Primary chain tensioner

Previously John Pullen-Appleby wrote:

Hello All,

I have just put the primary side (less clutch plates etc) in to my Navigator engine and--when vainly looking for a clutch puller on the web site. I noticed two items--a nylon type primary chain adjuster and a chain tensioner backing plate.

The primary side on my old thing does not seem to have suffered as much abuse as other areas but--what I am assembling is what I got--there was no backing plate. I have a mind to knock up said plate--it appears to be about 2mm in thickness judging by the two fat washers some one seems to have stuck on the screws

What is the story with the Nylon one--there are few marks on the steel one I have although most of the slots seem to have been taken up tensioning the other reasonable looking chain.

Any thoughts anyone?

JPA

Hi John,

just checked mine, only have the nylon one, my guess is it is quieter.

Andrew

Hi JPA

The first Jubilees had a metal Pri Chain Tensioner (20778), that was (hard?) chromed on the slipper face. These did the job very well - but maybe they were costly to manufacture, or noisy in operation, or ...whatever.

The powers that be knew best, so a Nylon Block was used instead (20779). Cheaper?, quieter?, easier to assemble?, ...etc.

BUT, the metal ones would survive a trip without oil - the nylon ones do not! Worse than that (as I found to my cost once), when the nylon melts (an unlubricated chain runs VERY hot), it gets in everywhere and the chain is scrap.

The nylon block is assembled with a 'backing plate' (23677) which I would put on the outside - the chaincase itself provides the backing....

The original nylon ones where off-white in colour - NOC now stocks a black version

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20778-9-tensioner-png

here is an example of an original white nylon one in use, with the 'backing' washer shown outboard

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pri-chain-jpg