Valve/Piston Clearance

[holeshotmoe]

I have a question about calculating (or anticipating) piston/valve clearance issues. While waiting for my short block build, I picked up a set of 264/272 cams, and a built head with 2mm oversize valves. I wasn't looking for bigger valves, but as I was ready to buy parts for rebuilding my stocker, I came across this other head for a good price. Lately I started wondering if I'm going to have an issue with clearance. So I guess for starters, my question is whether anyone has ran these cams with big valves? What do the aftermarket pistons do to valve clearance over stock pistons? I've been studying Jafro's Hyundai motor video where he notches the pistons to allow him to use the cam timing he wanted. He's advising not to thicken the head gasket for more clearance. So I guess I'll follow his procedure if needed. But if this combination is known to leave the standard .080"/.0100" clearances (which I'm doubting) then I'll stop worrying about whether I should be rethinking my build...or buying some solid lifters, softie valve springs and degree wheel, etc. Here is what I'm working with now:
264/272 hks
Evo8 lifters and rockers(1.7x:1 ratio...same as ours I think?)
stock crank (88mm)
pauter 1G (150mm) rods
wiseco 1G 9.0:1 pistons .020" over
Deck cut? I don't know yet.
Head planed? It was finished for MLS HG but I don't know how much material was removed. Can I measure this and compare to an uncut head casting?
Thanks all for any info!

 

[FlyingEagle]

To partly answer your question about how much material is or was left on the head, there are spots around the outside area (x2) where the head gasket meets the head material, where holes actually disappear or become flat if too much material is removed - that is the service limit of the cylinder head. At some point, there is a total limit that you can work with for head and block material removed, assuming stock gasket crush thickness and stock valve train and no adjustable cam gears. Your situation is one where you can accommodate and dial in the cams and confirm opening/closing events and total lift before any considerations for float come into play.




Not sure of the start point for depth at those two "plug" looking spots in that photo, but that is your measurement point to know how much material is left as compared to max machined removal.

You absolutely need to know the crush thickness of the head gasket you will be using, and if that changes, given a change in bolts and torque applied.

I have the following setup with no actual measurements to back up what I am using.

4g63t 1G 7.8:1 (low compression bowl OEM)
4g63t 1G head with unknown material amount removed - it has be resurfaced at least once in my use
HKS 264/272
Stock valves
Evo 8/9 springs/retainers
Stock compositve 1G head gasket
ARP head studs set to OEM bolt torque

 

[AllanL]

hope you get something from this:

click