Roller cam and FE engine

[scottj]

Originally Posted by olddog

Breaking in a cam, has alway seemed like voo doo to me. I'm hoping someone can really tell me what the heck there is to break in.

My way of thinking:
Since the lifter rotates in the bore, the bottom of the lifter must be flat, or it will quit rotating. Hence the name flat tappet. So there is nothing that needs to wear to a perfect fit here. Likewise the cam lobe should be the shape you want. Now neither the cam lobe nor the lifter bottom are pieces that are hard to machine.

The only thing that could possibly require being worn until properly mated would be if the lifter bores in the block are not perpendicular to the cam bore. And I have heard of the lifter bores being off enough the throw the valve timing off by 3 deg, but that doesn't mean they are not perpendicular. However if this were the case and since the lifter bottom has to remain flat in order to rotate, then the cam lobe must wear to the angle of the lifter bore missalignment. If this was the case then the lifter would need to be harder and have a rough enough surface to wear the cam. Then once the cam is worn to fit the lifter needs to smooth off and quit wearing the cam. This is crazzy. Just machine the block right to start with.

If the lifter bores were not perpendicular to the cam bore wouldn't the roller lifters have the same problems.

I guess I'm back to - I do not buy the claim that failed cams are caused by improper cam break in on start up.

If I'm full of it, please explain it so I can understan it.

uhh... one minor note: Lifters are convex on the face and cam lobes are tapered...that is why they rotate.



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[olddog]

Originally Posted by scottj

uhh... one minor note: Lifters are convex on the face and cam lobes are tapered...that is why they rotate.

Goly gee I always assumed they were flat.... least ways they looked flat to me. I guess I never gave much thought to why they rotate. I'm going to have to go over to my sons. He alway has something appart.

However, no one has yet to tell me what needs to wear to a final propper fit, when breaking in a cam.

I understand the ZDDP thing, but the lack of it can cause old engines with 50K, 100K miles, and more wipe a cam. It is not just break in.

My son fired up a rebuilt 350 chevy - all new parts, including high lift high durration cam with heavy spings. He fires it up with load pipes and keeps the rpms up for cam break in. Half way through the cam break in he hears it knocking. He shuts it down and calls me. I listen to it definate knock and the oil pressure has dropped off to about 15 psi, which he didn't notice from under the hood. Checked the oil and it had about a half gallon of gasoline in it. The mechanical fuel pump diaphram was bad (brand new pump). Pulled the engine appart and the rod bearing gaps got worse the farther they were from the oil pump. The front two had a good 0.030 clearance. The point to this whole story is this fact. The cam was not harmed. You couldn't get a worse lubrication problem on cam break in than this and that cam shaft held up.

Now another cam fails on start up, with good oil in the engine. I'm finding it hard to believe it was because the rpms were not in the magical range.

[olddog]

Originally Posted by scottj

uhh... one minor note: Lifters are convex on the face and cam lobes are tapered...that is why they rotate.

My son is building a SB Chevy for a dirt track car (yea I know he is on the dark side). So I pull the lifters out of the box and put a straight edge across the bottom. Indeed they are ever so slightly convex, as stated. By eye sight the center is 0.001 or slightly more longer than the edges. This is a solid lifter. The lifter diameter is about twice the cam lobe width. When it goes in the block (block not done yet), I want to look at how the lobes line up to the lifter bores. I suspect the lobe only hits one side of the filter, and that this is what causes the lifter to rotate.

A couple of the lifters are rough around the edge. They need touched with a stone. Finish quality is not all that great. I remember in the old days lifters were polish like a mirror and shinning. These are not.

Your going to love this. The cam shaft is in two pieces brand new out of the box. The box is pristeen. Not a ding or dent in the box anywhere. Looking at the place it broke the cast material is very course. I have seen pot metal of better quality. I'm not saying that every cam manufacture is the same, but I do suspect that metal quality has gone down, as almost nothing is made in the USA anymore.