Q: I recently changed the fork oil on my 2008 Kawasaki ZX-10 to save time and money on expensive dealer workshop costs.

It’s covered just over 30,000 km now and they (forks) started to feel a bit ‘wooden’ and I can’t even remember when they last received any form of attention. After taking them out and hanging upside down to remove the old stuff, which was black, smelly and vile, I then filled them with the correct recommended weight Motul oil (lightweight).

But, after refitting them and riding they felt exactly the same and nothing like they should. Shouldn’t they work properly again after an oil change, I would like to think so? So, any advice on what to look for would be appreciated?

Many thanks for your time.

Martin Woodbourne.

A: After that many kilometers with little or no attention the forks will definitely have built up residual sludge/paste inside. This will contaminate and block the very small holes and shim stacks that form part of the ZX-10’s damping abilities, which will make the forks feel ‘wooden’ like you’ve said. It will not come out just by turning the forks upside down.

You’ll have to take the forks out again and have someone who’s competent with suspension to strip, clean and rebuild the entire fork internals. And while you’re doing that replace all of the seals as well to save time and possible problems in the future.

Once done we’re sure the forks on your ZX-10 will once more function like they are new items.

Q: My father and myself have recently acquired a 1981 Suzuki GS1000G, the one with the shaft drive.

We bought it to do some team bonding and work on it together until it’s ready to be ridden on the road again. It does need a lot of cosmetic work but that’s our problem and the easy side of the story.

The problem, and why we’re asking you knowledgeable guys, is inside the cam cover. We took it off to have a look around and noticed the cam chain has chewed away at the rear top of the cover quite badly. But when we try to pull the chain off the sprocket it doesn’t move very far, certainly not enough to cause this ‘chewing’ effect.

So what should we be looking for and what should we replace before even contemplating to start the engine? The bike has 84,000km on the clock by the way.

Richard and Colin.

A: You’ll be glad to know this is quite an easy fix if you’re a competent mechanic. Basically, the cam chain is well past its life span. When the engine is revved it will ‘leave’ the sprocket due to stretching and therefore touch the top of the cam cover.

Please just check that the cam chain tensioner is working correctly as well. If it isn’t taking up the slack it will have to be replaced because it’s not a serviceable item I’m afraid. If you’re not sure how to check this go onto the Internet and download the workshop manual for your bike, which is easy to perform.

As for the cam chain, new one’s can be bought with a split-link so you don’t have to remove the crankshaft to replace it. Just check (twice) that you still have the correct settings for the camshafts, after installation. These figures can also be found in the workshop manual that I highly recommend you attain before you go any further.

Q: My Yamaha YZ125 two-stroke MX bike is really annoying me, after I’ve just spent loads of money on new parts!

Being a two-stroke and due to many reason it recently destroyed a piston and the barrel coating. So I bought a new piston and had the barrel plated again, all using genuine parts. I did notice there was some damage to the cylinder head (little indentations around the combustion chamber), which I cleaned up nicely.

So after I rebuilt the bike I took if for a ride and it ran hot and sounded ‘funny’ at high rpm – the jets are the same as I used before. So I stopped the bike and haven’t run it since, because I just don’t want to spend any more on an old MX bike.

So, do you guys have any idea what I could have done wrong, or anything else, before I throw it away forever?

Martin.

A: I’d say the problem lies within the cylinder head that you described you, ‘cleaned up’. The small indentations will glow red-hot around the edges when the motor is up to operating temperature. This will cause detonation problems, which is probably the noise you’re hearing at high rpm levels. If you keep riding it will eventually destroy the motor, melting the piston and throwing hot metal all over the crankshaft- then you might as well throw it away if it’s indeed that old.

The only way to cure this is to take off the head and get an engineer to machine the damage out and, machine in the correct angle for the squish band (normally 7-degrees). If you have to take off too much material to achieve this you might have to machine the top of the barrel as well to compensate, to return to the correct and specified compression ratio. Not an easy job at all, so be careful and choose the right people to attempt it please.

Q: I keep reading about closed-cartridge and open-cartridge forks found on modern day motorbikes. So, could you please take a few moments to explain what the difference is and why the closed-cartridge version is supposedly much better than the other?

Thanks for a great site as well, the best we have in SA by far.

Chris

A: Open cartridge forks have basically the normal fork internals we’re all used to seeing. The damping rod sits in the oil that is put into the fork tube when you have a service for example, which most people can do in their own garage.

But now, as you say, we have closed-cartridge suspension used by all Moto GP and World Superbike machines and indeed top of the range off –road motorbikes as well. This is in effect a sealed unit, set at the factory that drops inside the fork tube and cannot be serviced or messed with easily. Then separate oil is placed around the outside like a conventional fork, so there’s basically now two parts to the fork.

This prevents foaming and air contamination and keeps the damping process constant at all times, which is what racing demands of course. It basically makes the front fork now act in a similar fashion to the rear shock and is much more effective. The down side is that these types of forks are more expensive to produce. Hope that clarifies things, Chris?

Thanks for the support and comments as well.