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M48A1 Engine Running Again

MCTNKR

MCTNKR

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Fountain Hills, AZ
Looking for someone familiar with the AV-1790 ignition system. Our engine starts on the booster coils fine, but dies once the boosters are turned off. Is this caused by a problem with the magnetos?
 
Malyutkaman

Malyutkaman

Member
48
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Location
Des Moines, WA
Could be a problem with the magneto internal timing. Magneto to engine timing can be set perfectly but if the magneto internal timing is off it will only run with the booster.
 
J

jkftl

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Ft. Lauderdale
I've had my hands on these machines a bit. Before installing a mag spin it up with a power drill. If no fire, it is usually the magnets. After many years they lose and must be recharged. Many aircraft mag shops can recharge these units. Condenser must be checked and of course points, but only magnets will keep it from making fire on the bench. Once in the engine follow the book timing procedure CAREFULLY. It is not easy. Of course the mag must be set in the engine (correct timing mark!) with things set to match marks. Everything is in the manual.
These big engines are far more demanding than an aircraft engine. "Booster" is only used until engine is at idle, max 30 seconds. Starting is far faster and needs no ether if you use the hand primer, in any weather. Saves booster time, starter life, and batts.
 
M

murphy

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anita iowa
I hate to disagree but I have two running 1790s in my shop out of m-47 pattons and neither one is supercharged the one in the video isn't either if it has the stromburg carbs on it!
 
J

jkftl

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murphy said:
I hate to disagree but I have two running 1790s in my shop out of m-47 pattons and neither one is supercharged the one in the video isn't either if it has the stromburg carbs on it!
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Right you are!
I just assumed they had to get all power possible out of the 1790 as they did the 895. Only the late injected 1790 had the supercharger. Do you know these Stromberg carbs are also on the GAA? Mags also, I believe.
All are fabulous engines...nothing in the world like them. And starting one up (no pipes!) is a life-altering experience. The New Zealand video is accurate despite amateur camera work.
 
M

murphy

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jkftl said:
Right you are!
I just assumed they had to get all power possible out of the 1790 as they did the 895. Only the late injected 1790 had the supercharger. Do you know these Stromberg carbs are also on the GAA? Mags also, I believe.
All are fabulous engines...nothing in the world like them. And starting one up (no pipes!) is a life-altering experience. The New Zealand video is accurate despite amateur camera work.
Click to expand...
They do have a great sound!! Its a bit on the scary side when they fire the first time and you don't exactly know whats going to happen but it doesn't take you long to get all happy!! I start ours on a stand we built every few months just to keep them lubed and to hear them!! They will only run about 10min on the 2.5 gallon fuel cell we use (it takes a fair amount of that just to fill the float bowls). After you warm them up and rev them some they will shoot a blue flame 2 ft into the air!!!! Maybe not a good indication of fuel efficency but it sure is cool!!!!
 
J

jkftl

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Ft. Lauderdale
murphy said:
If you ever in Iowa Im just 3 miles off I-80 between Des Moines and Omaha stop in Ill fire one for you. Its way better in person!!
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Just curious...Do you have hulls for your 1790 packs? I drove M-47 as a teenager at an Army Reserve armory, 1959. The unique 'side-stick' steering is memorable. The thing has some WEIGHT. We have a nice M-41 here and it has become (after lots of hours work) a treat to drive. A great crowd-pleaser, not to mention driver-pleaser. Current project is a Stuart, with 6.2 GM/Turbo 400 trans. Runs 30MPH on dirt, sounds fabulous. Turret will go on this summer.
John Kessler
Ft. Lauderdale
 
J

jkftl

New member
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Ft. Lauderdale
MCTNKR said:
https://www.youtube.com/watch?v=hsLKmqQBHKo
This video is a little better quality shot last year of the 1790 idling in order to warm up the 16 gallons of oil prior to an oil change. The restoration of the M48A1 has been slow due to competing demands but the power pack should be re-installed this summer.
Click to expand...
I understand that in certain duty stations in Germany and Korea they installed 24V sump heaters powered by the APU. That sort of thing might be dead-easy to install...even in 115 or 230. I bet you will find the access cover for installing a heater directly in the sump. Our MTU 538s would not crank until oil pressure and temperature were up. Pre-lube pump and heaters are mandatory on ALL big recips.
A 538 MTU/Maybach is direct descendant of the Zeppelin airship engine. 6V/cyl and roller bearings! I consider it quite the peer of our Continentals.
John K.
 
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