Kz900 camshaft bearings

[thewormman]

Going to put new camshaft bearings in the head. The ones that came out looked like this, why would that be? What has caused it?

[sean_rfi]

Some of mine were very similar to the one in your photo. I posted on here and told they were fine.
They're back in the engine now and no problems....

[zed1015]

That's not uncommon and possibly due to impurites in or under the white metaling.
If you do fit new shells make sure you buy genuine Kawasaki items.
There have been many problems with the pattern ones causing shell failure and cam journal damage due to incorrect tolerences.

[BAFF1960]

I've seen various levels of high spots in original shells over the years but saying that that's an extreme example. If its original and was not causing an issue i'd still use it. I'm not a fan of pattern parts - even filters.

[thewormman]

Ok they looked knackered I'm amazed they are usable.

There are a couple though that are gone through to the yellow metal underneath are these also usable?
The cams are all good not marked.
Picture of worn through area

Markings on back of shells, are these original kawasaki?

[zed1015]

Yes! The are genuine Kawasaki.
The D5G-A is a batch code which varies and the STD is on all of them as they only come in one size and fit all Z900 through to Z/GPZ 1100 aircooled inline fours.
If they have worn through the white metal to the steel backing they are not usable.

[thewormman]

Not going to take a chance going to fit new oem ones.

Thanks for the help

[BAFF1960]

As they are worn through the white metal then they're scrap and you've made the right decision. Original shells are expensive but not as much as a set of cams. Out of interest what history and mileage has your engine had ?

[thewormman]

Out of interest what history and mileage has your engine had ?

Was supplied in Fleetwood PA USA originally in 1976, imported into UK Jan this year. It has done 34,000 miles

[thewormman]

[r3sc]

Nice tidy looking bike!

[ollie]

Good looking 900,not seen shells with those marks before ,but like Rob said it could well be impurities in the metal/oil .But i def would change them esp seeing as some have worn through.Just make sure you use genuine shells .Looks like you caught this at the perfect time .

[Kev1R]

Agree very tidy looking bike - really suits that Kerker.

[Gray17]

Strangely enough I'm just in the process of re stripping my engine down and rebuilding it after rebore (see my post). Now at the stage of refitting cams and my shells are showing same marks as yours too but luckily not in my case through the white metal. Its interesting that mine was also a us import and is same model KZ900 exhibiting identical marks and yet cams bearing surfaces are perfect. Perhaps from original like this or incorrect oil used at some point in its history?

[gray]

I suppose the highest/ furthest point in the engine is where any oil starvation or oil breakdown from poor servicing/ incorrect oil will show itself.