Rattling noise from dynamo gear

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T Batnes
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Rattling noise from dynamo gear

Postby T Batnes » Tue Dec 10, 2019 12:12 am

While turning over the engine by the kick starter (no head fitted, easy turning) there's a rattly noise/vibration coming from the dynamo gear, like it or the fibre gear beeing out of true. Dynamo is new, magneto is newly refurbished. Normal noise, nothing to worry abt?
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Re: Rattling noise from dynamo gear

Postby nevhunter » Tue Dec 10, 2019 12:31 am

Slip the gen out and reinsert it in different positions of the fiber gear and see if the gears mesh well or anythings running out of round. If OK make sure a bit of grease is on the gears and use it for a while It may well just settle in with a bit of use. Fibre gears run fairly quietly.. If the big gear is running out of true the sprocket would generally do so as well. Nev

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T Batnes
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Re: Rattling noise from dynamo gear

Postby T Batnes » Tue Dec 10, 2019 10:05 am

Could very well be that it needs to settle in. I tried to pull it, turn the dynamo gear some, refit it and tightened the strap little bit up before doing the nut up - it was little less rattly, but still. Should there be something between the dynamo body and the mag body, like a thin sheet of some insulation material or? There's the tiniest gap between the two before I tighten down the strap, maybe this is the cause of a misalignement and the noise?
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: Rattling noise from dynamo gear

Postby john.whiting » Tue Dec 10, 2019 10:38 am

Is the dynamo gear correct?...there are lots of different gears that fit the dynamo,only one is correct for the application......the wrong gear /wrong pitch will quickly chew up the fibre gear teeth.

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Re: Rattling noise from dynamo gear

Postby Brian_Walker » Tue Dec 10, 2019 11:28 am

Some new magneto fiber gears are not turned out to the correct internal diameter for the metal disk to keep them central when you tighten up the " "drag" star washer and the gear ends up running in an orbital rather than circular motion. This happened to me recently and a few minutes on the lathe and the plate ran central and drag washer snugged down properly.
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Re: Rattling noise from dynamo gear

Postby alan.moore » Tue Dec 10, 2019 6:21 pm

There is no spacer/insulation between the dynamo body and the area it seats on the top of the Magneto. On mine the dynamo makes firm contact with the top of the magneto even before the strap is tightened. I don't think the two gears should need to bed in and as Nev says they are normally quite. The are in constant mesh so there should be no rattles or vibration unless something is loose or misaligned.

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T Batnes
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Re: Rattling noise from dynamo gear

Postby T Batnes » Fri Jan 03, 2020 11:02 am

Further investigations; changed the dynamo gear for an old original one. The rattling, which was intermittent with the other gear, is now continous. My theory; the old, original gear has more wear and teeth clearence, causing rattling/back-lash between the fibre gear teeth/dynamo gear teeth. Back-lash is due to the new 12V/100w dynamo having permanent magnets, and a "rattly" feel from the coils passing the magnets, when you turn the gear by hand (same like a bicycle dynamo). The new (lower quality?) gear is probably tighter on the teeth clearence, bar from an area with higher clearance, making the intermittent clatter. I guess the clatter/back-lash will go away when rpm's are higher than when the kick-starter is turning over the engine.
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Re: Rattling noise from dynamo gear

Postby Dave.Barkshire » Fri Jan 03, 2020 1:37 pm

That sounds very loud to me. Although the fibre gear would probably bed in after a while there would be a big strain on the shaft and bearing which would be unhealthy. If the two gear wheels are too close you could try inserting a thin spacer such as a piece of biscuit tin around the dynamo to see if the noise disappears.
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T Batnes
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Re: Rattling noise from dynamo gear

Postby T Batnes » Fri Jan 03, 2020 2:45 pm

Powerdynamo in Germany sell a "Bosch" magneto, which is in fact a combined electronic ignition and 12V generator, with permanent magnets. The product can be seen here: http://www.powerdynamo.biz/eng/systems/7197/719710main.htm
This is what they write about gear backlash:
"With the unit mounted on the platform and tightened down, and with the drive cog fitted it should not be possible to rotate the cog backwards and forwards without the adjacent driving cog (usually an idler) moving. If this condition is not met then the unit may CLATTER at slow speed because the strong magnetic influence will act against the direction of the cog and take up any backlash present.
This adjustment of mesh is usually effected by placing shims between the unit and mounting platform. A worn idler may exhibit the same slow speed clatter even though the mesh is correct.
CONVERSELY if the mesh is too tight this may cause a WHINE."

Exactly as I suspect. The mesh between the two gears is to loose, and clatter at slow speed occurs. At higher revs this will not be a problem.
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: Rattling noise from dynamo gear

Postby simon.holyfield » Fri Jan 03, 2020 7:27 pm

Small point - don't forget that the magneto saddle is the dynamo earth connection. You don't want anything non-conductive in there.
Last edited by simon.holyfield on Fri Jan 03, 2020 11:22 pm, edited 1 time in total.
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