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BSA GS Engine noise #784342 09/15/19 3:39 pm
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pete Offline OP
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Hello everyone,

Went the other day for a ride with the DBD 34, and notice a knock/rattle coming from the engine only between 3000 rpm and 2500 rpm.
Before nothing, after nothing. Do it on all gears.
I check the tension of the primary chain / the tighteness of the nut of the crankshaft, tighteness of the bolts/nuts of the engine
=> All good.
Went today for a ride, the noise is still there.
I suspect a main bearing or connecting rod ?
Any thoughts ?
Many thanks.

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Re: BSA GS Engine noise [Re: pete] #784344 09/15/19 3:54 pm
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triton thrasher Online Content
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Under acceleration, deceleration, or light load? Or under all those conditions?

Engine speed frequency or half engine speed?


Amateur Loctite enthusiast.
Re: BSA GS Engine noise [Re: pete] #784349 09/15/19 4:35 pm
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pete Offline OP
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Only under deceleration, the noise appears between 3000 and 2500 rpm.
Engine speed frequency.
The engine was rebuilt by Pearson (bottom rebuilt and has a 90 mm wiseco)
I have done 3000 miles since but don't think that the noise was there since the rebuilt.

Re: BSA GS Engine noise [Re: pete] #784355 09/15/19 5:13 pm
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triton thrasher Online Content
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Unusual for an engine knock.

I think you need the clever Gold Star guys!


Amateur Loctite enthusiast.
Re: BSA GS Engine noise [Re: pete] #784382 09/15/19 9:28 pm
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I think I would check to see if something has come loose on the clutch side or the drive sprockets . If it were mains or big end I think the rattle would be on acceleration .

Re: BSA GS Engine noise [Re: pete] #784410 09/16/19 12:08 am
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Are you able to discern if it's in the bottom end or the top end? Or side to side? Are you sure it's not the fuel tank that may be up against the frame and creating a resonance at that rpm?



Bill B...


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Re: BSA GS Engine noise [Re: pete] #784481 09/16/19 4:02 pm
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pete Offline OP
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Thank you for your replies smile
I unscrew a little bit the fuel tank fixing nut (the one on the top), and the magdyno fixing nut as well and went for a ride today.
Well, the noise went away. Appears, that what I have done make the noise disapear, so all good for me !

Re: BSA GS Engine noise [Re: pete] #784497 09/16/19 6:56 pm
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It's important to keep the strap for the magdyno snug. If loose the mag will walk around and wear the platform it sits on. You may want to pull the tank up and make sure you have enough padding on the frame under the tank. There should be a rubber grommet between the tank bolt and the cupped end of the tunnel the bolt goes through. Make sure that isn't hardened from age. The end of the tunnel should be held off of the frame with the padding.


Bill B...


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Re: BSA GS Engine noise [Re: pete] #784601 09/17/19 5:26 pm
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pete Offline OP
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Thank you Bill for your reply and good advices that I will follow for sure !
Thanks again !


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