Hour Meter Question

ggfossen · Post by **ggfossen** » Tue Oct 24, 2006 6:34 pm

When wiring the dash on my '56 420, I found that the original tach/hour meter has/had only the mechanical hook-up to the engine. No electrical hook-up. I'm having trouble convincing myself that the hour meter is mechanically operated. Seems to me, there should be some juice running through it, but the mounting studs don't appear to accept wires.

Am I missing something?

Gary

wwattson · Post by **wwattson** » Tue Oct 24, 2006 7:34 pm

Someone smarter than me is going to know the specifics of your crawler but those of us that are airplane pilots are pretty familiar with the difference between "tach" time and "Hobbs" time. Airplane tachs are all mechanical devices that will accumulate 1 hour of time for every hour operated at the rated RPM of the engine. Lower RPMs means slower time.

A Hobbs meter on the other hand is wired to an oil pressure switch and runs at clock time whenever the engine runs and has oil pressure. Should make that big a difference for things like service intervals but can be a fair bit less when you're renting expensive equipment like airplanes byy the hour.

wwattson · Post by **wwattson** » Tue Oct 24, 2006 7:35 pm

I meant to say "shouldn't" rather than should.

ggfossen · Post by **ggfossen** » Tue Oct 24, 2006 7:43 pm

Bill,

I appreciate your input, but I still don't know how the hour meter works on my old 420. The studs didn't appear to be insullated from the case, but they could have been...I guess??

I also guess it's possible that the meter is to run at the suggested rpm level, or log time that way, but...I sort of doubt it???

Forty plus years ago, I logged a bit more than 20 hours in a T-craft. That doesn't make me an airplane pilot, but I certainly enjoyed the time in the T-craft.

Then again, come to think of it, owning a 420c doesn't make me a cat skinner, but messing with it is fun. Maybe not as fun as the T-craft, but fun.

Gary

wwattson · Post by **wwattson** » Tue Oct 24, 2006 8:16 pm

I sold my plane to support my tractor habit. Now I've got multiple tractors to the point where I could build my own airport and no plane. One thing is for certain; tractors like airplanes can be a lot of fun but both can kill you if you get stupid or careless.

Sure the two studs on the back aren't just the mounting studs? Seems like the tach on my 1010 has a couple of studs on the back either side of the center connection for attachment to a mounting bracket. Been a while since I had it out but seems like the tach was mounted that way.

ggfossen · Post by **ggfossen** » Wed Oct 25, 2006 7:51 am

Bill,

Yes, they are the mounting studs, but I don't know if they were to be used a electic in/out studs, too, as ammeters and such do. I guess, after I run it long enough, I will know if it's mechanical. It's just that I was trying to clear up all the little things before I put it to work.

I took in the generator, had it checked, and it's fine. Now, I have work by the regulator, and the meter. I may just be that the meter is bad. I need to run it a bit more to see if there is a variance on batt voltage. Then I will know if the charge is getting to the battery.

I mounted my 350 ROPS canopy yesterday. My mounts all lined up as well as could be expected. A few more holes to drill, and some longer bolts, and widow makers will be a threat no more.

Too bad you had to sell the plane. I don't have the room for a runway, or I would put one in. What stops me from returning to flying is the idea of travelling long distances to an airport, and having to hanger a plane. Sort of like having to tow a boat. A pain in the hind parts. Besides, I have no way of justifying flying. I still have to do that.

Gary

Post by **Lavoy** » Wed Oct 25, 2006 9:10 am

420 tachs are purely mechanical, not electrical hookups at all. Mechanincal tachs are quite common, we have tractors in the late 70's that still use them.
I also have new aftermarket SW tachhourmeters that fit right in the hole, and work with the original tach cable.
Lavoy

ggfossen · Post by **ggfossen** » Wed Oct 25, 2006 10:01 am

Lavoy,

Thanks for the response. The tach part is working fine. It was the hour meter about which I had concern, but, apparently, Pilot Bill is right about it being similar to airplanes.

I have about 2 inches of play on the clutch pedal. The adjustment appears to be against the internal stop. The clutch seems to work fine. Is this OK, or am I looking at busting the whole damn thing apart again?

Gary

wwattson · Post by **wwattson** » Wed Oct 25, 2006 10:04 am

What do you get for an SW tach Lavoy? The tach on my 1010 has the square drive hole stripped out and I intend to repair it at some point, but it would be good to have a working tach until that day.

Post by **Lavoy** » Wed Oct 25, 2006 12:53 pm

They are $135. They do have a backlight attachment with them if you wanted to hook it up as well.
Lavoy

hunter41mag · Post by **hunter41mag** » Mon Oct 30, 2006 11:32 am

Gary,

The mechanical tachs on trucks that had an hour meter built in use
100,000 engine revolutions = to 1 hr which works out to an average of 1666.6 rpm (operating rpm range of 1200 to 2100 rpm). So it all depends on what the engine manufacturer determines is the average rpm over its operational range. Its a ballpark figure but for best accuracy the electric type tied into a oil pressure switch is the most accurate.

Don

Eatern PA
JD 440IC

ggfossen · Post by **ggfossen** » Mon Oct 30, 2006 12:36 pm

Don,

Interesting. I never had, in my younger days, anything sophisticated enough to have a tach, so never really gave it much thought. All the newer stuff is electronic.

Amazing how much there continues to be to learn.

Thanks,

Gary

hunter41mag · Post by **hunter41mag** » Tue Oct 31, 2006 7:50 am

Gary,

I have been in the mechanical side for over 30 years and there is still not a day that goes by that I myself learn something new.

Don[/quote]

whybill · Post by **whybill** » Tue Oct 31, 2006 10:09 pm

Gosh seems that would be nice to have the hook up fot the tach lol My 420 was an old Forest service tractor and they never fixed any thing that wasn't absolutly necessary to make it run. They never even fixed the generator just recharged the batter once a week. That is saving to much money if ya aske me. Needless to say I have a good running 420 that is painted a terrible faded yellow over JD green hopefully I will get to dress up the old girl one of these days.

The tip about the copper wire for the plugs is absolutly true. they must be copper the carbon will not work... most parts houses have the wire you will probably have to make up the ends. (the parts man will probably go into a long spiel about how much better the carbon wire is but it will not work on the 420 for a fact.

Bill

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