• 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 The previous version was outdated and no longer supported.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

mikebru said:
So the piston kit is finally coming this week. I'll try to install it this weekend.

Being my 1st time doing a top end I want to make sure I break it in correctly. I've read opinions on doing it very controlled and letting it just rip. I tend toward the controlled method.

I couldn't find anything in the service manual on break in.

The closest Owners Manual I found was for a 2007 WR250. Does this look worth following?

Mix 32:1 for break in

RUNNING IN
To obtain the best settling of the engine moving elements, for driving your motorcycle to the best of your capability, run in the engine for several hours, following these procedures:
1. FROM STOP POSITION. Start the engine and run at idle, but open the throttle periodically and briefly until the engine is thoroughly warmed up. Within 3-4 minutes the coolant temperature will have reached approximately 60° C/140° F. (Do not ride the motorcycle).

2. Stop the engine, and let it cool down naturally until its temperature is equal to the ambient air temperature. This will allow the piston to align itself to any imperfections which might exist at the cylinder wall.

3. Repeat steps 1 and 2. (Do not ride the motorcycle).

4. Bring the engine up to normal running temperature. Ride the motorcycle approximately 10 minutes at moderate speeds. Then repeat cool down procedure. AVOID HARD ACCELERATIONS.

5. Bring engine up to normal temperature. Ride motorcycle approximately 15 minutes at moderate to high speeds. Again avoid hard accelerations.

6.Repeat cool down procedure.

7. Full throttle operation must be avoided until the engine has reached operating temperature, even after the break in process is completed.

When the above procedure is followed correctly, engine durability and performance will be greatly enhanced.
Click to expand...
I used this break in process the first time I rebuilt my 450... then it blew a rod
View: https://www.youtube.com/watch?v=G8Ms6JDLl-8

Now I use the "hard break in" method in the article above...
 
I used heat cycles do two or three then do an enduro.
The main reason to let it do heat cycles is to bed the rings in, on a two smoke if you give er the beans straight out you will glaze your bore and the rings will be sealing against glass.
Ever wondered why when you get a fresh cylinder back its honed with cross hatching?
Thats to trap oil and fuel mix so the rings have something to seal against.

I assume the heat cycles just harden the hatching.. I know its nikasil its hard as hell but it works.
 
Mike I used the manual method and it worked just fine. I run 35/36:1 anyway so just ran my regular stuff. I did 2 heat cycles at home, which is a great way to check your work and burp the cooling system to get coolant level correct. Then, as mentioned in my previous post, I spent the better part of a day taking it on the 10 and 15 min rides, followed by a longer ride at moderate speeds. Then I raced it, but didn't pin it to win it either. As long as you do a proper warm up before you ride it, there should be no problem.
 
So many of us did replace the pistons over the last weeks- did nobody realise the transfer ports are not fully opened when piston is on lower dead center?
or is it just my bike beeing different to yours?
 
Transfer ports are closed about 3 mm from bottom to top of piston crown on most bikes.
This isnt really a problem as when the piston rises it forces fuel mix down to the lower end breifly to lube the mains then piston returns the reeds shut the fuel mix is accelerated up the transfers into the cylinder above piston out exhaust and then gets pushed back into the chamber by the expansion shock wave from previous explosion.
Piston cycles goes through it again.
you can change port duration with base gaskets but compression ratio and squish will suffer.
Personally if your bikes not down on power I wouldn't worry, well i dont
Suppose i could of raised my cylinder and machined more off my head to get squish back but then the stroke will be affected.

summary who cares, just ride.
 
So it's done! Broken in and running well.

I think I averted a near disaster.

It started on 2nd kick for the 1st break-in warm up.

Had choke on. It started revving to like WFO for a few seconds! Took a few stabs of the kill switch to turn it off. Turns out my throttle cable was pulled tight out of the carb from when I put the tank back on. That actually happened to me on a normal ride day about a year ago. Took a while to figure it out then.

Once I adjusted the cable everything was back to normal. So it turns out maybe I inadvertently did the let'er rip break in. Hopefully, no damage was done. I proceeded to follow the manual's break-in instructions. Still have to do the last 15 minute trip but I think I'm good now anyway.

Thanks everybody for the help throughout this thread.
 
Most important thing in the whole break-in procedure is the cool down...let the motor cool down to stone cold between each break-in cycle is super important!!
 
Thanks. Just about did that. Not quite stone cold but cold/cool I'd say for the 1st 2 cycles. Definitely stone cold for the 10 minute ride.
 
Looking good joedints, i normally get reed block on while the cylinders out more access and less fiddle, you doing squish clearance now?
Lever the rings off the piston there not needed for the squishy testing its quicker changing base gaskets before the proper assembly.

Love a fresh rebuild.
 
How did you get that cylinder so clean, inside and out? Especially in the power valve linkage areas.

I spent some me time on mine with a brush, simple green and carb cleaner but it looks nothing like yours.
 
Now... If I can figure out the power valve... The actuator arm coming from the bottom end where it hooks up, the "d" shape is reverse of the arm it attaches too...
 
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