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Chain Idler Questions

I pulled both chain idlers off of my P-38, cleaned everything up and put new bearings in the idlers.
One of the idlers has an O-ring inside and there is a thicker and a thinner side to this idler. It looks to be made this way, not worn thin one one side.
The other idler does not have an O-ring and both sides are the same thickness.
Does anyone know or can someone check if your idlers are the same way and if so what is the orientation of these idlers?
The way I got the bike was that the idler with the O-ring was on the front/drive and the thinner side was facing toward the frame and the other idler was on the back under the seat.
It could be that this being an older bike that these idlers are not even Lightning factory parts?

Lightning bikes have two chain idlers. The front idler is not under chain tension and lives the life of Riley. It should last an extremely long time without wearing out. Though the bearing can get contaminated and need replacement once in awhile. It is a standard size cartridge bearing. A cheap replacement should be fine. The rear chain idler - the one under your seat - is under significant chain tension and will likely wear out and need replacement every couple years, depending on how many miles you put in. The idlers are made of a very tough and long-wearing thermoplastic called Delrin. Lightning can sell you replacements.

When the idlers are new, they have a little rubber o-ring stretched around them. The o-ring makes the drivetrain more quiet, but in my experience it wears away very quickly. Like after a few rides, if the rubber reacts with chemicals in your chain lubricant. I would not worry about replacing the o-ring when it wears away. The chain should "bed in" to the plastic surface and create a toothed pattern over time.

If your idlers seem to be worn asymmetrically, you might reverse the orientation. Kind of like rotating your tires on a car. But I would not worry about uneven wear. You could also experiment with the chain line / idler interface by substituting washers of different sizes on the bolts that the idlers spin on. As long as the idlers spin freely, you should be OK.

Safe riding,
Joel

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