exhaust and inlet valve sizes ?

Hello all, does any one know whether the valve sizes changed between the mk1 and mk2 z900, z1000 ? The prices vary massively on eBay (the earlier one's being cheapest) I know the head's were the same and the valves were bigger on the later j models. Any info would be welcomed. Thank you. Simon.

I would check with Larry Cavanaugh at Cavanaugh racing, he's an expert on this. :woohoo:
Regards
Ed

Valve sizes are the same for all KZ900 / 1000 prior to 81 model year. There are some things to note.

If you're looking at NOS valves what you want to watch is this. Old 900 heads had bronze guides while the 1000 heads had cast iron guides. The OEM valves are not the same for those two heads. Aftermarket stainless valves can be used in either head but where OEM valves are concerned you don't want to run an old 900 valve in a cast iron guide head.

You can run the OEM 1000's valves in either head.

LarryC wrote: Valve sizes are the same for all KZ900 / 1000 prior to 81 model year. There are some things to note.

If you're looking at NOS valves what you want to watch is this. Old 900 heads had bronze guides while the 1000 heads had cast iron guides. The OEM valves are not the same for those two heads. Aftermarket stainless valves can be used in either head but where OEM valves are concerned you don't want to run an old 900 valve in a cast iron guide head.

You can run the OEM 1000's valves in either head.

TOLD YA!! :woohoo:
Larrys the MAN!

You have to pay attention to the groove cut in the stems. 900 valves have a flat bottom groove whereas the 1000 valves have an evenly radiused groove. You cannot intermix the split keepers, but you can use the pairing of Z1/kz900 valves with their 'square' keepers on 1000 heads and the kz1000 (77-80) valves with the rounded groove and the matching keepers on Z1/KZ900 heads.

Thanks for that, my head looks to have replacement bronze guides fitted. If I could afford it I'd change them all for ape stainless one's but money is an issue. Thank you. Simon.

I think this may be where my problem lies. I had a cracked head and bought an ebay special which came without valves. It has bronze guides and I used my 79 valves . I spent ages grinding the valves in but have little compression. I thought this was down to my bores so had a
Rebore and fitted wisecos (1mm oversize) I think my next step will be to have my head pressure tested. I've fitted all new gaskets and torqued as required,. I've got fuel and spark but still not firing. It sounds as if my starters flying. It could be that I've bought a second duff head off ebay.

Maybe your cam timing is 180 off or plug wires hooked up wrong.

A leak down test should help determine the source of compression loss.

A leak down 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.

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. Or just use a portable compressed air tank.

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!

Thanks for that info. Unfortunately I do not own a compressor to do an air test.I'm thinking the problem must be at the head with the bike having a fresh rebore. I'm not sure whether to spend money on this head or look for a replacement (again) the first one I bought had a crack around one of the guides. It's a shame spare parts are so hard to come by in England and its such a heavy part to import. Thank you. Simon.

crackfox wrote: Thanks for that, my head looks to have replacement bronze guides fitted. If I could afford it I'd change them all for ape stainless one's but money is an issue. Thank you. Simon.

Stainless valves are overkill in most situations ,save the money and put it towards a cam chain and related parts if needed.

crackfox wrote: ... I spent ages grinding the valves in but have little compression....

If this means extended sessions with valve grinding compound, that isn't the proper way to achieve acceptable valve seating, and probably did more damage than good.

Good Fortune!