P/V clearance... Just Clay'd... At .010

[korn]

I knew it was gonna be close. As I was past the service points on the head.

I measures the clearance to be .010 inches On the exhaust valves. So I need a bigger gasket. I have a +.03 on hand, can I get away with that??

My research says .04 is the limit. What say the gurus??

[korn]

More pics.

[korn]

The clay is soooo thin it's tough to measure... Nearly falling apart...

[SkiFree]

I would not feel comfortable going that thin.

Personally like to see AT LEAST 0.080"Int and 0.100"Exh at a bare minimum

[ForcedFirebird]

I have gone as close as .057" intake and .073" exhaust without issue in a 7000rpm engine and IE cam and over size valves, but that made me sweat a little. You see, your rods will stretch about .040" at high RPM's.

But, that's not what you have to be afraid of. Once the head is shaved past a total height of 4.909" the dome on the pistons will hit the head and take out your rod bearings. Put clay between the head and the piston, if the valves are that close, I am going to guess the pistons and head are going to kiss. The engine example I gave above had .045" between the head and piston dome.

[digger]

depending on what pistons youre using you either need to deepen the pockets or a thicker gasket, you dont want to open the squish unless it doesnt have any

according to catcams 1.5mm ptov is the preferred minimum

[korn]

hmmm... i did the clay and did not see that it was close on the piston to the head. the thicker gasket I have is 2.05mm... that would put me at the theoretical minimum....


But I could order the play is safe MLS at .98"; that would give me another .40 and will be about .080 on the exhaust valves....


I am using stock pistons.

[ForcedFirebird]

Stock cam? Not sure how you are at only .010" VTP and the pistons aren't touching the head. I have taken heads down too far in the past and we were out of a 14hr race in 2hr because of it, and the valves were fine, motor had great compression - but once we pulled the head we saw the evidence of contact.

[korn]

just had the cam ground to 272

[korn]

problem is now I can't get a MLS gasket in the thickness I need for a week or two... I wanted to button this up this week!

[ForcedFirebird]

Something doesn't sound right. The engine in my post above had a 272 cam as well. I've never had a 272 be that close.

Cam timing off?

Measure the total height of the head.

[korn]

So; My measurement of that was done with the old compressed 1.75 gasket.

If I move to a 2.05 with copper spray; Will that be enough? ... i'm guessing copper spray wont really add any thickness... But this is a game of .001s!!!

[korn]

i measure 4.895

... Cam timing was on, i did 4 full rotations on the crank with the clay, and timing stayed on...

[digger]

measure piston to head clearance, 0.040" is a good number

[ForcedFirebird]

i measure 4.895

... Cam timing was on, i did 4 full rotations on the crank with the clay, and timing stayed on...

Your head is shaved a full .014" past spec. If it is a factory head, you should have dots in the corners that indicate when it has been planed one too many times. 4.909" gives about .035" with a stock gasket, and the reason the thicker ones are available.

Check piston to head clearance again, as Digger said, shoot for .040", then worry about VTP clearance.