The BSA A7-A10 Forum

Technical => Frame => Topic started by: Goldseeker on 12.07. 2010 19:11

Title: Identifying Speedo & Rev Counter
Post by: Goldseeker on 12.07. 2010 19:11
I'm hoping that someone can help me to check the speedo and rev counter fitted to my recently acquired RGS replica. The engine has been verified by BSAOC as a 1960 DA10R. Gearbox is an RRT2. I'm interested to know if these are correct for the period and application. Any information or pointers to where info could be found would be much appreciated.

The speedo is a Smiths Chronometric marked with these numbers- 'SC5301/09' and 1476 below.
Rev counter Smiths Chronometric marked with RC1303/03.
Title: Re: Identifying Speedo & Rev Counter
Post by: MG on 12.07. 2010 20:21
There you go.


Speedo SC 5301/09:

AJS/MATCHLESS 16C/G3C 1960-61
                       18CS/G80CS 1960-61
                       31CS/G12CS 1960-61

INDIAN Fury 500 1960
          Interceptor 692 cc 1960
          Westerner 500cc (G80CS) 1960-61
          Typhoon 600cc (G80TCS) 1961

TRIUMPH TR5A Competition (Export Only) 1961-62
             TR6 Trophy 1961-62
             T120 Bonneville 1960


Rev counter RC1303/03

BSA A10 Super Rocket 1961-62
      A10 Spitfire Scrambler 1961
      A10 RGS 1963

HTH, Markus
Title: Re: Identifying Speedo & Rev Counter
Post by: RichardL on 12.07. 2010 20:24
Goldseeker,

The number here that I am rather certain I understand is the "1476". This represents the number of turns per mile, or, the number of turns per minute to indicate 60 MPH. To verify your requirements:

1. Put bike in neutral and on the center stand.
2. Create some means to conveniently count cable rotations while rotating the rear wheel.
3. Mark the rear wheel and the ground or floor below it so that you have a good indicator of whole turns.
4. Rotate the rear wheel counting its turns and turns of the cable until both are whole numbers.
5. Now, I'm going to be a little arrogant and send you to my previous post where the math is explained:

http://www.a7a10.net/forum/index.php/topic,701.msg4399.html#msg4399

The other numbers are still a mystery to me. I hope this helps.

Regards,

Richard L.
Title: Re: Identifying Speedo & Rev Counter
Post by: bsa-bill on 12.07. 2010 20:47
Quote
previous post where the math is explained:

Richard mate do what you want with the tea but please leave our language the way you found - it's maths, with an s
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 12.07. 2010 21:28
WOW! so quick, can hardly believe it, thanks.

So Speedo is not a BSA fitment, shame but does it matter? Markus, can you tell me what the number should be for an RGS please, just in case I come across one? At least the rev-counter is correct for model.  *smiley4*

Richard, thanks for the calcs. Will be useful to check as the speedo isn't BSA.

Title: Re: Identifying Speedo & Rev Counter
Post by: MG on 12.07. 2010 21:40
RGS USA versions and Scramblers would be SC.5301/23.
The home versions would have SC.5301/03 for mph, SC.5301/12 for kph.

Don't know the calibration numbers though. Maybe yours is right or close enough anyway, then I wouldn't care too much about the wrong number on the dial.

Cheers, Markus
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 12.07. 2010 22:04
great stuff, thanks. ;)
Title: Re: Identifying Speedo & Rev Counter
Post by: trevinoz on 12.07. 2010 23:45
Goldseeker,
                   If you have a 46 tooth rear sprocket and 19 tooth gearbox sprocket you will need a speedo ratio of 1600.
If you have a 42 tooth rear sprocket and 19 tooth gearbox sprocket you will need a speedo ratio of 1465.
Standard A10s used 1450 speedos.
My RGS has a 1600 type.
Trev.
Title: Re: Identifying Speedo & Rev Counter
Post by: MikeN on 13.07. 2010 12:17

So Speedo is not a BSA fitment, shame but does it matter? Markus, can you tell me what the number should be for an RGS please, just in case I come across one? At least the rev-counter is correct for model.  *smiley4*

It doesnt matter at all. You can buy the correct dial face from any of the speedo recondioners who advertise.they are quite cheap. They will also be able to re-calibrate any chronometric to suit your bike.
Mike
Title: Re: Identifying Speedo & Rev Counter
Post by: RichardL on 13.07. 2010 12:39
Trev,

You've tweaked my imagination to find out if the chain-sprocket and gear ratios net the same result as my empirical method. Here is what I?ve found:

42/19 = 2.211  (rear sprocket / gearbox sprocket)
26/17 = 1.529  (gearbox constant mesh gear / layshaft gear)
6/11   = 0.545  (layshaft speedo drive gear / speedometer driven gear)

2.211 x 1.529 x 0.545 = 1.842

Considering my method came out as 1.83:1 by turning the rear wheel and counting revolutions of the wheel and the cable, I was rather happy with this result (and a bit surprised that it actually worked out this close).

Does this all sound right?

Richard L.
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 13.07. 2010 16:20
Goldseeker,
                   If you have a 46 tooth rear sprocket and 19 tooth gearbox sprocket you will need a speedo ratio of 1600.
If you have a 42 tooth rear sprocket and 19 tooth gearbox sprocket you will need a speedo ratio of 1465.
Standard A10s used 1450 speedos.
My RGS has a 1600 type.
Trev.

Trev, I'm not sure what number of teeth are on any of the sprockets at the moment but I will be taking the primary cases off during the winter and so will know for sure then. The rear sprocket will definitely be 46 once I get the new RGS brake drum on.

At the moment I am collecting info on everything I can and making a 'to do' list for later. Its not too long as yet but likely to grow  *smiley4*.

Col.
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 13.07. 2010 20:36
Another question if I may be so bold. This is my first experience of chronometric rev counters.

I have noticed my rev counter needle is far from smooth in movement, i.e. if I hold the throttle at indicated 1000rpm and then increase engine revs slowly the indicated revs stay the same for a while then jumps to a higher figure (hope that explanation is understandable). Is this normal or should the needle sweep smoothly like the speedo?

Col.
Title: Re: Identifying Speedo & Rev Counter
Post by: RichardL on 13.07. 2010 22:30
I guess the "maths" is just not interesting.
Title: Re: Identifying Speedo & Rev Counter
Post by: Stu55Flash on 13.07. 2010 22:43
Hi there

The chronometric refers to reference to a clock. The clock - escapement movement is powered by the drive cable. The purpose of the clock movement is to time the movement of a meshing gear which mates with another gear driven in relation to the speed of the drive cable. The meshing gear is in contact with the drive gear for 0.6 of a second. Thus the pointer moves in increments of 0.6s. The faster the speed  the further the pointer moves in the 0.6s it is engaged. This all means that the pointer jumps to a new reading every 0.6s. The movement in these speedos is a masterpiece of engineering. These speedos contain 100s of parts in comparison with the modern magnetic ones.

Hope this is clear enough?

Stu
Title: Re: Identifying Speedo & Rev Counter
Post by: trevinoz on 13.07. 2010 23:43
Richard L,
               Go to the top of the class!
Now to get the cable revs, multiply by the number of wheel revs per mile.
Supposedly 795 for 3.50/19 and for 4.00/18, 803.
800 is good enough for all intents and purposes.
Trev.
Title: Re: Identifying Speedo & Rev Counter
Post by: bsa-bill on 14.07. 2010 08:24
Quote
I guess the "maths" is just not interesting.

I had a good look at them ( always liked maths at school ) getting to be a lost art these days Richard what with spreadsheets and calculators.
but handy to have the mental agility learned pre chips
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 14.07. 2010 09:46
I guess the "maths" is just not interesting.

They were indeed interesting Richard and I will be testing my maths skills once I get my ageing head around them.  *smiley4*

Col.
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 14.07. 2010 09:57
Hi there

The chronometric refers to reference to a clock. The clock - escapement movement is powered by the drive cable. The purpose of the clock movement is to time the movement of a meshing gear which mates with another gear driven in relation to the speed of the drive cable. The meshing gear is in contact with the drive gear for 0.6 of a second. Thus the pointer moves in increments of 0.6s. The faster the speed  the further the pointer moves in the 0.6s it is engaged. This all means that the pointer jumps to a new reading every 0.6s. The movement in these speedos is a masterpiece of engineering. These speedos contain 100s of parts in comparison with the modern magnetic ones.

Hope this is clear enough?

Stu

Stu, very interesting, explains why the needle jumps as normal. However I think that mine may be jumping a bit more than it should. I will look at it again with a second pair of eyes as it was not easy trying to keep one eye on the dial and the other on the test meter.

Col.
Title: Re: Identifying Speedo & Rev Counter
Post by: flashblack on 18.07. 2010 16:22
Just for the record, this is mine in action: --- old link removed, correct link on my next post ---
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 18.07. 2010 22:15
Just for the record, this is mine in action: http://www.youtube.com/watch?v=c1dqq2Kt2ko  (ftp://http://www.youtube.com/watch?v=c1dqq2Kt2ko)

Link doesn't work for me  *dunno*
Title: Re: Identifying Speedo & Rev Counter
Post by: muskrat on 19.07. 2010 11:04
Not just you Col, I can't get the link either.
Cheers
Title: Re: Identifying Speedo & Rev Counter
Post by: flashblack on 19.07. 2010 15:40
Right i`ll try again: http://www.youtube.com/watch?v=c1dqq2Kt2ko  (http://www.youtube.com/watch?v=c1dqq2Kt2ko)

I think i`ve cracked it this time (should have done it before a beer!)
Title: Re: Identifying Speedo & Rev Counter
Post by: Goldseeker on 19.07. 2010 18:00
Right i`ll try again: http://www.youtube.com/watch?v=c1dqq2Kt2ko  (http://www.youtube.com/watch?v=c1dqq2Kt2ko)

I think i`ve cracked it this time (should have done it before a beer!)

Thats better  *smile*

I greased the cable this morning and now mine works very similarly to yours, result.  ;)

Col.