FORUMula1.com - F1 Forum

[ewgoforth]

Hello,

I was just looking at a site that had a bunch of pictures of an early seventies McLaren M23 on it http://www.britishracecar.com/PhilMauger-McLaren-M23.htm and noticed that it had a Chronometric tachometer on it, which seemed rather anachronistic. For those who don't know, a chronometric tachometer is totally mechanical in design and the needle kind of ticks around like in an old clock. They look very cool, but update their display every second or so, perhaps they're more accurate than the conventional tachometer of that time, but I doubt it.

I don't think a chronometric tach. would be very useful in the bottom two or three gears, the rpm would change so quickly, I think you'd be better off using your ear. I've never seen a street car with one, early sixties MGs, Austin Healey's etc. had magnetic instruments. Magnetic instruments use rotating magnets that induce eddy currents in an aluminum disk to which the needle is attached, the eddy currents then interact with the magnets which causes the needle to move in proportion to engine speed, the faster the rotation the stronger the eddy current.

Chronometric instruments were phased out in the early sixties or so in British motorcycles, which is where I'm more familiar with them. I've ridden a fifties BSA Golden Flash that had a chronometric speedometer. I remember the cars in the 1966 James Garner movie Grand Prix had them, but that movie was made several years before this McLaren was made. Any idea why McLaren was still using chronometric tachs in the early seventies?

-Eric

[LRW]

Thats an excellent read ewgoforth!

[What's Burning?]

I've no idea about the chronometric tach, it's the first I hear of it. What drives it if it updates once per second is it the same signal source from the coil?

Anyway thanks for the link the detailed pictures and descriptions were fantastic. Had no idea that in car fire suppression systems even existed back then and the first quick release steering wheel!

[ewgoforth]

I've no idea about the chronometric tach, it's the first I hear of it. What drives it if it updates once per second is it the same signal source from the coil?

Anyway thanks for the link the detailed pictures and descriptions were fantastic. Had no idea that in car fire suppression systems even existed back then and the first quick release steering wheel!

A tach that gets its signal from the coil is usually referred to as an"electronic" tachometer. Both magnetic and chronometric tachs have a spinning cable connected to them, typically this is driven off the camshaft. A chronometric tachometer has gears and escapements inside, like an old (or new high-end Rolex, etc.) watch. In British motorcycles they were phased out in the early sixties.

[Jabberwocky]

I always assumed that that type of rev counter was used for aging parts. So you knew how many revolutions the engine had done since install

Sent from Turing Colossus using Tapatalk 2

[What's Burning?]

That explains the beefy ass connection at the back of the gaugues. But the water temp and oil temp gaugues seem to have the same connectors so were they "mechanical" as well?

I've heard in the past that race teams sometimes took off proprietary or "secret" technology out of race cars when they sold them off to the public and when you first asked your question I thought maybe that was your answer but given that the tack would need a connection all the way back to the cam, that had to have been designed into the car as it would be impossible to backdate something like that as neatly as it seems to be done.

[ewgoforth]

That explains the beefy ass connection at the back of the gaugues. But the water temp and oil temp gaugues seem to have the same connectors so were they "mechanical" as well?

I've heard in the past that race teams sometimes took off proprietary or "secret" technology out of race cars when they sold them off to the public and when you first asked your question I thought maybe that was your answer but given that the tack would need a connection all the way back to the cam, that had to have been designed into the car as it would be impossible to backdate something like that as neatly as it seems to be done.

I'm more of a British motorcycle than car guy, so I'm not sure how those other guages worked. They look pretty much like the guages on MGs, Austin Healey's, etc.

[melville]

Chronometric tachs were jerky but just as accurate as anything at the time. It didn't take anything like a second to react, and on racing cars they had the tell tale needle as well