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Thread Like Summary
Allan G, Gary E, gavin eisler, Mark Parker, NickL, pushrod tom
Total Likes: 11
Original Post (Thread Starter)
by Semper Gumby
Semper Gumby
Perhaps I should be on the competition board but I thought I'd query the BSA collective first.

The Hornet Race bike Transmission (67 frame and a 71 motor) has left me High and Dry for two races now and i'm am unhappy.

What is going on: The transmission is dragging in neutral. I miss diagnosed the problem as the wrong shim on the layshaft but what I think is happening is gear(s) are push down the shaft toward the primary side and loading the shim on the primary side. I can feel something slipping which I thought was the Newby jumping a tooth but I think its in the transmission. As soon as I feel the slip in WOT I know that soon the bike will be dragging down on power.

When I remove the shim the rear wheel spins freely so when last I was there we machined a shim that would allow the wheel to spin freely. After one lap at Little Taledega today the bike is dragging again and now I cannot find CR2nd and CR3rd. Things are obviously out of position and STD1st and STD4th gears does not a race bike make.

I'm also running a Bob Newby Clutch and the SRM outrigger bearing. Fellow racer Mike Baker suggests I find the spec of where the fixed gears are supposed to be along the Lay Shaft and I can see the wisdom in that but I am worried that I am going to walk the gears around again in race conditions and end up with dragging and miss shifts. So any advise on how to accurately trouble shoot and attack this problem would be greatly appreciated.

Thanks in Advance.
SG - resting at wits end.
Liked Replies
by gavin eisler
gavin eisler
It seems like one of the fixed gears has moved on a shaft, if this is the case, then you need to find out why , there shouldnt be side loads on the gears if they all line up properly, i dont think the belt drive / newby clutch has anything to do with it.

i fitted an outrigger when I put in the 5 speed , same as Marks, havent had any issues with it, I did add a few more screws, and fitted them all with studlock.

possibly the sleeve gear bush is tight that would give drag in neutral.It would be OK in 4th when its direct drive,, and get more draggy in the lower gears.
2 members like this
by JER.Hill

I think you want to give "Barber" a miss and sort your engine out, your scatter gun approach to your issues is pretty hard to follow. There have been plenty helpful suggestion to your possible problem and methods of assemble.
I'd suggest you fix your crank float before to start with before you junk the motor. Fix the crank float them move on the the G/B. If the gearbox is dragging to the extent you say, then there will be signs inside showing heat and wear to give you and indication where to look first.
If you have a junk timing side casing, cut the crank area off and section the gearbox area, this will allow you to assemble the G/B and see what's going on in there, you'll learn a lot (yes I know all G/B layshaft shimming is different with each casing).
If your 4th L/S gear is being pushed off the shaft, then the shaft is worn.
One or two degrees is all you'll need to back cut the gears.
As Nick said it takes time and patience to get these boxes working good.

My tuppence worth

2 members like this
by Mark Parker
Mark Parker
Getting off the line for short races is talked about in the US quite a bit. I don't know if std 1st addresses that effectively because I've never tried it, but we use 20-40 with C/r 1st on a 750 And 20-38 on another C/r with 17" wheel, and neither take much to get going, or probably more to the point is once they get on the boil a straight should sort out who goes in front anyway? Getting good drive after you get away would be what I'd concentrate on, you still need to get away smartly without breaking anything, but a harder drive will soon round you up.

Wide gaps between high gears does people no favours. I watched video of Phantom's lovely Triumph with a big std 4-5th gap up a long straight, shifting into it meant bikes just keeping with him came past every lap, Kawasaki triple I think. That 4-5th gap is far bigger than a std BSA 3rd and 4th which is very good. Quaife made an A65 5speed with worse ratios than the 4 speed, big gap to top like the Triumph? Getting it right like the PES box helps the motor at every change. I think the C/r BSA 3rd was for 500s at Daytona trying to keep near peak power. I think the PES 4th is near that but with an extra gear and 1st is a little lower than the C/r 1st because it's spread over 5. The C/r 1st and 2nd make the 4speed very nice. But the taper on the main-shaft isn't great.

[Linked Image from]
1 member likes this
by Mike Baker
Mike Baker
I think the cr v std debate is not really the issue that needs to be addressed at this point. Bill takes the disappointment at the track well but if he can't get this bike sorted soon I fear my friend throwing in the towel. With the rear wheel raised bike in neutral, grabbing and turning the wheel feels like lifting weights. Much resistance. When he told me that it was fixed by grinding a shim smaller I knew it was not a true fix. Shims do not grow. I have known Triumph gearboxes where press fit gears have "migrated" on the shafts. Is it possible that could happen to a A65 causing a clearance to tighten up? Are there specs/ measurements of where gears should be on shaft? Something has moved, that much is obvious. Most likely scenario?
Thanks from a racer that would like to see a BSA finish a weekend without drama.
1 member likes this
by Mark Parker
Mark Parker
The beauty of these gearboxes is that they are a cassette. They can be inspected out of the case. Assuming you shim end float out of the lay shaft hold it and check gear engagement, the sliding gear may not go right in both ways so you can weld a track and file it to get it. But you problem is bigger than that so look closely at everything. Everything around the belt as well.
1 member likes this
by NickL
The stock gears have no rake/angle on the dogs, the twisting motion of the
shafts is what pushes them out of selection The shafts bow with the transmitted torque.
You are relying on the dog engagement and the camplate/selector forks to hold the gears
together. That's why shimming and getting full location is so important with these boxes.
A slight rake on the dogs will make the change slower but if you can live with that it will
improve matters. Too much cut angle will prevent high speed gear change and will knock
the dogs out more quickly. Getting the hardening right will not be easy, you could have
a stock gear tested first and try it at that.
The simple solution for your endfloat problem is to just use a ball race on the drive side.
That's all i have in the 750 race outfit i prepare at the moment, it won't live as long as a
roller but unless you plan to do the TT every month it'll be fine for a couple of years.

The engine is far from ordinary, it won more sidecar races in Europe and the UK than any
other back then, just put together well. Chris Vincent, Peter Brown etc never even used
an end feed setup, nearly all the troubles were with gearboxes not being able to handle
the power they were getting from the a65 engine. I used to push and beat 1200cc honda
4's with my old crate, you wouldn't have got a triumph twin to come anywhere near. we tested
a 650 at a meeting a few weeks ago up against an 840 triumph and a 920 norton, both had
5 speeds and both ran on methanol, Won 3 races out of 6. Not bad for a 650 eh?
1 member likes this
by JER.Hill
Hi Semper

Right. I understand now what you are referring to as "float", you are referring to work expansion. The timing side combo Brg is fine, you do not have to do anything to the crankshaft, so you can cut this from the conversation.
Now what you are identifying to us, is that your drive pulley is locking out on the crank spline and not against the inner race of the roller Brg as it should be.
Changing from the combi Brg back to bush is a none starter and just giving your self way more work.

What you need to do is determine your issues and concentrate on correcting them.
1) Inspect your pulley, spacers and identify all components are correct and shim to correct.
2) Pull the G/B, find and address the issues found, reassemble correctly.
3) Assemble the clutch and check/correct alignment as necessary.
Focus on what your issues are and correct, not jump around all over the place.

my tuppence worth

1 member likes this
by JER.Hill

So complicated. There are three types of people in the world, those good at maths and those that aren't.

I'll try again: This has the John Hill PES 5speed as well. This looks like a spread sheet I made up.

I had it so that you change primary and secondary gearing, wheel Dia and change speeds and everything else would change for you.

This site is rubbish as far as trying to add photo's or spread sheet. If you want to send me an email I'll send you the sheet. My email is [email protected]

1 member likes this
by NickL
So Mark, now do you believe me about the gearboxes?
It can be more dangerous than annoying when you come out of
a left hander at full noise with a drift on and the bloody thing jumps
out of gear, it makes you wish you were wearing brown leathers.

Like all the experts that tell you outrigger bearings aren't necessary.
1 member likes this
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