My new big block started making a knocking noise. I located it under the timing chain cover with a stethoscope. I removed the cover, put the balancer back on and started the engine for just a few seconds. The noise is the cam moving forward on each revolution. (cam not crank) It's a hydraulic, flat tappet, custom ground, Comp Cam about 18 months old. Actually it's the second cam, the first went bad on the dyno. What would cause this and how do I fix it?

Thanks,
Art

You can stop the cam from moving with a button but this is pretty much a bandaid as it shouldn't be moving forward at all if it ground properly. It should be trying to pull itself into the block.
I would be looking at all the lobes to be sure one or more isn't going flat & driving the cam towards the front.

Don't mean to steal your post though, but I have a question too. When the cam "walks" how come it walks forward toward the timing chain cover, and not to the back? Also how exactly does the button work?

Originally posted by TwoLaneBlackTop:
Don't mean to steal your post though, but I have a question too. When the cam "walks" how come it walks forward toward the timing chain cover, and not to the back? Also how exactly does the button work? The lobes on the cam are ground at a slight angle always pushing the cam towards the rear of the engine, A cam button sets in the middle of the top timig gear and makes contact with the timing cover and should always be used with a roller cam as lobes are ground flat and it will walk. They make some nice cam buttons with torrington bearings.

Sounds like the cam or a lifter may have a problem. I'll pull the intake in the morning. So what should I look for on the cam or bottom of the lifter and what would cause the cam lobe to wear whith so little run time on it? This is the second cam to be in this engine. Do the lifters turn in their bores and if it didn't, would that cause a problem?

Thanks Again for the Help

Yes, the lifters MUST rotate. If for whatever reason they don't you will have a flat lobe in very short order.
As to what causes the lobe / lifter wear,,, the list goes on & on but my list would start with Improper breakin,
Too much spring pressure,
Coil bind or the retainers hitting the guides,
A lifter too tight in the bore,
A "bargain" cam ground without enough taper,
A cam or lifter (probably lifter of late) problem like not properly hardened
And on a rat in paticular, the lifter bore
(or bores)improperly indexed.

My thanks to all for your help!!

Mike, The engine builder has a very good reputation so I think the cam was properly broke in. They rechecked the spring pressure and for coil bind after the first cam went bad. I didn't ask about a tight lifter bore though and I don't know what lifter bore indexing is. Could you explain indexing a little more?

Any other things I should check for?

Lifter bore indexing means to place the lifter bore over the cam lobe in both the position & angle it was intended from the factory.
Far as I know unless you happen to have a CNC machining center that is programed to do blocks from a known reference the only way to check it is with the BHJ fixturing that references off the front of the block where the timing gear rides that you actually use to put them where they belong.
On stock cams with 80lbs of spring it is rarley if ever a problem but when you start putting aggresive cams with more spring it gets a bit more important.
It is not unusual for the bores to be off but a little unusual for them to be off enough to cause a problem.
I have done blocks that were off enough that they would not clean up going from the stock .842 dia lifter to .875 lifters but again this is the exception.
If you have a lifter that does not rotate & it does this with more than one properly ground cam first thing I would do is switch lifters & if it still does not rotate on this lobe it is a pretty good indication you have a block problem.

Or,,,,it could be the car Gods are upset with you in which case you need to find a Ford to sacrifice to them for atonement for whatever sin it is you have commited :D :D