Piston to valve clearance

[Ed Wright]

.100" is safe.

[JeremyDuncan]

Originally Posted by Ed Wright

.100" is safe.

Way safe for Intake valve.

Usually .090 on Exhaust and .040 on Intake.

Bigger the camshaft diameter equals less flex and you can tighten clearances.

[Sean Cour]

I like to run them till they touch, then back them off a little!

[Ed Wright]

What Sean said^^^^^^^^^
Mine has .036" intake & .075" exhaust right now, but I hesitate to tell somebody that becauseI don't know how sharp they are, and I don't want to hear "I bent some valves doing what you told Me!", and him having to ask that......
No valve marks on my pistons, but no carbon there either. Just clean aluminium.

[SS Engine Guy]

You got some pretty good advice there. Only thing that I will add is to make sure everything in the valve train is up to spec and closely monitored. Also check P/V clearance at least 10 degrees BTC and 10 degrees ATC at each increment and log the readings for future reference. I usually log every 2 degrees to 20 degrees both ways and furnish that with other records on an engine. Good record keeping can make maintenance much easier.

[SSDiv6]

Originally Posted by SS Engine Guy

You got some pretty good advice there. Only thing that I will add is to make sure everything in the valve train is up to spec and closely monitored. Also check P/V clearance at least 10 degrees BTC and 10 degrees ATC at each increment and log the readings for future reference. I usually log every 2 degrees to 20 degrees both ways and furnish that with other records on an engine. Good record keeping can make maintenance much easier.

What he said!

[fordteacherguy]

I check valve drop (P/V clearance) in approximately the same range as the other posters but also set up a handy spread sheet that takes those valve drop reading readings and also contains my theoretical valve lifts at those designated points. My spreadsheet calculates P/V clearances by doing the simple adding and subtracting and giving me a total P/V clearance. I also set up some conditional values in Excel that turn the cells red if I'm below a minimum P/V threshold. I've found building a P/V spreadsheet useful because I can move the cam degree cells left or right (simulating advancing or retarding the cam) and see what the new P/V clearance should be with the cam at those various places. Using a P/V spreadsheet also allows me to check a different cam in a bare block with a crank, get the lift @ degree numbers off of that new cam, punch the numbers in to my existing motor valve drop measurement sheet and recalculate new clearances.

As always, you DO need to physically check P/V clearance that math=actual clearance but so far it has worked great for me.

[MAURICE BLENDHEIM]

Originally Posted by SS Engine Guy

You got some pretty good advice there. Only thing that I will add is to make sure everything in the valve train is up to spec and closely monitored. Also check P/V clearance at least 10 degrees BTC and 10 degrees ATC at each increment and log the readings for future reference. I usually log every 2 degrees to 20 degrees both ways and furnish that with other records on an engine. Good record keeping can make maintenance much easier.

X2. Good advice. Also make sure your cam drive (belt or chain) is in good condition. MB.

[Ed Wright]

I only do "valve drop" measurements to verify all cylinders have the same valve seat-to-valve pocket travel. I would never just do math to check my valve-to-piston clearance. I actually measure it in 2 degree increments 20 degrees from TDC. I have found the closest point being ten degrees from TDC to almost never does apply to my stuff. I measure it with the springs I'm going to run. I have an old Mr. Gasket on-car valve spring checker that I have modified to fit my Jessel rockers, to pull them down against the pistons. I use a long 1/2" drive break over instead of the torque wrench it was meant to use for checking valve springs. Checking with weak checking springs always show less room than it will have running.
I measure it with the cam two degrees further advanced than I expect to run it, and backed up two degrees further than I would expect to run it, on a new engine. After I settle in on where I'm going to be running the cam, the next time it's apart, if I have room, I close it up to the minimum. My pistons have a clean ring like the face of my Manley valves, and a round dark spot for the dimple in the center.

I quit using modeling clay about 1970, when Carrol Caudle told me "Ed, give that crap to a kid to play with, that is what it is meant for." LOL

If somebody tells me they bought an engine, and how much clearance should it have, I'm going to tell them way safe to keep them out of trouble.

[SSGN]

Originally Posted by Sean Cour

I like to run them till they touch, then back them off a little!

Okay I just spit my coffee on the key board

Kevin