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MP purple cam and lifter recommended preload?

They are 3/8", 24 tpi, ie 1 full turn = 0.0417", so our 3/4 turn is only 0.03125", so well short of being mid-way thru the lifter plunger's travel :rolleyes:
You know why there is plunger travel at all right? It's for machining tolerances and long term wear in the motor. So best case scenario, is the least amount of preload that it will be happy with. I'd go 1/2-3/4 ( or less if high rpm was a concern.
Or go with the comp pro- magnum lifter. You set those at .002 ~.004 hot.
If you bled the oil out of one of your lifters & then compressed the prod seat, the total distance is the....pre-load available.
Somebody mentioned 0.210" earlier in the thread. It does vary with lifter brands, but there is usually up to 0.150" or more available.
You can adjust your pre-load to anywhere within that available range. In the old days, a favourite trick was to adjust preload so that the prod socket was about 0.010" below the circlip.
This meant that if the lifters pumped up at high rpms, you only lost a little bit of HP. But you ran the risk of popping out the cclip.....
Because you have popped a couple of prods out, it sounds like the lifters maybe bleeding down after sitting, & coupled with a lot of pre-load [ plunger movement ] , there is enough gap for the prod ball to exit the socket. So the fix would be to reduce the pre load [ screw the adjuster IN ] so that the prod cannot exit if the lifters bleed down.
If the engine has iron heads it's simple to pull a tappet out and take it apart and measure plunger travel. I've done this multiple times and this will give you the correct info to begin the preload journey. Heck, I don't even take the intake off ( if it's sealed up good) for basic flat tappet cam changes anymore.

This basic discussion has turned into the making of a "mountain from a mole hill" thing. If you have an adjustable valve train you can do whatever makes you happy.

I've always thought the gravitation to hydraulic cams because they're supposed to be simplier and easier was nonsense. Throw that hydraulic tappet away and get off the merry go round.
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