Originally Posted by 68Gold/white
The flat tappet cam deal is a little complicated. I have wondered about how that mechanical invention came about.
There's a bunch of stuff that have to be in spec for everything to have a good life expectancy.
1. valve spring pressure has to be in line to keep the lifter on the cam, and not too much to put too much pressure on the lifter face. Stock cams are the best place for this. You go high RPM, and you need more spring pressure, AND the lifter gets more abuse, FASTER.
2. The clearance between the bottom of the valve spring retainer has to be adequate, AND you have to factor in space there for the valve stem seal(at the top of the valve guide). If the spring retainer hits the top of the valve guide, your cam goes flat, FAST!!!
3. The lifter HAS to rotate in the lifter bore. Not everyone has the understanding of how the flat tappet works. It spins in the lifter bore, and actually only rides on the back half (or so..) of the cam lobe. The lobe makes the lifter spin. As the lifter spins, it obviously rubs and creates friction (this is where the zinc is needed). IF, IF the lifter ever quits spinning, the lobe and lifter bottom start grinding each other up. You'd think that even with the lifter spinning, this would be the case...that's next...
4. The break in is very important, Factory flat tappet cams had no specific break in time in the engine (at least that's what I've been led to believe). It's amazing that different cam companies have different types of break in lube. Some actually RUN OFF the cam after sitting for a short period of time..Moly paste should be applied to the cam lobes and the bottoms of the lifters, using the minimum amount needed!
Remember that the lifter needs to spin in the lifter bore! If the cam is much more than stock, the cam manufacturer will recommend using the outer springs for break in.
The cam break in is tedious. Your timing needs to be set close, to fire up the engine and bring RPM's to 1800-2000 immediately, for 20-30 minutes!!! The carb needs to be one that you know will fire up and run immediately also. If you have to fiddle around to get the timing set and the carb adjusted with the engine barely running, this can have negative results the the lifters breaking in, the way you want...
All this said, the theory is to allow the lifters to make a wear pattern on the cam lobes, with as little wear as possible. When this occurs, the metal on the lifters and the cam lobe are being hardened, it's call work hardening. This initial pattern will stay essentially the same, for many miles.
The brand of lifters can make a difference. I only use Hylift Johnson lifters, regardless of cam make. THese are possibly the only, or one of a couple American made lifters. NONE of the cam folks use these, or sell them, they are more expensive, but not enough to make me buy another brand...
This info may not help anyone. I learned it all from my engine building buddy. It has not failed me, yet. There's just so many details in putting an engine together, most are not aware of...I could spew another 1000 words on this subjet, and NOT be done...
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