1969 Commando cam Chain Adjustment sense check

I use a ring spanner or socket wrench to rotate the camshaft backwards. This neutralizes the forces exerted by the valve gear, removes any chain slack over the tensioner block and tends to allow a more accurate reading for the top chain movement. 4mm or 3/16" is fine but try and get an intermediate gear spindle support to confirm this.

Norvil sell an intermediate support. Two versions: one for Commando and one for Dommie. (No idea why they differ...).  Nobody is likely to cut up a "spare" timing cover nowadays. My Dommie intermediate shaft moved too much until I added bearing seal.  Before that, the support was vital. Since then, not so much.

1 turn the crankshaft nut CW untiil the top chain run is tight as a banjo string (valve/spring is on any of the 4 cam opening ramp)

2 check the bottom chain run for being not to loose/tight on the adjuster/tensioner...tighten some if to sloppy.

3 holding the adjuster up lightly against the chain up with one finger, then tighten nuts.

The only left-hand thread on the big twins is on the crankshaft oil pump worm gear. Everywhere else they are right-handers. The crankshaft and camshaft nuts should be torque to 50+ Ft lbs. So should not loosen, when turned with a spanner unless the engine has seized.

It is easiest and probably quickest to purchase the Intermediate spindle support tool but making your own version out of 6mm alloy plate is not difficult. They also pop up at auto-jumbles, along with manky, corroded or damaged timing covers that could be converted. 

See attachment for simple version of support tool. use a timing cover to spot the relevant hole positions.

I am not too sure why there are different commercial versions of this tool for the Commando and Dominator engines. Possibly the answer lies in the differing intermediate gears and spindles.

I  took a cracked Dommie timing cover to make an idler tool for a Commando, the idler hole needed to be bushed to suit the Commando so there are small differences between the covers or the Dommie was modified for unknown reasons.

By chance I've just acquired the AN version of the support plate. Here are the instructions, which may illuminate the Dommie/Commando difference.

When replacing the cam chain back in 1980, I decided to check the upper run tension at several different points by rotating the engine (I know now that cam lobe loading affects the tension, but not then).  To rotate the engine, I sat on the bike, and with the plugs removed, slowly operated the kickstart with my foot while leaning forward over the tank, reaching down and gripping the chain with thumb snd middle finger - you may be guessing what happened next!  I carried out several engine rotations and tension checks, then did another rotation, forgetting to let go of the chain. My finger tip was drawn into the sprocket and the instant pain made me instinctively pull my hand away from the engine, which ripped the tip of my finger open like a flap.  A hospital visit to get the tip repaired then followed.

I didn’t try that tensioning method again!

Andy 

I have done a little more digging around and found some answers regarding the respective  Dominator and later Commando Intermediate Spindle lengths....... As follows.....

PART NO  06 7531

Fits all pre-1969 Heavyweight twins

Overall length:   2.580" (65.5mm)

PART NO 06 1078

Fits all Commandos  1969 onwards

Overall length:   2.125" (54.0mm)

This is quite a substantial difference in length....11.5mm.  The longer spindle needed to accommodate the thicker, double gear pinion of the Dominator engines. The spindle dia being around 0.561"  (14.25mm) for both.

I also was concerned at justifying the cost of a seldom used tool, but in the end decided to buy the AN one. Having used it I am sure that it was worth buying.

I have a cut-down Dommie timing cover, mesage me if you would like to borrow it.