Split Pistons and Pin Clearance - need help

M

Michael_Velling

Member
Hello,

i have ordered pistons from Mike (picture) and do not know which clearance the machine shop have to make.

Is 0,004 inch correct? I read 0,001 / Inch of diameter.

I have oversized pistons (100) = 3,9745 x 0,001 = 0,00397 Inch clearance ???

I also ordered new connecting rods. What clearance ist fine for the piston pins?
I read something about 0,0005 Inch???

Thanks a lot for help.
 

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No one has chimed in yet.So,,

I tend to run engines looser than most folks. All engines.

As for wrist pins, I like .001-.0015" which is a push fit. Much more than that though and they'll rattle.

Piston clearances, I also like a tad loose. The general wisdom says .001"/inch of bore. I tend to use a bit more.
However split skirts are supposed to be different, a bit less. But this I can't really respond to, sorry.
 
Was there a recommendation from the supplier? The machine shop should have the pistons in hand before boring/honing to final size.
 
.004" should be very good on piston to cylinder wall clearance. I too run more clearance than most guys, but pin to piston clearance should just be a light "thumb-push" into the piston, with a light coat of oil on the pins. .001"-.0015" is too loose for the pins, they will rattle when cold. New pistons usually come from the factory with pins installed, I loosen them just a tiny bit.
 
Michael_Velling said:
Thanks a lot for all those informations. The parcel from USA will arrive today via FEDEX and tommorow i will go to the machine shop.
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Good. I imagine a spec sheet should be included. I'm curious as to what it has to say.
I think the original engines had split pistons and only .002" clearance. But, I've not had an original apart.
 
Original Ford specs said a max of .002". Those were a different design, so doesn't apply anymore. Setting new style pistons at that will result in major problems.
 
Jim Brierley said:
Original Ford specs said a max of .002". Those were a different design, so doesn't apply anymore. Setting new style pistons at that will result in major problems.
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OK, I thought the originals were split skirted. I don't remember having one in my hand and I don't think I would ever install them.
 
Jim is correct.

Those pistons need .004 inch clearance between piston and cylinder bore.

Original Ford pistons had the expansion slot continue to the bottom of the piston and the clearance should be .002 inch.

Forged pistons need .007-.008 inch clearance.

Be sure to assemble with the expansion slot on the water inlet side of the engine.
 
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