CX 650 Custom Build Part 1

This project was something I have wanted to do for a long time.
A 650 engine into a 500 ZAB frame.

After waiting for a few years, a 650 eurosport engine came my way.

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THe engine sat for a couple of months and then I got some time to start the conversion.

The engine had one and maybe two blown head gaskets, so first job was to remove the heads and service them by cleaning checking and installing new valve seals. The valves themselves were also re-ground just to be sure.

Valves are in very good nick.

After completing the heads I put them to one side and tackled the back casing.

The plan for this engine is to use a 500 rear case Instead of the original one.
The reasons for this are that I need a 500 output shaft (have) to mate with the 500 drive shaft/swing arm.
I also need to install the ignition pickups from a 500 (have) combined with a G8 generator from the 650. A rotor from a 500 (have) will also be required and fits directly onto the 650 crank.
The combination of these parts will allow me to use anIgnitech ignition unit to give spark.

The photo below shows a G8 (later) generator on the left and the older generator (burned out) on the right complete with pickups and loom.

I started looking at the wiring required to come from the engine to the Ignitech

Managed to get all the required cables into the grommet.

The 3 yellows from the g8 had already been cut and soldered so i snipped them again and resoldered in new longer yellows taken from a burned out 500 stator.

Heat shrink finishes the job nicely. Robbed sleeving from the aforementioned 500 stator and pushed all cables through.
You have to remember the feed from the neutral switch when doing this, it travels in the same sleeve.
This is now ready for connectors but Im not going to put them on until it on the bike.

With all this done it was time for a trial fit of the rear cover onto the 650 engine.

Finished cleaning the inside of the rear case. Next job was to install a new water seal and a new oil seal.
Thankfully I have the seal insertion tool made by Derek in the UK. (Now deceased).

This tool makes life a whole lot easier.

Seal installed ……

Some re-assembly of parts onto the rear of the engine block including a 500 rotor.

Then it was time to install the rear case onto the engine. It went on fine as we gently persuaded it into position. We noticed though that it just didnt sit 100%. There was a bit of a wobble as if it was fouling something. Then I sussed it. The inside boss for the camchain adjuster was hitting the head of the bolt that holds the 650 auto adjuster (completely different).
You can see below the mark left by the hex head of the offending bolt.

First to be tackled today was the clutch. The plate carrier with the 4 prongs (for want of a better word) had a problem in that there was a bolt broken in one of the holes. The solution was to drill this from the back. I couldn’t believe my luck. The drill literally ran the broken stud out yahoo !.
After figuring out that my clutch parts were different to the manual. My clutch is like a 650 custom not a gl/ed it went together a treat. I did notice one difference to the 500. The 650 has 2 narrow gears at the back of the clutch is carrier. The 500 has only one wide one. The 2 gears on the 650 are slightly off with each other and on a spring system. This is called a backlash gear and it does exactly what it says o the tin. Probably to cope with the extra power of the extra cc.

Next job after the front cover went on was the sump. The sump on the engine was cracked – see photo. Thanks to our friend in France I have a replacement. Thankfully the old sump came off and left the gasket in one piece. A fair bit of grunge and rubbish in the bottom of the old sump.

After that I turned my attention to the head faces.
The 6mm dowels were welded into the heads. Luckily I have a tap/die set by Snapon that has a 7mm tap/die.
Run the tap down the dowel then into the treasure boxs to find a 7mm bolt off the top clamp of the forks, (the only 7mm bolt on a 500). Screw the bolt in and keep going – it drives the dowel out.

Today I tackled the rear cover after getting some advice.
I found a 14mm drill bit in a box and reamed out the chamfer on the inside of the rear case by hand, the drill is sharp and the aluminium soft.
I took 3 attempts to get this right, didnt want to take too much off – being super cautious.

View from outside with the case on and tightened.

Water Pump next, always worth a little care and attention. Dont forget that little collar.

Polo mint in with a bit of soapy water.

Copper washer …..

All tightened up with the correct nut and a bit of thread lock inside for good measure.

I put the pump cover on and then the water transfer pipe.
Im a 2 o-ring guy as you can see.

This pipe is off the 650 engine and I noticed that the original clamping locations were about 5mm different.

This got me to thinking about the overall length of the transfer pipe. Is a 650 one longer than a 500. The water pump is about 15mm further back on the 650. I couldnt find a 500 pipe with a quick look so I roughly mocked up an engine hanger and rad from a 500 to see if it would mate up the bottom pipe into the rad.
Seems ok.

Next I started to look at getting the heads back together. I have the RH one ready to go back together so thats a start.

All valves were reground, new seals installed.
The Honda genuine Head Gaskets were a perfect fit.
Both heads passed the petrol test with flying colours.

First job today was to torque up the heads.

Remember to put your wrench back to zero when finished.

Set the valve clearances,
I always find this tricky on a rebuild as you have to figure out when the cylinders are at tdc on the compression stroke. That is when all valves are closed. On a rebuild this can be hard to figure as the screws are all over the place. I sussed this out because on one stroke the screw holders were only a few mil from the top of the valves, on the other they were nearly 10mm away. This allows the screws down to do their job.

Job done on both heads.

Heads on. Starting to look like an engine.

Next is to sort out the the thermostat housing and pipes. Im using a 500 housing and the link pipes/elbows from the 650. Using the 500 housing allows the use of the 500 rad which will sit perfect on the 500 engine hanger.


This engine is nearly ready to go into a bike.
I mocked the hanger and rad again just to check everything

Starter motor was stripped cleaned reassembled.
Not doing any mods to it yet.

At this point the engine is back together and nearly ready to go into the 500 frame.
There are a few mods to be done to achieve this and you will find the continuing tale in part 2.