KX Guru Racing

We had a customer come in with a 01 CR125 in pieces.
He wanted it rebuilt and needed a estimate.
The first thing that I noticed is that one engine case was black and the other was natural grey.
The black case was on the left so I was able to get the Engine ID number and it was a 91.
According to Honda 90-92 used the same cases and 99-02 used the same cases.
I had heard that you could swap the cases from a large year range of CR125's but I could never verify it.
Well... it is now verified that you could interchange at least 90-02 CR125 engine cases.
Since we don't do service work (We only sell parts) we recommended a friend of ours Jason at JT Engine Works to do the build.
The customer agreed and Jason pulled the bike apart and inspected everything he needed to rebuild it.
A quote was given and the customer gave the ok.

So, Jason ordered all the parts for the build.
The crank and the cylinder were at new specs.
So, Jason ordered a few trans gears, all new bearings, trans circlips, seals, gaskets, clutch, water pump impeller shaft, plastics, chain guide and slide and probably a few other parts as well.
Then, Jason Steam cleaned all the engine components and the chassis.
After steam cleaning, all the parts were lubed to prevent flash rust.
Finally, the trans parts came in and Jason discovered that the new gears didn't match the trans out of the bike.
It looked like this build was gonna go right into the trash...

What went wrong is Jason assumed that the trans was from a 01.
In fact it was from a 91.
So he ordered the wrong gear.
Incidentally... when he was looking up the part numbers he didn't realize that he didn't have a 5 speed trans but rather a 6 speed trans.
It was a easy mistake to make.
So, I did a bit of research and it seemed that either trans might interchange.
After all we had a 91 and a 01 case set with a 91 trans and a 01 top end.
By the way, I verified the top end from pics of previous bike I had parted out.
I have over 1/2 million pics of mx parts
The next thing I did was get a 01 trans we had in inventory and had Jason measure and compare with the 91 trans.
It looked like it would work.
So, I pulled the shift forks, star, and drum from a 01 and he installed it.
It appeared to be shifting perfectly on the bench.
But the real test was yet to come.
By the way, no special tools or procedures were required

The customer took the bike last Friday and we are waiting for a ride report.

More details to come.

Sorry for the caps.

SO, YOU SHOULD BE ABLE TO SWAP FROM 89-01 CR125 ENGINES, TRANS AND CYLINDERS
HOWEVER, THE EXHAUST VALVES MUST BE USED FROM THE CORRESPONDING CYLINDER

Here is what he started with.
Here is what Rameen ended up with..