I bought my 1970 A65 many years ago, this summer I rebuilt the engine and gearbox replacing a couple of gears which had worn.
I had forgotten when I got it there was a second gearbox, looking at it I think it is a close ratio one.
I seems to me the 2nd gear is STD the rest is C/R, I was curious to know why, does it make practical sense.
The teeth are
Main Lay
1 16 24
2 22 26
3 22 18
4 23 17
A quick Look suggest the correct second gears (23 25) are like hens teeth, any suggestions?
I also wonder for a daily use if it makes no sense fitting it. I have read fitting 1 nd 2 or 2 and 3 can be good?
Thanks
Those numbers look a bit odd. There will be one constant set and three pairs of indirect gears since 4th is direct. Each ger should be the constant pair x the gear pair.
Normal
4th 1 : 1
3rd 1.144 : 1
2nd 1.6 : 1
1st 2.31 : 1
Close
4th 1:1
3rd 1.107 : 1
2nd 1.47 : 1
1st 2.03 : 1
I'm looking at the original A50 / A65 workshop manual and its anything but clear as it does as lot of "as per A50" or "as for A65" so you have to keep flipping pages.
Reading between the lines it looks like a lot of the US models (it refers to "West Coast") had close ratios with lower overall gearing (smaller gearbox sprocket) to get better 1/4 miles times. So whereas we would use a CR box with a high 1st overall they used it with a std 1st and low 3rd and 4th.
I have an original 1970 parts book and the teeth look right except 2nd which appears to be from a standard box.
Main. Lay
1 14 26
2 22 26
3 26 22
4 23 17
Thank for the ratios so I think they teeth are right except 2nd, which would give
2.03:1
1.60:1 instead of 1.47
1.11:1
1.00:1
Although I think my first on the STD cluster is 2.51:1 and not 2.31:1.
I am not sure it is worth fitting for normal use.
Thanks
I think you would find 2nd too close to 1st then a big gap to 3rd. I think it would feel wrong.
The manual doesn't have the teeth numbers so they don't make it easy!
Hi,
The second gear pair and the third gear pair are same in a STD box but reversed on the shafts. This means that by switching them the far less worn side of the cogs and dogs are used perhaps quietening down a whiney third gear and improving engagement. This also means that the second gear pair from a CR box can be fitted in place of a STD third gear pair. With me so far? The result is that the gap between STD second and third is reduced and the closeness of STD third and fourth is widened. This gives ratios a bit more like those of a STD A10 box.
I did this to make long climbs a bit easier on the engine. Often, to maintain reasonable momentum the engine either had to be revved like the clappers in second of almost laboured in third. Making the change meant that third would pull quite a happily.
Dave.
I know what you mean, its a pity they didn't fit a 5th gear.
I put a larger sprocket on the gearbox and it transformed it. OK first was rather high but once you were moving the gears made a lot more sense. Mine was a '71 OIF and when I took the clutch off the case was relieved to fit the teeth of the bigger sprocket so it could be slid on without stripping the box so BSA had clearly planned for this.
Maybe helpful
I live in an area where the roads are very hilly - 1in3 in several areas as well as long inclines where headwinds are the norm. I have gone for a 19 tooth front, standard rear, also hope to do some gentle off-roading - (not ridden it yet)
That diagram is really helpful, pity they didn't put that in the manual :D
The best thing I did on my bored and stroked A65 was fit a close ratio 2nd into 3rd gear position. It brings 3rd gear closer to 2nd. Making it a more enjoyable ride and a more useful gear.
For road use I wouldn't recommend most people bothering with the close box. Unless of course using that 2nd gear as mentioned (Thankyou to Dave Brady for the suggestion).
A close ration 3rd in a standard box is a complete waste of a gear. You might as well change straight into top.
I had a close box in my Lightning, but it's also tuned a little over standard. Different cam, higher compression, taller gearing too and I managed to run well with the close ratio setup - providing I wasn't riding in a group. Get on a group run and you're only using the first 2 gears. Don't forget the close box is setup for racing, the rpm drop is suited best for running at around 7500-8000 rpm, dropping you into the next gear at the power band.
I refitted the std box in my Lightning to make it more enjoyable and practical in group riding.
Hope this appraisal helps.
Hello
Thank you to everyone for the insight it is very helpful.
Cheers
Matthew