piston to valve clearance

lang williams · Aug 7, 2007

Hi, I just picked up my gtp heads after having them milled 40/1000ths, 3 angle valve job an tf springs installed. i put some silly putty on a piston, put an old head gasket on an turned the motor over. at the thinest spot it measured .06 is this safe? i'm running a crane 20/20 cam with .530 lift. i did the test fit with the stock stamped rockers, but i have fms rollers for the real deal. thanks

88mouse · Aug 7, 2007

thats really close.You running stock pistons? Think i would have them fly cut.

lang williams · Aug 8, 2007

I'm starting to think I might try shorter push rods or thicker head gaskets. i'd like to get that clearance up to .1 or a tad more.

88mouse · Aug 8, 2007

Sounds good. Go for it.

85_SS_302_Coupe · Aug 8, 2007

Personally i never do a PTV check with the head gasket....i like to check it WITHOUT because that means you've got that much more clearance.

What you've got would be too close for my comfort..

pwcracer · Aug 9, 2007

Do you think if the pistons are cut for 1.90 valves it would offer at least a little clearance for 2.02's?

ChromdOutDubs · Aug 9, 2007

85_SS_302_Coupe said:
Personally i never do a PTV check with the head gasket....i like to check it WITHOUT because that means you've got that much more clearance.

What you've got would be too close for my comfort..

Thats exactly what i did when i checked mine... I knew if it cleared with no gasket it would be fine with it.

-AJ

85_SS_302_Coupe · Aug 9, 2007

pwcracer said:
Do you think if the pistons are cut for 1.90 valves it would offer at least a little clearance for 2.02's?

Well i can't tell you it will ya know? I'd hate to be wrong and you screw up your valves and pistons. Like i said the safest bet is to do the check without a head gasket.....some other guys on here will say you're ok otherwise, and you may very well be, but if it were ME and my engine, i wouldn't. If i spent the money on 2.0+ valve heads and pistons and all that, i'd look for every fail safe i could get.

lang williams · Aug 9, 2007

i'm going to do the ptv check without a gasket this weekend, i'm putting ford gtp heads on so they're only 1.84 valves. i hope i dont have to shell out the $160 for the thick gaskets since i already have a set.

5spd GT · Aug 9, 2007

With or without a gasket really doesn't matter...

You just have to do a little math...

Most of the headgaskets (which will say on the headgasket package) have a compressed thickness of .038-.045."

So even if it 'clears' without a gasket you could still only have .040" of clearance

Just use your old headgasket...

.06x is awfully close, as I'm sure you know the rule of thumb is .080" on the intake side and .100" on the exhaust side due to heat expansion. I would give it more room if you have some old or weaker valve springs, so if it does decide to float a bit...you would have a bit more cushion...

A 2.02" valve's radial will make it harder to clear, it can 'override' the valve reliefs...

A headgasket is only going to get you .05-.010, depending on what you are already running...but if that is what you are looking for, then so be it...

Advancing or Retarding the camshaft can gain you a bit...although it compromises your performance and powerband.

Advancing the timing opens the intake sooner and closes the exhaust sooner. That will gain you some clearance on the exhaust valve, but you will lose clearance on the intake valve. Retarding the cam causes the timing to open the intake valve later, and closes the exhaust later. You'll gain clearance on the intake, and lose clearance on the exhaust. So changing the cam timing won't result in increasing clearance on both valves. So you need to see which one you need most...

So in your case with .060" of clearance on the intake, you could retard the cam a slot over...

But this isn't really preferred...

A dremel on the pistons could give you a bit more clearance where you need it...

The higher the rpm you plan to shift, the more clearance you will want...

lang williams · Aug 9, 2007

"A dremel on the pistons could give you a bit more clearance where you need it...

The higher the rpm you plan to shift, the more clearance you will want..."

I guess I could notch a little clearance in witht he dremel, how thick is the piston an how safe is it? i plan on shifting in the 5500 range cuz the cam peaks at 5200 an float occurs at 6000. thanks for the input.

5spd GT · Aug 9, 2007

lang williams said:
"A dremel on the pistons could give you a bit more clearance where you need it...

The higher the rpm you plan to shift, the more clearance you will want..."

I guess I could notch a little clearance in witht he dremel, how thick is the piston an how safe is it? i plan on shifting in the 5500 range cuz the cam peaks at 5200 an float occurs at 6000. thanks for the input.

Just take out the amount you need...maybe .020-.030 and make it as even as possible on all 8 pistons...

I do not know how thick the piston is...good question

.080 on the intake and .100 on the exhaust should be fine with that rpm...

lang williams · Aug 9, 2007

good deal, thanks for the info.

65ShelbyClone · Aug 10, 2007

Did you really use Silly Putty or was it actually modeling clay?

85_SS_302_Coupe · Aug 10, 2007

5spd GT said:
With or without a gasket really doesn't matter...

You just have to do a little math...

Most of the headgaskets (which will say on the headgasket package) have a compressed thickness of .038-.045."

So even if it 'clears' without a gasket you could still only have .040" of clearance

I know what you're getting at, but if it clears without a head gasket, you'd have however much it cleared by PLUS the thickness of the gasket. If you're super close without head gasket then i would be looking to add some valve reliefs because i wouldn't rely on the thickness of the gaskets for clearance.

5spd GT · Aug 10, 2007

85_SS_302_Coupe said:
I know what you're getting at, but if it clears without a head gasket, you'd have however much it cleared by PLUS the thickness of the gasket. If you're super close without head gasket then i would be looking to add some valve reliefs because i wouldn't rely on the thickness of the gaskets for clearance.

Tomato, 'Tamado'...

I just figure if the gasket is there (padding between head and block surface), you have the actual numbers - no math needed.

lang williams · Aug 10, 2007

i redid the check with play doe (yes all i had was silly putty the first time) without a head gasket an i had basicly zero clearance on the intake. i scribed the low spot into the piston top an i'm going to dremel it. looks like i just need to make the relief a little wider an back toward the center a little on the intake side. the slightly bigger intake valve an combustion shape of the gtp head moved it from the orig relief. i'm just going to make the stock depth relief a little wider an more to the center. thanks for the help guys.

85_SS_302_Coupe · Aug 10, 2007

Now aren't you glad you did the check? Think of what would've happened if you didnt

piston to valve clearance

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