Found this in Sump pan

[Alimacdee2]

Hi all,
Was changing the oil and filter today, and had a look in the sump pan, found this piece of metal, thank you Santa....been over 20,000mls since I last had a look in the sump, was expecting some residue in there, looks like there's black bits off the camchain guide, and some small bits of metal, not many, and this chunk of metal which looks sheared.
The bikes running and starting fine, though there has been an on off rattle, low down at the front of the engine, seems to have gone.
Any ides what this chunk of metal might be? and the prognosis? dreading this... part of the tensioner assembly?


Ally

[UK Pete]

Yes that looks to be a dog from the gear clusters , i borrowed this picture from sohc4
pete

[LesterPiglet]

Yep. Woof woof.

[SteveD CB500K0]

Is that bad then?

[Alimacdee2]

 yes thats it alright.. will it be okay to run, until I decide if I want replace the affected gears? been no trouble with the gearbox,  think I possibly I did this last week, when putting it in gear at traffic lights and I got that rattle /screech when I messed up the change.  Dogs and gear clusters, what does the dog do??  don't think they transfer power?

[Trigger]

Nice spot Pete. Have had a couple like this. Needs more investigation but, it needs to be stripped.

[Bitsa (Ralph Wright - RIP)]

Are you sure guys the break dont look right looks snapped off to me.If it were mine it will be in bits now
Cheers
Bitsa

[tom400f]

The dogs lock a splined gear to a free one adjacent to it so locking that gear to the shaft. So yes, they do transmit power.

If that's what it is then you need to take it apart. Well in any case really...

[Alimacdee2]

Ok cheers lads.. just assessing next step,  I see now I have the option to whip the lower crankcase off without disturbing the top end, that's handy....I'm considering if thats all I should do? or a full rebuild? ...because I've had an on/off low down at the front clatter/rattle thats been worrying me for a few months, and have been thinking its the camchain guide or tensioner pulley,  I'd notice it only in first gear, just as I let the clutch out to move slowly forward parking, and occasionally at idle, would this gear problem cause intermittent noise?

And anyone know if the later K model gears are interchangeable with the K0 gears?


Ally
 

[tom400f]

You wouldn't be able to replace the camchain at least. Seems a waste not to pull it apart completely. Plus all the cleaning of the externals you could do.

That would be my choice anyway.

[Trigger]

Ok cheers lads.. just assessing next step,  I see now I have the option to whip the lower crankcase off without disturbing the top end, that's handy....I'm considering if thats all I should do? or a full rebuild? ...because I've had an on/off low down at the front clatter/rattle thats been worrying me for a few months, and have been thinking its the camchain guide or tensioner pulley,  I'd notice it only in first gear, just as I let the clutch out to move slowly forward parking, and occasionally at idle, would this gear problem cause intermittent noise?

And anyone know if the later K model gears are interchangeable with the K0 gears?


Ally

Many of the K gears are the same. The F's have some gears the same but, different main shaft.
The only gear not available on the K's is the 2nd/3rd gear but, these cogs new are stupid prices. You can replace the gear box without a top end strip but is very tricky as you have to work upside down. You will also find once you are in you may have to replace the primary and cam chain, so a full strip will be needed in the end.
A full strip is advisable as you will not be sure if any of the oil ways are clear.

[Alimacdee2]

yes, good opportunity to restore some parts and repaint the engine, I did rebuild the engine and replaced the camchain/sprocket and primary chain with original DS parts back in 1988/90 approx 40,000 ago, but didn't replace their tensioners they looked good. 40,000 on a camchain? lifespan of a camchain? with oil changed every 1000mls. It has taken a bit of a thrashing when asked though, and never complained.
 Was hoping some of the gears would match,  looks like a full rebuild then.. dissapointed I only got 18 trouble free years out of it ..It spent first 8 years to 96 in my room, should have kept it there!

[Trigger]

Chain life depends on how the bike has been used. I have seen chains flapping about after 10,000 miles and i have just stripped a K1 engine that the customer has done 72,000 miles and they look good. OEM primary chains always seem to be better and the D.I.D cam chain is ready available. The blade and wheels on these old CB750's only wear once the chains go slack.

[Bitsa (Ralph Wright - RIP)]

Ali
Nice photo where,s the drive chain gone?
Cheers
Bitsa

[SteveD CB500K0]

Dirty things those chains.

You don't want them in your bedroom.