1967 Norton N15cs primary noise

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When engine hits 3000RPM you can hear a rattling. Sounds like primary chain rubbing inner primary case. Can anyone help? Thanks
 

texasSlick

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Do you hear the noise when:

A) power is applied, i.e. engine is pulling
B) throttle is closed, i.e. engine is braking
C) throttle is neutral, i.e. engine is just maintaining speed

Slick
 

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If it is not rubbing or overly slack, maybe it has reached its service limit and protesting under load.
It might need a visual inspection.
 

texasSlick

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At the very least, remove inspection cover and check chain tension. There should be about 1/2 inch up/down movement in the chain at mid run.

Tighten if required, check for noise again. If noise persists, visual inspection is in order. Check clutch center and rollers as well.

Slick
 
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Thank you both. I’ve done the chain tension and visual inspection. I’ve replaced the primary chain but not clutch center and rollers. Would they be impacted by increased RPMs?
 

texasSlick

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Thank you both. I’ve done the chain tension and visual inspection. I’ve replaced the primary chain but not clutch center and rollers. Would they be impacted by increased RPMs?
Refer to: https://andover-norton.co.uk/en/shop-drawing/512/clutch-road-models-manx

If somehow, rollers escaped from the roller cage Item 2, the clutch would tend to wobble.
If one or more of the clutch center "paddles" of Item 12, should fracture, the clutch would wobble.

Did this noise start after you replaced the primary chain? Or was it present, and induced you to change the chain?

Report back

Slick
 
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Thank you both. I’ve done the chain tension and visual inspection. I’ve replaced the primary chain but not clutch center and rollers. Would they be impacted by increased RPMs?

+1 to what Slick writes. Additionally, it is not uncommen for main shafts to be bent. This would of course lead to a lateral (in-out) movement of the chain.
Another cause for chain virbration is stiff links due to misalignment, lack of lubrication, or corrosion.

-Knut
 
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+1 to what Slick writes. Additionally, it is not uncommen for main shafts to be bent. This would of course lead to a lateral (in-out) movement of the chain.
Another cause for chain virbration is stiff links due to misalignment, lack of lubrication, or corrosion.

-Knut
Hi Knut,
"to be bent" means that the main shaft turns eccentric?.
Piero
 
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Hi Knut,
"to be bent" means that the main shaft turns eccentric?.
Piero
IMO you can't take this for granted unless you remove the clutch and check g/box mainshaft runout with a clock gauge, because if you have rubber shocks inside the clutch, these can cause sprocket runout. . . . . .
 
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Hi Knut,
"to be bent" means that the main shaft turns eccentric?.
Piero
Yes, in the sense that for the cantilever part, at a given cross-section the shaft center will rotate around the ideal straight axis shaft center at a radius 'r'. This will also result in an angular misalignment of the clutch hub which will cause the chain to vibrate in-out and up-down.

-Knut
 
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IMO you can't take this for granted unless you remove the clutch and check g/box mainshaft runout with a clock gauge, because if you have rubber shocks inside the clutch, these can cause sprocket runout. . . . . .
I beg to differ. The clutch hub is supported by the roller bearing, whose inner bearing race is a sliding fit on the clutch shock centre, which in turn is a sliding fit on the mainshaft.
Rubber pads have no say in this chain of interacting parts. However, to rule out the effect of wear and tolerances, it's still a good idea to measure runout directly at the shaft.

-Knut
 
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