Primary Chain Adjustment

As a rule any chain should have 1-2% of the centre distance as slack.

This applies to chain drives.

It is important to adjust the rear chain under max load as it will change with load.
So adjust for pillion. Within reason a chain cannot be too slack but can be too tight.

The power output is a bit of a red herring as torque in the drive decreases with speed
and as primary drives run at high speed........

Andy

PS Because of the high speed the Merc duplex makes a good substitute for the triplex
and I am pleases that more and more folks are using it.

Don't forget to check engine and clutch sprocket alignment (adjustable via shims on the gearbox mainshaft behind clutch hub) as well as engine drive shaft to gearbox mainshaft are parallel, in two planes 90 deg to each other. I'd be surprised if they were perfect, but it's worth checking to see what's what.

Mac ,a crude test for sleeve gear bush wear would be to bolt-down the box firm after setting recommended chain slack on upper run of the chain. Then grab the clutch basket with both leather-gloved hands and try to move it horozontally ,back and forth if you will. No sideways movements please because this is not a test for clutch wobble. Keep an eye on the chain top run and if it moves up or down from your fixed setting then you have some sleeve bush issues, only you can decide how much or little movement would have you rebuilding the gearbox. Bronze dust in box oil a sign too. Box oil entering primary other than the known pushrod tunnel path issue another. :|

willy mac said:

Hi Pete

No offense taken fella, I had the gearbox apart to check what layshaft bearing was in there a few months ago but never went as far as replacing bushes, the bearing got replaced and it's done around 750-1000miles since. The clutch drum has a wee bit of wobble but I've never really measured it till this thread came up so I might just have a wee looky again. I suppose the only way to see if the bushes are worn is to have it apart or is there another method or symptom.

Mac.

Click to expand...

We're cool, Mac.
I might think that that changing the sleeve gear bushes whenever in there should be good practice. Maybe overkill but for $9 a piece at such a critical area, it makes some sense. The other bushes are not subject to such stresses and do not ride in one spot.

I think it is also important to mic up the mainshaft were the sleeve gear runs. 1 or 2 thou out maybe exceptable but 3 or 4 may be right out.

Chains are cake.

Click to expand...

visually, they appear much more robust and therefore reliable and trouble free than a belt

The only problem I had with prior chain primaries were leaking outer covers and contaminated clutch plates.

I got so damn fed up with theses issues that I switched to a belt drive 15 years ago, problems solved.

The first belt still looked pretty good after 22,000 miles but I replaced it out of general principle.

The Mark3 really was a good solution to leakage with its oil tight multi fastener outer cover.

I must just be lucky because after installing a left side threaded gearbox adjustor I was able to easily
true the belt run and have not had to set the belt alignment or tension since original installation.

I switched to belt mostly for the weight loss. The box oil has to stay IN the box only. Nothing wrong with chain-sprockets except weight. Next thing will be battery factor. Dieting. :|

Supposeing you have the chainguard off , finger thru cap hole on primary , a hoof on the rear chain ( even the lower run )
will lift your finger if the bearings are slack or spinning in the case . Better to use your toe on rear chain . Firmly .

Matt's idea would work quite well to determine gearbox health too.

Yes and the primary/drive chain resonate flop thugging on loose tranny shafts can cause annoying isolactic hinge onset out the blue going straight or in very mild easy nicely banked sweeper. Its a good idea to flop the chains when set to correction tensions and imprint on that rhythm in case you ever feel it again drive train slackness comes to mind.

Plus a chain never wears evenly. Measure/adjust properly in one position ,rotate it a bit and get different observances. Why is that ? :|