Author Topic: What Should My Primary Chain Tensioner Look Like?  (Read 193 times)

Offline DJinCA

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Some of you may remember that I pulled apart a plunger motor for parts to put my bike together (51-52 A10 GF) and that it had been somewhat mistreated before I received it (the crankcases were welded together  https://www.a7a10.net/forum/index.php?topic=14290.msg118579#msg118579)

Some previous owner welded a nut and the chain adjuster screw onto the bottom of the adjuster.  I am not sure what they were thinking, as this made the adjuster fixed in place.  I cut it loose and need to re-profile the bottom of the adjuster in some fashion.  I have a new adjuster screw and lock nut, but I don't know what this should look like.  Should it be relatively flat?  Should it have a recess for the end of the adjuster?

The tensioner I have is actually for a three row chain, as used on a Super Flash.  I have the three row sprocket, but not the clutch. I have a two row sprocket and clutch, so I will probably go forward with them.  However, I only have this tensioner.

Any guidance appreciated.

Thanks,
DJinCA




Offline a10gf

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #1 on: 11.11. 2019 13:44 »
> https://www.a7a10.net/forum/index.php?topic=2590.msg16838#msg16838

Should not look like something with a bolt\nut + welding :O) Must have been worn through.
Surely more pictures around in the forum, try search.

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Offline Swarfcut

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #2 on: 11.11. 2019 14:30 »
The original design relies on a spring plate to locate the tensioner  firmly against the crankcase, but free enough to allow it to slide  to adjust the chain. The underside of the tensioner is plain, and bears on a simple jack stud with locking nut, with a somewhat coarse Whitworth Thread for such a fine adjustment. The crankcase thread here is invariably sloppy, and a dab of Loctite and a washer under the nut is usually OK to prevent oil drips.

 They are not made with any real precision. The 90 degree bend sometimes isn't, and this results in the deeper wear pattern on one side or the other. In theory, the new chain cuts into the slipper surface, until the rollers make contact, then the rollers take the load and the rate of wear and oil contamination with metallic debris slows. The running surface is hardened by all accounts, and also has a flash of chrome to prevent wear, in some cases.

 Lining the running surface with a sacrificial material, teflon, nylon, polypropylene etc is a good mod, details elsewhere on the forum. Width of the slipper for a standard  duplex chain is 30mm measured on one I have to hand.

 Swarfy.

Online morris

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #3 on: 11.11. 2019 15:53 »
Don’t have any pictures at hand but the underside should be smooth to start with.
On mine some PO forced a metric bolt through the case so I had to make an oversize bolt and nut.
You can easily go to 3/8 WW if the need arises.
As I had to turn a new bolt anyway, I rounded off the top where it pushes against the slider.
The sliding face wasn’t too worn but I lined it with some Teflon material anyway, and that seems to withstand wear very well
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Offline DJinCA

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #4 on: 11.11. 2019 16:32 »
Thanks to all for the replies.  I have the spring/shim that goes between it and the crankcase.  I thought that I would try to grind the bottom where the nut is welded on to a flatter profile, but wasn't sure of what I was aiming for.  I will check it for a 90 degree bend and look at adding a slipper pad of nylon, teflon, etc. to the wear surface.  Mine is somewhat worn.  I have not measured the width of the slipper surface, but my thought is that if there is a wider triple row chain version, I will leave the width alone as having a little extra width there shouldn't cause any problems.

DJinCA

Offline Swarfcut

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #5 on: 11.11. 2019 18:25 »
If the original securing studs are to hand, they are shouldered to match the slotted holes in the tensioner.  Assemble the tensioner against the crankcase, followed by the spring plate. The raised areas on the plate face outwards, away from the crankcase, so tightening the nuts and washers spreads the force over the tensioner, clamping it against the case. The shoulders on the studs allow the tensioner to slide. Nuts are tightened to bottom against the shoulders on the studs. Lock the nuts with locking wire, in the usual figure 8 manner.

 The jack stud simply presses on the underside of the tensioner, so grinding off the added nut and smoothing the area for the stud to exert its force should be fine.

 Swarfy.

Online muskrat

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #6 on: 11.11. 2019 18:56 »
G'day D.
Here's a pic of my tensioner with the nylon slipper.
Cheers
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Online Greybeard

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #7 on: 11.11. 2019 19:10 »
Is that pad made from a lump of chopping board Musky?

Offline DJinCA

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Re: What Should My Primary Chain Tensioner Look Like?
« Reply #8 on: 12.11. 2019 01:01 »
Thanks Swarfy,  I must be an idiot to think that my motor, with the welded tensioner and the crankcases welded together might have been assembled correctly.   The shim/spring plate on mine was between the tensioner and the crankcase.  Thanks for setting me straight. 

Musky, thanks for the photo.  I have some PTFE on its way. 

Today (Verteran's Day holiday in the US) I ground the bottom of the tensioner to even up the bottom, including the nut previously welded on.  I also trued it up to 90 degrees.  I will fashion a PTFE pad for it and attach it with countersunk screws.

Thanks for all of the advice.  I feel that I am well on my way (at least with regards to the primary chain tensioner) to moving forward.

DJinCA