speedo ratios

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snowy
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speedo ratios

Postby snowy » Wed Aug 16, 2017 10:52 am

Good morning gents and gentess's
A word of clarification on speedo ratios to diff ratios if you please
I may be buying a r100/7 later this week, the seller hasn't got the speedo head ( as well as numerous other bits that are missing!), I, as yet, don't know the final drive ratio.
I have in my collection a 1.112 speedo, what would that fit?.
Now has one of you learned people ( see how well I creep) already compiled a list that will explain what I am after, I would like to print it off and once laminated keep it as reference in the future.
thanks in advance
Snowy

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SteveD
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Re: speedo ratios

Postby SteveD » Wed Aug 16, 2017 12:21 pm

Scroll down about half way..
http://bmwmotorcycletech.info/ringgears.htm
Cheers, Steve.
1982 R100RS, 2006 K1200R.
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snowy
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Re: speedo ratios

Postby snowy » Wed Aug 16, 2017 5:30 pm

Thanks Steve
It seems that the old unit I have in my spares will do, saves a few bob.
cheers
snowy

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Re: speedo ratios

Postby snowy » Fri Aug 18, 2017 9:05 pm

Hi All
Have now got the bike in my possession, on checking the diff I find that it is a 32/9.
After referring to the list Steve supplied the speedo should be a 1.318, now the list goes on to say that it was fitted to an R65 of 1974 -1977 vintage, the bike is a 'W' reg 1980, R100RS, scratching head and getting splinters.
Have I misread the sheet or is it for guidance only?
comments please gents.
cheers
snowy

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boxerman
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Re: speedo ratios

Postby boxerman » Fri Aug 18, 2017 9:44 pm

I've never even heard of that ratio. It's certainly not from an R65 of that era as they weren't introduced until '78.
Phil Hawksley 'The Boxer Man' - aka 'Dangermouse'
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Re: speedo ratios

Postby CaptAirhead » Fri Aug 18, 2017 10:52 pm

32/9 (3.56) : Speedo Ratio 1.318.

Snowbum States:-
White numerals 1974-1977 R65 models had 3.56 & 3.44.
R50/5 and R60/7 had 3.56.
Books may show Kph ratio as 0.811, miles ratio as 1.297.
With 200kph speedos, W=800. With 120mph speedos will have W=1300.
HTH.
Ian.
If you don't make mistakes, then you aren't trying hard enough!

1979 BMW R80/7 (ex-Police)
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snowy
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Re: speedo ratios

Postby snowy » Sat Aug 19, 2017 6:51 am

Good morning All
Cant sleep thinking about the work I have to do on the R100RS, going to take before and after photos this time, then I can see/remember how much work was involved.
Thanks for the confirmation Ian aka Capt Airhead, so I read the info supplied by Steve correctly.
looking forward to getting all the bits together for the basic rebuild before stripping and paint/powder coating.
Once again thanks
Snowy

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Re: speedo ratios

Postby snowy » Sat Aug 19, 2017 7:24 am

just an update, I have found out that my bike is a R100/7RS of January 1981 vintage, had to do a search as the Vin plate was removed in prep for frame painting and lost. Can I get a replacement.
Frame and engine numbers on bike are correct as on V5c, so I it won't burn my pinkies when I work on it.
cheers
snowy

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boxerman
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Re: speedo ratios

Postby boxerman » Sat Aug 19, 2017 8:55 am

White numerals 1974-1977 R65 models had 3.56 & 3.44.
You might want to drop the bum a line on that one then 'cos there's clearly a typo as the 65 wasn't introduced until '78. I'd guess it should probably read R60/5
Phil Hawksley 'The Boxer Man' - aka 'Dangermouse'
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Re: speedo ratios

Postby ts » Sat Aug 19, 2017 9:07 am

Is the bike black, with a non-RS seat, and also misses exhaust, front mudguard & headlight?

Just curious!
ts
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'73 R75/5, '78 R80/7, '83 R80RT

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Re: speedo ratios

Postby barryh » Sat Aug 19, 2017 10:46 am

The early model R65 had a 31/9 and the R45 had a 35/9 so this ratio you have is something in between and quite inappropriate for an R100.

It will be geared at 14.23 MPH/1000 RPM

At 70MPH you'll be doing a busy 5000 RPM instead of something like 4250 RPM that an R100 should be doing

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Re: speedo ratios

Postby snowy » Sat Aug 19, 2017 5:44 pm

Hi TS, yup you are right, that's the one, the engine is definitely a 1000cc, the frame number states its a R100/7 as does the engine number, methinks its a bitsa, the tail light and indicator wiring doesn't have the 6 pin ( 5 in use) block but a 4 pin type, now changed to the normal type.
Thanks for the explanation Barryh, Best I look for a proper diff for it during the rebuild. mind you should get away from the lights in a hurry ha ha.
It is in a bit of a state, even the alternator screws are missing, no wiring in that area at all, have found some in my bits and pieces but even the loom doesn't seem right, all good fun.
incidentally the seat is beyond recovery, rotted out.
cheers
snowy

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Re: speedo ratios

Postby ts » Sat Aug 19, 2017 8:27 pm

Thanks snowy, saves me from trying to get a reply from the seller. For the rest of the thread followers, it was listed on eBay.

Sorry to hear that someone have bunged on a final drive not really suited for R100 duty, and about the rotted out seat. But I hope you managed to use that as bargaining points. I'd be interested in hearing what offer the seller accepted, please feel free to pm me if you'd prefer not to state it here on the forum.

I hope the rebuild goes well!
ts
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'73 R75/5, '78 R80/7, '83 R80RT

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snowy
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Re: speedo ratios

Postby snowy » Sat Aug 19, 2017 9:34 pm

TS, price agreed on the phone and via email, went down to get it and paid over the shekels, the main reason for getting was the fact that I had approx 50% of the required spares, however once I got it home and got into it further it isn't such a good buy, but I have nothing to keep me busy during the winter, just to get the K100 trike resprayed professionally and the drum brakes changed for discs, so between spending my time on the trike, this r100 and my ham radios might just find time to eat and kip. snowy

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Re: speedo ratios

Postby CaptAirhead » Fri Aug 25, 2017 12:45 am

Boxerman has caught Snowbum out in a typo. Definitely should read R60/5 and NOT R65 which was introduced in 1978. Not that it is any help to the numerous problems to be sorted on this bike but interesting to know that even Snowbum can get it wrong on occasions.

Seems like you need a replacement 33/11 final drive (smooth case type) for a 1.112 ratio speedo ( which you already have) and a new main loom + engine loom to get this project on track. ( Unless you're competent to modify the 'wrong' loom you've got).
There's a few 33/11 diffs on ebay from £150 upwards. Wiring loom for R100 from £50 upward. Engine loom from £20. So to get the job started with proper (used) parts for this model you're going to have to spend a couple of hundred quid just for starters. Then there's the seat and I think someone mentioned an exhaust so unless you have some of that stuff lying around, your pocket money is going to be tied up for a while.
I'm rebuilding a R80/7 TIC which was fully intact and working when it was laid up 13 years ago and I will have spent around £1000 by the time it's back on the road. £300 of that is just on tyres and a battery, then there's the Surefoot stand (£90), the full tool kit and special tools(£100), filler cap and key (£65), Panniers and rack (£100) not to mention service parts, lubes, paints etc etc etc.
Presumably, you factored all this in when you negotiated the price so you might as well do the job right and get the proper parts, starting with the stuff I mentioned above. Good luck with the build and looking forward to your progress report and maybe some pics.( I love bike porn!)
Ian.
If you don't make mistakes, then you aren't trying hard enough!

1979 BMW R80/7 (ex-Police)
2002 Yamaha Fazer 600


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