Gauge identifying 10000 tachometer.

[Thomas lundeval]

Would need help identifying this gauge, marked on the back page 10.65.
The front upper edge VDO 0002.

[304065]

Thomas,

Odd: 6-zyl suggests it is an early 911 tachometer. Likewise the /1 for the tach input lead and +12v, that means 911, not 356 or a boat.

But the 2500 rpm redline? Only thing I can think of is an airplane or blimp motor.

[RennTyp]

Why would you use a 10k tacho for a motor with a 2.5k red line??

[Harvey Weidman]

Maybe it was some sort of minimum RPM forgetting going or warming up?
H

[304065]

It is odd. It's not an opel, borgward, BMW, mercedes (needle only sticks out one side)

The face looks rescreened with those numbers and the line. Huge diesel trucks and buses have a redline of 1500-1700 rpm.

Also, airplane engines may have a prop RPM of 2700-3000 RPM, but the engine rpm (assuming a gear reduction drive) is still engine RPM-- so the redline for the prop would be expressed in terms of engine RPM, not prop.

[dummkopf]

No way it's aircraft. I am thinking a "stay away from rpm". Like a harmonic vibration. I have flown aircraft that had an "do not operate zone" and two of my hi-perf boat motors have it too. Do not linger there or bad things may happen.

How old do you think it is?

[Flieger]

Aircraft engines are designed to produce near max power all day long for many hours between overhauls and to spin slowly so as not to require a gear reduction that uses horsepower to overcome friction, adds weight, and adds another failure point. Low revs also help with the TBO.

It is odd. It's not an opel, borgward, BMW, mercedes (needle only sticks out one side)

The face looks rescreened with those numbers and the line. Huge diesel trucks and buses have a redline of 1500-1700 rpm.

Also, airplane engines may have a prop RPM of 2700-3000 RPM, but the engine rpm (assuming a gear reduction drive) is still engine RPM-- so the redline for the prop would be expressed in terms of engine RPM, not prop.

[WCB4]

Lower side of the powerband for the 2500 redline? I used to mark the lower side of the powerband on my Kawasaki 750cc two-stroke tripples on the tach at about 3500. Just kind of a reminder. Cool tac ya got there though. Dose it show any signs of being serviced?

[andyjboy]

My guess would be that it's an early tacho that's been converted to 10k & had the face silk-screened to match other gauges (speedo, etc) in a Porsche-engined 'special'.

The red mark at 2500rpm looks too insignificant to be any sort or rev 'limit' - maybe it represents reaching the legal speed limit (when in top gear) ?

[304065]

Aircraft engines are designed to produce near max power all day long for many hours between overhauls and to spin slowly so as not to require a gear reduction that uses horsepower to overcome friction, adds weight, and adds another failure point. Low revs also help with the TBO.

True, but a couple observations:

1) The rate limiting factor is prop RPM-- props are efficient at lower rpms and higher pitch-- take, for example, the old Rare Bear, which used a prop hub from a Connie and blades from a P-3 (a militarized version of the Lockheed Electra) for example- lots of power turning a slow-moving prop. If you spin faster you have to deal with bad harmonic vibrations (see poster's comment about yellow arcs on the tach) and the tips going sonic (hang out at a seaplane base and listen to C-180s with 88" props, they make a hell of a racket from the tips)

2) Reduction drives are not unheard of: the PFM used such a drive (albeit decades later), not that it was a successful aviation motor, but we're trying to figure out where this tach originated. Rotax engines use a reduction drive, they are one of the most popular kitplane motors (and powered early versions of the Predator before they went to the Garretts used on the MU-2 ( a friend of mine couldn't get parts for his. . . .because somebody was buying them all. . .

Anyway, enough hypothesizing.