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 GRiSO rattles

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Pete Roper
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PostSubject: GRiSO rattles   GRiSO rattles Icon_minitime1Wed Jul 15, 2015 11:01 am

Hi

Need some advice..

Once my GRiSO has warmed up I notice that in idle it rattles in neutral, (sounds like a ducati with a dry clutch but nit as loud), however if I pull in the clutch the rattle goes. So it must be clutch related right? Only thing is it sounds like its on the left hand side cylinder, so maybe tappets?? Really confused.

Thanks
Simone..
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Pete Roper
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PostSubject: Re: GRiSO rattles   GRiSO rattles Icon_minitime1Wed Jul 15, 2015 2:18 pm

Most likely poorly balanced throttlebodies or someone has messed with the throttle stop screw trying to lower the idle.

Throttle body balance is very important. The thing to remember is that crank speed is not constant. It will speed up on the power stroke and slow down as a piston comes up against compression. On a 90 degree twin with a shared crankpin this issue is exacerbated by the uneven firing intervals of 270 and 450 degrees and if one cylinder is working harder than the other it will be even more pronounced.

What is causing the rattle when the clutch is not engaged, (Lever released.) is that the input shaft and primaries in the gearbox are accelerating and decelerating with the crank and the 'Knock' is the backlash between the gears as they biff against each other first one way and then the other as the crank speeds up and slows down.

It's another reason for the slightly higher idle than in previous engines. The comparatively light flywheel, (Which is essentially a 'Battery' for kinetic energy.) doesn't do as good a job of smoothing out the power pulses of the bigger, higher compression, cylinders/pistons. If it ain't set up right it'll rattle like a bastard.

Pete
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CPB
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PostSubject: Re: GRiSO rattles   GRiSO rattles Icon_minitime1Thu Jul 16, 2015 4:06 am

^^^ Dang, ask and you receive. Some great knowledge in the ghetto. Thumbs Up
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sidrat
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PostSubject: Re: GRiSO rattles   GRiSO rattles Icon_minitime1Thu Jul 16, 2015 6:12 am

Pete Roper wrote:
Most likely poorly balanced throttlebodies or someone has messed with the throttle stop screw trying to lower the idle.

Throttle body balance is very important. The thing to remember is that crank speed is not constant. It will speed up on the power stroke and slow down as a piston comes up against compression. On a 90 degree twin with a shared crankpin this issue is exacerbated by the uneven firing intervals of 270 and 450 degrees and if one cylinder is working harder than the other it will be even more pronounced.

What is causing the rattle when the clutch is not engaged, (Lever released.) is that the input shaft and primaries in the gearbox are accelerating and decelerating with the crank and the 'Knock' is the backlash between the gears as they biff against each other first one way and then the other as the crank speeds up and slows down.

It's another reason for the slightly higher idle than in previous engines. The comparatively light flywheel, (Which is essentially a 'Battery' for kinetic energy.) doesn't do as good a job of smoothing out the power pulses of the bigger, higher compression, cylinders/pistons. If it ain't set up right it'll rattle like a bastard.

Pete

Is there nothing you don't know about the GRiSO!!!

Can you tell me where i have left my spare key??
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Blue
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PostSubject: Re: GRiSO rattles   GRiSO rattles Icon_minitime1Thu Jul 16, 2015 11:32 am

sidrat wrote:
Pete Roper wrote:
Most likely poorly balanced throttlebodies or someone has messed with the throttle stop screw trying to lower the idle.

Throttle body balance is very important. The thing to remember is that crank speed is not constant. It will speed up on the power stroke and slow down as a piston comes up against compression. On a 90 degree twin with a shared crankpin this issue is exacerbated by the uneven firing intervals of 270 and 450 degrees and if one cylinder is working harder than the other it will be even more pronounced.

What is causing the rattle when the clutch is not engaged, (Lever released.) is that the input shaft and primaries in the gearbox are accelerating and decelerating with the crank and the 'Knock' is the backlash between the gears as they biff against each other first one way and then the other as the crank speeds up and slows down.

It's another reason for the slightly higher idle than in previous engines. The comparatively light flywheel, (Which is essentially a 'Battery' for kinetic energy.) doesn't do as good a job of smoothing out the power pulses of the bigger, higher compression, cylinders/pistons. If it ain't set up right it'll rattle like a bastard.

Pete

Is there nothing you don't know about the GRiSO!!!

Can you tell me where i have left my spare key??


'Use the Force'.................
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Pete Roper
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PostSubject: Re: GRiSO rattles   GRiSO rattles Icon_minitime1Thu Jul 16, 2015 11:49 am

There's a shitload I don't know about GRiSO's but having owned both an 1100 and a 1200 and working on Guzzis professionally for nearly forty years as well as racing an older one I have a lot of experience. Stuff like the rattles holds true for any 90 degree shared crankpin design though and is basic mechanics/engineering.

If someone asks a question I can answer I'll try to. I'm actually a better teacher than I am a mechanic.

Pete
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Charlie J
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PostSubject: Re: GRiSO rattles   GRiSO rattles Icon_minitime1Thu Jul 16, 2015 12:56 pm

I found that when I moved the pin out in the clutch lever the rattle at idle was much less.
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