After doing several searches and reading up on this, let me know if this is the way that PtV clearance should be measured:

1) Install checking springs on both valves on #1 cylinder.
2) Install adjustable pushrod on one of the valves.
3) Install rocker arms and tighten.
4) Adjust pushrod to zero lash and be sure not to compress the checker spring or lifter plunger.
5) Install dial indicator on top of valve or retainer.
6) Rotate engine from 20* BTDC to 20* ATDC in 2* increments, taking measurements at each increment by opening the valve by hand until it hits the piston and note measurements.

OK I have a couple questions....when you are rotating the engine by hand, will the lifter plunger depress at all or will the light tension checker spring prevent this? Obviously I dont want the plunger depressing in the lifter or this will skew my measurements.

I spoke to Tony Mamo @ AFR last week and he was saying that when you are checking PtV clearance the numbers on the dial indicator are different then what it actually is. He said that you want the dial indicator to show .065 minimum on the intake and .080 minimum on the exhaust. He said the measurements on the dial indicator will reflect the actual measurement of .080 intake and .100 exhaust at the piston. Has anyone ever heard this before?

 

Your procedure appears to be correct. Not sure what Tony is talking about, the dial indicator will be on the valve spring retainer, right?

 

I couldnt quite understand why he told me that either...I wouldnt think the measurement would change from the top of the valve stem to the head. The dial indicator goes on the retainer right? That way you can push on the valve stem rather than the retainer. I learned to not push on the retainer with the checker springs in place as it will let the locks fall out.

 

If you are careful, you should be able to put the dial indicator on the retainer and use the rocker to move it down slowly until it just touches the piston. Maybe you should PM Tony, I am curious why he said that too as I plan on checking mine in a few weeks using the same method.

 

Procedure is perfect. The checker spring isnt enough to depress the plunger. Tony may have been assuming you were taking your measurements on the short side of the rocker. If its on teh retainer, you should have accurate measurements.

 

Possibly, I'm going to go ahead and use the specs I had originally decided to use before talking to Tony. I'm going to send Tony this thread and see what he thinks.

 

I agree with GuitsBoy, the rocker ratio has to be calculated in if you are measuring at the lifter or the pushrod end of the rocker. I did this exact procedure today with a cam I just installed. I have .028" min. intake clearance at 10* ATDC. The exhaust is fine. Looks like I will be giving LG a call to see if I can rent their cutter and head.

 

I sure hope I dont have to flycut...I wont even be able to take these measurements for at least a few more weeks until I get my F13 back. I'll be measuring on AFR heads milled down to 62cc and a .040" cometic on stock pistons.

HavATampa - What cam/heads you running (lifts, milling, etc.)?

 

Josh...

What I said was that the minimum I would like to see (if you want any margin for some error for missed shift etc.) is .065 (Int) and .080 (Exh) when checking with the dial indicator. What your confused on is the fact I told you that those #'s are actually conservative and that if checked with the "real spring", not the light checking spring, you will actually have .015 - .020 more due to defection in the pushrod, camshaft, and rocker arm when the true spring pressures are applied. You will notice when you use the clay method and keep the regular duty springs in place you will have more clearance than if you checked with a dial indicator and light checking spring.


Hence the reason I told you that you could get away with .065/.080 (when using the light springs) when in reality those figures would get you closer to .080/.100 which are the typical "textbook" minimums for P to V clearance.

Tony M.

 

Ahhh....that makes sense Tony.You always have a way of explaining this stuff to make it easy to understand. Josh, I'm running 5.3 heads milled .010, 2.02 intake valves with .040 Cometics. The cam is a Comp grind, 230/236 dur. and .589/.597 lift.

 

AH OK I got ya now...so the jist of what you are saying is that when measuring with the light checking springs and the dial indicator you get approx .015-.020 less than if you checked with the clay method? So if indeed I do check the clearance with the checker springs, and have say .068 intake and .085 exhaust I would in reality have approx .083 intake and .100 exhaust and would be alright? Obviously these numbers were just thrown out for examples.

 

You got it Josh....The stouter the "real" spring the more clearance you will actually have.

 

Tony is exactly right. I did both methods on my engine. With the clay method I got 0.149 and with the dial indicator I got 0.118 on the exhaust. On the intake with the clay I got 0.178 and with the dial indicator I got 0.150. So there is alittle difference between the clay method and the dial indicator method. I am running a solid lifter so I was able to do the clay method also.

 

Alright cool, thanks for all the replies. I'm sure this thread will help others in the future as well when they are making this vital measurement.

 

Great, this threads a keeper

 

I'm going to bring this thread back from the dead, i'm running dart 225, the cam in my sig, and a .040 cometic gasket.

I checked clearance with a checker spring and dial indicator and got .100 with my exhaust so thats ok, but on the intake i was right around .063 which from reading this is the bare minium.

Question is should i just flycut the intake to be safe since its that close, or do you think i'll be fine.

Justin

 

If the minimum is .065 then I would flycut with a measurement of .063.