Topic: Stock-ish 750 rebuild con sabor

[Ceebeehead]

Greetings all.  I recently acquired myself my first bike; a 1972 k2 750 with a few surprises stored inside.  I'll be posting more pics of earlier in the rebuild but I'm at my wits end and I could use some expert advise on how to identify something.  I've had idle issues since the get go after rebuilding the carbs twice(and a third in the plans), some smoke from the exhaust and out the crank vent tube.  With a ring replacement, honing and regasketing in mind I got to work removing the motor and stripping it's clothes off.  Lo and behold, non-stock pistons, 3 are good, 1 is toasted on top, 64mm wide and a design that I cannot for the life of me find a replacement for.  They look very similar to the TRW pistons but don't have l2424 engraved on top.  It says "true forged" under the top and a triangle with an F inside.  I'm hoping there is somebody out there who can point me in the right direction to a replacement or a trustworthy machinist who can make a reproduction.  Every combustion chamber looks clean with no pitting on the valve side and all of the cylinder walls look good even before honing.  In advance I sincerely appreciate any help because I'm too young to be losing this much hair over this. 

Hopefully the links work properly.

[knowsnothing]

Its looks like you are off to a great start.  I have no idea what those pistons are, but you might want to start a thread over in the SOHC/4 bikes (http://forums.sohc4.net/index.php?board=2.0)area as opposed to here in the project area.  More people will probably see it over there that might know.   Good luck

[Ceebeehead]

Thanks a bunch knowsnothing.  I'll see if the mod can move this.  The hunt shall continue.

[knowsnothing]

You don't need to move it.  Keep this one to document your progress and just make a new one over there.   

[Ceebeehead]

My major issue with the piston was the second compression ring was completely collapsed and stuck in the groove.  Forced it out and found out the groove was just too small but the PO apparently didn't care when they built it.  I considered my options and began looking for a possible replacement.  After finding nothing, thought to myself "screw it," I'll save a few hundred bucks and make this work whether she likes it or not.  Enter hacksaw and sandpaper to make the groove work for me.  Gonna put this crazy lady together no matter what, ride her until she implodes then rebuild her better...faster...stronger.  After a good wet sanding job of the ring groove with 400 grit the ring is sitting and spinning nicely.  As soon as the new ones come in everything should fit nice and snug.