Low Compression

I have a 1976 KZ900 with a stock motor, as far as I know. I can install new plugs and they will be oily and wet after being run for a few miles. I did a compression test on the motor when the motor was cold. All of the cyclinders are between 70 and 85 psi, which are all low. Should the compression test be done on a cold motor or be done after the motor is up to normal operating temperature ? Thanks.

BIGKEVIN wrote: I have a 1976 KZ900 with a stock motor, as far as I know. I can install new plugs and they will be oily and wet after being run for a few miles. I did a compression test on the motor when the motor was cold. All of the cyclinders are between 70 and 85 psi, which are all low. Should the compression test be done on a cold motor or be done after the motor is up to normal operating temperature ? Thanks.

If not already doing so, the throttle should be held in wide open position when performing the compression test.

Can add a teaspoon of motor oil through the spark plug hole to determine whether it affects the compression figures.

Would also check the valve clearances and assure the clearances are within specs.

Good Fortune!

I will try adding a teaspoon of oil to the spark plug hole to see if it makes any difference. Does it matter if the engine is hot or cold. Do you know where I can get good instructions on how to check the valve clearance ?

Valve clearances should be checked when the engine is stone cold.

When compression testing with a warm engine, the oil between pistons and cylinder walls helps seal compression as it does during normal running.

Good Fortune!

BIGKEVIN wrote: ...where I can get good instructions on how to check the valve clearance ?

Thickness gauges are used to measure between each cam base and shim, with the cam pointing away from the shim.

The Factory Shop Manual has the best instructions.
May use this link to download the manual from KZr's FILEBASE.
Click here > www.kzrider.com/filebase/doc_download/43...asaki-service-manual

Scheduled maintenance calls for checking valve clearances at intervals of 4000 miles.
Click here > www.kzrider.com/filebase/doc_download/346-periodic-maintenance .

Good Fortune!

I read over how to check the valve clearance and it doesn't look hard to do. Forgive me if the questions I have seem stupid, but this is my first time doing anyting with the engine. How many valve clearance readings will I be taking ? will it be 4 or 8 ? 4 on the intake cam and 4 on the exhaust cam. How do I know what shims to order if the valve clearances are too tight ? Thanks for any replies and help.

You will need to do 8 measurements, if this is the first time you are doing it it will just take a little while longer as after you make each measurement (assuming you need to change any shims) you will need to take each shim out and record what size it is so you know which shim size to order. I would do that anyway so you know what's in there for the next time you do the valve clearances. I just did all that, I had to change 6 of the shims and luckily found I only needed to order 2 as I did a little musical shim chairs with the other 4. You will need the shim changing tool (if you haven't got one yet) Z1 enterprises has all of that good stuff.

BIGKEVIN wrote: I will try adding a teaspoon of oil to the spark plug hole to see if it makes any difference. Does it matter if the engine is hot or cold.

Compression test has to be hot.

I did redo the compression when the bike was hot and all 4 cylinders were between 95 and 105 lbs.
When I do the shims, do I order the same size shims that are in there now ? Thanks for the information thus far.

You have to measure the clearance then calculate the shim you need to make the clearance correct.

I have two more questions. Is the special tool needed to get the shims out ? I would like to order the shims and the special tool at the same time. Also, if the clearance is too tight, how can you determine which shims you need to bring it within specs ?

Unfortunately it's going to be a double order deal.... you need the special tool to remove the existing shims as the size numbers should be installed facing down, before you know what new shims you will need to order. You first rotate the cam to leave the lobe depressing the bucket as far as possible, then you install the special tool, then rotate the cam to get the lobe out of the way so you can pull out the shim with some strong tweezers....and you do that 8 times of course!! When you say "if the clearance is too tight" that you cannot even get a feeler gauge in to measure the gap? If that is so you may have to 'borrow' a thinner shim from another valve so you can measure the tight one. I just went through this whole thing for the first time a few weeks ago and it took me a few goes till I got the hang of how it all works....one of the things that got me was one valve I just could not get the new shim in place till I discovered that the tool was interfering....the gap you have when using this tool is a little tight and I had to re-position everything for it to work. The only remedy was a swift beer :laugh: :laugh: :laugh: