Topic: clicking noise in front drive sprocket

[ZanVooden]

1978 CB750K.  I bought the bike used and test drove it a very short time so I don't know if the noise preexisted a rebuild.  Engine was removed, upper end rebuilt,  carbs rebuilt, forks rebuilt, swing arm, etc removed and painted.  Got it all together and have ridden it about 1,000 miles but I heard and felt a noise right from the start.  Mainly at lower speed 30-45 MPH I could feel a tapping in the right foot peg.  Almost always on decel or maybe holding a steady speed.   

I spent quite some time checking for loose parts, engine mounts, exhaust hitting, suspension parts loose, etc. and all were good.  After 500 miles I adjusted and synced the carbs, checked point dwell and timing.  Engine had been running great but I wanted to check and adjust after the initial break-in.  I add this because I have been reading other posts here about engine pulses causing driveline noise.

So after several hundred miles now I felt that tapping getting worse and could even hear a snapping type noise long with the tapping feeling.  This tapping feel can best be described as what one would feel if while sitting on the bike someone was tappiing on the bottom of the right foot peg.  This as led me to believe that the source was on the right side of the bike.  It is for this reason that I ignored the drive chain tension.  Now that the symptom has worsened I broadened my search.  This led me to a drive chain with 2"+ of slack.   I tightened the chain to 3/4" slack midpoint between the sprockets while on the center stand (as directed by the manual and from posts on this forum).  I was also conscious of the angle of the rear axle and not relying on the index marks and measuring.  The noise was unchanged.  At this point I ordered a new chain and plan to use the old sprockets since they are not showing any wear.

Tonight I installed the new chain, adjusted it as above and rotated the rear tire while on the center stand. While rotating I can hear and feel some snapping at the front drive sprocket.  I checked the retaining bolt for this sprocket and it was slightly loose.  I torqued it to spec but I still have some snapping happening in that area.  It snaps maybe about every 1 1/2 turns of the rear wheel.  I've not started it and ridden it yet because I am concerned of causing (further?) damage.

Am I unnecessarily concerned or do I need to investigate further?

[MCRider]

I'd like to see the front sprocket. I know you siad they don't look worn, But we'd like to see it. Did you change it or has it ever been changed?  I'm not one who thinks it needs to be changed with every chain, but every third chain at least. Nevertheless, it can be ruined with the original chain as you have the 630 I think which can last a long time.

And to answer your question, you must be concerned as the noise and feel is not right. It should be a nice "shoosh" sound when you spin the wheel, no sounds or pops.

So if the sprocket has even slightly "sawtoothed" teeth, it will pop and snap enough that you can feel it in the pegs. The chain sprocket interface is about the only thing that can do what you describe.

Setting the chain on the centerstand will almost always result in a too tight chain. I know that's what the manual says, but do this. Sit on the bike (or have someone else sit on it) and test the slack of the chain. If it was 3/4 inch on the centerstand it wil be tight as a rubber band with weight on it. That ain't right. And it will exagerate any feel or sound the sprocket/chain interface is making.

Adjust the chain to 3/4 inch with weight on the bike. Then put it on the centerstand. It will be more like 1 inch+. Memorize that slack as that is where you will want to adjust it on the centerstand when you don't have a buddy to weight the bike down.

A less likely issue is one of your drive output bearing. It is behind the drive sprocket. It could be in bad shape but if its so bad you can hear and feel it, you need to stop riding ASAP.

[754]

 First off, chain MUST be adjusted at its TIGHTEST spot, if you are not, you can cause extra problems..

 Second, and I have only seen this happen on 78's, the spline the front sprocket sits on can wear out, pull sprocket and check.

 Fixing this mean engine removal & splitting cases, be carefull if you swap shaft, you may have to re and re the gear on the other end.. count teeth..

[Hush]

Shot in the dark but have you replaced the chain with the same type/model that came off the bike?
Maybe the one fitted to the bike was incorrect and you have now fitted a new but incorrect chain.
There are many different sizes for chains, it's quite confusing believe me I have been there on a couple of bikes.
I'm probably wrong but if you lie down beside the bike and watch the front and back sprockets as the chain passes over them you will soon see if the chain is not fitting the sprocket teeth correctly.
Best of luck anyway finding your solution.

[ZanVooden]

Thanks guys,  I replaced the chain with 630 o-ring chain and I didn't replace the front sprocket as I felt it looked good.  Is it removed by simply removing the center bolt?

[ZanVooden]

As for chain adjustment with weight on the bike, I'll do that but right now I still have it on the center stand following the new chain install with some play (3/4") and am rotating the wheel.  I've not tried it out on the road yet since I was hearing (and feeling) the noise in this initial try after the chain install.  I'll pull the front sprocket and get a picture for you MCRider.

[754]

Take the bolt/washer off and sprocket will pull off.

 As soon as you loosen it, you will know if there is play, if the chain is off.
 Re adjusting the chain;
 Adjust it at tightest point on stand to day 1/2 inch play, then get someone to sit on the bike that weighs close to you, then check... see if it changes.. Pretty easy to figure out how much it need if setting it on the stand.

[ZanVooden]

I removed the sprocket, cleaned and and now see two, what I would say, wear areas.  On one edge of each tooth are slight dished areas about 1/16" down from the outermost portion of each tooth.  The second is on the backside of the sprocket (I believe the side that has the raised center portion around the splined senter).  There is some wear around the outer perimeter where it appears the lower part of the chain or its inner radius rides.

More concerning is that I can turn the splined shaft on the engine and can feel and hear a click as it turns.  Is some noise normal with this?

I will try to post some picutures of the sprocket

[MCRider]

As all sprockets wear, the teeth appear to get a tilt to them kind of like a saw tooth. Yours appears to have that. Holding it against a good one would tell the tale. But a new chain in a sawtooth sprocket would be noisy with clicks and pops as the rollers adjust into the pockets between the teeth.

Any appearance of saw toothing is too much.

As to the spline wear problem, I think that is unique to the 77/78 models with the 630 chain and I am not familiar with the problem, others are.

[ZanVooden]

Any recommendations for a source for a sprocket?

[754]

 The SPLINE.. check the Spline...
 On a buddies 78 the problem was the spline, and yes, it was clicking..

[ZanVooden]

Sorry, 754, I forgot to mention above that I checked the splines and they are ok.  Without the center mounting bolt and sprocket slid onto the the splined shaft there may be just a very slight amount of movement.

[MCRider]

Any recommendations for a source for a sprocket?

I see you've responded to 754 about the splines.

I'd go to a dealer and see if they have one you can look at to prove to yourself you need it.

As far as buying: dealers, motogrid.com, sunstar, sprocket specialties. Just go nuts with google and see what comes up.

Curious do you know how many miles on the original?

[Grnrngr]

looks worn to me too, got my new one from the dealer on my road trip last yr...in fact...
Big props to CARL'S HONDA in Boise Idaho, got there about 1:30 in the afternoon after they had already received their daily shipment from the warehouse, my chain and front sprocket completely toasted. They didn't have one on the shelf, so they sent someone to the warehouse, got one for me, and let me use their tools to replace it all in their parking lot. That's customer service!!

[754]

I was treated pretty good by the Honda sealer in Twin Falls Idaho last year, and the one in Salt Lake City..very low labor rates/good prices.

 Back to the shaft, if it is clicking with sprocket off, it is probably the bearing or the gear,, I am thinking, if it takes a few turns to click, it may be the big gear or the bearing.

 Try starting it, put it in gear and rev to 4 grand.. without sprocket or cover.. this will absolutely eliminate chain or sprocket caused noise..

[ZanVooden]

As for the miles on this sprocket- the bike only has shows 17,000 miles and I see no reason to doubt that.

As for the clicking:  When I had the chain on it was clicking/snapping about every turn to turn and a half of the rear wheel.

With the sprocket/chain removed I can hear a clicking noise in the transmission(?) when I turn the splined shaft.  It is more regular and I would say constant. 

Unless you guys think different, I think I will order both sprockets to go along with my new chain and see what happens.  Hopefully the noise I am hearing deeper internally when I turn the shaft is typical noise from the gears inside.

[Grnrngr]

It's another of those areas where mileage isn't as important as maintenance..my rear sprocket seemed OK considering my budget at the time, but I'll probably change it next time. My bike had 19k on the odometer but sat for a long time outside before I got it and was fairly rusted up. In spite of cleaning and oiling it, the rust I couldn't get to (and the 200-300 miles/day and the occasional ton plus run on that trip) just ate up the chain and put more stress on the front sprocket and ate it up too.

[crazypj]

It's pretty obvious its worn.
It's also more obvious it's been running out of line    (which is probably what the clicking was, chain dropping sideways).
 You need to check rear wheel spacers are in correct place , correct spacers, swing arm not bent then do alignment when you get new parts

[MCRider]

As for the miles on this sprocket- the bike only has shows 17,000 miles and I see no reason to doubt that.

As for the clicking:  When I had the chain on it was clicking/snapping about every turn to turn and a half of the rear wheel.

With the sprocket/chain removed I can hear a clicking noise in the transmission(?) when I turn the splined shaft.  It is more regular and I would say constant. 

Unless you guys think different, I think I will order both sprockets to go along with my new chain and see what happens.  Hopefully the noise I am hearing deeper internally when I turn the shaft is typical noise from the gears inside.

Yup new gear wheels can't hurt and then see what's up.

[ZanVooden]

You need to check rear wheel spacers are in correct place , correct spacers, swing arm not bent then do alignment

I agree some misalignment could be a contributing factor when I see the wear on the backside of the drive sprocket.  Is there something somewhere in the forum already covering the process of checking/confirming?

I'm not sure how I will know if I have the correct spacers or how to test this.

[Terry in Australia]

I'm interested to see where this goes, last time I rode my F2 I heard a similar clicking noise, replaced the chain and sprockets, made no difference, so put it down to my failing starter motor. (it "Gronches" a lot) I might do Franks test, then take the starter motor off and do it again and see if it eliminates the "clicking". Cheers, Terry.  

[ZanVooden]

I've ordered front and rear sprockets - hope to have them by the weekend.  I'll check for misalignment at that time.  I'll update with success or failure once installed and road tested.

[ZanVooden]

New chain and new front and rear sprockets have taken care of the noise.  I drove it about 10 miles tonight and all went well.  Will fine tune the chain adjustment tomorrow when I have someone available to sit on the bike while I check the slack.
I didn't find any reason for misalignment.  I even switched the rear axle spacers by putting the wider one on the left.  That was the direction I felt the rear needed to go but the tire would come close to hitting the swing arm.  Plus I measured another 750 and the wider one was on the right.  Apparently the wear on the side of the front sprocket was caused by the loose retaining bolt.
Thanks to all for your help. 

[Bruce845]

Sorry, 754, I forgot to mention above that I checked the splines and they are ok.  Without the center mounting bolt and sprocket slid onto the the splined shaft there may be just a very slight amount of movement.

Thank you.  I have a 1993 Nighthawk 750 making a concerning clicking noise from the drive sprocket and feared it was the bearing.  Thanks to this thread I purchased a new front sprocket and that fixed the problem.  I did notice the splines were worn and sloppy.  Did not expect that.  Not sure now if the noise came from the chain/sprocket or the splines.  The noise was most evident when I was going 30mph with no torque being applied (mostly coasting along).