Piston Question?

[special fx]

I'm rebuilding a 763 Big Bore and need to replace a piston. The pistons were Wiseco 84.5 regular domes. I ordered a new Wiseco piston and it's different from the one I'm trying to replace.

The old one has a huge recess around the wrist pin area and the new one does not. Both are stamped "757M08450" and that's the only part number I found in the Wiseco list. However, the old one also has a "9764H" stamped on it, where the new one has "8565K" on it....not sure what these #'s represent and they're not listed on Wiseco's listing.

I weighed the pistons and the new one is an ounce heavier than the old, which makes sense since it's got a bunch more material.

What's the scoop on these Wisecos???? Where can I get a replacement for the old piston......or will I have to just replace both???? :banghead:

 

[#ZERO]

The older Wiseco pistons were heavier with lighter wrist pins and they used completly different rings too. The older pistons used the thinner 1.2mm TD style rings with the half notched ring ends and the newer pistons use the thicker 1.5mm KD style with a 7-degree keystone taper and rounded ring ends which are not interchangeable. I wound not use these pistons together in the same engine because of the internal friction and weight differences.

 

[special fx]

Yeah, I have no intention of running these pistons together. I'm just trying to figure out if I can get a replacement for the old or do I need to suck it up and buy two of the newer style.

 

[#ZERO]

I only have one of the 83mm old style pistons remaining which won't help since you're using the larger size. The old style pistons are hard to find but you might want to check on fleBay. They're easy to spot from the pictures with the wrist pin area open and the piston tops brown with a bright silver center slug on top.

 

[special fx]

I gave up and ordered another new piston so I'll be putting two new ones in. It seems a shame since the old style seems better quality with an ounce of fat machined off. It would've been nice to save 2 ounces of recipricating weight!

 

[Foximus]

On a side note, would you recommend going with the new wiescos? Thinking about going from my 81mm and OE pistons to a 83mm topend. Do the new changes make the weisco friendly to motors and not oval out as much when warmed up? Or should I stick with ProX?