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Working on the M37

mkcoen

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you say that now but i think you will find the m37 is one fun little sucker to drive! i would trade my bobbed 5ton in a second to have my m37 back.
It's the wife's truck and I know, if she could, she'd be driving it every day. Work requirements and the fact that we're 20 miles from town (which she'd be hard pressed to be patient enough to drive at 45mph) will keep it in the shop except on weekends.
 

mkcoen

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Well work grinds to a halt. I was blasting some small items this morning and my air compressor croaked. I've had it about 15 years (Home Depot bargain 6hp/60gal) but never put it through the paces like I have over the last month or so working on the M37.

I'm hoping it's just the motor and I can replace that cheaper than buying another unit. If not, I guess I can plumb a completely new compressor into the old tank and have a 60gal pony tank.
 

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mkcoen

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This might give you an idea of the catastrophic failure of my 15 year old DeVibliss compressor. Both connecting rods broke and it ate most of one piston head and part of the other.

The motor is still fine and Keith_J is going to give it a shot reconfiguring it from a direct drive on the old aluminum pump to a pulley driven set up on a new cast iron pump. That should save around $500 compared to buying a new compressor and make me happier than I've been all week.
 

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mkcoen

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Keith_J made some amazing progress on the compressor yesterday. He engineered and fabbed the mount for the pump and a sliding mount for the motor (so we can tension the belt - old compressor was direct drive). The only thing left today is to get the correct belt length, wire the motor up, plumb the line from pump to tank, and test it.

If this is my last post then something went terribly wrong and the shop, Keith, and myself are now missing. Don't bother sending a search party.

Pics:
1) New pump
2) Mount
3) Pump on tank
4) Pump and motor
 

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mkcoen

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Nice!

How does it compare to the old pump, piston-size wise and speed wise?
Not sure on the piston size but:

Old pump: 14.6 scfm@40 psi and 11.1 scfm@90 psi
New pump: 11.1 scfm@40 psi and 10 scfm@90 psi

Motor stays the same at 6 hp

But man is this new pump quiet. Oh, and it's working great!
 
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Keith_J

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Nice!

How does it compare to the old pump, piston-size wise and speed wise?
This is a much larger compressor, also twin but parallel twin instead of 90 degree V. This makes the pump deliver two strokes every revolution, one every 180 degrees so there isn't any higher order harmonics. A 90 degree V twin does two strokes every revolution too, only they are 90 degrees apart, with a 270 degree "dead zone". This is why Harleys have that "potato-potato" exhaust note.

This one also turns at 950 RPM. But because the pistons have three compression rings, all lubed by oil, it has much less blow-by. So the advertised rate is more realistic than oil free compressors that have one piston ring which leaks, cracks and runs hot.

Finally, the slower piston speed of a belt drive means less compression heating. This makes it more efficient because the energy from the motor is turning into cooler compressed air.

I sized the motor pulley to run it at the higher RPM range since the motor is a 4+ HP. Because it is rated for 145 PSI and the switch is a 120 PSI, the higher RPM isn't an issue. Since the unit has a good unloader, the compressor doesn't start at a 90 PSI dead head but rather the pump and line to the tank is drained. This lets the motor's start capacitor to spin up to where the motor will make more torque. The 60 cycle power has a condition where current lags voltage, a start capacitor corrects this and once the motor is up to about 2000 RPM, a centrifugal weight-spring system switches that off, relying on the run capacitor (the two bulges on the motor are the capacitors).

I could have suggested the larger compressor, rated for 5 HP and ran it slower but that is an overkill. Safety here is from the 120 PSI operation of a 145 PSI rated compressor, even though it is running at the upper RPM range. The motor is rated at 14 amps max running, that is 3220 Watts. that is 4.32 electrical horsepower. Sure, lock the rotor and the current will go to 20 amps, there you can say it is a 6 HP motor but it isn't doing any work. Take the SCFM ratings on many compressors with a grain of salt, that is under hypothetical situations.

Compressors are just reverse engines. Just like (some) generators are reverse motors. Or air conditioners are reverse steam engines. Thermodynamics, the laws were only discovered by humans. Nature wrote them. This is why engineers are better than lawyers rofl
 
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Keith_J

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I am not worthy to carry water for James Doohan. All I gave my country is time, he gave a finger, even though from friendly fire.

I just like making stuff work. Eventually, this M37 will be First Sergeant acceptable.

Oh, did you hear? Those monster C-clamps work well in breaking beads of rusted split rims? Yeah, that wheel is broken down, ready for refinishing. The split side was a bit more rusted, the other side pulled off.

Next big project is replacing the right side cowl sheet metal. Then the bed front patch piece which needs flanges bent. I got a little sheet metal brake, going to beef it up for a 30" long flange. More welding :p. Will need another 125 of argon soon.

Oh yeah, I got a 10 pack of 0.040" (tiny) tungsten electrodes. No more stopping to grind, just swap and go. They didn't have ceriated (non-radioactive) so I am falling back on thoriated (radioactive) but that is only alpha (helium nucleus, stopped by paper). Still, any electrode grinding will be done outside since the solution to pollution is dilution. Diamond disk in a Dremel works fast.
 

Keith_J

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I guess we cannot talk about the novel Great Expectations since the nanny censor edits out Delta India Charlie Kilo. The story of poor Pip will go without mention of the author, Charles ****ens :p

Oh well, that doesn't pertain to former military vehicles or M37s.
 

mkcoen

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Life issues have gotten in the way the last week but I'm back at it part time now.

I'm trying to get the front section of the frame cleaned up for painting and part of that has included cleaning up the front axle. Here's a couple of pics of the left front. Who knew there was an actual shape other than "blob" in there?

Pics:
1) Lt front axle before
2) Lt front axle after

TexAndy actually cleaned the right side up but before we took any pics. It was just as nasty.
 

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mkcoen

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Well the wife has been seeing a whole lot of tear down and very little reassembly so I thought I'd throw a couple of pieces back on just to make her feel better.

Here's the left side engine cover back in place. I'll have to take it back off to finish the cab panel but for now it'll hopefully make her feel a little better about it getting put back into a running vehicle.

Pics:

1) Left side engine panel 1
2) Left side engine panel 2
3) Right frame rail after paint
4) Left frame rail after paint
 

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linx310

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Cool. We tried like the ****ens to get that tire off the rim. Dang thing was glued on.
Thats why I took my m38a1's old tires and rims to discount tire...it was well worth the money rather then 8 hours of cussing and broken parts.
 

mkcoen

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After finding 3 clues that our truck once belonged to the Israeli Defense Force (Hebrew on spare tire, correct color under the current OD green, Israeli phone token buried in grease on frame) the wife decided she wants it dressed back in IDF colors. In this case Sinai Grey (thanks to M813rc for pointing me in the right direction). At least the Grey was painted over the OD the original go around so I don't have to sand everything back down just paint over it.
 
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