kz750 twin pistons/rings

Don't know about the 750 twin, but the 4 cyl. models are .004 to .007 .

Your probably going to have a tough time finding shims for the 750b.
They are for that engine only,no other KZ shares that size.
Some European model cars might share the same size.


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My valve shims that I pulled out had numbers on them. Intakes were both 260 , front left was 250 and front right was 245. After measuring these I can conclude that the front are still 250 and 245 but both rear shims measure 2.58 which is pretty close to 260. What is the gap that I should have between the shim and lobe? I don't understand why all the shims are just about what they say on them and all of them touch without a gap. Now from what my brain is telling me, If there is suppose to be a gap, and the shims are what they have written on them. That would mean who ever put these shims in did not put the correct size. I read somewhere that the gap should be between .010-.015 .If that's true then my clearances are waaaaay off.

Removing the shims before accurately measuring the clearance is a mistake. If you did that you have no way of knowing what the new shim sizes should be because you cannot measure the valve clearances with the shims out. I highly recommend you get a copy of the manual, no KZ owner should work on his bike without one. Ed

I actually just now found my manual. Lost it in a stack of papers. lol. I drew up a diagram of where each shim goes in accordance with what size it has written on it. Looked up my clearance in the manual and it says .005-.010 So looks like I will be getting a new feeler gauge with a lower measurement since mine only goes down to .008 . Also I took the shims out because I need to change my valve guides ( seals ). I took the top off and immediately noticed my front right valve on top had a puddle of oil covering the shim and so did my rear left valve. The other two were fine. I soaked it up but it just flooded out again so I take it this is another sign that the valve seals are done?

Is your bike on the center stand standing strait up ?
That oil should drain to the crank case.

If you had some oil on top of the shims (labeled #1) that is not a bad thing. That oil is intended to prevent metal-to-metal contact between the shims and cams. The valve oil seals (labeled #7) are intended to prevent oil from leaking down past the valves into the cylinders. You said you plan to replace the valve oil seals, but are you positive the current ones are bad? Ed

Bike is on kick stand, might put it on jacks if I can get my friend over to help lift it up. For now though, all is well. Has a slight tilt but shouldn't gravity take care of the rest? I might be wrong but if need be will lift it up.

I did a leak test and my compression didn't change, and from what Ive been told these seals go bad and leak oil onto the spark plug. My teacher in my college class whos a retired motorcycle mechanic told me that if My bike is at 90 for compression on both sides, that a faulty valve seal can cause that compression drop. So I went ahead and bought 4 of those Viton valve seals that I hear are much better than stock ( made sure they were for my bike). Im pretty sure its these seals, but if it isn't then I can atleast cross off valves seals from my to-do list . :lol:

Please ask your retired motorcycle mechanic to explain. Compression builds up when the valves are closed, not open. If the valves are sealing well against the valve seats in the cylinder head compression will not leak past the valves and therefore bad valve seals cannot affect compression under that scenario. If, for some reason the valves are not seating properly and compression escapes past them, it would take the path of least resistance and exit through the carbs if the intake valves are leaking or through the exhaust system if the exhaust valves are leaking. Even if the valve seals were super-duper and not allowing a scintilla of compression to leak past them the amount of compression drop caused by leaky valves would be the same. Consequently, I cannot imagine a scenario where worn or damaged valve seals can cause compression to drop. Those seals are intended to prevent oil from draining from the top of the cylinder head, past the valves, and into the cylinders. PLEASE ask your teacher to explain his theory, as inquiring minds want to understand.

Oil on the plugs can be a sign of leaking valve seals or bad piston rings; are your plugs oily? I'm not trying to rule out the possibility that you need new seals, that is certainly possible if you have oily plugs. I simply do not understand how bad seals would ever reduce compression. Ed

I myself dont know the whole compression loss valve seal theory that he was talking about . I know He was saying that compression can leak past the valves or seals . I will ask him tomorrow about that, as for my spark plugs yes they were gloss black with a very funky smell. Had both my uncle and father smell the plugs for opinions and they told me it smelled like gas AND oil which i would of figured . What are other signs of piston ring wear? is there anything else I need to test or is the leak test my only arrow of direction ?

Apologies as Im not trying to start a battle of the brains. Looking for answers from knowledgable riders . I will ask him about that though as I am curious myself. Can valves out of spec cause lowered compression in the chamber? I want to understand what can cause this Because I have had the same compression since day one when I got the bike . Tested it cold but never warm because i was too busy working on ignition stuff.

After you are sure the valve clearances are in spec check the compression again with the motor warmed up. Then put a little oil in each cylinder and check it again. If the compression increases with the oil added you probably have an issue with the rings. This check tends to work because the oi you add to the cylinders will help temporarily seal the rings against the cylinder walls, so if compression was leaking past the rings now less of it will because of the oil. If however the rings are good and the compression is leaking past the valves adding oil will not increase the compression, so valves become the likely suspect. Ed