Where did I go wrong? - Wiseco piston

Hey All,

I have a 1992 KDX250SR... I've been wanting to do a top end on the bike for some time now. I bought the bike used with who knows how many kilometers on it. A compression test showed 150psi that improved to 175psi with a squirt of oil down the plug hole. So I thought I'd go ahead and do it.

Being in Manila, I do not have a ready source of bike parts - unless you happen to have a DT125... So I did some research and found out the bore and stroke of my bike is 67.4mm x 70.0mm and I had heard that some Stateside KDX250 owners were putting in a late 80's or early 90's KX250 Wiseco piston in their bikes so I ordered up a Wiseco kit from my friend in the US and had it handcarried over here by another friend of mine.

Today was the day... I pulled the cylinder (head still attached) and removed the piston. It looked pretty good (I'm glad - you'll find out why later) but I was looking forward to having a new piston, rings, pin and bearing in the beast.

Upon comparing the just removed old piston and the new piston I was horrified to see that they were not the same configuration! The overall height is the same, the diameter is the same, but the location of the wrist pin hole is different! What's up with that?

If I measure from the bottom of the skirt to the bottom edge of the wrist pin hole on the Wiseco I measure roughly 1- 1/16 inches. If I measure the same dimension on my old (soon to be put back in piston!) I measure 1-1/4 inches - a difference off about 3/16 inches! If I had installed the Wiseco piston, on top dead center it would have protruded about 3/16" into the compression chamber - not a good deal.

Any ideas where I went wrong? The specs say 67.4 X 70.0 for my engine, but a piston made for a KX/KDX of those specs don't seem to be right for me.

Unfortunately, I can't even use the rings from the Wiseco... the top ring lands on the old piston are "lodestone" shaped not rectangular on the cross-section. Rats!

Any other KDX250SR owners out there who can steer me towards piston options that will work on my bike?

Thanks.

more data...

Dear canyncarvr and C. Dave,

Yes, I did order up the Wiseco 607PS for the 91-94 KDX250... I just assumed it would be the same piston for the SR mode... you know, Kawasaki 250 engine, same vintage, same bore and stroke specs... wrong assumption.

My motor does not have the main exhaust KIPS valve only two side valves... maybe when Kawasaki put the main valve into the Stateside 250 motor they needed more cylinder length to get all the extra parts into the mix and consequently a piston configuration that would go further up the cylinder (pin hole further down from the top of the piston)

The wrist pin hole is closer to the top of the original piston than on the Wiseco. So, the Wiseco would go 3/16" into the compression chamber if I installed it! Even the wrist pin on the Wiseco is 18mm while the original is 19mm... so nothing from my Wiseco kit is usable in my bike. Rats! Anyone need a complete BRAND NEW Wiseco 607PS kit? Email me - let's make a deal!

C. Dave, as I'm trying to get my KDX250SR into good shape, I'm finding more and more little differences between the SR and R models (mostly in the engine)... I'm sure the same is true with the 200's ,too. When we were Stateside in summer 2000, my son bought a stock 1995 KDX200 and that bike would make mincemeat out of my 250! The SR model is very timid in comparison... Sure wish I could find an R model on this side of the Pacific!

A photo of my bike is on page 10 of the Reader's Rides of JustKDX.

Thanks.