Another Valve Question (1981 KZ750E2)

Hi, all. This is my first post, so be kind!

I just picked up an 81 KZ750 from a friend who is moving out of province. The last time the bike was running was about a year ago. The PO took it off the road because he was having some issues with missing. He figured it was electrical.

Anyway, I just went in to check the valve clearances and some of them are very tight. All the exhaust values are within spec (right at 0.007"), but the intake valves are tight. They are all at 0.0015".

I am assuming this could cause the issues he was talking about. What are the chances that the valves are burnt (especially on those two really tight ones)? Is it worth my while to simple re-shim all of the valves to the loose end of spec and hope all is well, or do I need to dig in deeper to check the valves? I really don't want to take the head off. Is there any other way to determine if a valve is OK other than ripping it apart?

Thanks for the help.

Mid life crisis wrote: Hi, all. This is my first post, so be kind!

I just picked up an 81 KZ750 from a friend who is moving out of province. The last time the bike was running was about a year ago. The PO took it off the road because he was having some issues with missing. He figured it was electrical.

Anyway, I just went in to check the valve clearances and some of them are very tight. All the exhaust values are within spec (although some are right on the edge at 0.003"), but the intake valves are tight. One is at 0.003" (just on the edge of spec). Another is at 0.0025", and the last two are a bit less than 0.0015".

I am assuming this could cause the issues he was talking about. What are the chances that the valves are burnt (especially on those two really tight ones)? Is it worth my while to simple re-shim all of the valves to the loose end of spec and hope all is well, or do I need to dig in deeper to check the valves? I really don't want to take the head off. Is there any other way to determine if a valve is OK other than ripping it apart?

Thanks for the help.

Hello, Mid life crisis, and WELCOME to KZr!

With a stone cold engine, a valve ought to seal even with bare minimal clearance.

A cold compression test showing acceptable compression would indicate that the valves are still in good enough condition to seal inside their seats.

A leak-down test would be even better.

Adding a teaspoon of oil through the spark plug holes and repeating the compression testing may produce higher figures by reducing the amount of compression that's lost past the piston and rings.

But the leak-down test is best, and provides more specific information.

Here's the poor man's version.

No dis-assembly is required, other than removing the spark plugs.

A leakdown test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor man's leak down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window. Be sure it's the T "mark" which doesn't necessarily align exactly with the letter T. The actual T mark is sometimes located beside the letter T.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune!

If needed, here's a site with a Factory Service Manual that may be downloaded.

After accessing the site, scroll down to and click on "The Bible."

Click here > kz.bike-night.com/

The procedures for replacing the shims to achieve correct clearances, as detailed in the manual, are very important. Failure to follow the exact procedure may result in bent valves. Changing the shims entails removing and replacing the camshafts without changing the cam timing.

Good Fortune!

If your valves are tight, loosen the cam bearing caps a turn or so to get clearance. then recheck compression/ leakdown to see if the tight valves being lose will correct it.

Thanks for the quick replies! I now have some direction as to what to do next.

Hopefully all will be well and I just need to set the clearances. I will post back once I get a chance to try out the suggestions.

Here is a real newbie question...once the T mark is lined up with the case mark, does that mean that all 4 cylinders are at TDC or just two of them? Edit* Never mind, I now see that there are other marks for the other cylinders.

I think I do have air escaping from the intake port while both valves should be closed. I will now loosen the caps to see if the valve seals up.

I guess the next step is to pull the head to see what the valves look like. I am in this to learn, so I might as well dive in. I now have the manual (thanks for that), but are there any common pitfalls or tricks I should know about before pulling the head off? Can I reuse the head gasket if it looks to be in good condition?

Thanks again.

No you'll definitely need a top end gasket set to have the head off. You'll need the gaskets and stem seals. It will come with a cylinder base gasket, which I would re-ring it if you do a valve job. That is if the bore clearances etc is still serviceable. That way the Top End is fresh and should run with serviceable compression for many miles with only needing a valve adjustment/ check at service intervals.

Makes sense. If I were to tear it down, I would be silly not to freshen everything up.

I just loosened the cam cap bolts and now the cylinder seems to be holding the air. I think I will go ahead and order the correct shims and see how it goes. I can always pull it apart again if there are still issues.

Thanks again for all the help, and I am sure I will be asking more questions in the near future. :blush:

That's good to hear, hopefully the adjustment will get the compression back to well within the serviceable range.

How do you order the correct shims without removing the originals and measuring them?

You did remove the cam chain tensioner before removing the valve cover?

I took off the cam according to the manual and have the shims in hand. Luckily I can read the numbers off the shim, so I didn't need to measure them.

I then used the chart in the manual to determine which shims will get me back into spec. I will go my local Kawi shop tomorrow to see what they have (they will most likely need to be ordered).

The automatic tensioner was released prior to pulling the cam, but not prior to me pulling off the valve cover. I had a section of the Haynes manual when I started. It said to pull cover off and then take off the ACT. The "bible" I just downloaded indicates to do the opposite. Hopefully it won't ruin anything, but what done is done.

When it comes to clearance, should I go to the top of the spec (0.007")? All of the exhaust are at 0.007", so I will leave those alone, but I have read a few places that say intakes should be about 0.004". I was going to open up the clearance all the way to 0.007" on the intakes as well so I don't have to worry about them.

All the intakes are at 0.0015", so I was going to drop the shims 2 sizes to make them all 0.0055". Should that be sufficient?

Thanks again.

Mid life crisis wrote: I took off the cam according to the manual and have the shims in hand. Luckily I can read the numbers off the shim, so I didn't need to measure them.

I then used the chart in the manual to determine which shims will get me back into spec. I will go my local Kawi shop tomorrow to see what they have (they will most likely need to be ordered).

The automatic tensioner was released prior to pulling the cam, but not prior to me pulling off the valve cover. I had a section of the Haynes manual when I started. It said to pull cover off and then take off the ACT. The "bible" I just downloaded indicates to do the opposite. Hopefully it won't ruin anything, but what done is done.

When it comes to clearance, should I go to the top of the spec (0.007")? All of the exhaust are at 0.007", so I will leave those alone, but I have read a few places that say intakes should be about 0.004". I was going to open up the clearance all the way to 0.007" on the intakes as well so I don't have to worry about them.

All the intakes are at 0.0015", so I was going to drop the shims 2 sizes to make them all 0.0055". Should that be sufficient?

Thanks again.

Absolutely. Always shoot for the loose end of the range and point the lobe straight away from the bucket when you check the lash.

I've had several 750 heads with chipping valve seats. Generally the chipped areas are filled with carbon so you can't tell. They chip at the top edge. Some were so bad the seats couldn't be cut. If you take the head off at some point, have the chambers glass beaded. If the seats are chipping, it will show up then.