CR 500 jetting issue

They dont need to be more knowledgeable about what specifications I should use, they need to be able to deliver the machine work to the specifications I give them.

i did a little kdx 200 years ago, an 87 a/c model. put a new slug in it, gutted the pipe and put an allow muffler on it. ran sharp but on its second ride i took it to the beach Idiot!!. got about 300 metres down the beach and heard the noises, felt the slight drag so i locked the back wheel on full throttle, too scared to roll it back through the needle jet. let it cool for a bit and it fired up and was fine after that. i dropped the needle clip and that helped. back home i went up a couple on the MJ and that sorted it. Stripped it down at a later date and there was minimal damage c/w what i thought had happened.. lucky escape!

Piston clearance depends on the piston material so the clearance from the motorcycle manufacturer is only correct if you are using the OEM piston. Any other piston should use the piston manufacturers specs at least as a starting point. The person in the link you posted was most likely working on a Japanese motorcycle which all come with cast pistons and he was using a Wiseco piston. OEM Japanese pistons are cast, which dont expand as much as the forged Wiseco so the Wiseco is going to require more clearance.

Gutted to say, she seized up(milk crate) yet again in qualifying at Farleigh. The good news the spare (silver bike in the picture) rode like a dream and got me to 15th overall from the second row of the grid. So its' back to the drawing board.

Sorry to hear that. What jetting are you running on the milk crate?

A 360 Main jet (i'm told is too small ?)
35 Pilot jet.
7F7 Needle
She seized good an proper...

Ouch. Try this:
410
7F7
AA5
3.0
40

was that 360 the most main it would handle?

I did try a 380 with a 2.0 slide and it ran horribly. When I've re-built the motor, I've got a mate with a dyno and he's going to put it on there and see whats going on....Hopefully..

It's not gonna work with a 2.0 slide.

you didnt try changing them both at the same time right? 370 would be the next step, and that change alone.

Is it only seized on the intake side or all four corners?

just a outside point...i had a mate who had several seizures on a 250 and it was the middle head bolts being too long by a poofteenth and bottoming out in the cyl before tightening the head down sufficiently... took some pistons to sort that out.

There was a Husky service bulletin about those head bolts being too long. It's something I check on every motor I build. One would think the issue had been solved by the time the 500 came out, but I'd rather check than bet.

I forgot about this post from husqyhamm. Notice the main jet size.

Nope...she seized worst on the exhaust side

Four corner seizures are usually (but not always) caused by the piston expanding too fast for the cylinder during warm up. Its interesting that it does not appear to be seized above the ring. Other than running it too hard before it is thoroughly warm, which I do not think an experienced rider like yourself would do, I really dont have any ideas.

That hurts.
Looking at piston ring in frontal part of seizure, you can see it did not seat properly with cylinder causing blowby and a hotspot beneath it.
Cylinder likely out of round.

Is that the black line you can see on the face of the ring you are talking about ?

Yes, rest of what one can see of ring is silver, indicating full surface contact and seating.