Finally got my carb issues sorted out on the SS80, and I took it for an hour-long ride this morning. My question is this - what's a comfortable cruising speed for you other C15 owners?

I'm finding once I get around 45-50, the bike still performs well, but it feels almost like it's a little under-geared. Given the Achilles heel of these bikes, I don't want to come anywhere close to thrashing it. I would hope to be able to cruise at 50 without stressing the engine.

Thanks,
Dean

I have a C15S that I deliberately geared high. I have to slip the clutch a little from a dead stop but then the high gearing comes into its own. I don't remember the engine sprocket (which should be the standard one) but with the 52T rear sprocket I put on it the bike has a calculated redline of 84 mph. It cruises very nicely at 45 mph and does 65 mph (i.e. 77% of redline) for 5-10 miles at a time w/o problem.

Dean,

SS80 was so named because BSA claimed the C15SS could get up to 80 mph. Well perhaps down a long hill with a tail wind. What is the Achilles heel with the bikes other than spaghetti forks, small brakes and lack of power? The engine is more robust to misuse than the much peppier B25 motor.

You bike comes with a 45 tooth rear sprocket. What do you have on the gearbox? 17 or 18 teeth would be about right.

Peter

Thanks guys!

Peter I have a 17 tooth sprocket. I know that the early C15s had fragile bottom ends, but it seems like nearly everything I've read about the SS80 mentions that they weren't particularly reliable, especially when thrashed by their often young owners. I've never read anything specifically on what fails on them though. I just figure for a 50 year old 250cc bike, I don't want to hammer on it.

Dean

The SS80 had steel flywheels and roller bearing big end, the normal C15 started with cast iron flywheels and plain bush big end. Your SS80 is not bullet proof but not going to die next week either. I stuck a 28T instead of the 23T engine sprocket on a SS90 B40 and it still went well.

At 65 you ass and hands will go numb so you won't be riding at that speed very long even if you could.

Ahh, I'm not looking for 65, but a steady 50 would be good.

Kommando, with your 28T engine sprocket, did you have to slip the clutch much at takeoff? I'm planning on doing the same mod to a B40FE, but don't want to totally lose all off-road capabilities. Any recommendations on the other sprockets?

Sorry for the swerve of topic!

Steve,
not much extra over before the change but never took it off-road. It was a funny beast, SS90 cam and head but also ported, B44 piston in shortened barrel with C15 barrel studs and shortened pushrods. It was a std B40 bottom end but I added the needle roller timing side main bearing conversion. Gearbox bushes were its Achilles heel, forever changing the mainshaft one in the timing inner cover so an F type would be a good. It was in a 1969 B44 frame, 17T gearbox and 52 on the rear wheel.

Dean, A steady 55-60 should be no problem. Yes, it might vibrate a bit but it shouldn't be unbearable. If it is, you should look at the engine mountings and make sure packing washers are installed where there are gaps and that nothing is being forced. It's amazing what a difference that will make. The only real achilles heel on these is the layshaft thrust arrangement in the gearbox. This gave them the reputation of having "weak" gearboxes. On a road bike it's easy to prevent this from being a problem though by minimizing the amount of time spent with the clutch pulled and don't rev the engine with the clutch pulled. If it's already knackered, there is a fix.

Performance wise, make sure your jetting and your timing is right. Strobe timing is essential for the latter...the "distributor" makes static timing too unreliable.

Other than that, they really are pretty robust but were subject to much abuse by hamfisted wannabe cafe racers with L plates who made their reputations suffer.

I have the same setup on mine and it works really well. Cruises well at 60-65, easy passing at 75-80 and, given enough time it will definitely do 90.

Yeah, and then your conrod will come up and hit your chin!

Happen to you a lot?

Mind you the taller gearing helps here because there is another weakness, particularly in the C15S/SS and that is that with low gearing they will pull right past where they should. The roller big ends don't like revs over 8000 rpm (the rollers don't roll any more, they slide). This I know from experience . Mind that limit, though and a properly assembled roller big end will tolerate just about anything other than running out of oil.

The C15 doesn't get the respect it deserves, largely because of people repeating things they had heard of problems suffered 50+ years ago by the very earliest non-roller bearing engines.

My C15S (with roller bearing) suffered ~5000 miles of hard use at my hands before I turned it over to John O'Regan in Cork, Ireland to undo the cumulative damage I had done. I've subsequently put another ~1000 miles on it, with all ~6000 miles spent making it keep up with the 500s and 650s I ride with when I'm using that bike in Ireland.

As I wrote in an earlier post I have my C15S geared for a redline of 84 mph and it purrs along effortlessly at the 45 mph many of the roads limit it to. However, when needed to keep up with the bigger bikes on main roads it goes miles at a stretch at 65 mph, with power to pass cars even at that speed. However, I try to limit top speed to 65 because the bike is located thousands of miles from me so I want it to last a reasonable length of time between major work.

Two more things about a C15S. Wherever roads limit top speeds to ~45 mph a 250 performs as well as a 500. Or, even better, in that it is more maneuverable. Also, at the end of a long day, when it's time to start the bike one last time for the ride back to the hotel, kickstarting a 250 is a lot nicer than kickstarting a high compression 500.

Thanks Alex!

I will have to strobe time it, and I've only just sorted out the jetting. I ended up going with a new Concentric. It's close and certainly rideable as is, but still a tick rich.

Dean

Thanks Magnetoman - I appreciate you taking the time to share your experience with this.

It's a bit of a pain since you have to take the primary cover off and have to make your own marks, but well worth it.