Piston Pin Height

[Muad'Dib]

I was looking over the FAQ for pistons just now, and i noticed that there is a variance in pin height.

What is the purpose of changing the pin height? I know the pin height would change if your using a 4.2 or 4.0 rod, but why the variance in all the pistons that use a 4.2 rod?


Thanks, and sorry if this is a really noob question

[PolloLoco]

If you get the right pin height / connecting rod length combo it is possible to get zero deck clearance without any machine work to the block.

[5-90]

Changing deck clearance and changing quench clearance are the first two that come to mind.

NB: "Piston Pin Height" is also often listed as "Compression Height" - both refer to the same thing; the vertical distance between the piston static deck line (not inclusive of any domes or dishes) and the centre of the gudgeon pin bore.

[eastin82]

whats the combination where you get zero deck height havent heard such a thing hmm.. must b the 4.0 rod havent been researching that

[Muad'Dib]

whats the combination where you get zero deck height havent heard such a thing

The block FAQ covers this pretty well in the following post:

viewtopic.php?p=2817#p2817

Basically its the measurement from the center of the crankshaft to the top of the block.

Im pretty sure that when people talk about "0" deck height they are refering to the piston deck clearance. So at TDC, the piston top will be flush with the top of the block.

[IH 392]

The aftermarket tends to "destroke" the pistons to compensate for over bore and decking of the block, but they tend to over do it and it opens the quench to much.
There are also minor variances in production models over the years.

[Shark]

what combo of piston pin height and rod length give zero block decking?

[PolloLoco]

what combo of piston pin height and rod length give zero block decking?

RAPTORFAN85 got a set of custom diamond pistons that when used with the 4.0 rods gave him a 0.005" deck clearance. He intentionally got the 0.005" deck clearance in case the deck had to be machined to be flat. IIRC the Hesco HESDP45030 would give a zero deck clearance with 4.0 rods, I was intrigued by it the other day but decided to keep with the KB945 piston plan.

[gradon]

The 4.0 6.123" rods and a custom piston with a 1.382" pin height. The eagle 6150s and a custom piston with a 1.355" pin height(too bad the KBs can't work with em, cause they're close). Or a 4.2 rod and a piston with a 1.62" pin height. Or you can pick one of the available aftermarket pistons and try to find a non jeep rod that'll work(easier just getting the custom pistons).

[Muad'Dib]

what combo of piston pin height and rod length give zero block decking?

RAPTORFAN85 got a set of custom diamond pistons that when used with the 4.0 rods gave him a 0.005" deck clearance. He intentionally got the 0.005" deck clearance in case the deck had to be machined to be flat. IIRC the Hesco HESDP45030 would give a zero deck clearance with 4.0 rods, I was intrigued by it the other day but decided to keep with the KB945 piston plan.

I bet you could call Diamond and get a better price than that! Thats just crazy.

[eastin82]

hmm.. if my deck was good and i used my 4.0 rods that would almost offset the price for the pistons. to late though maybe next time.