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Discussion Starter #1
I have a '78 Honda Hawk CB400a that I commute to work on in warm weather. I want to take advantage of the cold weather to make the necessary repairs on my bike.

I have owned the bike for 4 years, it is my first. It is in very good shape for it's age.

I am mechanically inclined. I have never dismantled a motorcycle in any way. I generally do basic maintenance to cars, lawn mowers etc, on my own.

Late this summer, the bike developed an intermittent grinding noise when under hard acceleration.

I'm looking for guesses as to the cause and opinions on the "degree of difficulty" on the repair. I would guess the bike is only worth about $1000 so I'm concerned about cost also.

Comments please?

Thank you in advance.
 

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You need to try to isolate the source if the noise. I have seen clutch or rotor/stator or cam chain tensioner as the source of grinding noises
 

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Grinding noise?! What the heck?!
Any clues where it's coming from? What kind of "load"; going up a hill, real fast- what? Does this noise stay- or come and go? Does it sped up when you go faster, or is it the same volume / pitch, etc all the time, in all gears?
 

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Since you asked for guesses,here is one. Your grinding presents itself when the torque is high. Perhaps your drive chain is loose or worn/stretched,your drive sprockets are worn,or both. My bike did this once when the chain needed replaced.
 

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Discussion Starter #9
I hope I haven't waited too long to get some responses here. I haven't checked back into the forum for quite some time.

The issue still exists.

The noise occurs when accelerating hard from a stop. It seems to come from the engine. If I back off the acceleration, the grinding stops.

Once the bike is up to speed, the issue does not occur. If I baby it (who want's to do that all the time?) there is no indication of an issue.

Now that I think about it, while inspecting chain/drive sprockets, I did notice that the rear sprocket appears worn beyond what I would think is normal.

I'm a newer user and can't post a link to a photo of what I am seeing but it appears like a saw blade where the teeth are almost curved.

It never dawned on me that this could be a slipping chain....I'm really not an idiot, it just looks like it. I'm betting it's a worn sprocket.

Thanks guys. I appreciate any advice you have or can offer.
 

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Discussion Starter #11
Grinding probably isn't the best way to describe it. It isn't a violent grinding of gears.

When I accelerate hard it makes kind of a "chuck-a chuck-a" sound and you can feel a momentary jerk the bike.

If I accelerate slowly it's fine. And, once I'm up to speed, if I hit hard to go from 30 mph to 40 it's ok.
 

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Discussion Starter #12
Replaced chain and both sprockets. Feels, sounds and rides great!

Rode to work today for the first time.

Learned a lesson. I need to pay a bit more attention to those parts.
 

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Sounds like a dry or worn drive chain to me too..
I'd be on board with that too - IF the chain is in proper adjustment. Improper adjustment to the point of being too tight will make a grinding noise.

Otherwise the CM400/450A bikes only have a torque convertor and two gear sets for a transmission set up. The only internal grinding possibility would be the primary drive from the crank to the torque convertor.

I'd be looking to see if the chain is in proper adjustment, then if sprockets are hooked and if the chain can be pulled back off the rear sprocket at the 3:00 o'clock position to the point of being over 1/2 the tooth height or if you can see a gap underneath. Both are indications of a worn out chain and sprocket set.

Edit: :coffeescreen: a day late and a dollar short... story of my life...
Still I think the comment was worth leaving in general.
 
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