Tuesday, 20 October 2020

W/NG - Primary drive & clutch assembly

Now that the engine is essentially finished, we can turn the whole bike round and reassemble the primary drive. There's not enough room in the workshop to get to both sides - there are five bikes, four of them Ariels, in here at the moment.


First job is to look at the inner case and to clean up the joint face. This is a close fit, but it does contain the primary chain oil so we will fit it with a dose of Threebond.


With the inner case fitted, we will add the single internal retaining screw with some Loctite 243. You don't want this coming out in service.


You'll note that the spacer behind the shock absorber is already fitted, so we can grease the mainshaft ready for the shock absorber:


Next comes the sprocket and the splined half of the shock absorber. These look odd and confuse people because the outer half of the cam is much bigger than the inner half, and it looks like you have a mismatch of parts. Don't worry, it is supposed to look like that on an Ariel single.


Next comes the spring, cap and the first nut, followed by the special lock washer:


Then comes the second nut. The tabs on the lock washer bend alternately over the inner and outer nuts.


In the previous picture I had test fitted the clutch sprocket only to find that it was making a rubbing sound. That turned out to be this homemade oil trap and the rivets holding it in place:


You can see the witness marks on the back of the sprocket. I pushed the offending part of the aluminium ring towards the gearbox a little, and relieved the rivet heads somewhat with a riffler, which seemed to do the trick.


I've never been troubled with a leaking primary case on this bike, so this trap seems to be working.

I have some new Renold primary chain, and I need 80 pitches. I've cut it to 81 pitches just to make it easier to check - avoiding the rest of the 10' length that I bought. I couldn't get it to fit, so I checked the teeth on the sprockets - 20 on the engine and 44 on the clutch, standard for the W/NG.


I'd loosened the rear chain and moved the gearbox forward as far as it would go, but it still wasn't going to go on with 80 pitches. Eventually I walked away and took the dog for a walk, which always clears the mind. Comin back later, I found the rear wheel spindle was stuck in the frame lug and the chain wasn't as loose as I'd thought - with that free, everything fitted as it should.

When cutting chains, you can use the chain splitter from the bike's toolkit - these military bikes are very well equipped. However, if you are on the workshop, it's much better to grind the staked end of the pin off. Whilst the splitter tool will happily push a pin through, it will also separate the roller from the side plate on the inner link which you will have to fix.


Before you finally fit the chain, make sure the inner primary case joint faces have been scraped free of old gasket. do it now, or it will end up in the chain. Scrape the outer half too, and clean out the screw holes with drills or taps, whatever you need.


I use Threebond 1215 on these cases. Way over specified, but it is what I have and it's a good colour.


Did you spot this earlier? The chain is out of alignment and the outer case won't fit. I have the clutch sprocket on backwards.


That's better. fitted and screwed down; clutch next.


This is the later tab washer for the clutch basket screws. Here, I've bent the corner of each tab up a little, which is very difficult to do when they are in situ:


And here is the clutch centre with a new nut and tab washer. I have done these up tight but I will not lock any of the tab washers until I am sure that I have fixed the rubbing problem.


I'll fit the pressure plate, cups, springs and nuts and we can use the kickstart to get some oil pressure.

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