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MG Midget and Sprite Technical - What colour is your pinion?

This is directed at Type Niners. The speedo drive pinion. I think that the number of teeth on the pinion varies with the colour. I have seen black, brown and green but cannot remember the number of teeth on each, or which gives the closest approximation to accurate speedo.

I have just switched in my rebuilt gearbox with a green pinion. 3.9 diff and 165/70 13 tyres. I think it is reading high for speed but low for distance travelled!
Guy Weller

Guy -- I don't think it is possible to be high on speed and low on distance, as they are both a product of the number of revolutions of the speedo cable.
Mick - nearly ready to paint

Guy - you are clearly in the grip of a worryingly convincing halucination. Did you have mushrooms for dinner last night?
Nick

Mick, I am definitely reading low, by over 10% on distance.

And am pretty sure I am high on speed. I have a green pinion at present.
Guy Weller

Guy,

Are you running a separate speedo and odometer, if not then it can't be indicating high on one and low one the other as they are driven from the same input, unless your speedo needle has suddenly started to bind.
David Billington

Mick,
David,
I think that the odometer and speedometer can be out, despite working off the same drive.

On mine, I think that the gearing is making it read low on distance.
And I think that either the little hair spring for the needle is tired, or that the needle is fixed to the spindle in the wrong position, so that it reads high at any given revolution.

Still interested in what colour pinion others are using.

Guy
Guy Weller

so first port of call would be a fully functioning speedo head !! then see how far out the readings are!!
Mick - nearly ready to paint

Find a friend who can loan you a satnav long enough to get a second opinion. I agree that it is possible to have the needle on the spindle wrong so that the speedometer agreeth not with the odometer.
David "not on speed" Lieb
David Lieb

Hi Guy,

I think you are correct that the pinions are available in different colours. However, the drive gears aren't. I think there are about 16 drive gears.

If I find my broken black pinion I will count the teeth on it.
Daniel Thirteen-Twelve

Mick,
The speedo head is just fine - it just reads wrong!

I reckon I can correct the speed reading by re-positioning the needle on its spindle, but there is no point in doing that before sorting out the correct gearing. Which is why I was asking about colours of pinions. I have a green one fitted at present. I have a spare black one and somewhere I have a brown one -but it may take some finding.

I was just trying to find out which one most people had installed.

I know that the different colours have different nos of teeth - somewhere around 19 - 22 as far as I recall. But they mesh with the same drive gear on the output shaft.,

Guy
Guy Weller

definitely high on speed from what I can see.


How come noone else caught that one!
Tarquin

I was waiting for someone to notice! Why else would my pinion be green? What colour is your pinion, Matt?
Guy Weller

huh

high on speed

huh

I'm sure you all know how I feel about such artificial stimuli

Mr W

Green gear has a gear diameter of 29.75 mm (making allowances for wear and moulding differences)
Grey gear (yes I have one) as a diameter of 25.95 mm but also a smaller number of teeth

green = 23 teeth 29.75mm
grey = 24 teeth 25.95mm

I have the black one in my car at present and it runs an MGB speedo (120mph on the dial) at just slightly "fast"

Yesterday on the main runway at RAF Marham she did 100mph (Sigma timing) with 110 on the speedo

105 = 115mph but bear in mind I didnt have a lot of incentive to look through the holes in the steering wheel at the Sigma at the time...

Sadly the distance recording function on the speedo has been disabled, some bugger has had the advance wheel and ratchet and pawl device away...

I cannot lay me hands on a brown gear at the moment to compare them, sorry


hth
Bill

Thanks Bill,
So you are a bit high on speed as well.
I will check the number of teeth on the black one tomorrow - (today)
Guy Weller

wasnt much of a night for me from a techy point of view yesterday

reprise

grey=== 23 teeth 25.95mm
green== 24 teeth 29.75mm

I really must start drinking at night again, sobriety has little to recommend it except for hangover control

100+ on a drying track has a lot to recommend it though, especially after an evening of draught Bud

And the tyres didnt wear away after all.
Bill

I think I have a yellow one. Is there a yellow one?

I too have a 120mph speedo, with a 3.9 diff. I read a good 10% over on the speedo, so 70 speedo mph is roughly 80 real mph. No wonder we were passing so many cars when I thought we were only cruising!
Tarquin

This thread was discussed between 13/04/2008 and 14/04/2008

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.