Questions on valve clearance with AFRs

[ex-lt1-guy]

hi everyone, im having a 347 built at a machine shop here locally, my question is i have bought a new rotating assembly with probe pistons. They are not a dome style piston. I was thinking of using the afr 185cc or the afr 205cc, but i was unsure if i'd have to notch the piston to get the clearance i need to use these heads, i thought maybe factory pistons u HAD to but aftermarket u wouldnt. If anyone has any input let me know

[Idhomustang]

Ok,

Will I have to notch, isn't really a question of yes or no? It more of a question of lets see? First off you'll have to dummy assembly your motor.

You can do this my using 2-3 complete sets of main bearing and one set of rods or you can go all out and use four sets. Why so many? Well your going to want and check you deck clearance at the same time. This is the mount of piston left in or out of the bore. And you can also see from this how close you block is to being square while doing this. This is one of many things you do while blue printing an engine. Sound complicated? It isn't, many good books, and folks willing to help.

Next you will or should aready have installed the timing chain, camshaft and and cylinder heads, I installed my heads with out gaskets, these head bolts are only used to hold the head in place. Don't forget to add the head gasket thickness, when compressed into you calculations later, these numbers are availvble for all poplular heads gaskets. I then adjust valves on set of lifters that have been pumped up BY hand in a small container of oil. I have at this point used a small peice of modeling clay, rolled flat sandwiched between to pieces of plastic saran wrap. It is then placed on the piston over the valve notch.

I then rotate the engine, after the valves have been adjusted, then I disassemble the heads and remove the modeling clay, measure the intake and ex. recording the measurements. I slice the modeling clay into two sections intake and ex, then slice these again, and use a mic to measure the thickness or "valve clearance" usually it runs in excess of .100 which is the recommended my 393 ran .300 on intake and .250 on ex. pleanty of room, for a bigger cam, I'm running a .540 cam, which meets afr, max spec, for the heads I have and the valves, and springs.

I also record the other measure ments as well, the piston to deck numbers front and back on the corner holes. If your within 5-15 thousandth's of an inch you good to go for a good street engine. If not you'll need to have your block decked, alot of guys are into the zero, decking, which sometime complicates their lives, my costing tons of money to machine the block and then rework the pistons, etc. notching the valves can be done by hand with a drill, by obtaining a notching tool, from moroso, and crower some of these big names make them, the better ones have a adjustable stop, so each valve notch is the same.
All of the numbers you generate are used to calcultae the compression ratio of your engine, based upon a countless amount of varibles. Yes this is a math based info, your in the big time now..:>)

Bottom line is this, you need to check, will you have problems, maybe but usually not, the manufactures like SRP, "Probe" already notch them pretty deeply, if your cam is mild under. .500" more then likely you will not have problems, but my suggestion is that you always check.

Building engines for race is all about numbers, and you should generate a bunch each time you build, these should be kept for further use, in other words recorded and secured, for later use.

Sorry didn't mean to write a book. :>) Mac