Attending to Tomos #1: chain

If it looks like this you'll probably need a new one

You can be pretty sure any machine that's sat around for a while unloved will have need of  serious chain maintenance and my little Tomos was no exception. The secondary drive chain was stiff, dirty and seized in several links.

Off it came and, after a wire brushing to remove the worst of the crap, into a bath of bubbling hot oil for twenty minutes. Putoline chain wax (the large dishes you heat on the stove) is the best stuff (or make your own cheap alternative with melted candles) but I'm using up a stash of chainsaw oil which is almost as viscous, warms to a thin oil which creeps into the links and cools to a thick coating that doesn't drip.

On this occasion though, no go. Despite freeing the chain it was pretty clear it was worn beyond redemption and fit only for the bin. Fortunately, the Tomos uses a moped-standard 415 chain which is super cheap. I bought a Triple-S 415H for less than a tenner on eBay. Out of the packet it has 120 links and a split link, and the idea is you shorten it to suit the application.
 

Moped motive matter: the ubiquitous 415 chain

Tomos A3s and A35s have 90-link drive chains so you end up with 30 links as a useful back-up if any seize in use. ’Course, with proper maintenance that shouldn't happen and nor should you mix and match new and worn bits of chain but make your own mind up, for this application I'm happy to salvage wherever I can…

To shorten the chain, count backwards by the required factor, mark the link to be removed with chalk and set to with a link splitting tool if you have one. I don't cos I don't like them. I use the old fashioned method of file and punch (or in this case, the slightly newer fashioned method of grinder and punch).

The best kind of chain splitting tool

File or grind the heads off the two pins of the link you want to remove and use a punch to drive them below their link plate. As you do so the plate will spring off, freeing the link and splitting the chain. It's far easier to do than describe.

At the machine, remove the spark plug, wind the new chain over the rear sprocket and towards the gearbox sprocket until a few links engage then use the kickstarter to rotate the sprocket and chain until it reappears beneath the bike. Join the now dangling ends with the split link provided.

Everyone knows this of course but… be sure to put the retaining clip over the link with its closed end pointing in the direction of drive.

Split link: closed end in the direction of travel

Chain sorted and with the bike still on the bench, I crimped a new 2.8mm female spade terminal to the rear brake light which previously, was shorting and stuck on. I also drained and refilled the gearbox.

Rear brake light switch required new terminal

This latter requires 220ml of transmission fluid. Out of the box, the Tomos ships with Type A. I use  Type F as do many other aficionados. Cheap, easily available and fine for purpose. Your experience may differ…

Good enough!

Panhead primary palaver

A few months sitting in the corner of the garage going nowhere and my 1956 Harley-Davidson FLE panhead needed love. Working through the service I came to checking and adjusting the primary chain. Panhead primarys run inside 'tins' – pressed inner and outer covers which, despite a cork gasket, aren't oil-tight and aren't meant to be. There's no oil bath, instead, a feed from the motor's oil pump drips lubricant onto the chain as the bike runs – a bit like a Scottoiler on a drive chain. The feed rate can be varied but it's not exactly sophisticated. NB Forgive the lousy pics here – I'd rubbed a greasy finger tip over the lens without realising it…

Panhead primarys run in pressed inner and outer covers
which are decidedly non-oil tight

Sitting unloved does nothing for the health of the primary chain and, sure enough, rotating it and checking for free play through the inspection hatch, there were a couple of tight spots tighter than a very tight thing – hmm…

With the cover off it was obvious what was amiss: the chain had a murky reddish brown hue to rival the hull of an abandoned trawler. Given the hit-and-miss oiling arrangements it's not surprising Panhead primary chains are notorious for rusting and this one, despite being quite oily, was also rusty. I oiled it and rotated it this way and that for a while but it was clear that nothing useful could be done with the chain in place so it was time for a 'tear down'.

Removing the chain is a relatively simple task presupposing you can shift the nut holding the motor sprocket in place. They come in two sizes and on my bike it's 1-5/16". There now began a tedious saga of sourcing a suitable socket (which I thought I had but didn't) the bottom line of which is: don't trust the given size of an impact socket (the hex type with corner relief, not bi-hex) but measure it first with a vernier before handing over your hard-earned. I'll spare you the boring details but may document it another time.

After a tip-off from a posting on the HDRCGB forum I turned up a 33mm impact socket at, of all places, my local Halfords. Own-brand and under a tenner. It fitted fine and, with a bit of muscle from an impact wrench I borrowed from Geoffrey Chaucer, the nut was off in a blink. One tip: use a jam bar (ie a length of flat steel bar) between the motor and clutch sprockets (which has a left-hand thread) to stop the crankshaft turning when you apply force. I use an old Dunlop tyre lever which is a perfect size and shape.

With the nut off it's possible to lift away the sprocket and chain from the crankshaft and work it out from the under the lip of the inner primary and over the clutch basket. Mine was stretched and came off without even loosening the tranny.

Chain and motor sprocket removed

Examining the chain, it was obvious that two links about three inches apart had siezed. My usual strategy in this case is to get the offending link 'spitting' hot (ie not hot enough to change the metallurgy) with a blowlamp and drench it in oil, repeating the process until the link frees, but neither link would give in. Next I waited until my wife was out and then boiled the chain on the kitchen hob in a pan of thick chainsaw oil for 15 minutes but still to no avail. Bollocks! Time to shell out for a new chain.

Only to be attempted with the wife out or otherwise occupied…

Diamond is good but expensive, Tsubaki cheaper and not bad. Hello Tsubaki. About 60 quid plus postage for a 428-2 chain. Offering this up it was clear a battle was looming. I freed off the tranny bolts and adjustor but even with the gearbox moved fully forward I had to use a lever to work the sprocket with the chain back on the shaft. The trick when using a lever, of course, is not to bugger up the threads…

Tsubaki 428-2 – around 60 quid

New chain in place

Use a jam bar when tightening the sprocket nut

Anyway, 10 minutes of cursing, levering and cursing some more, and the thing was back in place. Now comes the adjusting. As mentioned above, early pan primarys are adjusted by shunting the tranny to and fro which also affects drive chain and clutch adjustment. Later models have a shoe.

Non-standard tranny adjustor can just be seen sticking out
from the rear of the mounting plate

Being rigid, the secondary chain has about a half inch of play and setting it is a simple matter of freeing off the axle nuts and turning the adjustors an equal amount to loosen or tighten the chain while maintaining wheel alignment. It's simple but a bit of a palaver! And when all that's done and both chains have their regulation half inch, everything's good and tight and the tins reinstated, there's the 'mousetrap' clutch booster to wrestle with and that device is the mother and father of all palavers! (Actually, dead easy when you know – a how-to will appear here in a future instalment.)

Reset the mousetrap, adjust the rear chain and the job's a good ’un!

Still a few jobs to do but the old pan is once more readied for fun!