250-500cc wr 360 2002 piston selection/ options

hi im rebuilding a spare top end and was wondering what the best or most commonly used piston is.
At moment its the standard one and tbh it looks to be in good condition, its marked A so its first bore?

also if i englarge the three holes in the piston skirt that ride the exhaust bridge to 1/8th am i correct in thinking it will help reduce bridge heat and lubricate as the rings have chipped over the top of th epower valves.

so wossner?
wiseco?
pro - x?
mitaka?
oem?
or any others that spring to mind with amazing longevity?

weisco, install as recomended by maker. warm it up too some before ya hammer on it. if you are catching rings its caused by not relieving the ports after boring/worn out piston and rings.

bubble and squeak! what's that???

yeh i purchased the head from your neck of the woods the sleeve was done by kustom kraft and the edges were razor sharp, ive now chamfered them and evend up the vertical axis of transfer ports as these were more wavy than krinckle cut crisps.
i know the theory of .002 smaller than bore and am not one to hammer when you can clamp it down an use kickstart, more torque.

Wiseco makes a piston for the 360? The only 78mm 2t piston I can find is for an Artic Cat snowmobile.

yikes! he's right. maybe a call is in order...sorry pips. bad intel on my part. leme know if ya want me to make some calls this side of the pond for ya mate.

the stock ones are available, Rancher1 has one, the A is the size, the smallest of three, they made 3 sizes and they are within thousands of each other for fitment purposes
you can not bore these as the are nikasil type cylinders and do not use a sleeve like early bikes, the reason is heat dissipation
if not stock I am looking at Wossner

Wossner....could go Athena but l recommend Wossner for a 360 (over 180hrs out of a piston and with olny changing rings at 90hrs).

Porting... l leave that to a 2t expert...depends on what you are after really?

yeh its been slleeved 2premo, thinking wossner, the barrel was sleeved by kustom kraft and had wavy bridges, the exsisting piston is
77.75- to 77.25 thats base reading to top reading ive yhet to measure the barrel but i would imagine im looking for a few more thou as this piston looks to have done a few hours..., chipped rings on exhaust bridge.
the bore is in ver good condition.

thanks for the offer on call arounds but i think wossner will be the way ahead.

ohmygawd, re porting, im no expert but i know that the port edges should be chamfered atleast a little, i could of drawn blood they were that sharp, im trying to releave the stress on the replacment rings, im not changing the duration al though just out of curiosity ive calculated the timing area and there is a little that could be done, not worth the time imo tho.

I hear mate, if you got a die grinder or dremel then go for it...sorry thought you wanted to go down the path of changing the port sizes, read it wrong.

PS. Mahle then Wossner were the OE piston manufacturer for 360's if l remember correctly

yup i got dremal and alot of patience.
wossner's the won to beat.

right my bore measures
78.03
its out of round by .06 thou, am i safe to justgive it a good hone to suit?
also im looking at 78mm piston as this states .06 clearance??
bit confuddled
thanks in advance.

This is from Wossner FAQ on how to measure piston, bore, rings and piston to cylinder clearance. Hopefully this helps you determine which piston size is needed.

thanking you good sir

pipps- if yer bore was out of round youd see a vertical 'egg' in the bore in most cases above/below the ports where the ring dont contact the cylinder (not including weird spots by the bridge and what not). if there's none of that wonkyness yer fine. yer new bore should have a good final hone-to-size pattern already. gently and ever so breifly deglaze if glazed or stained. then, wash in hot soapy water- not solvent. the pattern and grit makes a diff in some cases so ask the ring maker if there's a prefered method or if she's ok with just a deglaze- its 3-4 passes thereabouts plunging up and down say 1 cycle a second with the drill on slow, it dont take much. and again- hot soapy water, not solvent to clean her up.

that new avatar works too mate. barooop!

yeh i got her back to round shes looking good with the 45 criss cross pattern, just need to find a piston now to suit a 78.06 bore it was tight down very bottom where the rings dont run... ive bedded in rings and done rebuilds befor but ive only sent stuff off and got it matched by the blokes doing it, i will give them a call to see if they can suggest a good match, it needs a few thou clearance as its a sleeved liner mow, its a spare so i can retire the old head at end of season... cheers for help guys
to any off topic readers sorry it dont look like you got much. p.s. ktm an husky i think could turn out good if the keep bombproof husky engine in new sussed frame, roumor has it steve perrir is going to thry an get husky into the supermoto scene again.
BOOM

I used a wossner. It is a one fine piece of metal.