Boxerworks.com

I'm looking for the Tachometer ratio on a boxer made in 1973

the electric I repalced mine with didn't last so maybe if I find a ratio I can adapt something?....

Relevant information is in the BMW manual ...
beyond that, displacement might be necessary criteria to answer the question, eh ?.

would not the geared ratio used on the /5 motor be the same for the Tachometer? 1969 to 1973
Motor orginal R75/5 1973

Tachometers didn't come with "ratios" that I know of. Speedometers did, though.

Kurt in S.A.

As far as I can tell from the BMW info I have, the mechanical tach counted crankshaft revs and the "meter" read in RPMs sorta like a speedo. All crankshafts had the same mechanical apparatus. (as in: ONE rev/crank = 1 RPM)
Electronic (older ones) takes signal from points side of a coil and counts impulses. Still does not involve any "ratios".

I believe Lyman is looking for the ratio between engine rpms and tachometer cable rpms so that he may fit some alien tachometer to his airhead.

My mistake, motorhead.
I read "tach" but was thinking "speedo" because of the request for a "ratio".

As to after market tachs / rev-counters –
It might be difficult to find a mechanical (cable operated) replacement to fit.
But any electronic tach intended for 2 cylinders should work.
Some tachs / rev counters are designed specifically for 2 cylinders,
others are # of cylinders adjustable, but careful,
many of these will only calibrate to a minimum of 4 cylinders.

The tach drives on all BMWs from 70 to 78 (or when the electric tachs arrived) is a 1 to 1 ratio, but it is driven off the CAMSHAFT. So you need a 2 to 1 ratio tach.

vanzen@rockerboxer.com wrote:My mistake, motorhead.
I read "tach" but was thinking "speedo" because of the request for a "ratio".

As to after market tachs / rev-counters –
It might be difficult to find a mechanical (cable operated) replacement to fit.
But any electronic tach intended for 2 cylinders should work.
Some tachs / rev counters are designed specifically for 2 cylinders,
others are # of cylinders adjustable, but careful,
many of these will only calibrate to a minimum of 4 cylinders.

the 2 cylinder electric Tach I picked was a Harley aftermarket.
In thought I figured a Tach for a harley woud work great as less Vibration and less Voltage spikes
My BMW is Modfied almost too far in work/operation as a sperate switch keeps light and day run seprate but the Tach worked funny in start ups and thats what killed it



when I switch on the tach, it wound up and went to 0 rpm, I'd start the motor and when it was ready to go, I switch on the lights and the tach would wind again to zero then motor RPM again at least it worked to the end of my trip when I found my 500.00 heads were not as rebuilt as sold

Mostly from experence if a tach is crank run its 1:1 if cam then 1:2 if more cam's then ratio can be set to calbration conditions from what cam is used and what time between crank and that gear to map RPM

I can see the drawing on BMW book the cam has a worm with 4 teeth per quater so to the drive that matches had 10 teeth? I currenty have no part to inspect teeth..... so I guess I need to get off my arse and just stick something into the drive turn the motor 1 crank and see how many time the cable drive moves for ratio

so I think its 1:4 or 2:4 as Garnet points out its cam driven....... if you have sound Info lets hear it thanks

Somone on ADVRider installed this:

http://www.advrider.com/forums/showthre ... ht=ACEWell

Kurt in S.A.