Author Topic: Another noise question -A7SS  (Read 4812 times)

Offline BSA500

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Another noise question -A7SS
« on: 05.04. 2016 09:21 »
Hi,
 A bit of background first....
Work done last year-New timing bush,Roller bearing,replacement big ends no wear on crank,new small ends new pistons and rebore. Rode around for a while fell off in summer *sad2*. Repaired bike and then started with horrible vibration so over winter(this year) took the engine down and found I had cocked up the shimming(twat).
 So to the present,back on the road running well etc etc(recommend the Bosch Plugs btw) , but, I have what sounds like knocking. Oh bugger you say but here's the strange thing its only at around 2,700 rpm in any gear,below or above that figure and no noise and no vibration,well nothing out of the ordinary vibration  :!. Goes well  *conf* *conf*.
 Not to push this into a particular direction I know there is some wear on the crankshaft splines.
Help
Andy

Offline BSA500

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Re: Another noise question -A7SS
« Reply #1 on: 05.04. 2016 09:25 »
Opps forgot to add I pulled the sump off last night no bits in the bottom-carry on   *smile*

Offline morris

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Re: Another noise question -A7SS
« Reply #2 on: 05.04. 2016 09:32 »
Pinking?
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Offline BSA500

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Re: Another noise question -A7SS
« Reply #3 on: 05.04. 2016 09:35 »
No pretty sure its not that. The noise -difficult to put into words-happens when I not 'on' the throttle hard just 'sitting' on 2,700 rpm with a little pull on the twist grip. Sounds rubbish I know.

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Re: Another noise question -A7SS
« Reply #4 on: 05.04. 2016 12:10 »
Does the noise come from the drive side ? if so or any way try placing a large screwdriver on the primary case and use it to listen for any noise from cush or clutch then repeat on timing side ,worth a try.Bob
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Offline BSA500

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Re: Another noise question -A7SS
« Reply #5 on: 05.04. 2016 12:50 »
Does the noise come from the drive side ? if so or any way try placing a large screwdriver on the primary case and use it to listen for any noise from cush or clutch then repeat on timing side ,worth a try.Bob

 I would say the noise does come from the drive side, but only audible when riding at the rpm mentioned so it might be tricky to shove a screwdriver up against the casings. Could be fun to try  *smile*. I have ordered a SRM cush nut and timing set as there is no way I have got the old nut up to 65 ft/lb so that is a good place to start.

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Re: Another noise question -A7SS
« Reply #6 on: 05.04. 2016 13:20 »
yes a good point ,try explaining that to mr plod er    "I was only listening for a knocking noise ,honest " hope the new bits help, bob
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Offline BSA500

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Re: Another noise question -A7SS
« Reply #7 on: 05.04. 2016 18:29 »
Bump for the evening crew

Offline muskrat

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Re: Another noise question -A7SS
« Reply #8 on: 05.04. 2016 21:26 »
G'day BSA500.
Sounds like harmonics. You know how an out of balance car tyre can be felt at between 50 and 55 MPH but not (much) above and below. Same can happen in a motor, something out of balance. The new pistons might be a fair bit heavier/lighter than the old and upset the crank balance factor.
Then it could be as simple as a loose (not tight) engine mounting bolt.
Cheers
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Offline BSA500

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Re: Another noise question -A7SS
« Reply #9 on: 05.04. 2016 22:18 »
G'day BSA500.
Sounds like harmonics. You know how an out of balance car tyre can be felt at between 50 and 55 MPH but not (much) above and below. Same can happen in a motor, something out of balance. The new pistons might be a fair bit heavier/lighter than the old and upset the crank balance factor.
Then it could be as simple as a loose (not tight) engine mounting bolt.
Cheers
Yep I hope you're right that's why I am putting the cush drive nut from SRM to eliminate a loose cush. I could never hope to tighten the original nut any where near to the 65ft/lbs required. I will check all the things you said and more. As for the balance of the crank who knows without strip dowm *sad2*

Offline metalflake11

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Re: Another noise question -A7SS
« Reply #10 on: 05.04. 2016 22:35 »
Check your chains, I had a similar problem at slightly higher revs that was due to bad wear on about six inches of the drive chain. How that happened I know not, but a new chain cured it.
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Offline BSA500

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Re: Another noise question -A7SS
« Reply #11 on: 06.04. 2016 10:11 »
I have a new chain on the primary but I will check both chains and maybe the dynamo chain as well. Its a pity you can't start the bike without the primary chain on just to eliminate chain and clutch basket noise  :!

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Re: Another noise question -A7SS
« Reply #12 on: 06.04. 2016 12:08 »
A little thing to check is the that the fuel tank is really solidly attached. I had a very strange and scary noise soon after I put my old girl back on the road. I think someone here suggested checking the tank attachments. Seems the petrol tank can resonate with vibration. I gave the attachments a good nip up and the noise went away.

Offline BSA500

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Re: Another noise question -A7SS
« Reply #13 on: 06.04. 2016 12:46 »
I feel I will be doing alot of nut nipping  *smile*

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Re: Another noise question -A7SS
« Reply #14 on: 06.04. 2016 13:45 »
I feel I will be doing alot of nut nipping  *smile*
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