Not mine,just saw the auction

http://cgi.ebay.com/ebaymotors/JAHNS-PIS...sQ5fAccessories


And other auction
Cast pistons I believe.
http://cgi.ebay.com/ebaymotors/Chevy-307...sQ5fAccessories

MBHD

The Jahns have circlips so the piston pins must be full floating.
.060 over no rings
very interesting!

How hard is it to convert stock 250 rods to full floating piston pins?

You can still use a pressed pin. Just do not use the circlips.
That is a cheap price. But they are a old design piston that is probably 25-30 years old. Still better than cast.

Not hard @ all,just need to hone to size on a con rod machine.

I have seen it done & used.

MBHD

Like hank said it is not hard to do or have done.I have done that to my stock rods and I also drilled a small hole at the top of the rod to act as a oiler for the pin.

somebody explain to an oldtimer why are the 307 pistons (3.875 bore with 3.25 stroke) such a cat's meow in the 250 motor with it's 3.875 bore and 3.52 stroke. It seems the 307 would be better suited and just dandy for a 230 (3.875 bore and 3.25 stroke). Wont the 307 piston poke up above the deck on a 250? Or do you shave the piston tops as a "without saying" thing when using them.

Then a TRW 307 piston would be a bargain if it would work (Traco used to use them in the days of TransAm and CanAm racing, 'cause they used to be the greatest piston bargain around- machinest trusted their quality so much that they would go ahead and bore your block without the pistons on hand 'cause they knew there would not be a .001 diff in a set, unlike most others.

No they do not stick up above the deck.A 283 piston will.The wrist pin height is where the difference comes into play.That is why a 307 is good for a 250.And a 283 piston is good for the 230.

Edski, the additional deck height of the 6cylinder block compensates for the stroke difference; half of the stroke diff. is .140 and that will put the piston anywhere from even with the deck to .010 down depending on the accuracy of the factory deck....the v-thingy piston is calculated from a 9.00" deck height but most measure around 9.025....fats

Slick !! Never checked out a mouse's block height ASSUMED it was the same as a possom motor (possoms are longer than both mouses and rats). Nor did I think of checking leo's book for deck info-forgot it was in there.

Some shoestringing oldtimers around D/FW area used to run 327 F.I. pistons in their bored out 292s. According to TRW that would be 1.792 comp. ht. + 2.06 half stroke, +6.76 rod = 10.6121, - 10.875 block height =.263 down the hole. Without a lot of conjurgation, it dont seem like a lot of compression, but it is a good cheap piston to fill a four inch hole.

Thanks for the primer class!!!

The standard deck height for the 250 is 9.150" +- 0.007". The cast pistons, Federal Mogul Sealed Power 295P, are standard aluminum alloy, no silicon. They are as pictured, and do not have the top edge chamfer, which is rare. I called. These pistons have a stated compression height of 1.655" instead of the common 250 rebuild piston compression height of 1.640". So installed they are closer to zero deck height.

That's one of the reasons I posted them.


MBHD

Well I use a Sunnen hone almost daily, so I might give it a try.
How many thou clearance between the rod and pin?

I thought you had to have a bronze bushing in the little end of the rod for full floating pins ?
Cutting the rod out for a bushing with a .100 wall would weaken the rod?

I like 0.0005 / 0.0007".

Using a bushing is the preferred method, Carillo has a .975 OD x .927 ID bushing that is perfect for this. If you have access to a Tobin-Arp, you can correct the center-to-center length while you bore the S/E to accept the bushings.

No Tobin-Arp. I'm going to talk to "my" engine builder and see how much he charges to bush the rods since he will be punching out my spare 250 block .060.
Also looking at Scat rods. Confusing online catalog.
They list a 6" bushed rod for a GM inline 6 that is drilled from the big end to the little end for pin lube. Have to find out if they sell a 5.7".

Well I got them here.
Dont think they are Jahns, but I dont know my piston history very well.
On the underside of the crown is stamped ANSEN and across from it is DIFC0513. Part number? could be a 6 instead of a 5

There are no other marks either stamped or cast in.
Piston-575g
Pin -175g
Diameter- 3.930 [ one is 3.931]
Pin diameter .9277
C/H -1.64
Total height 2.944
Standard rings 5/64 5/64 3/16
I have to determine the pin offset. Being for a v8, the offset should be backwards on 4 of them.
So 2 quiet and 4 power or 4 quiet and 2 power?
cyl 1 and 6 quiet and the rest power?

Put the other 2 in backwards..!!!

SCRAPPY,

I like how you think.

the offset should be backwards on 4 of them

Only if they have valve reliefs.
If they don't have reliefs, if they have 4 reliefs, or if you don't need the reliefs, the pistons are all the same.

panic the pistons are these ones:
http://cgi.ebay.com/ebaymotors/JAHNS-PIS...sQ5fAccessories

What's the question?

Can't tell if they have domes. If they do then SCRAPIRON'S comment about pin offset is valid.