TOPIC:

Hello, anyone here on the forum who has changed valve seals without disassembling the cylinder head by holding the valve up with compressed air on Z1 900 Z900 KZ900 Z1000 KZ1000?  Tips, tricks, special tools needed...or the other end.  «It's not possible»

 

OK so it is possible ( I have used the method on cars but not a bike) there are a few things to be wary off

1. carry out a compression test ( if the valves aren't sealing then the air pressure won't hold them closed)
2. Remove cams
3. Rig a reliable air line adaptor that fits into the spark plug hole
4. Rotate the engine to TDC on the cylinder you are working on ( this way if you loose air pressure the valve can't fall into the cylinder)
5. Make sure the rear wheel is clear of the ground
6. Put the bike in gear (ideally you could do with a friend at this point to hold the rear brake firmly on as the engine will try and turn when you apply air pressure)
7. Make sure you have a suitable valve spring tool to hand
8. Apply around 70 psi to the cylinder, ensure the engine didn't rotate away from TDC and you are good to go
9. When you remove the spring compressor after reassembly give the valve stems a "tap" with a hammer to ensure the collets have seated (if they are going to fly off better now than when it's running)
10. Repeat the process for the other three cylinders

As above.
Use compressed air with the piston at bdc or rope down the plug hole hole at tdc.
However there are no off the shelf special tools to compress the springs in this situation so you would have to fabricate your own.

Thanks for the quick reply!  I myself have used the method many times on a car but not on a motorcycle or a Z1... What I envision is the place to push down the valve plate to remove the lock on the valve stem and reverse the process for assembly … Must make tools myself yes

You will need to potentially rework an off the shelf tool such as the below You would need to make a tube to hook it too, the main difference is that with a car you can apply the handbrake to stop the engine rotating whereas with a bike you need to watch it doesn't kick the wheel and knock it off the stand when you hook up the air

 

I would just pull the head and replace them. Id have that broken fin fixed while I was at it. 
Steve

I have never done this but having experience with compressed air in a cylinder to do a poor mans leak down test, I can tell you how fast the piston will slam to BDC, not something I want to ever experience again. So I agree with Zed BDC. If your concerned about a valve dropping out pack the cylinder with rope even if the piston is at BDC. In all practical aspects it should work. 

Thanks for the good tips!  To avoid the engine rotating when pressurizing, it may be possible to create a patent that blocks the rear brake completely locked …

and after valve drops you end up pulling head off any way ????

increasing wrote:

Thanks for the good tips!  To avoid the engine rotating when pressurizing, it may be possible to create a patent that blocks the rear brake completely locked …

I have been thinking about the rotation issue having no handbrake as I do prefer the extra reassurance of doing at TDC so as not to drop a valve - what about if you had a "Y" piece in your air line so that you could pressurise the cylinder for repair at TDC and and an opposing cylinder at BDC simultaneously. surely with it "in gear" and opposing cylinders pressurised rotation shouldn't be an issue ???

www.harborfreight.com/universal-overhead...ompressor-59343.html?

Hi could this be modified to work? Inquiring minds would like to know……

Forget compressed air. Raise the piston 3/4 way up to TDC. Stuff as much 1/4" rope as will go into the cylinder. raise the piston as far as it will go. The valves will be held closed by the rope and no chance of the piston blowing down and valves dropping.