Topic: Using a Smiths reproduction speedometer on a SOHC4?

[Sheik Yerbouti]

I searched as well as I could, but couldn't find quite what I was looking for. My gauges are in pretty good shape, so I was planning on selling them to somebody who needs a set. I won't need a tachometer so I just want a vintage speedometer. I see that ebay has a bunch of Smiths reproduction speedometers, and they're the perfect size and look for what I want. Is there a way to interface these speedometers with my 78 750K instead of the royal enfield they're made for?

I did find this document:

http://home.comcast.net/~rhodes/speedo.pdf#search=%22recalibrating%20speedometers%22

Is it just an issue with calibrating it to my wheel? Or is there something more?

I was hoping to use something like this:

http://cgi.ebay.com/ebaymotors/REPLICA-SMITHS-SPEEDOMETER-0-120-MPH-WHITE-FACE-_W0QQcmdZViewItemQQhashZitem1e5f292c45QQitemZ130445552709QQptZMotorcyclesQ5fPartsQ5fAccessories

Thanks for your help!

[Sheik Yerbouti]

Desperation bump.

I need a universal analog speedo, but want something bigger than those 2.5" ones that dime city sells.

[JBMorse]

I'm not sure there's a way to match the speedometer ratio so it would be correct for your bike.  You should do a little searching for speedometer ratio info on this site, as that may point you to some more gauge options.  The old Brits used different ratios than the japanese bikes.
Mikes XS sells some Smiths replica gauges that work with the XS650s.  THey'd probably work on your Honda too but they're not as cool as the one you found on ebay.

http://www.mikesxs.net/products-46.html#products

Good luck!

[Sheik Yerbouti]

I'll send those guys an email about that smiths reproduction for a 750. Thanks!

[Nikkisixx]

I have oe of the repop speedos for my Trumpy.  I'll look it over and see if it would work, just give me a few hours to get a chance to go out and do it.

[Nikkisixx]

Wife put me in a holding pattern so I just did it now while I wait for her 

The drive cable is the same as a honda's, a small square.  The nut that holds the cable on is different (bigger on a Brit Bike), but if you get the "kit" from India that has the driver, cable, and speedo you can use the nut and put it on a Honda cable maybe?



A Brit bike speedo drives off the rear wheel - so the driver won't interchange, you use the Honda front wheel driver:



The ratio of this reproduction driver seems to be the same as a stock Triumph which is 1.25 (15 to 12).  Confirm that is what a Honda's speedo driver ratio is and with some McGuiver work on the cable you could possibly use the Smith's repop.


I hope that helps a bit?  PM if you have specific ??

[Ricky_Racer]

Just FYI... The Indian-built Enfield Smiths repro speedo uses a 2:1 ratio. RR

[FunJimmy]

Someone recently posted about these GPS Speedos and they look great.
Not sure if there’s a review yet, but you might wanna give it a try.

http://www.speedhut.com/gauge_products-gauge_type-speedometer_GPS.htm

FJ

[Sheik Yerbouti]

Somewhere on this site was mention (link) to these really cool classic analogue speedos with built in GPS tracking. They looked the part and I would have gone that route if I saw it earlier, but didn’t.

I’ll try to find a link.

FJ

Sounds spendy, I remember seeing a european company offering really nice looking speedos with analog faces and digital readouts, but they were approaching 500 bucks.

Thanks for the pictures! I'll have to think about it a bit more and do some more research.

[Nikkisixx]

Just FYI... The Indian-built Enfield Smiths repro speedo uses a 2:1 ratio. RR

Right you are Ricky!  Good catch!  It looks like the ratio is the same on a Honda - 2:1?  Looks like all you need to do is modify the ferul on the speedometer end of the cable.

[Ricky_Racer]

Nikki, I'm not sure what kind of Honda you're building, but the CB750 speedo ratio is 2240:60.  RR

[Sheik Yerbouti]

It appears Harley has a few models with that same ratio? Drag Specialties makes a whole line of Speedos for that ratio but they're "for Harleys"

https://www.phatperformanceparts.com/ProductDetails.asp?ProductCode=DS224060SPEEDOMETERS

12mm threads on the drive cable. Would something like this be the ticket?

[Nikkisixx]

Nikki, I'm not sure what kind of Honda you're building, but the CB750 speedo ratio is 2240:60.  RR

The speedo drive from a '75 750 was sitting on the bench and I spun the wheel side 1 time with a resulting 2 revolutions of the cable side.  Even if I'm off a little, it isn't  37 to 1 is it?  Is the 2240 number the cable revolutions per mile?

[Retro Rocket]

2240:60 is 37.3333333333333333333333333333333333333333333333333333333333333333333333333  recurring to1
So it has to be 2240:60 to read correctly....If using the cable

[Nikkisixx]

2240:60 is 37.3333333333333333333333333333333333333333333333333333333333333333333333333  recurring to1
So it has to be 2240:60 to read correctly....If using the cable

Hang on a second.  You guys are telling me that the cable turns 37 times for every rotation of the wheel?  I find that hard to believe after tinkering with the speed drive sitting on the bench.  That little gearbox isn't big enough to house that kind of ratio, or those are TINY gears in there!  Maybe we are not communicating clearly via the interweb?

Sorry for the threadjack that has now occurred...

[Sheik Yerbouti]

Sorry for the threadjack that has now occurred...

Eh, no problem. I'm curious how this all works anyway.

[Retro Rocket]

Actually it is 2240RPM = 60MPH. Not exactly sure of the correct drive ratio

[Nikkisixx]

Actually it is 2240RPM = 60MPH. Not exactly sure of the correct drive ratio

That makes good sense.  The drive ratio is 2:1 or very close to it, but knowing that only gets you part of the way there.  The speedo accuracy is also dependant on the diameter of the wheel.  An Enfield's rear wheel is shorter than a 750's front wheel by a couple of inches.  SO, the speedometer accuracy would be compromised.  Maybe a KM/hour guage would read right in MPH? 

FWIW: I also have a digital speedo/tach combo from China that is ok.  It uses a magnet on the rotor to trigger the speedo and is adjustable for accuracy.  It is not as nice as a Motogadget but neither is it as spendy:
http://cgi.ebay.com/ebaymotors/Digital-Speedometer-Tachometer-Fuel-Gauge-Cockpit-SP2-/370452401263?pt=Motorcycles_Parts_Accessories&hash=item5640af0c6f

[FunJimmy]

Actually it is 2240RPM = 60MPH. Not exactly sure of the correct drive ratio

This doesn’t make sense to me either.
Now I’m no math genius, but the numbers don’t add up.

If the speedo ratio is actually 2240RPM = 60MPH as RR has suggested, than the wheel diameter would need to be 90 inches. That’s some wheel.

60 miles travelled is 316800 feet or 3801600 inches.
If the speedo ratio is 2240RPM = 60 MPH then that is 2240RPM x 60 min = 13440 RPH = 60MPH
3801600 inches divided by 13440 RPH = 282.85 inches per revolution
282.85” divided by 3.14 (pie) = wheel diameter of 90 inches

Have I missed something here, or is this a bigger mystery than we realize?

[Sheik Yerbouti]

Look at the can of worms I opened

[Nikkisixx]

Actually it is 2240RPM = 60MPH. Not exactly sure of the correct drive ratio

This doesn’t make sense to me either.
Now I’m no math genius, but the numbers don’t add up.

If the speedo ratio is actually 2240RPM = 60MPH as RR has suggested, than the wheel diameter would need to be 90 inches. That’s some wheel.

60 miles travelled is 316800 feet or 3801600 inches.
If the speedo ratio is 2240RPM = 60 MPH then that is 2240RPM x 60 min = 13440 RPH = 60MPH
3801600 inches divided by 13440 RPH = 282.85 inches per revolution
282.85” divided by 3.14 (pie) = wheel diameter of 90 inches

Have I missed something here, or is this a bigger mystery than we realize?

Yeah - divide by two for the gear reduction in the speedo driver?

edit:  On some brit bikes the ratio is noted in cable revolutions per mile.  Don't know if that applies here 

[Sheik Yerbouti]

A bump to see if anybody knows the answers to the above questions.