My Hobbs is INOP

aftCG

aftCG

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Joined
Apr 3, 2018
Messages
526
Location
Tacoma, WA
It's only got 125.5 hours and appears toast. What the fruit?
Wires on the back are on solid. I have two oil pressure gauges that both work. Tested resistance across the Hobbs terminals with one wire removed. Infinite.

Did a Google search and found a thread on PoA with about fifty responses telling the guy why he didn't need a Hobbs and should just move on.

I instruct in my plane and have a new temporary partner. I also use it as my gas gauge.

Is this common? First time in 1500 hrs/23 years I've seen one go tango uniform.
 
Dunno. I just tried to stick an overhauled recording tach in the J4. Doesn’t fit, after a $160 overhaul and setting the odometer to airframe time.

So now, to sort of keep track of airframe time, I too will install a “Hobbs.” (We will take 20% off for taxi time)

I gave away my spare Hobbs, so am looking for an inexpensive alternative. Will report back - a buddy found a motion sensitive counter for $25. Put it in his Chief - no electrics. Works, apparently.
 
A quick search. $5 to $33. Less than a glass of beer, all the way to the vaunted Hobbs from Aircraft Spruce for the cost of a nice lunch.

No wonder they fail once in a while - mass produced in China.
 
Here’s the one I am getting.
https://www.aircraftspruce.com/cata...HFsEA1IUzygA9eFa_QsWCUILOKwJKItYaAqkdEALw_wcB

Don’t forget - most have a pressure sensor. If you trust your partners, bypass that and see if the meter starts counting. The pressure switch is for flight schools, where students turn the master off after takeoff. Foil that by going direct to the battery with the pr sure switch being the on/off. Hook it to the master.
 
Bob Turner said:
Here’s the one I am getting.
https://www.aircraftspruce.com/cata...HFsEA1IUzygA9eFa_QsWCUILOKwJKItYaAqkdEALw_wcB

Don’t forget - most have a pressure sensor. If you trust your partners, bypass that and see if the meter starts counting. The pressure switch is for flight schools, where students turn the master off after takeoff. Foil that by going direct to the battery with the pr sure switch being the on/off. Hook it to the master.
Click to expand...
That's the one I have that's broke. They must be made in an old flash bulb factory.
My understanding is the oil pressure sending unit is the switch (why I mentioned both gauges still working). It should just send 12V if it detects above a threshold. Before I throw down $33 more I'll going to test that principal with a running engine (and a good set of chocks). Given the position required to test it I need a person sitting in the back with throttle and brakes at hand.
 
Why not just jumper 12 v to the back of the Hobbs? Safer! Six minutes is long enough to see movement.
 
Interesting follow up. I blindly ordered that Honeywell Hobbs in the link above for $33. Didn't realize the version in my panel is identical except that it occupies a 2-1/4" instrument hole.

Thought about ordering the round one. Found out they are $135. Not a typo.

I thought maybe there would be a readily available adapter plate. Nope.

I scrambled across town to Spencer Aircraft to get a 2-1/4" plastic instrument panel blank. Carefully measured and cut the rectangle hole and installed the affordable version.

Did examine my engine bay for pressure switch after reading where I should expect there to be a pressure sending unit and switch to be manifolded on the firewall. It is a clean install but there is only one device on the firewall for my dual pressure gauges and Hobbs. Both oil pressure gauges indicate fine.
 
Yet another follow up. The newly installed Hobbs never moved a digit. So I did more research and more crawling around in the plane. I was quite mistaken that my two oil pressure gauges and Hobbs used the one sensor I found on the firewall.
The fitting from the flex line to the firewall mounted sensor was an almost invisible T fitting that pierces the firewall and a hard line goes to the factory oil pressure gauge. Right where it goes to the gauge is another T, and the oil pressure switch is mounted on that. It's just a few inches from the Hobbs.

Oil pressure switch on the way from Spruce, and I reinstalled the old Hobbs since there is likely nothing wrong with it
 
Lessons learned here about throwing parts at a problem. Turned out to be a broken ground wire on my clock and a blown fuse back by the battery.
All better now.
 
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