Chapter 17. Tanking along

I’m getting there slowly! I’ve run a lot of marathons in my time (my other passion) and can equate this last stage of the build with that feeling I always have in the last mile, flogging along the Thames Embankment with only the right turn into Parliament Square, up Birdcage Walk past St James’s Park and the sweeping right hand bend in front of Her Maj’s pad to get within sight of the finish. It always seems to take forever to get across that finish line. However, I’ve been able to list the last few jobs for Marge on a sticky note, a couple of missing parts to buy and hopefully….

I have been trying to get out on my other bikes a bit more regularly though, as I’ve got a nice safe route sorted, have filled my five gallon jerry can with Premium unleaded, and can head off to the Surrey Hills for an hour or two of social isolation. It was the BSA C15T’s turn a few weeks ago so you can imagine my horror when as the petrol went in the top, a drip – more than a drip to be honest – started coming out of the bottom. Its one of the alloy trials tanks, I think from Terry Weedy, but can’t be sure. They’re about £300 new and annoyingly I passed up a used one the other day for a bargain basement price. My first option was to try a repair – bearing in mind I can’t weld aluminium alloy with my kit. I didn’t fancy going the Lumiweld route as all my attempts in past have resulted in either the rod not flowing or the workpiece melting. The BSA tank feels very soft so I thought the latter outcome would be most likely. Talking to others and consulting the oracle that is Google provided a variety of solutions, which as we all know provide totally conflicting answers. Its amazing that one on-line thread will say a method or technique works perfectly another will predict total disaster.

By now I had identified the cause as a pin-hole in the left hand base of the tank, less than 1 mm across, and came up with a Hybrid solution. JB Weld came across as being petrol resistant and most probably ethanol resistant, so this was the basis of the technique I planned. This is a two-part epoxy and is both tough and to a degree flexible. Having thoroughly cleaned the tank I applied a small layer over the defect and screwed a miniature self-tapping screw into the hole. This was followed by another layer of JB Weld. This was all done externally as there was no way I could get access through the filler cap. The idea of the screw was to provide a mechanical component to the repair, and I expect would have probably stopped most of the leak on its own. I left it almost a week to harden, filled up again and the repair held, except petrol now came out of another pin-hole. I had only just been able to see the first hole, but the second one was more visible, so I decided to take a photo. I wish I’d done this in the first place as by placing my phone camera on the filler nozzle the flash gave me a perfectly clear shot and revealed the extent of the problem. Here it is with the right hand side as a comparison;

 

On these tanks there is only one petrol tap on the right-hand side. A significant residue of petrol is left in the left side. The only way I have ever been able to use this “reserve” capacity is to lean the bike right over, something I’ve only done once. My guess is that over a period of time ethanol in the petrol had absorbed water. The left-hand side had tended to concentrate this water content which separated to the bottom, and during the period of inactivity led to corrosion taking place. I know many bikers drain their tanks but as in normal circumstances I try to use my bikes regularly I don’t do this. Perhaps I will have to revise my lay-up procedures. Further testing revealed that many of those visible defects had minute leaks.

I very much doubt that it’s economic to replace just the tank base, but in any case I need to wait until I can take it to an alloy welder to see what he can do – and importantly agree a firm price. I will continue search for a good used replacement but thought is was worth trying a proprietary sealer In the meantime. Another period of research of the available products came up with about six alternatives, as before with totally conflicting reviews. Those that appeared to come out best were Frost POR 15, Caswell and Tapox. Based on price and availability I went for the latter. It’s a two-part product which I purchased from Villiers services.

My tank was already pretty clean, and obviously rust was not an issue, so I repeated their cleaning instructions and blocked up the tap hole. The two parts are mixed in the larger can and then poured into the tank, followed by rolling the tank around to ensure a thorough coating. I had protected the inside of the filler cap with a couple of layers of cling film. The two-part mix is surprisingly “thin” – i.e. not at all viscous, even to the extent that it found a further minute pin-hole with the first application. At this point I applied duct-tape to the left hand base to keep the sealant in the tank. Per the instructions, after a thorough coating, I poured the residue back into the tin, resealed the lid, put in in a sealable plastic bag and popped it into the fridge. At this point in time I believe this went undetected as I placed it between a couple of ground coffee tins of about the same size. This of course may be a fools-paradise and retribution is still at the early planning stage.

24 hours later, tin extracted in a covert operation, the application process was repeated. This time I felt the layer of sealant went on a lot better. I guess you could apply it a third time but I didn’t want to push my luck on either score. Tapox requires a week to fully harden, so allowing for this I filled up with BP Premium (my research shows this has the lowest percentage ethanol) left it overnight and with no leaks next morning headed off for a great ride. The little C15T went like a dream and was treated to a photo-op at my current favourite stopping point, at the crest of Stable Lane between the Old Guildford Road and Shere. I’ll keep you posted on how the repair holds up, but if anyone sees a suitable spare tank please let me know.

Marge has also had attention to the petrol tank. You may recall from an earlier blog that the two filler necks had an unusual thread, just over 2” and 16 t.p.i. I’ve been unable to find anything to fit and was planning to turn up some bespoke caps on my lathe. This has stalled over the last few weeks as I was baulking at the price of a brass billet in the size I would require. I could have used aluminium but was not too confident it would not gall in the chromed steel filler neck. I share bike problems with my brother, and believe me I get a lot of his problems back in return. He was admiring his Royal Enfield Café racer the other day and observed the flip top cap was about the right size. He did a bit of research and found very similar units on eBay.

At this point rivet counters probably need to look away (I don’t actually think we have many / any in our team - we ride the bikes and don’t just look at them) but I found a slightly better product which is actually a retrofit kit for a new Mini. This came with a brass bezel or bush, threaded on the outside to take the cap, and I assume would be a press fit onto the filler neck. My plan was to bore out the brass bush slightly and press onto the tank. When I got the kits I measured up the bushes and their ID was 57.7 mm. My filler necks are 58.0 mm OD. Data tables gave me a thermal expansion for brass of 0.018 mm per degree centigrade, and a calculation showed that plus 75 degrees would increase the diameter by 0.45 mm, 100 degrees by 0.60 mm. A hot air gun didn’t quite get there but a few seconds with a gas torch was enough to enable the bushes to press into place and provide a very secure shrink fit to the tank. The chrome caps then screwed on to the bushes. I had the foresight to mark the angle rotation of each bush so the cap aligned correctly when tight. I’m not sure about the period look of these caps, but the Napier Railton has one, so hopefully it won’t ruffle too many feathers.

 

Otherwise progress has been limited to completing the brake linkage and pedal stop and fitting the rear tyre. The events I’ve done riding pre-war bikes has shown me that use of the rear brake is essential. Hopefully this linkage gives me enough leverage, without too much pedal travel. I hadn’t really thought about it, but the rod ends up more or less parallel to the chain stay.

When I was younger fitting a motorcycle tyre was routine, but for some reason its now a job I dread. It may be that I’ve just lost some upper body strength, or that the tyres these days have much tougher beads. The worst experience I had waw trying to fit the Pirelli Super Corsas to my Ducati. The rear went on fine but in trying to get the front tyre on I managed to damage the paint on the rim. It was an expensive mistake as I ended up taking the whole lot down to Snells in Alton, where they re-painted the rim and fitted the tyre properly. Definitely one of those occasions when I put my credit card in the payment machine and screwed up my eyes so I couldn’t see the total price. Anyway I’ve has a nice new Dunlop K70 rolling around the workshop for months now and I had to be sure it would clear the mudguard fastners, before stripping these parts down for painting. Several improvements to my procedure have made the job a little easier.

I’ve got a fixing hole in the centre of my workbench to secure the wheel and leave both my hands free.

I bought some Bike-it Tyre levers – they’re really not expensive, but seem a lot tougher than many others, are slightly longer and correctly shaped.

I use blocks of wood to hold the bead opposite the section I’m levering in the well of the rim.

And last but most importantly I apply talcum powder around the edge of the tyre. I’ve tried other lubricants but they just make the tyre hard to hold. This powder was lilac, so now the smell of my workshop somehow reminds me of my granny, but there you are.

 

The tyre fits nicely and no rework required, I now just need to get out there on a track and wear off those casting flashes.

Stay safe and well

Gareth