The Ford Barn

BobM · 11-29-2011, 03:30 PM

My Offy heads have been milled .020" and when I set them on the block with no gasket the head lifts up when piston hits TDC; is this to be expected? The only thing preventing catastrophic failure is the head gasket? When I clay with gasket & head torqued to 50lbs. I get .040" at the piston edge, does this make sense? I know the head is coming off the block with no gasket almost .040". Nervous & confused

Junknshit · 11-29-2011, 03:58 PM

You get .040 at the edge, what do you have in the center of the piston? Was this engine running before and all you are doing is changing heads? If fresh build, do you have piston, rod, crank combination right? Are the heads new? or have they been milled before?

flatjack9 · 11-29-2011, 06:32 PM

Something doesn't add up. If you have .040 clearance with a torqued gasket, there must be some area that is tighter that you haven't measured. Are you sure it is lifting .040?

BobM · 11-29-2011, 07:13 PM

Quote:

Originally Posted by flatjack9

Something doesn't add up. If you have .040 clearance with a torqued gasket, there must be some area that is tighter that you haven't measured. Are you sure it is lifting .040?

Here are my measurements: .040" piston edge .043" at midpoint between edge and center of piston and .085" at center of piston with gasket & head torqued to 50lbs. Actual lift off block is about .038" with head & no gasket at TDC. This engine has never been fired, Merc crank, full floating rods because crank had to be turned way down and Ross pistons. With .085" at piston center I think all the parts are matched correctly, could milling the head .020" be the reason head raises up?

Ol' Ron · 11-29-2011, 07:22 PM

Sounds good to me

Ronnie · 11-29-2011, 07:24 PM

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Your measurements are they with gasket i presume. .040" .043" .085".

You only get lift with no gasket? With gasket you have clearances.
.050" is desired but you "may" get away with .040"!! Some gurus will chime in.Whose gasket are you using?

R

Vergil · 11-29-2011, 08:22 PM

What Offy numbers are the heads? When it's at TDC was it on compression stroke? Are you sure it is the piston lifting the head and not a valve? If the heads are 400 or 375 and they were milled .020" plus a high lift cam the valve may be lifting it.

Vergil

BobM · 11-29-2011, 08:52 PM

Quote:

Originally Posted by Ol' Ron

Sounds good to me

Ron, sure hope so, I'm not sure what to think about head lifting with no gasket; is that to be expected? Thanks, Bob

BobM · 11-29-2011, 09:08 PM

Quote:

Originally Posted by Vergil

What Offy numbers are the heads? When it's at TDC was it on compression stroke? Are you sure it is the piston lifting the head and not a valve? If the heads are 400 or 375 and they were milled .020" plus a high lift cam the valve may be lifting it.

Vergil

Vergil, the heads are 425 Offy, valve pockets cut to depth of .445". Both valves are closed on top of power stroke and then I rotate 720 degrees just to make sure valves open fully. I can see the exhaust valve at full lift through plug whole and is not making contact with head, intake comes out .002" further than exhaust with a net lift of .354", when I clay intake valve I get .081" Maybe I should clay intake valve at different locations; I clayed on outside edge of valve with alumna peas. How do you change font size on this site? Thanks for your input. Bob

Vergil · 11-29-2011, 09:30 PM

When you post go to adavnced and pick your font size by the Verdana font name, this is set to 3.

Vergil

flatjack9 · 11-29-2011, 11:07 PM

Obviously something is lifting the head. The places you have checked are not the culprit. You've got to check different spots. Put some blueing on the valves and piston, crank it over with no gasket and see where you get a mark.

Ol' Ron · 11-29-2011, 11:21 PM

I use alum balls stuck to the piston at several places to determine clearance. Do the same with valves, but not at the same time.

BobM · 11-30-2011, 10:53 AM

Quote:

Originally Posted by Ronnie

Your measurements are they with gasket i presume. .040" .043" .085".

You only get lift with no gasket? With gasket you have clearances.
.050" is desired but you "may" get away with .040"!! Some gurus will chime in.Whose gasket are you using?

R

Only lifts with gasket off, am using Best graphite gasket. Yeah, I think .040" is a little scary but I have seasoned rods and hope they don't stretch at upper RPM. I just don't understand how it got so tight even with milling the head .020", have heard of guys who milled .050" off a head but maybe they weren't Offy heads. Yes, those measurements are with gasket and torqued to 50lbs.

BobM · 11-30-2011, 10:56 AM

Quote:

Originally Posted by Vergil

When you post go to adavnced and pick your font size by the Verdana font name, this is set to 3.

Vergil

How do I go to advanced?

Vergil · 11-30-2011, 11:41 AM

Quote:

Originally Posted by BobM

How do I go to advanced?

Ol' Ron · 11-30-2011, 04:39 PM

I have one engine running with .035" head clearance. It has close to 10,000 miles on it.

BobM · 11-30-2011, 06:39 PM

Ol'Ron, your post couldn't have come at a better time, just got done re-claying the piston at different locations and got a .037" reading, made me real nervous, feel better now. I need to get address for your book. Thanks, Bob

BobM · 11-30-2011, 06:41 PM

Vergil, thanks, got it now!

11-29-2011, 03:30 PM	#1
BobM Senior Member Join Date: May 2010 Location: Las Vegas, NV Posts: 213	Piston to head clearance? My Offy heads have been milled .020" and when I set them on the block with no gasket the head lifts up when piston hits TDC; is this to be expected? The only thing preventing catastrophic failure is the head gasket? When I clay with gasket & head torqued to 50lbs. I get .040" at the piston edge, does this make sense? I know the head is coming off the block with no gasket almost .040". Nervous & confused

11-29-2011, 03:58 PM	#2
Junknshit Banned Join Date: Oct 2011 Location: Wash. Posts: 233	Re: Piston to head clearance? You get .040 at the edge, what do you have in the center of the piston? Was this engine running before and all you are doing is changing heads? If fresh build, do you have piston, rod, crank combination right? Are the heads new? or have they been milled before? Last edited by Junknshit; 11-29-2011 at 05:02 PM.

11-29-2011, 06:32 PM	#3
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,543	Re: Piston to head clearance? Something doesn't add up. If you have .040 clearance with a torqued gasket, there must be some area that is tighter that you haven't measured. Are you sure it is lifting .040?

11-29-2011, 07:22 PM	#5
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,904	Re: Piston to head clearance? Sounds good to me

11-29-2011, 07:24 PM	#6
Ronnie Senior Member Join Date: May 2010 Location: Canada Where it snows Posts: 2,058	Re: Piston to head clearance? Sponsored Links (Register now to hide all advertisements) Your measurements are they with gasket i presume. .040" .043" .085". You only get lift with no gasket? With gasket you have clearances. .050" is desired but you "may" get away with .040"!! Some gurus will chime in.Whose gasket are you using? R

11-29-2011, 08:22 PM	#7
Vergil Senior Member Join Date: May 2010 Location: Tehachapi, CA Posts: 361	Re: Piston to head clearance? What Offy numbers are the heads? When it's at TDC was it on compression stroke? Are you sure it is the piston lifting the head and not a valve? If the heads are 400 or 375 and they were milled .020" plus a high lift cam the valve may be lifting it. Vergil __________________ Bigger fonts to aid in reading

11-29-2011, 09:30 PM	#10
Vergil Senior Member Join Date: May 2010 Location: Tehachapi, CA Posts: 361	Re: Piston to head clearance? When you post go to adavnced and pick your font size by the Verdana font name, this is set to 3. Vergil __________________ Bigger fonts to aid in reading

11-29-2011, 11:07 PM	#11
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,543	Re: Piston to head clearance? Obviously something is lifting the head. The places you have checked are not the culprit. You've got to check different spots. Put some blueing on the valves and piston, crank it over with no gasket and see where you get a mark.

11-29-2011, 11:21 PM	#12
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,904	Re: Piston to head clearance? I use alum balls stuck to the piston at several places to determine clearance. Do the same with valves, but not at the same time.

11-30-2011, 04:39 PM	#16
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,904	Re: Piston to head clearance? I have one engine running with .035" head clearance. It has close to 10,000 miles on it.

11-30-2011, 06:39 PM	#17
BobM Senior Member Join Date: May 2010 Location: Las Vegas, NV Posts: 213	Re: Piston to head clearance? Ol'Ron, your post couldn't have come at a better time, just got done re-claying the piston at different locations and got a .037" reading, made me real nervous, feel better now. I need to get address for your book. Thanks, Bob

11-30-2011, 06:41 PM	#18
BobM Senior Member Join Date: May 2010 Location: Las Vegas, NV Posts: 213	Re: Piston to head clearance? Vergil, thanks, got it now!