The Ford Barn

edmondclinton · 03-10-2015, 09:07 PM

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Quote:

Originally Posted by Ed Northrop

I took a big block Mopar to the machine shop along with a set of 30 over TRW forged pistons they refused to use pistons spec as they said the clearance was to tight. They allowed .008 for clearance or they would not do the work. I have to say they must have been right as there is no piston slap.

Were the specs from TRW for street driving at moderate RPM's on standard pump gas?

edmondclinton · 03-10-2015, 09:31 PM

Quote:

Originally Posted by Ron W

Ron W
PS Too loose will run, too tight won't!

Very true, and too loose can also = loss of power...

Kurt in NJ · 03-11-2015, 07:13 AM

I remember reading --I think Murry Fahnstock --that the model a piston could run at .001 tight, I looked in the service bulletins and found-- on page 455--"In production pistons are now fitted to cylinders with a clearance of .0005 to .0025" --so even the model A was designed to run tight piston clearance

Ed Northrop · 03-11-2015, 08:16 PM

I would have to look back in my records I do not remember I do remember they were new but around 20 years old. I believe I was told new pistons do not swell as much.

Ron W · 03-11-2015, 08:52 PM

Page204 of Service Bulletins calls for loose on .002 and tight on .004. Ron W

Dodge · 03-12-2015, 02:54 AM

Sponsored Links (Register now to hide all advertisements)

Also remember there are no water jackets in the lower part of a Model A Motor they need
the clearance. Those Keith Black pistons are amazing, they don't grow much.
When they were first coming out with them they gave us pistons to play with. We ran
them all over the board, first loose, they were ok at .003 but started making noise at
.0035 and they didn't quiet down when they warmed up. Then we kept making them
tighter and tighter they really seem to like .001 to .0015 and thats in a race motor.
I took a while to figure out that the top ring needed a lot more clearance and thats
how they run them now.
They are strong also, one motor dropped a valve and it when right through the piston
leaving a round hole, dropping the valve into the crankcase. The rest of the piston was
intact with the rings still on it still going up and down. Another motor lost a radiator
hose and got so hot it seized up when the driver lifted his foot off the gas. After
the car cooled down it was started back up and the pistons didn't make any noise.
When the motor was torn down later there were no scuff marks on the pistons. These
were in at .0025
There is a Keith Black 283 piston that fits and a hemi piston that also fits a Model A Motor.
So have fun and clearance is your friend.......

03-11-2015, 07:13 AM	#23
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,159	Re: Tight Piston Clearance, Not Model A I remember reading --I think Murry Fahnstock --that the model a piston could run at .001 tight, I looked in the service bulletins and found-- on page 455--"In production pistons are now fitted to cylinders with a clearance of .0005 to .0025" --so even the model A was designed to run tight piston clearance

03-11-2015, 08:16 PM	#24
Ed Northrop Senior Member Join Date: May 2010 Location: Naples, New York Posts: 182	Re: Tight Piston Clearance, Not Model A I would have to look back in my records I do not remember I do remember they were new but around 20 years old. I believe I was told new pistons do not swell as much.

03-11-2015, 08:52 PM	#25
Ron W Senior Member Join Date: Jan 2011 Location: Central Me. Posts: 260	Re: Tight Piston Clearance, Not Model A Page204 of Service Bulletins calls for loose on .002 and tight on .004. Ron W

03-12-2015, 02:54 AM	#26
Dodge Senior Member Join Date: Nov 2011 Location: Sonoma, CA. Posts: 1,495	Re: Tight Piston Clearance, Not Model A Sponsored Links (Register now to hide all advertisements) Also remember there are no water jackets in the lower part of a Model A Motor they need the clearance. Those Keith Black pistons are amazing, they don't grow much. When they were first coming out with them they gave us pistons to play with. We ran them all over the board, first loose, they were ok at .003 but started making noise at .0035 and they didn't quiet down when they warmed up. Then we kept making them tighter and tighter they really seem to like .001 to .0015 and thats in a race motor. I took a while to figure out that the top ring needed a lot more clearance and thats how they run them now. They are strong also, one motor dropped a valve and it when right through the piston leaving a round hole, dropping the valve into the crankcase. The rest of the piston was intact with the rings still on it still going up and down. Another motor lost a radiator hose and got so hot it seized up when the driver lifted his foot off the gas. After the car cooled down it was started back up and the pistons didn't make any noise. When the motor was torn down later there were no scuff marks on the pistons. These were in at .0025 There is a Keith Black 283 piston that fits and a hemi piston that also fits a Model A Motor. So have fun and clearance is your friend.......