deal (only about 1/8 of the lobes left running on the lifter!). Confused, I hit the phones and started comparing camshafts. I set the Lunati, Comp, and an original GM cams on their ends and i found that both the Lunati and the comp cams were somewhat shorter than the GM. Lunati was about 3/16" shorter and the comp was 1/8" shorter. Thinking it would solve my problem i opted to use the comp 280 thinking with it being a little longer it would not "walk" as bad. I found that it didnt walk as bad, but still enough to scare me. I went ahead and used the comp cam. Now, 2 months later, I have a flat cam and I dont know if this was the cause. I've called around and asked machinists what could be making my cam walk back and the only logical explination is that my 73 block came with a "thrust washer" to prevent rear "walk". Can someone please help me?! Michael

All flat tappet cams (hydraulic or solid) are constructed of a length that the cam lobe CANNOT ride dead-center on the lifter...plus, all the lobes are ground with a taper from back to front. All this is done so that, 1) the lifter spins while doing its gyrations (giving even wear), and 2) the cam is "driven" towards the rear of the block.

If you think about it, the only thing holding the cam in the block is the relatively flimsy timing chain. The only thing that keeps the cam from taking a walk out the timing chain cover and colliding with the water pump is the cam lobe taper...and the only way for that taper to work is if the front half of each lobe rides on the back half of each lifter. I really, really doubt that any problems you're having are due to too short a cam.

Not to overly belabour the point, but "cam walk" usually refers to the cam walking "forwards". In actuality, they're supposed to be pushed backwards while doing their thing. But I will say that if only 1/8 of the lobe is running on the lifter, that does seem a little small. From my own experience, usually close to half of the lobe rides the lifter. Still, if the cam is being pushed towards the back of the block, and the lifter is spinning, I can't see how there'd be a problem.

And if you're interested, roller cams are another story: A roller cam lobe should ride closer to the lifter center, since roller lobes (and lifters) have no taper. And since they have no taper to keep them in the block, you'll notice that when using a roller cam the manufacturers insist upon some method of keeping the cam in place...be it a thrust button and reinforced timing cover, or more usually, a cam retention rig...usually a gizmo that mounts to the block concentric to the cam and keeps it (the cam) from going anywhere. Special cam timing gears are usually required for these to give clearance for the retention mechanism.

If you have cam lobes going away, IMHO it's more likely a problem with break-in procedure, or too high a lift cam for the springs you're using (spring bind, etc.). I'd look at that first before calling up a cam mfg. and asking about overly-short cams.

Mike,
Larry's explaination about covers it from a theory point of view. I would like to add a couple of things. 1. It is very common for big blocks to wear the cam thrust area on the front of the block. Dont ask why, I just know that we see a lot of them that way. The previous owner may have had the front of the block machined for a brass thrust plate that is designed to repair the problem. If the block has been machined for the plate and you are not using it, the cam would be back into the block around .080" further than it should be. Also, make sure the cam sprocket was not machined for a thrust washer or torrington bearing (compare it to a new one) That will do the same thing. All of the cams should be close to the the same length except the real new hydraulic rollers made for use in the Gen 6 Blocks with a thrust plate from the factory. There is some variations. Wolverine in particular locates thier lobes further to the rear of the block to supposedly promote better lifter rotation. If you want to measure your cam end to end and then the thickness of the front journal, I can compare it to a known good one for you. 2. The oil galley plugs behind the timing chain should have a very small hole in them. This is designed to keep from getting an air lock in the lifter galleys but also does a real good job of lubricating the timing chain area, including the front of the cam. This may help you as far as where the lifters are riding on the cam, but I have to agree with Larry that unless they are real far off, something else caused the wiped lobes. Make sure the valve springs are correct pressure, and not coil binding. You also did not mention whether the cams and lifters were new or used, If the cam in the motor had been run and you put a different one in without installing new lifters, that will almost always wipe the new cam also. If you have any other questions you can e-mail me and I will try to answer asap.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md