125-200cc What pistons interchange on Wr125?

On a Wr125 like 02-09 what other pistons/manufacturers interchange?

Yamaha YZ125 What Years?

Honda CR125 What Years

KTM 125 What Years?

Gas Gas 125 What Years?


Just Curious?

Darin,

The Yamaha and Honda are direct bolt ups. The issue is going to be the top of piston design and the exhaust bridge holes. Use all latest model piston's. They all have the piston pinned on the center line. The Honda has a domed piston, yamaha has a slight lifted platform that ends up being a skidge higher than the stock husky piston. Always check your squish when you make this swap. I don't know that you can swap these into the stock head. Now your 144 EG head is a different case all together. Actually the best piston for that head is the Honda 58 mm piston made by wossner. It is light and with EG's work actually brings the squish in line. His head milling works best with a domed piston. Your compression will also jump to about the 180-185 psi range. The GasGas piston should also work but I haven't tried it. I believe it is a domed piston too. The exhaust port holes are a sinch to drill. Use a 1/16" drill bit and match the patern on the stock husky piston. I always mount the piston without the ring and slip on the cylinder then mark the bridge through the exhaust port, insures accurate centering of your holes. Takes 5 seconds with any piston other than the Mahle piston that George uses in the 167 kit. Then you need a very sharp drill and some patience, you'll be there a while.

Another tip is that you should use the stock Husky top end bearing. It is a much better bearing than the Wiseco or any other after market piece. The price is very competitive too.

I used a FBF piston - Wiseco which were $50 on ebay - didnt have circlips though
My compression is only 150 psi after rebuild

Whats wrong with the OEM piston? It is cheaper than a Wiseco and obviously works good.

Thats what I say, after hammering the heck out of Husky 125's over the years with 0 and I mean 0 failures, I would NEVER think of a different piston. Is it it get more compression or what?

Just curious to see what else guys have used, if any. Might be able to put the yammy in and boost compression rather than cutting the head a little? I like the tip on the Wossner with domed piston and EG 144 kit.

When I was a toddler, I always played in dirt with my tonka toys. Now I am just older, own Huskys, still play in dirt, but now they are my tinker toys.

Nothing wrong with OEM just $350 in Aust. for a piston kit

The stock husky piston is great. The only reason to use an aftermarket piston in my opinion is like the EG example. He used to include a Wiseco piston with the kit. His head work has a huge squish when using the flat top piston(I had well over 2mm). Before Husky had a 144 piston available I was looking for a domed piston that would work and create a better squish tolerance at the same time. The best I found was the Wossner Honda 58 mm piston. So that is the story such as it is.

So a large squish with flat top piston could be why my compression is only 150 psi

The biggest problem with the large squish is that it reduces the speed with which the gasses are forced into the combustion dome. I think RB designs gets a lot more out of the motors by optimizing the squish and then recutting the dome to keep compression at stock or not if you want to raise your compression. I probably get away with the domed piston and using pump premium simply because my lowest elevation(house) is ~4000'. If I was to spend much time riding near sea level I would be using some fraction of race gas. My guess is that my compression is approaching 200psi at sea level. Oh well what do I know.

Walt,

Makes sense. That's pretty good compression with that Wossner domed piston. I think that'll be the route to go with the EG 144. Still looking @ the 167.

Darin

Does anyone know how much clearance you should have on the top of piston and closest area to the head? 2mm, 3 mm?

Thanx!

From what I have read most guys are shooting for between .8 and 1.0 mm. I actually always think in thousands being a dynosaur so my target is .040". When you look at the EG head you will notice there isn't a well defined squish area. He just mills a constant tapering into the dome area. With the flat topped piston, I couldn't get any contact with my 2.5mm solder. With the domed piston squish isn't ideal but at least it is below 2mm.

Walt,

Ever think about becoming a walking service manual?

Could you do a side x side photo of the wiseco piston versus the Wossner? That's only if you have them apart and you can do it easy.

Don't go thru the trouble of taking something apart to do it.

Thanx!

I know RB shoots for .040"-.045" for a weekend warriors motor. Race motors that get weekly teardowns can run much tighter.

I would find the cheapest (yes high quality) piston option and set the head for that. Will save you lots of cash in the long run.

Squish in the 167 is at .038" set by George at Uptite.

The Piston on the right is the Wossner Honda 58 mm piston. The piston in the center is the stock Husky CR 125 piston. Both of these are new. The piston on the left is the Yamaha 58 mm Vertex piston that I ran for the first half of this year.

Sh*t the first pic is upside down....oh well

Walt,

Thanx a million, good comparison! I can see the Yamaha lip and the Wossner dome versus stock Husky.

Darin

I just had RB do my 144 head. Stock squish was 1.22mm. It is .9 now. He said the shape of the squish band is good on the Huskys so he only had to mill the head which is only $45.

Yep if you have the stock Husky head there is no reason to experiment with other pistons. Just let RB mill the head and away you go. The EG work on the other hand is far from ideal and to improve the head would require a complete re-shaping of the head.