converting a MPH speedo to KPH or vice-versa

[Mayor_of_BBQ]

Hi All

I purchased a '79 CX100 from out of Canada.  The speedometer is a stock us/MPH marked one ...  but by my second ride I realized the PO has converted it to register in KPH.  I am pretty good on 'ole metric, so I know I'm doing 50something MPH when the speedo says 80 or 62mph when it reads 100

However, it is running the ODO way up too quickly, and that will be a problem if I ever sell the bike. Also makes gas stops/tracking a little trickier.

I know nothing about how these speedos work, exactly what do I need to swap or alter to convert back to MPH? Also, is it possible to run the ODO back a bit to compensate once I get it sorted?
Perhaps I would be better off swapping it for a working used model with 10-12k less 'miles' on the odometer? I know Koso/Speedhut/whatever is an option... but I would rather keep the stock gauge and Speedhut at least doesnt make a gauge in the same size for the stock dash.

[ozarquebus]

Speedometer Overlay Sticker for velocity, but no helponodo.
https://www.ebay.com/itm/183768199598

[Tom H]

I would think the difference is in the gearing at the trans. You might have a look at a parts book for the gear.

I did a quick look for the parts. There are KMH and MPH speedo's. Is it just the face markings or is the gearing in the speedo? I think there are two different trans drive gears?

Tom

[Mayor_of_BBQ]

I would think the difference is in the gearing at the trans. You might have a look at a parts book for the gear.

I did a quick look for the parts. There are KMH and MPH speedo's. Is it just the face markings or is the gearing in the speedo? I think there are two different trans drive gears?

Tom

I'm saying I have the stock Speedo and it is a MPH marked speedo. But when you ride, it is indicating the speed in KPH

...so I am riding down a rural divided highway near my house, the speed limit is 45mph and I am generally cruising along near 10-over (flow of traffic speed)... I ride this road all the time and I am going a normal speed. But I look down at the speedo and it is indicating 80mph. I know dang well I am not going 80 mph.  Then I hit the beltway/highway into town- speed limit 55. I am riding at a normal speed, flowing with traffic... so along about 62mph... I look at the speedo and it says I am doing 100mph.

Then I remembered the bike came from Canada, so I had a brief chat with the PO and he said he had converted it to KPH. I dont know how he did that.  I am just assuming he changed some gear in the speedo or changed the part where the speedo cable hooks into the transmission? This bike has a lot of mods, so it was a wide-ranging conversation and I never circled back to that little detail.

Hope that makes sense.

[Tom]

I bet it really going fast while parked!  Sorry I couldn't resist.   

Gearing in the speedo would be easier than in the trans. but again maybe an adaptor on the trans. cable end....?

[Zenermaniac]

The odometer is indicating kilometers. 1.6km=1 mile.

[Mayor_of_BBQ]

Maybe I am not being clear, it is a stock MPH speedometer

But it is indicating speed in kilometers and recording odo in kilometers

It's not just a mph speedometer that is "off", because the amount it's "off" is exactly the difference between MPH and KPH

I am saying I ride down the road at 50mph (80KPH) actual speed <per GPS>....  the speedo reads 80mph

I ride down the road at 62mph actual speed <per GPS> (100 KPH)... the speedo reads 100mph

If I travel .62miles (1KM), the odo shows 1mile

[rocker59]

I would start with the transmission speedo cable gear.

With it racking up mileage in its current state, you have no idea how many miles are on the bike, so value based on miles is moot.

You might be best served by sourcing a replacement speedometer, if it turns out the PO fiddled with the speedo's internal workings.

[Old Jock]

Google kph to mph mech speedo converter & you'll see that there are devices to convert the cable speed to suit.

I'm unsure about the thread type on them but it may give you something to research furhter.

While on that topic I'd also check both ends of the cable, but especially down at the gearbox to check that the PO didn't just use one of these clever little gearboxes to change it to kph in the first place.

Just a thought

[centauro]

The dial part of that unit must have been changed to a US/MPH, otherwise, as a Canadian model, the dial would read in KPH for both speedo and odometers.
These gages, with some dexterity and care can be taken apart and worked on. If you could find a US gage and transfer the guts, it would be one way to do it.
In my case, my '84 US SP had the mandated 80 mph speedo that I did not like.
So, I bought a used KPH unit from Reboot Guzzi spares in France and kept it on the bike until I sold it. I gave the new owner the stock mph one and noted the mileage difference. Much less work this way.