Quote:
Originally Posted by 19Fordy
Drilling the holes is a lot better method than grinding. Don't even consider grinding.
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He's not talking about the holes that are used to insert a punch/rod to stop the lifter from turning, he's talking about the fact that with a high-lift cam (which means small base circle), the adjusting nut is not up high enough to get a wrench above the lifter boss to adjust the lifter. This makes it a REAL pain in the butt in that you now have to turn the crank to get the lifter up, adjust it with a guess, then turn the crank to get it on the back of the cam again . . . then measure and keep repeating this until you get it right. This can add HOURS to the job - and lots of chances to get it wrong.
If you grind the top of the lifter boss down a bit, then you can get your wrench in there.
So, to answer the original poster's question, the amount you need to grind is strictly dependent upon your block, your cam and your lifters. I would put the cam, and two lifters, two valves (one intake, one exhaust) and see how far down the adjuster is. Then you'll now how much to grind the lifter boss.
You need to go the right depth and then wide enough to be able to turn the wrench.
Also, grind the heck out of a 7/16 quality wrench to make it your special "tappet wrench". Make it about 1/8" thick and grind the sides to give you more turning radius in the lifter bore area.
On an engine that I'm currently building with a Potvin 3/8 cam (.375 lift), it takes about a 3/16 grind on the lifter bore - the width of the boss, to make it easy to adjust the lifters.
Once you've done, you should deburr the edges.
Also, you have to thoroughly clean the engine afterwards. This includes removing the cam bearings and doing a complete soap/wash, rifle brush, etc.. The last thing you need is the cast iron filings laying around somewhere in the block - just waiting to be picked up in oil so they can wipe out your bearings.
I usually do ALL the above work - before I bring the block to the machine shop for all the boring, valve, etc.. work.
Good luck!