piston to wall measurement
- Thread starter Darren
- Start date
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bOb shingler
Well-Known Member
yes, well sort of. they don't want any more than two and a half thousands.
69MOPE
Well-Known Member
2 to 2 1/2 thousands
I believe that means that the bore needs to be 4 to 5 thousands (.004 - .005) larger that the pistons diameter measured at the manufactures specs.
Clearance (.002-.00250)(one side) plus piston diameter, plus clearance (.002-.0025)(other side)
I believe that means that the bore needs to be 4 to 5 thousands (.004 - .005) larger that the pistons diameter measured at the manufactures specs.
Clearance (.002-.00250)(one side) plus piston diameter, plus clearance (.002-.0025)(other side)
daredevil
Well-Known Member
What he said.^Too much and the skirts scuff.
80fbody
Well-Known Member
I don't believe that KB is telling you to double their measurement as mentioned above. If you were to do the same with the Icon forged you'd be at 10-15 thou of clearance.
That said, KB believes they can be run tight in the bore. Not sure I'd agree with that. Mine is a race only with KB's & it's going to be 5-6 thou after it comes back from the shop for a re-hone. I'm not sure it's correct but I'd rather a little loose then to lock a piston in the bore. I'd try to get with the machinist as they've probably done plenty of chevys with these type of pistons. I'd like to know how the pros set these up.
That said, KB believes they can be run tight in the bore. Not sure I'd agree with that. Mine is a race only with KB's & it's going to be 5-6 thou after it comes back from the shop for a re-hone. I'm not sure it's correct but I'd rather a little loose then to lock a piston in the bore. I'd try to get with the machinist as they've probably done plenty of chevys with these type of pistons. I'd like to know how the pros set these up.
My last 440 had kb 237 pistons that had piston slap. So i tore it down and found out the bores were to large for the kb pistons. So i ended up getting another block, the machine shop bored to kb specs and it was fine. It was street car only. I dont want to make the same mistake twice. Thanks
I also did the stated ring gap as per kb info sheet. And installed the pistons myself.
One thing i dont get is my new kb pistons have wrist pins with spring clips. How do i use these wrist pins as a pressed fit? Thanks
One thing i dont get is my new kb pistons have wrist pins with spring clips. How do i use these wrist pins as a pressed fit? Thanks
I understood bore size was .004 to .005 larger than piston size?
69MOPE
Well-Known Member
That would mean that you only end up with .001" between the piston and wall. I think any piston expands with heat more than that.
So if i want presed fit wrist pins i got use my old wrist pins?
Is it possible they are designed for both? I just bought a new set of Speed Pro's for my small block build and they are for press fit OR full floating.
How do you make them preesed fit if the pins slide in the pistons so easy? Thanks
Pressed fit is in the connecting rod, I do believe. Someone correct me if I'm mistaken.
The pistons I have, the pin slides in and out with no more than a loose interference fit. Once in the bore, it's not going to move side to side if it's tight in the rod.
I hope my thinking is correct. :-D
........ur right bruce.......the pins are pressed into the rods......kim...
first the wrist pin is offset in the piston /and how you use the piston determines wall clearance keith blacks have a special dome with a accumulator groove on the top to hold the heat in so you run tighter clearances less ring wear .stock .0015/.002. stockcar 2/barrel .0025 /.0035.4barrel .004/.005 on the bottle.006/.007.also a different ring gap for all types of racing.
CPMotorworks
Well-Known Member
X2
But, if your block isn't being honed with a torque plate, gasket, and matching hardware, you will have problems.
You should be able to stick a piston in the bore and slide a .002 feeler gauge between it and the bore on one side only. When the piston is centered in the bore there should be .001 clearance on each side. If you mike the bore and the piston and subtract the two numbers you should get .002 and they recommend no more than .0025. I put my Egge cast pistons in at .003 with one hole @ .0035
tmm
pishta
I know I'm right....
Cast pistons are crazy snug, like. 0002, forged and hypers are looser. Measure 90 from the pin at the skirt. Pins are pressed into the rod. Floaters are Spiro locked or retained in the piston only, slide in piston and rod. Only thing good about those is you can disassemble them easily. Down side is more parts to fail.
moper
Well-Known Member
Like Pishta and the others said..
The bore size is normally the "oversize"... so a 360 nored .030 over would have a bore finished to 4.030". The clearance is built into the piston - so measuring the piston (assuming it's a KB hyper) should give you 4.028 to 4.0275.
Pressed pin or floating pin is a function of the rod. 360s are factory pressed pin so the rod pin end is heated, and the pin is slid through the piston and heated rod, and when the rod cools (seconds if that) the rod grabs the pin. So no pin locks are used or needed. Full floating pins mean the rod's small end has the larger diameter and normally a bronze bushing and the pin will slide in and out of the rod. That's why you need the pin locks to retain the pin and keep it out of the cylinder wall.
Normally the floating pin is best in terms of putting up with abuse. The pressed pins can "walk" out and into the cylinder wall under heavy abuse.
The bore size is normally the "oversize"... so a 360 nored .030 over would have a bore finished to 4.030". The clearance is built into the piston - so measuring the piston (assuming it's a KB hyper) should give you 4.028 to 4.0275.
Pressed pin or floating pin is a function of the rod. 360s are factory pressed pin so the rod pin end is heated, and the pin is slid through the piston and heated rod, and when the rod cools (seconds if that) the rod grabs the pin. So no pin locks are used or needed. Full floating pins mean the rod's small end has the larger diameter and normally a bronze bushing and the pin will slide in and out of the rod. That's why you need the pin locks to retain the pin and keep it out of the cylinder wall.
Normally the floating pin is best in terms of putting up with abuse. The pressed pins can "walk" out and into the cylinder wall under heavy abuse.
Yes. However by the time you do that and have good rod bolts installed and have the rods resized, you could have bought a whole new set of rods with good rod bolts and already bushed.
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