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ET: Engine (Twin) Dynamo Sprocket


Website User
VOC Member
New discovery (for me)

PD15/1, dynamo sprocket.

While cleaning up my dynamo sprocket, it appeared to me that the gear teeth were not centered in the thickness of the sprocket. I laid the sprocket flat on a surface plate, put a dial indicator by the root of a tooth, zeroed the indicator, then flipped the sprocket over, and checked. @.015 - .018 difference. I don’t know if all sprockets are the same, or if it’s just machining differences on mine.

In my case, that means that when fitting up my dynamo to the primary drive chain, I can vary the clearance on the chain just by flipping the PD15/1 over.

Im new to all this. Has anyone else noticed this, or am I rehashing old knowledge?

Robert Watson

Well Known and Active Website User
VOC Member
As the sprocket engagement both radially and axially is held by sliding the whole dynamo in and out or rotating it to roughly centralize it on the centre row of the primary chain and give proper engagement with the rollers I can't see how you it matters.


Website User
VOC Member
My understanding of the fitting of the dynamo is as follows:

1. The face of the dynamo is supposed to be tight (but not sealed) against the back side of the primary case.
2. The dynamo sprocket is supposed to engage & operate @ in the middle of the 2nd row of the primary chain.

In order to make the above come together correctly, the factory offers 3 spacers (PD19, PD19/1, PD19/2) of varying thickness that fit between the face of the dynamo and the back side of the primary case.

However, due to the varying manufacturing tolerances, the use of the above spacers may not result in an ideal fitting.

My thought / question is: perhaps the factory purposely offset the teeth on the dynamo sprocket, so that the sprocket could be flipped over to help obtain a better fitting of the sprocket in the middle of the primary chain?

I am new to Vincent’s, so I defer to more experienced persons.

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