• 2 Stroke Husqvarna Motorcycles Made In Italy - About 1989 to 2014
     WR = 2st Enduro & CR = 2st Cross

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

    When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.

    Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.

    Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.

    Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.

    Thanks for your patience and support!

250-500cc Another Piston Thread

Huskynoobee

Huskynoobee

CH Sponsor ZipTy Racing
Staff member
OK, so I researched a little here, shopped on Ebay, etc. My 250 has unknown hours and runs awesome, but when I lug it, I hear a little bit of slap/knock. Have not tested compression, runs on 50/50 110race/100llav gas mix at 35:1 Lucas syn mix oil as run by PO who knows his Huskies and is a regular here on the Cafe. It's been long enough however he can't remember what he did last time and when he did it because it was his practice bike. No biggie, it's gotta come apart at some time to look it over so all shall be revealed.

Just to be safe for the upcoming race season I'm considering just doing the top end. Hopefully it's standard bore because my first choice is a Wiseco piston which is only offered in the 66.40mm size.
I did find that the 761M06640 is the 2 ring version and the 768M06440 is the single ring. To me 2 rings is a good thing. I will also probably spend the extra $20 for a new wrist pin bearing because it's worth the peace of mind.

If I'm in the situation where I'll need a B or larger after measuring bore, the options are Athena, Prox and Vertex. I would like to avoid a cast piston if possible/reasonable but would like to hear your experiences with these other brands while I'm still in the planning stage. Heck I'm going to ride it with my son this week so I'm not in any hurry. I haven't rebuilt a top end in a loooong time, so it's gotta be the good stuff for racing desert next year. :banana:
 
I used a Wossner, they are forged and have A through D sizes I beleave. Only a Wossner wrist pin bearing will work with the piston and rod. I think if memory serves me right they are the same as the KTM,s. Very good high quality piston.
 
Ahh, knew I was forgetting something. Gosh they just gave holeshot awards at the last National. Thanks
 
Vertex would be the first choice, measure the bore and the old piston make sure you dont need a new plating.
No reason not to use cast.
 
Don't get hung up on cylinder size, wiseco 66.4 will work in abcd cylinder. I replace small end bearing because they are cheap and its easy. Yes go for the 2 ring piston.
Cant think of any reason for going cast apart from quick warm up.
 
Good point, thanks to Halls having the parts catalog on their site, I made an interesting discovery. The entire range of pistons from A thru F measure 66.335 to 66.365 mm. So theoretically it's true the wiseco will work in any cylinder. The only variable would be ring gap.
 
It's more than theoretically true, it's practically true.
I'm pretty sure the wr250's only came with a,b or c cylinders. Most people can't measure that accurately!
 
Huskynoobee said:
Good point, thanks to Halls having the parts catalog on their site, I made an interesting discovery. The entire range of pistons from A thru F measure 66.335 to 66.365 mm. So theoretically it's true the wiseco will work in any cylinder. The only variable would be ring gap.
Click to expand...

All of the pistons use the same same ring regardless of letter size, so the only issue with ring gap would be when your cylinder is worn out and ready for a re plate.
 
gwynfryn said:
It's more than theoretically true, it's practically true.
I'm pretty sure the wr250's only came with a,b or c cylinders. Most people can't measure that accurately!
Click to expand...

It is both practically and really true. People get stuck on the piston sizes that have a maximum size difference of .01mm thinking it is a big deal and don't look at the the reality that is way less than a 1000th of an inch, .00039 ten thousands of an inch maximum to be more exact. Good luck measuring the difference even with a micrometer.
 
I only got a wossner for my 300 because the 165 slugs from Walt are wossner n look beautiful(you know what I mean-almost to good to put in ya bike). No probs with the oem vertex for 100 hours each
 
Shawry 0.01 may not be an issue, 0.1 may cause a cold seize.
I currently have a 93 cylinder on my bedside draw with a brand new wossner piston the reason its not in my bike is with 0.06mm clearance as stated by wossner the thing seized in four places.

Now 0.06mm may usually not be a problem but it is a steel liner so your metals now expand at different rates. 0.01 can be an issue in some curium-stances.

Measure by eye dude you will be suprised at how acurate your eyes are.
 
Did you get a chance to replace your piston yet? My 2010 WR250 just started doing the exact same thing. When lugging at very small throttle openings Im hearing a piston slap type noise. Almost sounds like pre ignition or pinging. Went to the next richer metering rod in my Lectron and started running 50/50 av gas and pump gas. Seems to have reduced it some but not completely. Ran pump gas no problem all summer without hearing it. Compression is 185 and piston looks good looking in from exhaust and intake. Im second owner bike has 1200 miles on it. Just dont want to have a catastrophic piston failure
 
It's on the list this month. I still haven't checked the compression, but I can tell she's tired. I'll post up the results of the swap when I'm done. Right now I'm a long way from home...
 
Today it begins. Will check compression (with my new Harba Flate tester with threaded inserts) then the tear down. I'll try to remember to click some pics.

Wiseco piston kit and wrist pin bearing and Athena gasket kit should be here this week.
 
I'd like to do my top end this winter, also. It will be my first.

I want to go the same route you did with the Wiseco.

Would you mind writing where you bought each component?

I.e., piston, rings, clips, pin - Wiseco direct?
Small end bearing?
Gasket kit, o-rings - Athena direct?

Your help is appreciated.
Mike
 
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