OK, been a while, but still busy with bikes.
The poor old US 125K has been sitting dusty and broken for quite a while, but behind the scenes i was ordering parts and getting things built like cranks, spare cylinders etc.
The Euro K has been going gangbusters. Finally i think we have a great K. Took ages to iron out all the bugs, but i have learnt a lot and i seem to be able to build a robust engine.
We swapped pipes the other day from the OEM version to the Jemco cone pipe and DG muffler combo. The boy loved it.. Here is a short video.. she sounds sweet and really rips..
https://youtu.be/kCwyjg5IVDoHere she is after her recent rebuild...
So this one is ready for VMX racing, and the boy loves it.. so its time for me to get the yellow K going to that i can ride as well.
First thing was to go through my shed and track everything down. I had a cylinder and new piston kit in one box over there... a crank under there.. bits and pieces everywhere. Took ages to gather everything up and give it a good clean.
Now, heres the story. When i blew a hole in the piston of the Euro K, i decided that the bottom end would need rebuilding. I had the good bottom end from the yellow K from when i seized that one up. So.. the new top end from the Euro K went onto the good yellow K bottom end, and thats how we got the Euro K running really well.
Now, with the yellow K.. i had the seized top end (Eric Gorr ported cylinder), and the ruined Euro K bottom end.
I needed to start from scratch. So, the bottom end was thoroughly washed out and blown out with compressed air. New main bearings were fitted, along with new main seals. A freshly built crank with new rod kit was fitted. This was all closed up with Threebond rubber gasket goo.
For the top end, the cylinder was sent away and came back with new piston kit.
I checked ring end gap. 0.5mm Perfect. I did some squish tests.. This bike also requires two base gaskets to get the required 1mm of squish. I used copper gasket spray on the two new base gaskets. I also copper coated the gasket at the reed block and used some silicon on the rubber block side.
I torqued everything up and then did the leak down test with my new Motion Pro leak down tester. Perfect.. no leaks from anywhere. All seals and gaskets holding tight at 6 PSI.
I then went through and bolted the rest of the engine together. I replace the PVL ignition with a genuine 24X stator and rotor unit. I set the timing to 1.88 BTDC using my dial gauge down the plug hole. Everything was checked and rechecked, oil added, and finally she all came together to make a nice fresh engine....
This will be going in the yellow K soon and run in.
Hopefully that will be the end of all the woes. Lots of lessons learnt over the time.
Main lessons were to check squish and adjust as necessary. Do proper leak down tests, as these old girls leak everywhere, even with new gaskets. Start stock, and slowly add mods.
I have a brand new genuine Mikuni and jets to fit up to this old girl. Hopefully, once she is running nicely, i will slowly add the mods again. I have the bigger Mikuni to go on later, cone pipe etc.
I think one of the main reasons i kept seizing the yellow K was the PVL ignition. It was sold as a complete unit for the K, but i believe the curve was way to advanced. I have a digital timing light and later down the track i will play with it using the stock ignition to get some base readings. I will then swap to the PVL to see what was happening there.
Anyway, thats it again for now.
Cheers,
Once
