78 650B top end

There is a fellow named Chris Schumann who sells valve seals on ebay which are made of VITON material. From the test data I have seen on VITON, it is so much better than commercial rubber used in OEM style seals it should always be used if possible. You might check ebay and see if they have VITONs for your engine.

I found them:

cgi.ebay.com/ebaymotors/Kawasaki-Z1-KZ90...fPartsQ5fAccessories

The URL is there just above this line even if it doesn't show up. Do a "quote" on this post and you can copy it and paste it into your browser head bar. For $25, VITONs are well worth it.

Agree with bountyhunter on the viton seals. Viton is a farrrrrr better material for this application than the EPDM or Buna-N elastomers usually used because they're cheaper
.....just nowhere near as durable or suitable as viton.

If your looking for the best valve guide seals try APE...
the 900/1000 ones will fit and I can tell you that they do not leak oil - they are a better design than OEM and they are thicker so they do not deform over time.

It'd be interesting to get more info on these APE seals regarding material.
Anyone ???

In an industrial application, Viton seals are a MUST if you intend on running synthetic oil as the synthetic oil will cause a standard rubber seal to degrade and “weep” oil quite quickly.

I would suspect the same thing would be true on a bike.

My 2 cents…..

the athena valve seals are made from viton i use cometic gaskets all the time the nice thing about them is that they make bottom end only sets because when you run big motors stock size head gaskets are usless i also use there copper head and base gaskets and some fiber base gaskets[none of my motors are stock or stock size too boring]i have had good luck with them the gaskets that you get in the wiseco big bore kits are cometic by the way.and my star big block came with them as well. so they must work well

From APE web site :

VALVE GUIDE SEALS
APE seals are the best available. Won't dry out and crack.
Keeps the oil out of the motor for maximum performance.
Insist on the best.....

#99199 - KAW 650 thru 1100 - 2 valve $18.95

Cannot confirm material is Viton or EPDM without a call/email into them... what I do know is that compared to
a stock seal they are more ridgid and have an extra sealing lip, plus the retention clip is more heavy duty than the stock items.