Two Stroke top end rebuild *not 56k friendly*

[c-m]

I bought a KH125 in March of this year. It's a 1996 model and should be good for upto 70-75mph.

After a couple runs of around 60-65mph and taking it too the beach, the bike began performing poorly. I found that I was only able to reach 50mph at a puch and changing to 4th gear resulted in a max speed of 39MPH. Not much fun a NSL road.

after many posts in the workshop thread, I decided to take a look at the top end. After taking it apart I found this:

https://www.eastcoastlacrosse.co.uk/carl/DSC01343.JPG

https://www.eastcoastlacrosse.co.uk/carl/DSC01346.JPG

It seems the piston had suffered a mild siezure and was quite badly scored. I ran my fingers around the barrel which also appeared to be scored, hence my lack of compression.

I ordered a new +1mm piston kit and took the barrel to my local reconditioners. It cost around £25 for the rebore. After getting the barrel back I was told it would need a thorough clean to get rid of all the debri from the re-bore.

https://www.eastcoastlacrosse.co.uk/carl/build/barrel.jpg

In the mean time, my piston kit had came and I prepared the bike.

https://www.eastcoastlacrosse.co.uk/carl/build/bits.jpg

Here's a pic of the bike all stripped ready for the rebuild.

https://www.eastcoastlacrosse.co.uk/carl/build/Image415.jpg


After taking out the old piston, I prepared the new one and placed the bottom gasked on. I had read somewhere that is much easier to place the piston in the barrel, before fitting to the crank. That way you do not risk damaging the rings, while trying to slide the barrel over.

https://www.eastcoastlacrosse.co.uk/carl/build/1.jpg

Basically you insert one circlip, then slide the top part of the piston into the barrel. This should told tight. From there Slide the barrel onto the studs, untill the piston lines up with the crank (I had already placed the small end bearing in the crank at this point).

https://www.eastcoastlacrosse.co.uk/carl/build/2.jpg

Then slide in the pin and finally put the last circlip in. That was deffinately more difficult that it sounds. I used the old piston to support the weight of the barrel, leaving me both hands to add the final circlip.

https://www.eastcoastlacrosse.co.uk/carl/build/3.jpg

After that it was a simple case of adding the top end gasket and then fitting the cylinder head.

https://www.eastcoastlacrosse.co.uk/carl/build/4.jpg

That's an old gasket just for show, I did use a new one in the build.

And that is basically it. torque up the 4 bolts in the order 1,3,2,4 etc.. screw in the spark plug, add the fuel tank, connect the fuel hose and then add the seat. Gave her a few kicks and eventually he fired up.

The sticker on my tacho says 4000rpm for 500miles then 6000rpm for another 300. That is painfully slow and difficult to get upto speed in a hurry.

Just a little comparison between the old and new small end baring.

https://www.eastcoastlacrosse.co.uk/carl/build/smallend.jpg
____________________
Motorcycle headlight bulbs and HIDs
Blogging about my bike and trips
https://ridershandbook.com/

[c-m]

After the rebuild I rode her around for a while, then used her to commute for a few days.

I then left the bike standing for a few days and while it fired up, it died after a minute of idling and wouldn't start again. I switched the plug and it was fine. Then next day I came to start it and nothing.

I had a quick look over the weekend and not getting a spark. Can't think whats wrong.

Luckily I had bought an NS125R over the bank holiday. So I think the little KH will be up for sale.
____________________
Motorcycle headlight bulbs and HIDs
Blogging about my bike and trips
https://ridershandbook.com/

[Gazdaman]

Well, no spark isn't related to your rebore.

Firstly I'd suspect the plug cap and HT lead. After that, start digging deeper.

Gaz