Bits of metal found near inlet valve

[AshimotoK0]

Just thought I should post a pic of the offending bike.  I dident think I would need to pull the engine apart.  So there we go.  Its not a K0.
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I did actually get the top exhaust from dss. And the bottom one from Germany (I think).

Honda never really changed/improved much in the cam chain tensioning arrangement....  Even for the 500T. The main problem is that one end of the exhaust camshaft can get poor oil supply at start-up and the associated cam lobe is often pitted. The key is to warm up the engine up fully at start up ...but yours is a USA bike so possibly never happened.  If you think that idler is hard to source ...try getting the one with one  sprocket and two rubber rollers... now that isa hen's teeth item with rollers that are not badly worn or rock hard. I took me 8 years to find a NOS one for reasonable money.

Cappellini do sell a cam cover modified to improve oil feed to the exhaust cam I believe.

[K2-K6]

I remember you chasing a source of that camshaft Ash.

It was of course part of the "Dutch" thread in topic too.

That really made me think, and alter my fundamental approach in looking at failure of this type across different engines.

There's currently something of an epidemic in car engines that moved to "reliable" cam chains as opposed to toothed belt that gives a lot of failures to examine.

This honda problem just looks like oil supply, particularly the initial phase of running after just starting. I do think synthetic oils can offer a better outcome as well ....the Dutch thread more or less proving that, in my view. Hadid go the wrong way on viscosity though as he ultimately chased oil pressure as absolute and not the "replenishment" rate at bearing sites.

Low incidence of oil replacement is fundamental  ... that now being seen with long gap in modern cars from silly service intervals. They also struggle with guide failure, often plastic in entirety, and fracture being common. But immediate supply of oil to components is of very high value, low viscosity usually helping that rather than "stalling " oil flow durometer pump by the pressure relief valve opening when cold ... effectively  causing nil supply to reach extremities through that initial period.

[nairb]

So, is there a particular reason these things fail.  Is it a poor design or an oil way that gets blocked.
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This engine has had regular mineral oil changes and not revved too hard.  Its done only? 12.5k miles. 
I am surprised it failed.  I am not looking forward to getting the cam-chain back on with all the timings correct.

Nairb

 

[K2-K6]

Do you have more detail in photos of tge failed parts ? I looked at your original image early in thread, but couldn't see everything of interest in detail.

Did the centre bearing stay intact, and what does the spigot surface (that the r9llers run) on look like ? Is the bearing free and not gummed with sticky oil  ?

Its a pretty harsh life in cam chains and their support guides etc, but that may shed some more light on it from detailed images.

Are you changing the chain, has it got obvious signs of length extending through wear ?

[AshimotoK0]

Do you have more detail in photos of tge failed parts ? I looked at your original image early in thread, but couldn't see everything of interest in detail.

Did the centre bearing stay intact, and what does the spigot surface (that the r9llers run) on look like ? Is the bearing free and not gummed with sticky oil  ?

Its a pretty harsh life in cam chains and their support guides etc, but that may shed some more light on it from detailed images.

Are you changing the chain, has it got obvious signs of length extending through wear ?

My experience (I had several used examples of that idler assembly) is that the needle roller bearing (same bearing as used on CB750/CB250/350K cam chain tensioners)  fairs pretty well ... its the teeth on the sprocket that seem to get knadgered quite badly. Also the cogged rubber roller on the cam chain tensioner gets pretty hard and chewed up too.

[K2-K6]

Interesting Ash, about the teeth. They usually wear generally if given a chain pitch out of ideal tolerance.  Suggesting that the culprit us primarily of cam chain lubrication.

It would be interesting to see the original chain on this one, wrapped around one of the sprockets, then the opposite side from the two ends pulled up to assess for wear.

The design of these looks to be marginal in that later designs (750 as example) move to more curved guide rails, ultimately this mitigates chain "twang" which can be significant contribution in cam drive arrangements.  Reducing noise too.

[nairb]

Do you have more detail in photos of the failed parts ?

Here are 3 more pics.  Nothing rotates or turns.  It all seems seized up.
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no 2
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and finally
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Still not replaced the wheel yet.... Do I drill or unscrew the centre part.

It gives the impression of lubrication failure.  But all the other wheels seem fine.
I have cleaned out the centrifugal oil filter.  It was not too bad.  Maybe I will simply re-build the top end.  I think it was factory finished and not been apart.
I did mean to add that a brand new did chain will be fitted.  I have not checked the old one.  At 12.k miles on the engine, I think it should still be service-able..... But I should check

 

[AshimotoK0]

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