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A65 at what RPM do vibrations kick in #25005
05/20/07 5:22 am
05/20/07 5:22 am
Joined: Mar 2007
Posts: 8
sparta N.J.
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dave da mann Offline OP
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dave da mann  Offline OP
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sparta N.J.
Hello All,

I am resproketing an 1970L model, and was curious about what speed/rpm causes the vibes to start. I am either going with......

G-BOX/REAR WHL ----4TH gear 3500RPM
teeth 20/47 ---------------- 56 mph
'' '' '' ''21/43 ---------------- 64 mph
'' '' '' ''20/43 ---------------- 61 mph
TELL ME WHAT YOU THINK!!
what is your experiance with this subject?
TKS Dave help 2c confused

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Re: A65 at what RPM do vibrations kick in #25006
05/20/07 8:32 am
05/20/07 8:32 am
Joined: Aug 2001
Posts: 3,918
argyll. scotland, uk
gavin eisler Offline
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gavin eisler  Offline
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argyll. scotland, uk
Smooth period is 4-5,500 on my bike, gets a bit rougher the further you leave this zone.
21/ 43 is too tall for a stock 650 IMO.
You will need to change down from top to overtake briskly at 60.
Cheers
Pod


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A65 at what RPM do vibrations kick in #25007
05/20/07 9:41 am
05/20/07 9:41 am
Joined: Sep 2005
Posts: 5,963
NL
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Ger B Offline
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NL
Mine (A65T) starts to be nasty above 3500 rpm.


Ger B

Re: A65 at what RPM do vibrations kick in #25008
05/20/07 12:26 pm
05/20/07 12:26 pm
Joined: Aug 2001
Posts: 5,075
Stone Creek OH USA
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Rich B Offline

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Rich B  Offline

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Stone Creek OH USA
Go 21/47, it works. 21/43 is too tall, My LC is 20/42, which is very close to your 20/43. I seriously doubt you will ride it hard enough to make it work. 4th won't work at that ratio on a stock 650 unless your doing about 80 when you upshift. Fun, but not practical. laugh And most people are afraid to twist an A65 that hard to make it work.

My 68 doesn't even start to get noticeable until about 6k. Dynamically balanced cranks help. The 65 gets noticeable about 5500.

Do a search on this board for "packing pieces".. It gets discussed a lot recently. Nothing more than shimming the engine to fit the frame. A rigidly mounted engine does wonders. Head steady and balanced timing do wonders for A65 smoothness.


Life is too short to drink cheap, bad beer.
Re: A65 at what RPM do vibrations kick in #25009
05/20/07 12:56 pm
05/20/07 12:56 pm
Joined: Mar 2006
Posts: 1,011
43.34 (4320') | -79.81 (-794...
Gunk Offline
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Gunk  Offline
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43.34 (4320') | -79.81 (-794...
6K, I never reach a speed where vibration is a problem in normal riding.
Like Rich says, dynamically balanced.
'69 A65L

Gunk


"he who laughs fast, laughs first"~Gunk
Re: A65 at what RPM do vibrations kick in #25010
05/20/07 1:15 pm
05/20/07 1:15 pm
Joined: Jul 2005
Posts: 1,919
new jersey usa
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John RGS Offline
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J
Joined: Jul 2005
Posts: 1,919
new jersey usa
650 to 8000 RPM!


,_o
_ -\_<,
(*)/'(*)

NOPGS #2
Re: A65 at what RPM do vibrations kick in #25011
05/20/07 1:26 pm
05/20/07 1:26 pm
Joined: Apr 2005
Posts: 2,383
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
My 2 cents is; I'd figure if you're planning higher speed highway cruising 20-43 may not be too bad a trade off, I don't think I'd go taller, with a stock engine. I built a stock '70 Firebird which I fitted 21-47 and I would have liked that a bit taller 20-43 is about equivalent to 21-45, not for everyone, but it depends what you want. We use 20-40 on a hotted 750 and it pulls that easily.


mark
Re: A65 at what RPM do vibrations kick in #25012
05/20/07 11:48 pm
05/20/07 11:48 pm
Joined: Mar 2007
Posts: 8
sparta N.J.
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dave da mann Offline OP
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dave da mann  Offline OP
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sparta N.J.
Hey now,
looks like 20/43 is the winner so far.
I am going to be running highway speed most of the time. All said 21/43 was too tall, and 21/47 was a little short.
SO IF no one disagrees its a done deal!
thanks to all-Dave beerchug

Re: A65 at what RPM do vibrations kick in #25013
05/21/07 2:28 am
05/21/07 2:28 am
Joined: Feb 2007
Posts: 2,234
Atlanta, GA USA
S
Semper Gumby Offline
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Semper Gumby  Offline
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S
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Posts: 2,234
Atlanta, GA USA
I changed the 18/47 to a 21/47 on the '71 T-bolt. Makes it a much more enjoyable experience. If I was going to make it taller Iguess I'd put a 46 on the rear. Baby steps.

my .01 (since I'm still pretty new on the BSA's I don't think my comments are worth .02 yet!!!!)

My bike has a resonance at 3500 rpms and is smoother above and below. I haven't looked at shimming the motor mounts yet (but its on the list after I figure our the oil pressure thing)

Hi Ger - thanks for the pictures!!!! Your bike looks great.

Bill


Gaggle of BSAs
a Honda
an old BMW
and a Montesa
Parking lot Elf in training
Re: A65 at what RPM do vibrations kick in #25014
05/21/07 10:15 am
05/21/07 10:15 am
Joined: May 2004
Posts: 3,743
Sydney Australia
B
BSA_WM20 Offline
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Sydney Australia
If we put every A65 on this list on a dyno and determined the "sweet spot" I seriously doubt that any 2 would be the same.
Put you bike back on the road with your old chain & sprockets on and go for some nice long rides.
Note the revs & road speed where vibrations are the least in both 3rd & 4th, under acceleration, at a constant speed & on the over run.
This is called the sweet spot & it will be different for every bike.
Now decide which road speeds you are liable to spend most time riding at and gear your A 65 so your normal riding speed is some where in the middle to top 1/3 of the "sweet range".
Then go out and enjoy the pleasures of the road.


Bike Beesa
Trevor
Re: A65 at what RPM do vibrations kick in #25015
05/21/07 12:26 pm
05/21/07 12:26 pm
Joined: Jul 2001
Posts: 12,844
Central Virginia
Lannis Offline

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Lannis  Offline

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Central Virginia
I'm running 21/47 on the Firebird that I ride to work every day, including some 70-75 mph sections of city freeway. I'd never gear an A65 HIGHER than this; you'll end up spending a good part your time slipping your clutch to start up, and half of your riding time in 3rd gear to avoid lugging the engine.

21/47 gives me 65 MPH at 3600 RPM; 20/47 (which the East Coast Firebirds came with stock) is probably the best overall gearing; it's what I'll go back to when these sprockets are worn out.

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: A65 at what RPM do vibrations kick in #25016
05/21/07 2:41 pm
05/21/07 2:41 pm
Joined: Aug 2001
Posts: 5,075
Stone Creek OH USA
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Rich B Offline

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Stone Creek OH USA
20/42 - 4.35 ratio, 80 mph @ 4550 rpm
20/43 - 4.45 ratio, 80 mph @ 4650 rpm
20/47 - 4.87 ratio, 80 mph @ 5000 rpm
21/47 - 4.63 ratio, 80 mph @ 4800 rpm.

If your dealing with a stock A65, and are a typical modern day A65 rider, your delusional to think your going to make 20/43 work. A 650 is not in the meat of the power band at 4650 rpm @ 80 mph. Your going to be lugging it at speeds below that. Lugging an A65 is a good way to murder an A65. It overheats, it pings, and then dies a violent death eek

If you have a heavily modified motor (displacment increase, head work, or other major modifications), yes you can run taller gearing. If you run the snot out of it, and expect to rev to 6500+ in each gear, yes you can make it work. Most riders today, won't wring hte snot out of an A65 to achieve that.

For what I see of a "typical" A65 rider at various events, 20/47 works. For those of us who flog them, 21/47 is a good gearing arrangment. BTW, my 68 got flogged again this morning. 80+ on the way to work. And it is geared 21/47.


Life is too short to drink cheap, bad beer.
Re: A65 at what RPM do vibrations kick in #25017
05/21/07 3:09 pm
05/21/07 3:09 pm
Joined: Jul 2001
Posts: 12,844
Central Virginia
Lannis Offline

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Lannis  Offline

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Central Virginia
RichB -

Assuming that my tach is reading right, I note the following characteristics of my Firebird vs. my riding style with 21/47:

1) I spend 99% of my time between 3000 and 5000 RPM. 3000 RPM is about 50 MPH in 4th, and if I'm idling along in traffic, or in a lower gear going slower, and the engine is NOT being required to "Pull" then it's happy and non-snatchy at 3000. There's no real need to ever run it below 3000 except to idle at traffic lights.

2) If the engine is Pulling, or Cruising down the road, 3500 - 4000 RPM is a happy speed for the engine. 4000 gives me 70 MPH (corresponds to your noted 4800 RPM/80 MPH) and the bike would like to run all day like that, I think.

3) I don't use the 4500-5000 RPM range EXCEPT when accelerating through the gears. Just on general principal, I shift at 5000 RPM when moving away from a light or stop sign with no traffic in front of me.

4) The 5000-6000 range I reserve for when the Hortator calls for "Ramming Speed", coming down an on ramp, or showing the big-V-twin rider with loud pipes that he's not running away from me. 6000 RPM is "thrashing it" on my bike, and since I need it to take me lots of places this year (including OVBSAOC in August, a 1200-mile weekend for me), so I don't do much of that.

5) 6000 RPM - my self-imposed Red Line.

But that's just me, other people with other riding styles, modified engines, or shorter rebuild intervals may have something different in mind.

I'm positive that more A65 engines have been ruined by lugging them at 2000-2500 RPM, trying to emulate the low-speed performance features of a big V-twin, than have ever been blown up by too much time at high RPMS.

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: A65 at what RPM do vibrations kick in #25018
05/21/07 4:20 pm
05/21/07 4:20 pm
Joined: Aug 2001
Posts: 5,075
Stone Creek OH USA
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Rich B Offline

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Stone Creek OH USA
Lannis sez:

"I'm positive that more A65 engines have been ruined by lugging them at 2000-2500 RPM, trying to emulate the low-speed performance features of a big V-twin, than have ever been blown up by too much time at high RPMS."

Your preaching to the choir laugh . You know I feel a lot of ills of A65's can be cured by moving the right wrist. They like to rev. Lug them, and damage occurs.

20/47 was done to satisfy the American stop light drag race market. 21/47, 19/42 is closer to A10 gearing. Which is where it should be. The A65 needs to rev a bit more than an A10 to work, but not buzzing at normal speeds. The 2 different gear options based up the rear drum option gives a good compromise on gearing that suits an A65 power band.


Life is too short to drink cheap, bad beer.
Re: A65 at what RPM do vibrations kick in #25019
05/21/07 4:49 pm
05/21/07 4:49 pm
Joined: Aug 2005
Posts: 1,145
Indy
Vox Teardrop Offline
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Indy
Mine vibrates at about 5000 rpm but that's where the powerband is. Just have to live with it.


95' Triumph Speed Triple
72' Triumph T120
64' BSA Lightning Rocket
Re: A65 at what RPM do vibrations kick in #25020
05/21/07 5:49 pm
05/21/07 5:49 pm
Joined: Mar 2007
Posts: 8
sparta N.J.
D
dave da mann Offline OP
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Holy Gear Range Batman!!!!!!!!

So its nice to get shot down.
I hear the lugging=death message.
So in light of this
I now think 20/45 is the way to go as it equals 21/47.
The bike will need to do 65-70mph for 2-1/2 hours, or all day at 45mph.
Yes the motor will be totally stock,and see alot of use.

So do we agree this would be the best of both worlds?????????? Thanks :rolleyes:
Dave

Re: A65 at what RPM do vibrations kick in #25021
05/21/07 5:59 pm
05/21/07 5:59 pm
Joined: Jul 2001
Posts: 12,844
Central Virginia
Lannis Offline

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Lannis  Offline

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Central Virginia
Dave -

Sounds good to me.

Your "all day at 45 MPH" will probably be in 3rd gear though. Otherwise your engine will be turning 2600 RPM or so, and you don't want to be pulling up hills or passing cars there ....

I'm glad to hear that your A65 is going to get that much riding! Not many people mix the terms "all day" and "my A65" in the same sentence.

I've seen the Holy Grail though ... clean, oil-free A65s with full hard bags, windshields (or not), and 70,000 miles on them, 3000 of those in the last week, stock timing-side bushing and all. Thank goodness for the inspiration of the International rally!

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: A65 at what RPM do vibrations kick in #25022
05/21/07 6:14 pm
05/21/07 6:14 pm
Joined: Aug 2001
Posts: 5,075
Stone Creek OH USA
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Rich B Offline

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Stone Creek OH USA
20/45 - 4.66, 80 mph @ 4850...that will work laugh . Your going to be happier, so is your engine. It will still pull in the lower gears, be turning about the right RPM it needs to be in the power band on the road.


Life is too short to drink cheap, bad beer.
Re: A65 at what RPM do vibrations kick in #25023
05/21/07 9:50 pm
05/21/07 9:50 pm
Joined: Aug 2001
Posts: 3,348
Michigan, USA
BONZO R.I.P. Offline
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BONZO R.I.P.  Offline
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Posts: 3,348
Michigan, USA
I wouldnt go any taller than 20/47 . I do an awful lot of riding at freeway speeds and this works great for my single carb A-65 .I had a 21/47 setup a long time ago , hated it ,sent the 21 T sprocket to a good home and never thought about it again .
FWIW-BONZO

Re: A65 at what RPM do vibrations kick in #25024
05/22/07 9:44 am
05/22/07 9:44 am
Joined: Apr 2005
Posts: 2,383
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
Thing is if you have the capability to alter rear sprockets from 43-47 a 20 on the front will give you some adjustability after you try a ratio and see what you want. Rich hasn't got 20-40 on his list like our 750, or 21-36 like my 883, though it has a 17" rear wheel, it does 80 at about 3,740RPM.


mark
Re: A65 at what RPM do vibrations kick in #25025
05/22/07 12:14 pm
05/22/07 12:14 pm
Joined: Jul 2001
Posts: 12,844
Central Virginia
Lannis Offline

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Lannis  Offline

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Central Virginia
Mark -

Well yeah, but I don't think that he's assuming that part of the re-gearing process involves sawing your crankshaft into two pieces and welding it back together 90 deg out of phase, or making new camshafts, and all like that.

When you have that kind of flexibility, the options open up a bit more .... !

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: A65 at what RPM do vibrations kick in #25026
05/22/07 2:18 pm
05/22/07 2:18 pm
Joined: Aug 2001
Posts: 5,075
Stone Creek OH USA
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Rich B Offline

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Stone Creek OH USA
Mark,

I know what gearing your running, but didn't list it since your engines a bit more than stock laugh . Figured that would just add confusion to someone who is dealing with a stock A65.

Dave,

Wasn't trying to shoot you down, but just trying to make you understand an A65 typically can't handle tall gearing. You were listing ratios that, IME, would be difficult for the typical A65 rider to make work. Most people don't like revving to 6500, let alone shifting at 6500, which is what some of your choices would require. It is fun, but not practical, especially if you say riding all day at 45 mph is a requirement.

I do ride an A65 with tall gearing. It can be done, but you better be ready to ride the snot out of it. Typically, when upshifting from 1st, it is doing 40 mph. And don't even think about 4th until 80+. BTW, it isn't my daily ride. laugh But it is A LOT OF FUN.


Life is too short to drink cheap, bad beer.

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