Engine hour meter overestimates

I've become suspicious that my engine-hour meter overestimating the time, so I started recording the times I started and stopped the engine. It is high by about 12%. This past spring I calibrated my odometer with a laser Tach, adjusting the set screw in the back of the Tach to match the laser unit. Is it possible that the Tach adjustment has put off the hour-meter?


Jim
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Probably not related to adjusting the tach cal. But if you want to hear a rant, here it comes.

Most hour meters SUCK!! Ones on tachs fail, stand alone ones fail, half are not accurate, and the other half jam, then unstick randomly.

I put two new meters on my rig when I built it. New VDO tach with digital HM. New Datcon HM for gennie. The VDO HM display randomly gives garbage, but seems to clock accurately. The Datcon I caught in an overnight gennie run clocking zero hours. Next overnight run it clocked 10hrs in an 8hr run. Trying to make for the previous night, I guess.

I have a box of dead HM's from other peoples boats. All brands represented.

Digital electronic ones suck in their own special way. When they die, you have absolutely no clue what the hours were.

I thought the Datcon was used in aircraft when I bought it. Those guys would not put up with this crap, or do they?

Pilots- Who makes your HM's? Tired of this crap.

Ski in NC said:

Probably not related to adjusting the tach cal. But if you want to hear a rant, here it comes.

................................Pilots- Who makes your HM's? Tired of this crap.

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I've had good results with the few Hobbs meters that I've used in various applications over the years.

A few dead Hobbs in the box, too. Grrr.

Chuckle!

So it's case of "Relax! Don't worry! Have a Homebrew"


Jim
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Take it to an airport that rents aircraft by the hour, they will pay ya big bucks for that one.



Most of the A/C I am acquainted with are reciprocating and use Hobbs, mine as well.

The more I think about this...it's part of the tachometer, so I must have put it off when I adjusted the tachometer.


Jim
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What kind of tach is it? Most electronic ones start clocking as soon as ign is on AND there is an AC signal coming in. Got to have both. Should not matter what the cal adjustment is.

Old Stewart Warner mechanical tachs did not really have hour meters, but rev counters. Those rev counters matched hours at 1800rpm, and then varied by factor above or below.

"Clock" type hour meters seem simpler. They simply measure the time the ignition is on. Mine is accurate. My engine's alarm goes on when the ignition is on and the engine is not running.

I like the ones that run off a fuel pressure switch. Pretty much like a stopwatch started and stopped by fuel flow. Matched my logs exactly.

Put one of these in the charter boat when the one in the Cummins panel died. Seems accurate and reliable at least for the last 900 hours. $20 was worth the gamble.

Ted

Ski in NC said:

What kind of tach is it? Most electronic ones start clocking as soon as ign is on AND there is an AC signal coming in. Got to have both. Should not matter what the cal adjustment is.

Old Stewart Warner mechanical tachs did not really have hour meters, but rev counters. Those rev counters matched hours at 1800rpm, and then varied by factor above or below.

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It's a Motorola model. I had an earlier thread on this forum called Tachometer Adjustment and you gave me some input at that time. I might look into an electronic hour meter rather than a mechanical one with a reference card indicating the date of the install.


Jim
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O C Diver said:

Put one of these in the charter boat when the one in the Cummins panel died. Seems accurate and reliable at least for the last 900 hours. $20 was worth the gamble.

Ted

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Yes. That's the ticket! How is it wired? Can I jumper it from the existing electronics in the panel when they are powered up by the alternator?


Jim
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Since we've owned Hobo we have lost both tacks (upper and lower helms) at different times. I added the Dacton meter after I lost the first one and mounted under the dash. It seems to be the most accurate.

JDCAVE said:

...How is it wired? Can I jumper it from the existing electronics in the panel when they are powered up by the alternator?...

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We wired ours into the key switch.

JDCAVE said:

Yes. That's the ticket! How is it wired? Can I jumper it from the existing electronics in the panel when they are powered up by the alternator?


Jim
Sent from my iPad using Trawler Forum

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Mine is wired to the key switch.

Ted

They can be wired to the oil pressure switch as well or even on their own oil pressure switch using a T.

Then they only measure running time and not switch time if you forget and leave the switch on and go to dinner. Not that I have ever done that,

Aircraft tach. time is not really straight time as it is RPM dependent, the higher the rpm the faster the tach. time, the slower then the slower the tach. time.

This is not how most aircraft are billed when renting however, it is only used for maintenance purposes. It is cross checked against the elect. hour meter in case the renter gets creative with a screw driver and disconnects the Hobbs meter for some discount flying time.

We had Hobbs brand meters exclusively in many of the planes I flew in my early years. For years, I thought the name of the instrument was a Hobbs meter. Only later did I learn that it's a brand of meter like Kleenex is a brand of tissue. But we always seemed to call it "Hobbs time" vs. tach time.

A Hobbs counted every hour when the engine was running, regardless of engine speed. The tach meter counted one hour of time when run for an hour at full 100% or 1/2 Hr of time if run for an hour at 50% RPM. It served more for maintenance requirements while the Hobbs was the meter used to determine the rental costs.

Fly, Must be that echo in here, thought that sounded familiar.

SCOTTEDAVIS said:

Fly, Must be that echo in here, thought that sounded familiar.

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Yup!!! Like you said!

SO its off , make a correction table.

Works for your compass , why not the hour counter?

Just proof that the hours on engines meters means very little when buying used.

funangler said:

Just proof that the hours on engines meters means very little when buying used.

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That's so true, even if they are accurate and have never been replaced.

Low hours would be more frightining than high hours on a diesel boat.

The maint involved with NOT using an engine can be more costly than from normal operations.

Low hours can also mean a replaced meter at some point as they tend to not last forever, this should be noted in the maintenance log but is not always.

Most marine hardware dies from time and neglect and is not worn out, while I type this stuff on the boat is breaking.

What is best way to troubleshoot tach? My starboard tach died this summer on my trip.

When I replaced my hour meter a few months ago, I wired it to a 12v battery until it had clocked the previous HM hours, which was about 350 hours. That way it began its duty with the correct number of hours.

Cheers, Bill

Found this old tach in a box of parts. It came out of an old wooden boat that was being scrapped. I think it had a Perkins 354. I did not even look at it til it was back at the shop.

52963 x 100000 rev's is 52963hr at 1667rpm.

This HM did not break. I tested it with a drill and it still works.

Mechanical tach. Can't find brand on it anywhere!!! Looks like a Stewart Warner.

Montenido said:

When I replaced my hour meter a few months ago, I wired it to a 12v battery until it had clocked the previous HM hours, which was about 350 hours. That way it began its duty with the correct number of hours.

Cheers, Bill

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Mine would have taken 230+ days.

Ted

Ski in NC said:

Found this old tach in a box of parts. It came out of an old wooden boat that was being scrapped. I think it had a Perkins 354. I did not even look at it til it was back at the shop.

52963 x 100000 rev's is 52963hr at 1667rpm.

This HM did not break. I tested it with a drill and it still works.

Mechanical tach. Can't find brand on it anywhere!!! Looks like a Stewart Warner.

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Kinda hard to imagine 52,963 hours out of one Perkins engine. Maybe it was used on more than one engine.

Ted