Topic: Broken Tooth on Sprocket

[alfego]

Just got done looking through the Search for broken sprocket teeth and would like to know how common it is to find sprockets with a broken tooth or more?  I discovered a broken tooth on the front sprocket of my '74 CB750, and I was curious how this could have happened.  There is no other evidence of serious damage, although the lower securing screw for the sprocket cover was missing and the threaded portion for the screw in the case is half gone, cracked off I imagine.  I'm gonna replace both sprockets as they are toast, the chain looks good and will check the stretch to see if it is still in spec.  Also, anybody know why there is a chain oiler on my '74, I thought they got rid of that before that year.
Alfego

[KingCustomCycles.com]

Someone will know more than I on the chain oiler year breakouts.  If the shaft is drilled, it could have been added, or eliminated easily.  I have never seen a broken sprocket tooth, front or rear, in 7 years of wrenching on over 100 vintage Hondas.

[dhall57]

My CB750K6 doesn't have a chain oiler, but I think all the years before did.

[cookindaddy]

It sounds as if a previous chain has separated and caused the damage to the sprocket and the cover retaining screw hole. Often the damage is much more severe. You should clean the area on the engine just ahead of the sprocket and look for any damage there. Like this one:
 http://forums.sohc4.net/index.php?topic=60825.msg659910#msg659910
as often the chain packs there and cracks or punches a hole in the engine case. That can be repaired with varying success. Usually the chain and the sprocket cover are toast and in your case, the sprocket as well. Perhaps a previous owner replaced the sprocket cover and the chain after the incident? This kind of damage results from running an old chain or having a chain that is too loose.

Some here suggest that both sprockets and the chain all be replaced at the same time and if the bike is otherwise in good shape, it might be worth the expense to do that for your peace of mind?

Don't know about the chain oiler, the K7 and K8 don't have them but some of the earlier ones did.

[alfego]

 I bought this bike in July and I haven't even started it yet, and I'm just going over everything to make sure all is well.  My normal maintenance proceedure on chains & sprockets is to clean the goo off of them, and there was lots of that around the front sprocket area!  There is no damage to the case and I have no idea if the sprocket cover is original to the bike.  I had never encountered broken teeth on sprockets in my 45 years of riding/repairing/and restoring, but this is my first Japanese made motorcycle.  The bike has 18,300 miles, I believe these sprockets are original, the chain looks newer for sure.  A good compadre of mine, couldn't remember when the oiler was eliminated but he thought it was before '74.  He used to be the 750 Man in its day when he worked at the Honda dealer.  But hey, lot's of water has gone under the bridge in all those years, and we sit around scratching our heads & @$$#$ a lot these days trying to remember stuff!!
Alfego