Hour-building tacho?

[Mechta]

A friend recently bought a used tachometer (rev counter) from a well known auction site, and fitted it in his permit aircraft for a ground run to see if it worked.

The tacho appears to be the AC/Mitchell mechanical type often used on Lycomings, with a speedometer-type cable input on the back and a row of numbers to show accumulated hours, based on an assumed cruise RPM.

https://www.aircraftspruce.com/catalog/inpages/mech_tachs.php

When doing the ground run, the 'hours' started building up at an alarming rate. After removal and dismantling, it appears that a gear has been moved along a shaft and secured with a blob of epoxy to gear the hours readout to six times the normal rate.

Can you think of a legitimate reason to modify a tachometer in this way, as falsifying one's hours (e.g when working to a commercial licence) is the only reason that currently springs to mind?

[OpenCirrus619]

Perhaps it had been used in something (boat?) where the cruise RPM was around 500.

Just a thought.

OC619

[PA28181]

Can you think of a legitimate reason to modify a tachometer in this way, as falsifying one's hours (e.g when working to a commercial licence) is the only reason that currently springs to mind?

Nope. Who uses the inaccurate hours count from a tacho to log their hours no-one I should think. Six hours difference!!!, so logging six hours against a one hour flight I don't think so. Bad enough using a Hobbs for logging flight time let alone a tacho.

So long as the revs are accurate, forget the hours on it, there irrelevant..

[9 lives]

bought a used tachometer (rev counter) from a well known auction site

Was it certified for the installation? Yeah, I know it was a permit aircraft, but this does not exempt it from the need to have the correct parts installed!

Different tachometers have been made to account for the differing output speeds of the engine tach drive - it is not always 1:1.

I hope that "hour building" would be of lesser interest to a pilot than gaining piloting experience.

[Genghis the Engineer]

Sounds like it was installed in something with low revs.

That said,Genghis Sr, now long retired, but once an engineering sales manager, once had to fire a sales rep whose mileagere-imbursement was based upon the odometer of his company car. Turned out the chap had disconnected the cable and connected it to a power drill to add miles, and thus income.

But six times, sounds more likely to be attached to something as already said, rotating around 500rpm. Kit gets used in all sorts of applications.

G

[Ebbie 2003]

Does sound as if it was used on something legitimate - some thing that spoofed an extra 10/20% may be an hour building wheeze.

That said - if it was one's own plane the "traditional" booking of "Parker Hours" seems the best option for a fraudster.

A meter that over records would only have value to a fraudster renting out his plane - but a factor of six - one may get a little suspicious if if took four hours from Lydd to Le Touquet:)

[Mechta]

Thanks for the replies.

A factor of six for fraudulent hour building does seem a bit implausible. OC 619's suggestion of a low-revving engine in a boat would seem more likely, but for the fact, which I didn't mention, that the seller was also selling the other instruments from a light aircraft panel, makes this less likely. From the description in the adverts for the tacho and his other instruments, I suspect the seller did not know a great deal about what he was selling.

My friend isn't unduly worried as he now has parts to either fix the original tacho, or get this one working again properly.

Step Turn, I appreciate your concern, however the owners do understand what can and can't be done within the regulations for this aircraft.