Hi,

Sorry, this is not Kit Car related, as my Haynes Roadster is fine. But I’m currently renovating an old Kawasaki GPZ 550 from 1984 (ZX550) and there is so much expertise on this forum that I’m sure I can find help here .

Yesterday, I removed the valves from the head, and, after having given them a good clean, I saw that they were pretty marked by time. And I’m a wondering if I should change them or not.

The 2 first pictures are of an admission valve, the 2 last ones are of an exhaust valve :










I can also use the valve grinding paste, but I’m afraid it will just affect the valve seats, and not the valve itself. Am I right?

So, to your mind, should I change these valves, or use the valve grinding paste and reuse them?

Thank you.

tbh I'd bin them all and get the valve seats and new valves refaced at a machine shop. That valve second from the bottom, what a mess...

At least one of the cylinders may have been running too lean. Not sure bikes are the same but valves are usually not that expensive and getting the work done at a machine shop quite cheap. You'll really notice the performance improvement of it done properly.

Only the edge of the valve is the sealing face. You can re lap the valves by hand with some grinding paste. The pitted areas don't touch anything so not critical.
You could clean the pitted areas if you wanted by putting the valve in a lathe or pillar drill whilst facing them with some emery tape.

fazerruss is correct that it's the outer edge of the valve that performs the sealing process. IMHO the rough, pitted surface of the valve heads will cause disruption to the flow of air/fuel in and exhaust out though. Personally for the cost involved I'd replace the valves and seats to make sure you get the smoothest quickest flow possible from the rebuilt engine.

yes I looked at the first two and thought they look new, lap them and put them back in.
But the third one is a bit oof a mess
If you want to put some miles on it then replace them, but if its just a go and show bike and on a budget theyd still be ok for some time yet

Are they clean? That looks like polished carbon build up to me... If you can scratch that and leave lines ....keep cleaning and then make a decision

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Originally posted by Theshed
Are they clean? That looks like polished carbon build up to me... If you can scratch that and leave lines ....keep cleaning and then make a decision

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Clean them up on a bench grinder fitted with a wire wheel before deciding or if you haven’t got access to one try gasket stripper. Are new valves available? The valve seats do not need changing , they can be recut if pitted but try lapping before recutting . All of the valves I have seen or replaced have started to burn away from the sealing area of the seat that has started as bad pitting . Even if the seats are good is the valve stem to guide clearance OK?

Thank you very much for all your answers.

Yes, new valves are available, but normally quite expensive: more than 20 euros a piece! Si cost was an issue and that is the reason why I didn't want to buy new ones unless absolutely necessary.

But I found an add for a full set of new valves (4 admission, 4 exhaust) for 40 euros only, so I bought them, as this expense is acceptable. I'll receive them shortly.

Now for the seats.

I'd like to avoid bringing the head to a machine shop. And visually, the valve seats do not seem damaged. So can I match each seat with each new valve with valve grinding paste when I receive the new valves, and will ths be enough?

Thank you.

Check valve guides for excess play. Check seats for pitting. Grinding paste and lap them in. Should be fine?

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Originally posted by coyoteboy
Check valve guides for excess play. Check seats for pitting. Grinding paste and lap them in. Should be fine?

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