500 seizing on a fresh top end.

[juicypips]

Fairly severe but wire wheel no no no that causes gaulling and make the issue worse a fine file lightly across the piston is what i have done in a tight spot far more accurate.
Wouldnt reuse just to be safe.
Light hone on cylinder an check ring gaps etc an go gingerly on warming up

 

[fran...k.]

After it seized then cooled down it wasn't seized any more is the way it seems to go. The ride could continue but most likely just ride it out then disassemble. Then the hard part may be getting the ring un stuck without breaking it. It is not perfect but nothing (just the piston/cyllinder) that I would let keep me from entering more events with it. I have not previously seen what a woosner 500 two stroke husky piston looks like. They do offset the pin for the 430 that the origonal didn't there may be other things you notice. Boring these things probably is set to do it in one pass with no compensation for warming. Remember the space shuttle mirror they made it and inspected it on the same piece of equipment.

 

[husqyhamm]

Jetting not bad. I run AA5 at altitudes up to 2000m. Find AA0 somewhat lean in midrange, particularly at lower elevations. 380 is ok for crisp midrange, recently ran a 500 AC in on asphalt circuit with 420 with ordinary mineral 2T at 20: for first tank. It splutters and spews black oil but theres plenty protection and ring seats quicker than with synthetics.
Needle and seat original 3,2 uhmm no. 3,5 from Yammie 465-490 yes.

0,08 clearance is where its at. Woessner is way lighter than Mahle or Wiseco. like 80grams difference. Never used them and dont know how they change dimension on heat cycle. Friends of mine used them in 500 huskys with no problems and performs very strong.

Bore out of round and tapering occurs very easily when boring and honing. Particularly on bigbores i have the barrel torqued to spec in a specially made up jig. Careful use of torque plates and rings will also do that job. Youd be shocked how much a sleeve changes dimension when releasing the torque. bore measurements before and after process are taken under torque and im with the machinist when its done. Rebuilding old airhead BMWs quickly teach you this lesson.
Plateau hone job. Ring takes much longer to seat but ultimately a better finishing process.

Real safe ring gap measured at piston tdc is 0.6mm. Ive run 0,4mm gaps on Mahle with carefull breaking in. Their rings are wider than Woessner and exert more wall pressure. Never assume a ring gap, check.

The rest about leakdown tests have been said. Paramount. It should hold 8psi for at least 5minutes without any pressure loss. Ive stripped several rebuilt Husky 500 engines and replaced new crank seals particularly on the lefthand side for this reason. Best seals ive found yet were orange silicone ones with directional grooves, in used state they still held better pressure than new vitons.

Stock Husky fuel tap passages minimal for 500. Clarke tap works and fits the plastic tanks. with allu tanks i install exit nipple and inline ballvalve.
Deep float bowl nut with mainjet extender.
Carb passages blown out with compressed air, properly. Top lid must have good seals.

Husky produced 4 types of 500 production exhausts and two head squish designs between 82 and 84. some are better than others. The wrong exhaust system can raise exhaust port temperature to extreme levels. From the type of riding you described this is unlikely your problem, but consider, especially with its been repaired in some fashions.

Good luck for the next round of rebuilding.

 

[SA63]

id be increasing the clearance. I ran into the same issues with the 510 4 stroke (repeatedly even on a motor with 4 hours on it but high rpm) went to 0.1 or 4 thou and no probs. (wiseco piston)
0.08 is probably fine for a watercooled bike, but the a/c run hotter hence more clearance is better.
The seize has happened in a similar manner to mine, the metal bridge supporting the piston pin has expanded into the bore.
I also put extra oil holes in that area, but I think clearance was the major problem.
Paul Rooney also advises more clearance...

 

[suprize]

Paul Rooney also advises more clearance...

that's the good oil....!

 

[gday]

I guess the question is … how much more clearance.

 

[fran...k.]

I think ice racing is the most severe where the cylinder is cold and the piston is hot. What really counts is how the piston expands relative to the cylinder, the cylinder will not expand in. By the third or fourth semester of college physics/calculus the effect of one ring inside another and heated and how the fit changes was covered the way I remember it. That is with no port holes, fins etc.

As to this quote from above
"0,08 clearance is where its at. Woessner is way lighter than Mahle or Wiseco. like 80grams difference. Never used them and dont know how they change dimension on heat cycle. Friends of mine used them in 500 huskys with no problems and performs very strong."

80 grams is about the difference between the 430 and 500. The water cooled pistons for bikes in this section had more removed from the sides and the ring was raised a bit closer to the crown. On the 430 the mahle water cooled (most likely the replacement part) weighs like the woosner and wiseco. There is a length of wristpin issue also at least for the 430 making the earlier heavier.

As to the compression jig to bore I know when harley came out with their spiney lock Iron liner in aluminum fins they called for a jig and boring those had a different price, more $ to bore. For what it is worth note the over bore is larger here than an origional option.