2 Strokes Down Under

Hi guys

Does anyone know of an after market piston that can be used in an 1984 KR250 A1?

Cheers Terry

If you do yourself a massive favour and change the rod yes.

Hi what is wrong with the original rods? and what can it be replaced with?

Cheers Terry

If you change the rod you can use a better and more readily available piston. The rod is to short to use a alternate piston. Nothing actualy 'wrong' with the KR rod.

You can use Kawasaki KMX125 pistons, but you have to find 2mm oversize. I haven't found any for sale in Aus but they are available overseas. Standard rods are fine.
Quote from KR250.org-
"It's very difficult to find new pistons/rings for the KR these days. I've been looking into alternatives and the best tip so far is to use parts from the KMX125 (but +2.00mm oversize - standard KMX bore is only 54mm). I've not tried them myself but I've measured some and they appear to be the same in all dimensions. If you try them or you know of a better match, please let me know."
Find here:
http://kr250.org/KR_service.htm

KMX is not a performance bike, as yet nobody has run a KMX piston in their KR.

please keep us informed as i have one that needs a top end rebuild

cheers mike

Here's some specs:

Make Model- Kawasaki KMX 125

Year- 2003

Engine- Liquid cooled, two stroke, single cylinder

Capacity- 124cc

Bore x Stroke- 54 х 54.4mm

Compression Ratio- 7.8:1

Max Power- 22hp @ 9500rpm

Max Torque- 1.7kg-m @ 9000rpm



Make Model- Kawasaki KR 250

Year- 1984

Engine- Liquid cooled, two stroke, parallel twin cylinder

Capacity- 249cc

Bore x Stroke- 56.0 x 50.6mm

Compression Ratio- 7.4:1

Max Power- 45hp @ 10000rpm

Max Torque- 3.7kg-m @ 8000rpm


As you can see, the specs are very similar per cylinder for the two models and I would not hesitate to use the KMX125 pistons if they are indeed the same dimensions as the KR250.

-Grotty.

I discovered that Beet used to make a 310cc kit for the KR250. They used a KE175D piston. All piston measurements are exactly the same except for the diameter and probably weight. The windows and ring pins are also in the correct place. You must use thrust washers on either side of the small end though. KE175D pistons can be purchased from Bikes & Bits Importers in WA. You would need to bore the cylinders out to 62.5mm and have head gaskets made or the heads o-ringed.

This may not be the perfect solution, but may resurrect a whole bunch of dead KR's out there.

whats going on with those pistons around the gudgeon holes?

looks like they forged it with a waffle iron haha

That makes it easy to find where it orginaly cracked before it shattered into a million pieces.

Any success with pistons?
Has anyone tried using jp in Adelaide for pistons apparently they do one offs
http://www.jp.com.au/JPPistons.html
Or was an alternative found and used ?
Have a kr 250 tandem twin in need of pistons, rings & a lot of tlc!

JP pistons would be OK for you 1938 Heinkel 174cc OHV but something that is a bit more sporty I would be giving them a wide berth.

As I said if you swap the rod there are a multitude of pistons. Actualy have a fellow from SA KR cylinders , that you Seb/Sheik? He can fill you in ton the details

Hi guys new to the forum.i just got a 84 kr250 engine and wireing loom for a dirtbike project and seen your post and was interested in the ke175 piston swap and wanted to know more about it like would I need to have th e cranks rebalanced for the bigger pistons I seen that wossner makes forged pistons for the ke175

Azza1980 wrote:Hi guys new to the forum.i just got a 84 kr250 engine and wireing loom for a dirtbike project and seen your post and was interested in the ke175 piston swap and wanted to know more about it like would I need to have th e cranks rebalanced for the bigger pistons I seen that wossner makes forged pistons for the ke175

If your getting the cranks re-balanced then you'd be crazy not to swap the rods over while you there.

new rod = more piston choice, Id imagine there would be many piston options for you if you changed the rods.. including cagiva mito, suzuki rgv, and a few early 125mx bikes.

if the rod is also a long rod then its even better, as it will boost the midrange for you

spoiled for choice.