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CB750 K1 Valve Timing Question

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cbxman:
Nigel,

Some photos of the follower faces.

The transverse line on each of the valves are smooth to the finger nail touch.

Some of the tappets have irregular tips.  Not all just some, one photo shown.

I have noticed that there is wear on the No 3 & 4 exhaust rocker shafts.....  Could this be it?  Shame they can't be rotated, or can they be swapped inlet shaft for outlet shaft?

Cheers,
Jerry

Oggers:
I have an issue with erratic idling on my old Velo - which has a slide carb. The cause here seems to be worn slide or throtlle body. There is a small amount of play if you wiggle the slide which then effectively acts as an air leak. Not sure if yours has slide carbs...Another possibility is the old chestnut of a more obvious air leak somewhere. The classic is the small nozzles for the carb synchronization/balancing on the carb outlets - if you have them -  are letting in air. The sealing caps can come off. Another is the flange faces, another is the vac take off etc etc.   

Bryanj:
No vac take off, the sync ports are sealed with screws and never seen honda slides that worn

cbxman:

--- Quote from: Oggers on May 02, 2022, 12:13:56 PM ---I have an issue with erratic idling on my old Velo - which has a slide carb. The cause here seems to be worn slide or throtlle body. There is a small amount of play if you wiggle the slide which then effectively acts as an air leak. Not sure if yours has slide carbs...Another possibility is the old chestnut of a more obvious air leak somewhere. The classic is the small nozzles for the carb synchronization/balancing on the carb outlets - if you have them -  are letting in air. The sealing caps can come off. Another is the flange faces, another is the vac take off etc etc.

--- End quote ---

Oggers,

Thank you for your suggestions.

As Bryanj suggests.  These carbs show no wear at all on the sliders.  The inlet manifold rubbers are recent and are soft with the bands fully tight. Balance port is sealed with 'O' rings rather than aluminium washers.

Cheers,
Jerry

K2-K6:
Rockers are interesting as wear pattern looks pretty even, a test may be to drag some "catchy" fibre material across the surface (like a traditional yellow duster) to see if the surface picks up any fibre and give indication of surface characteristics.

Some of those adjuster screws look a bit rough from manufacturing as far as I can see. Looks like an inclusion in one of them, low risk as they don't actually have to do much.

Rocker shaft wear, obviously ideal if it wasn't there and may be one reason why there's difficulty in setting the lash as you want it. Between this and the screw tips would seem to make it tricky.

To see if the cam lobes are out one to another you'd need to put the degree disk onto the cam direct and measure that way. Must admit I've never measured a cam to that level and so wouldn't know if there's potential production variation in samples.

The inclusion on one cam lobe looks the most concerning longer term, doesn't make that much difference as it's polished away a little, but think you be speculating at longer term prognosis. 

Brutal overview, needs to be kept in perspective though as it's really quite good condition in there, is that it's at some point run with compromised oil condition (likely fuel dilution from short runs or long change interval, possibly both) as the wear surfaces appear consistent with that.

As I mentioned earlier, it does sound very good mechanically when running in comparison to others and so the above I see as very critical but overall it's not a showstopper.

Perhaps given the cam concern it would be ideal to use another cam ultimately. Can't emphasize enough that it's a very good example overall.

Nigel.

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