Gentle Reminder - Primary Tension

robs ss · Sep 5, 2020

Most of you guys will already know this but it creeps up on me from time to time so I thought a reminder might not hurt...
In spite of torquing the top gearbox bolt properly (and tightening the rear adjuster to push forward) I find that my primaries (3 bikes) always tends to tighten. Makes sense that the final drive will overpower the primary every time.
Just readjusted the Commando today - not a big job - but could be damaging if forgotten.
Well worth a 10 minute job!

If anyone has a secret of how to prevent this phenomenon please chip in.
Cheers
Rob

maylar · Sep 5, 2020

robs ss said:
In spite of torquing the top gearbox bolt properly (and tightening the rear adjuster to push forward)

The key here is to adjust for dead tight then bring the gearbox forward. That takes the slack out of the top bolt. If done correctly and locked down with the adjuster bolt the gearbox should not be able to move rearward.

marshg246 · Sep 5, 2020

robs ss said:
Most of you guys will already know this but it creeps up on me from time to time so I thought a reminder might not hurt...
In spite of torquing the top gearbox bolt properly (and tightening the rear adjuster to push forward) I find that my primaries (3 bikes) always tends to tighten. Makes sense that the final drive will overpower the primary every time.
Just readjusted the Commando today - not a big job - but could be damaging if forgotten.
Well worth a 10 minute job!

If anyone has a secret of how to prevent this phenomenon please chip in.
Cheers
Rob

One way is to add an adjuster to the timing side. Edit: drive side, timing side already has one!

grandpaul · Sep 5, 2020

TORQUE THEM NUTS, DUDE!

NPeteN · Sep 5, 2020

I keeps them chains loose and them nuts tight. As long as nothings rubbing or slapping I'm OKAY.

jbruney · Sep 5, 2020

I only get that wenIdoWatIshudn'tDu. For instance kicking a fiffy year old bike in the ass too hard too often.... Naughty you. For shame at your age too.

Always have to check that after I've been playing too.

ludwig · Sep 6, 2020

robs ss said:
..If anyone has a secret of how to prevent this phenomenon please chip in.

No tensioner, but a plate on each side to effectively stop the box from moving.
( here on my N15)
It has a primary belt drive, so no need for adjusting.
Maybe not practical if you ( still) run a chain..

robs ss · Sep 6, 2020

ludwig said:
No tensioner, but a plate on each side to effectively stop the box from moving.
( here on my N15)
It has a primary belt drive, so no need for adjusting.
Maybe not practical if you ( still) run a chain..

Thanks Ludwig!

robs ss · Sep 6, 2020

marshg246 said:
One way is to add an adjuster to the timing side.

Unfortunately - no room, with cNw estart (I think you meant primary side)

Matchless · Sep 6, 2020

The problem lies with the adjuster which is a poor design, as it is clamped by the top gearbox bolt which runs through it making it difficult to back off accurately. Matchless had a far better solution with the adjuster bolt behind the top gearbox bolt, meaning the chain tension could be set by pushing the gearbox back by hand against this & then tightening the top gearbox bolt. Pre unit Triumphs used a similar method to Norton but the adjuster sat over a boss which was part of the top nut, meaning once the gearbox was set & tightened the adjuster could be moved forward to push against the bolt.

Martyn.