At what point should this be an issue typically be a problem? I am considering up-sizing my cam to where the max lift will be at .599. I am running 210 AFR heads with a .031 compressed head gasket with flat top pistons zero decked. What is the minimum allowed? The lift on the new cam is .022" higher with more duration. I really don't want to remove a head to check.

 

I think you should pull a head and be sure.

 

The important clearance is overlap where the piston is up and both valves are slightly open. Thats where the piston is closest to the valves! It can be done without removing the head if absolutly necessary. I would substitute wheel cylinder springs and stack up the valves as softer and easier to move for checking.

 

I bought a set of springs from the hardware store and used a dial indiactor to check P/V clerance. turned up i had to go to a .039 gasket to get the clerance i needed. I was using less lift then you are with a set of 292 heads.I set a degree wheel on my crank, got 0* TDC with the head off and got the wheel dialed in. I replaced two of my valve springs with lighter ones from the hardware store and bolted on the head with no gasket. Then I set a dial indicater on the valve retainer and zeroed it every ten degrees before and after TDC on both the exhaust and intake valves on there opening cycle. every ten degrees I pushed down on the valve to bottom against the piston and recorded the distance. obviously you are trying to not remove your heads but the same basic method should work.It was my first time trying it and i did it more then once twice or thrice but eventually i was satisfied Ihad the corect numbers.

 

Well, if I have to remove the head, I might as well just use some putty on the piston method. Anyone know what the clearence should be?

 

You should have .100 valve to piston clearence on the exhaust and
at least .080 intake on any motor.
Eddie

 

Thanks for the info!!

 

Aftermarket JE SRP, wiseco, ross..... All of these are set up for big lifts and valve diameters without machining.

I would word what Iron cross said a little differently. Here is a roller cam that I ran in my 383.

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 15.0 BTDC 45.0 ABDC 240 °
Exhaust 59.0 BBDC 9.0 ATDC 248 °

The intake is open .050 and the piston is still 15 degrees before top dead center. The exhaust valve also is closing until 9 degrees after TDC.

So valve lift with a roller cam also happens allot faster. High total lift with low duration numbers will have more clearance. I have not owned a sub .600 lift cam in years and I have never had to machine clearance the pistons

Anyway with my latest cam with 248/250 and .680/.710 lift clears my wiseco pistons .046 with standard 23 degree heads like your AFR's with 2.08 intake valves. I'm not going to have the pistons machined. .100 is the normal standard. I run big enough springs that valve float is not in the picture.

 

Gkull,
What is your piston in the hole dimension and gasket thickness?

 

.015 P to D .026 MLS gasket for .041 quench. I actually used my AFR 210's for a about 3 months on my 427 small block. They were even a worse case senario because I had them flat milled to 62 or 64 cc. Which would bring the valves closer to the piston than stock AFR's

The intake valves were actually lower than the flat chamber area of the heads. I was running .620 net lift at the time and I had @.085 clearance with my 242/248 solid roller.

Without taking it apart you might put a bore scope in the spark plug hole and see how close it gets. Claying is the only 100% method. 99% probability that your just fine. You could also retard the cam timing just 2-4 degrees and gain additional intake valve clearance.

 

I am looking to go with that solid roller and a Victor Jr. intake. How did you like that combo? I have the 74cc heads. Your CR must have been quite high !

 

427 Dart small block Forged 4340 crank, Eagle H-Beam Rods, Ross Forged pistons, Holley Modified 830cfm, DUI HEI Ignition, AFR 210cc ported heads, Air Gap RPM intake, 10.5 CR, CC XR288-HR cam, 236/242 @ .05, 1.6 ratio Pro Mag roller rockers, TKO 600, Rebuilt rearend w/ HD bearing caps & bolts, tuned and polished Eaton Posi, Carbon Fiber Clutch Packs & Yukon 3.73 gear, Spicer U-Joints, Hooker 1-3/4 Headers thru 2-1/2 pipes & Flow Master Super 40's. 450 RWHP/475 RWTQ.

I forgot that you and I have the same basic engine. Both your Ross and my Wiseco pistons are top of the line forgings. As I said I used the next step up solid cam with 1.65 rockers and I didn't have a clearance problem.

I also felt like the 242/248 was really kind of mild when combined with a 5 speed. I had the shifter linkage separate and I drove home 20 some miles in fourth gear. Lucky for me I never came to a complete stop. I got down to where it was lurching and then would take off again. That is why I went for the bigger cam this time. It was really tame. I go out to the race tracks and it just didn't have what I wanted. The only thing that kept me up with the 500+ ci off road Vipers was my much lighter weight.

450 rwhp is very respectable. Mine is probably about the same. The 427 small blocks really are kind of fun to drive. As for a intake manifold. The best bang for the buck is probably the Mowtown single plane. It has a smaller plenum volume than the super victor/Dart/Brodix

 

Thanks a bunch for the tips!!