Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board BSA C15 Scrambler project .....

That worked. It just had a hex-head bolt and a spacer under there, I can't make out how the PO got it on in the first place. My son pulled up hard on the tank while I put the rattler on it, and it was off in three seconds. The frame fitting is intact, so just need a new bolt and rubber bushing....

Lannis

There are a number of different length tank bolts, spacers and rubber bushings which can be a minefield, tanks differ too so pick the replacements carefully.

kommando wrote….”There are a number of different length tank bolts, spacers and rubber bushings which can be a minefield, tanks differ too so pick the replacements carefully.”

Amen……it’s a simple set up. The “spacer” which IME seems to be missing on a lot of set ups….is the key. It places the rubber buffer where it needs to be and creates a stop for tightening the nut.

I’ve witnessed a lot of bodges which usually means something isn’t working like it should……a lot of time it’s just a carriage bolt slipped in there without a spacer.

The correct parts also help with install and removal…..kinda like the engineers who designed them had a clue.

Something I need to get a head start on ... the carburetor. I have not examined the Monoblock that is on the bike yet.

I want an easy starting, reliably idling, good running bike. ASSUMING that the existing carb body and slide are not warped or worn out, what does the panel think is the best option?

1) Rebuild the existing carb with a complete kit including correct jetting? (Given my budget goals, this would be the financially preferred option.)

2) Buy a new Monobloc?

3) Buy whatever the modern trouble free upgrade carb for these bikes is?

I don't want to do it twice. What would you guys do?

Lannis

Monobloc's were better made than the Concentrics, so if you want to stay original then a rebuilt Monobloc with sleeved slide, new jets etc would be the way to go. Exception would be if the current Monobloc body has been warped in which case go new Monobloc.

So far, the items that I've gotten from bsasingles.com have all fit and all been for the right bike. I'll order the set-up for the tank mount for this bike (including the rubber bushing, correct bolt, correct spacer, and the three rubber support spacers) by part number and I'll bet they'll be OK.

Bad news, Gordon - I thought that the short headlight ears that you sent "on speculation" would fit, but when I went to fit them up, they are about one inch too long between the top and bottom clamps. I'm hoping that parts 40-5099 and 40-5101 will be the right ones, although I'm almost crying that NOS ones are $140 a pair. Since they not only mount the headlight BUT provide a mounting flange for the tops of the gaiters, you really can't do without them unless you want your forks filling up with water..

Now that I have to pay for new ears, I will try to rebuild the existing Monobloc rather than pay $375 for a new one. The existing carb is crusty and ugly, but the slide seems to be a good fit in the bore, so I'll get a rebuild kit and add a couple things like the gas inlet fitting to it. I really don't like the stock cork push-pull petcocks, so I'll upgrade to a "modern" lever tap.

I notice that there is only one gas outlet on the tank. It looks like the gas on the other side of the tank saddle is trapped there with no way out unless you tip the bike over. Is that really how you get "reserve" on this old-timer? All my other bikes either have two petcocks, one of which is used as the reserve, or a fuel line connecting the two tank sides, with one petcock with a "reserve" standpipe.

Wiring looks pretty darn simple, especially with the high-beam switch right on the headlight shell. I'll assemble my own harness for it, I think.

Onward and upward ... Rear end is next after I get the forks back on when the next order comes in. I'll eventually get to the motor, ignition, alternator, clutch, tranny, etc ....

Lannis

I was afraid of that Lannis. Completely different part numbers but you never know until you try.

Just don’t have anything around here for those early swan necks.

I’m curious though……does the seal holder tool fit the early holders or did I strike out completely?

"Never know until you try" is correct; I couldn't tell if the ones you sent were the right size or not until I actually "offered them up" to the forks, then found that both the ears and seal holders were just a LITTLE bit too large for the C15S forks.

The seal holder tool, however, turned the fork seal installation from a bodge with a pipe wrench into a leak-free proper job. I used PTFE yellow thread sealer on the threads and gap, and predict no leaks. Thanks! I'll get it all back to you at TSMR, or send it if you need it sooner.

Into gas tanks, wiring, seat and rear end .... the spec calls for a "1/2" x .335"" rear chain. I assume that this is "520" chain in modern parlance? I know that O-ring chains won't fit an A65; will they fit (in case I decide to try it) on the C15?

Lannis

Could be 428 chain???? If you’re not in a big hurry I think I have some left over from my TL125 days??? But it’s been awhile since I looked at that stuff.

Thanks to Dennis Brown (RIP) I use X ring chain on all my unit singles.

That last unit single I purchased had 530 chain mounted on 520 sprockets…..a true testament to the versatility of a BSA.

I’m glad to hear the tool worked……so it wasn’t a completely wasted effort. I’m not planning on doing another front end this year….no worries.

I don't have any 428 Lannis.....I strike out again

BUT......if you figure out a way to use 520.....I can turn you on to one of Dennis' X ring chains. The only downside is the side plates are "pressed on" so it helps to have the correct tools to get them on and off which there's a good chance you already have those??

With my early rear hub from a B40 I used 428 chain, plenty of clearance so its X ring.

The bike should be 428 if still stock? ( as much a question as a statement) That doesn’t mean that’s what it’s set up for. Easy enough to measure the sprockets.

So the sprockets are 23 teeth on the gearbox and 68 teeth on the rear wheel, and for 428 chain. This is a .338 ratio. Stock C15S gearing was 16t front and 56 tooth rear, or a .285 ratio. I'll reread the "recommended gearing" answers to my question earlier, but my current question is ... Since both sprockets are worn and need replacing (and so does the chain), is there any advantage to installing sprockets for 520 chain, and using a 520 instead of 428?

I mean, it's not like the bike is going to make massive horsepower and pull a 428 chain in two. A 428 would be lighter (and I want the bike as light as I can make it) and it's what it had stock. Would a 520 be an upgrade or just more beef the bike doesn't need .... ?

Lannis

Be careful, look inside the primary first and check the crankshaft primary sprocket, there were 3 different teeth counts, 18.23 and 28 which will affect the overall gearing.

520 normal chain has no advantage over 428 X ring, well it will actually wear quicker and be heavier.

Good point about the primary gearing, thanks. And I'll stick with the 428 chain, and try an xring. It's all got to come apart anyhow.

Lannis

Work continues. I received a pair of NOS ($!$!) headlight ears from bsasingles in a 50-year-old original sealed package, along with the correct fuel tank mounting bolt and spacers. It's all the right stuff.

Got Rupert Ratio volume 2, so I'm researching what I'll have to do to get a proper air filter, side cover, and battery mount.

I'm replacing the cork on the Ewarts petcock, my son is working the front hub tin cover smooth, I'm cleaning and oiling the "cosmetics" (tank, bars, fork clamps, oil seal holders, wheel rims), because so far I've spent $300 on parts and $100 on books, so anything that will functionally work for this working woods-and-road bike is being reused for the sake of the budget. All the bearings, cables, rubber, and seals are being replaced, along with chain and sprockets, and I haven't even peeped into the engine yet. I still have to true up the front wheel (it's a fiddly job) and install a front tire before I can finish the front end. I'm doing the bike one section at a time - front end first, back end second, motor next, then tinware and wiring. No completely disassembled project for me any more!

I'll probably be asking for folks to root around in their parts-I-haven't-used-in-25-years stashes as I come across unobtainium things I need .... just think of the pleasure in being a part of getting a 60-year-old BSA back on the road!!!

Lannis

Hey Lannis…..

Not sure how much of a stickler you are for original, but a Yamaha TTR90 battery box can be buried in a number of places on a unit single. It uses a YT4B battery which is tiny.

The battery boxes are cheap on fleaBay, batteries are under $30 on fleaBay as well….

Thanks, good to know that that's one possible way to go. I don't know exactly what tinware I need yet ... there's a couple combinations of air cleaners and side-covers that might be "right", but I'm not going to be a stickler about originality at this point, since those things are easily upgraded later if I want.

Also, there's nothing but the ignition, headlight, taillight, and horn stressing the electrical system, so a very small 6v battery will do just fine for this.

Lannis

The LH side tool box is shaped like a mirror image of the oil tank and held on with 2 thumb nuts. There is a plate of sorts that it mounts up against. Here's a photo from my owner's manual. It is the road model but the competition models are basically the same.



The air filter is basically a joke for our drier dustier American conditions, at least the western US. And since it can be covered up with tinware, you can hide whatever you like in there.

In the UK there are lots of bantam parts which on the tinware side look like C15 but do not fit. On my battery tray I modified a C15 tray to take a later B25 type rubber band battery strap so different sized batteries could be fitted.

At the recent Talmag Trophy trials event, I managed to photo a nice BSA C15 trials bike, see below.

The bike appears to have the chrome rear Shocks you are after and also some other mods:-
- looks like the handle bar levers have been changed for modern equivalents and also the throttle.
- a hand made silencer has been used and fits snugly under the rear frame member.
- an alloy replacement oil tank has been used, dont know from where, maybe Sammy Miller parts, see http://www.sammymiller.info/
- Sammy Miller also sells air filters and side panels, so maybe worth a call.

That C15T sure has a lot of pretty mods on it to lighten it up. Probably lost 30 pounds just in the wheels! Lots of custom work there to make what looks like a competitive vintage trials bike .....

Lannis

Pretty accurate guess. That's about exactly how much putting Husqvarna wheels on my C15 lightened it up. Very much worth doing.

Tedious, tedious, tedious .....

Truing the wheels. Although the rims, spokes, and nipples are in generally good shape, the nipples have a good bit of corrosion where the spokes thread in.

So I'm having to take each spoke out by holding the spoke with pliers to keep it from turning, and use a 7mm wrench to turn the nipple, screeching and complaining all the way. Then treat the spoke and its threads with steel wool, brass brush, and oil, and turn the spoke back onto it with the wrench until the corrosion is gone and the nipple spins with fingers alone all the way down, then reinstall in the wheel.

Now I've got the wheel on a truing/balancing stand with a micrometer probe against it .... the offset is 1/8" (front) as it should be, but there's about 3/16" side to side (axial) runout, so now it's tighten/loosen/tighten/loosen/tighten/loosen ....

You gotta have patience to deal with wheels, and I'm not good at patience!!

Lannis

Truing old dirt bike wheels is no fun. Froze up nipples, bent rims. Straight spokes only makes it worse. I'd be using vice grips to keep the spokes from turning.

Have you done the bent rim roll check yet? It's super easy on a flat, smooth floor. Just roll the rim slowly away from you and watch if it rolls straight up or or if it does a quick lean to one side or other and then rights itself.

If it does the leaning thing, you have a bent rim which won't true up very well. That will really try your patience.