125-200cc Another possible 125 big bore option

I didnt know that !!!


Well KTM obviously built plenty of reserve in the 125 design...if it can accept a 6mm increase in stroke.....and still use the same crankcase....the husky case is parred to a minimum

the point I am trying to make is....if you look at most modern 2T bore and stroke dimensions....they are more often than not pretty close to square dimensions.....increases from bore size will only work to a certain point...strength is another kettle of fish altogether....

Some people have built KTM 170s by using a 200 top end with a 125 crank. I think it is an expensive conversion but those who have done it say it is a really fun motor. It seems like it would be way too over square but maybe it works. It seems like Husky could just make a factory cylinder that is a 150. If TM could whip a 144 out months after the rules were changed Husqvarna should be able to do it. I bet they would sell a ton of them. That is of course assuming they put a decent gas tank on the bike which they almost certainly would not.

Being oversqare does have one big advantage..in that it does does lower piston speed....

but its harder to get a good burn with a wider flame front like that.....it would however have the capability to rev to the moon....

this is all conjecture of course.......


I think the reliability of the 144 method has been proven that its does work well.....

Yes I know....

The point I have been trying to make is....the length of the stroke...should be changed in relation to the displacement or bore increase...many factors here....how long the piston travels down the bore determines how much charge gets on top of the piston....the aftermarket must compromise I know....

But when look at TM and KTM 144s....ever notice they didnt just bolt a bigger jug on the thing.... it would have been real easy just increase the bore...but chose to alter both dimensions...for eg the 125 is 54x54 the 144s are 56x58.5.....I suspect there is good reason for this....all to with balance...and midrange torque etc

just saying......

Agreed...good stuff

Obviously the most practical way for a displacement increase is a 144 bore kit for husky.....

I believe the theory with regards to crank radius...the longer stroke gives a low end and midrange advantage....and the OEM KTM and TM choose this route....not only an increase in disp....but also some grunt...

If I am not mistaken the 250wr is very under square.....?

I wonder if husky has toyed with some longer cranks for the 125 or if there is room......

i ran across a bored and stroked 167 today.

i was very excited, got the guys number. ill give a report of what he did and who did it. later.

the place is called maxpower. they are in wisconsin. they make BB 4 stroke cylinders and they have had a 167 yamaha for several years. i talked to them today. you sent them your motor, complete, they work it over. they use the stock rod and crank. just re-arange thinggs to get the increase in stroke. then the BB it to the 144 bore to get the bore. they use a different piston then the 144, was told its a bit longer then the 144 to make up for the stroke.

yep, those are the guys!