bit revvy

[spyke]

Hi Chaps

My standard ish tune A10 seems to be a bit too busy at even moderate cruising speed ie 45 , I couldnt remember what all the sprocket sizes were when I built it so Ive just stripped the primary and have found E.21
CLU.43
 GB.19
 REAR 42
This seems standard gearing according to my book?  and I was a bit surprised to find it so. I know there are charts on the forum but could someone suggest  the best way to gear it up a tad and by how many teeth.
50-55 max cruising would be fine by me.

Cheers Spyke

[MG]

Hi spyke!

Your gearing is standard, you should have below 3200rpm @ 45 mph, 3800rpm @ 55mph. Nothing to worry about, leave the throttle open in 2nd or 3rd, you'll be surprised what she'll do (75 in 3rd easily).  


The engine sprocket is the easiest one to change. 23T will give you roughly 3500rpm @ 55mph, 22T result in 3600rpm. Don't forget that a large engine sprocket will make it harder to kickstart!

Cheers, Markus

[chaterlea25]

Hi spyke,
Another thing to consider is the rear tyre size fitted?? smaller or low profile tyres make a considerable difference!!

Markus, Think again about your reasoning on a bigger engine sprocket??????????????
Bigger engine sprocket means less engine revs at kicking speed but easier to turn over
then its down to how good the mag is at lower speed
HTH
John O R

[spyke]

Tis true John I have an 18" er ( ooh ah vicar ) but its sheathed in a 4" trials tyre so should be ok, shouldnt it? 

[groily]

Running a 19 inch rear with a boring Avon SM on (circumference of just over 81 inches), I've been using a 20 on the gearbox for ages (standard on the other 3 sprockets) and it's sweet. Iron head, flat pistons, soft cam. Enough oomph (for what it is) on hills and into wind, and cruises comfortably in mid-60s all day. Very smooth to approaching 40 in second and 55-60 in third, then you notice there are large lumps under your bum. As MG says, over 70 in third is there if you want, but frankly with a soft engine  . . .

[MG]

Markus, Think again about your reasoning on a bigger engine sprocket??
Bigger engine sprocket means less engine revs at kicking speed but easier to turn over
then its down to how good the mag is at lower speed

That's exactly what I meant, John. Easier to turn the engine over, but you might have to give it a really good swing to produce enough of a spark to get it started. Getting the engine over TDC usually is much less of a problem with a twin running a lowish CR. The standard 43:21 ratio seems to be a pretty good compromise in this respect.

Cheers, Markus

[Topdad]

Hi Markus, i hadn't given that a seconds thought when i changed my engine sprocket to 23 , but I have got 17and a half stone to help swing it, regards BobH

[chaterlea25]

Hi All,
Although somewhat lighter than Topdad 
I have no problems starting my SR with 8.3:1 pistons and a 23 tooth engine sprocket (touching the nearest lump of wood )
The rear tyre I have fitted is a 100/90 x 19 which is as near to 3.50in. in height as makes no odds
It indicates 3300 rpm at 60mph (calibrated cycle speedo)
I calibrated the rev counter, driving it from a small instrument lathe with a strobe checking the chuck speed
These figures are at some variance with Markus's calculations, but tyre pressure /wear and so on all have an effect
I still feel as if it would pull a taller top gear,  ???? ????,  as it will accelerate well in top gear up some long fairly steep hills around here
Over the winter I intend to rebuild the gearbox, as its dropping some oil out the sleeve gear bush 
So I may fit a 24 tooth engine sprocket and see how it goes???

Cheers
John O R

[MG]

The tyre perimeter in my calculation spread sheet is based on rough measurement of my rear tyre's diameter, so there definitely will be some variance between different bikes with different tyres as you say, John.
Those tyres can make quite a difference also when brand new, as I know since the woes with the CSR....

[Topdad]

Shame on you John, living in Ireland with the best food in the world (probably) and the wonderful blackstuff!! I'd have thoght 17and half stone was a light weight!! Seriously It was Ireland that my wife blames for me putting on weight in the first place has back in the '70's I worked over there in Dublin for 14 weeks went out 12stone came back 14and a half worked hard but boy oh boy i enjoyed myself .Always thaought the roads were great for bikes though ,is that still the case. best wishes Bob H

[chaterlea25]

Hi Bob,
I'm struggling with my 14 1/2 stone  
I blame "proper" Irish spuds, washed down of course by some Murphys
Also agree on putting up weight working away from home, (evenings spent in the pub!!!!)

Yes, some great biking roads here, Now spoiled quite a lot by privatised speed cameras B***ards!!
I'm probably very biased towards the roads, scenery and Mountains of West Cork and Kerry, all within easy distance of home!

Regards
John O R

[Topdad]

Good morning John, are you close to Cork? I only ask as my son is greatfriends with a family that hail from there and spends quite a few weekends over there,i think there surname is Falvey ,they owna pretty big chemists. You never know could be a small world,regards BobH.

[chaterlea25]

Hi Bob,
I live near Monkstown, about 8 miles from the city
The nearset "Falveys" chemist is about 5 miles from me ( they take my cash every month LOL)
Yes, small world indeed!!!!!!!

Cheeers
John O R

[Topdad]

Hi John,wierd indeed .Next month ask if "connor " is in ,at least you'll get served by the boss -who is my Son's (rob) best mate ( was best man at my son's wedding ) How did you get into BSA's John and gain so much knowledge??  regards BobH.

[chaterlea25]

Hi Bob,
I got my first bike, A Puch Cheetah scooter, the day after I left primary school ( aged about 12?)
I was always into mechanical stuff, How I came to serve my time as an electrician is another story!!!
I had been doing mech eng at college, but with no jobs around it seemed like a good idea at the time
Anyway, I never had any money to buy a "new" or modern bike, so I ran all sorts of stuff usually gotten for practically nothing!!
I had encouragement and help from older club members which is how I got into earlier stuff,
I could always make "stuff" and people asked me to help or repair their bikes

I have always been into BSA's and had wanted a ""shiney red six fifty"  ever since I can remember 

The helping others developed into taking on various projects and restorations as a sideline,
I took voluntary redundancy two years ago and now work "almost" fulltime on Classic and vintage bikes

I dont want a full time job ???? had enough of that for 34 years

Cheers
John O R