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1942 Clarktor 6  MILL-44 Heavy Aircraft Tug         Last Modified: 
On This Page:  Restoration/Operation of my U S Army Air Force issue Clark aircraft towing tractor

April 3, 2010

We rolled out the tug with the new bumper plate countersunk and bolted to the tug chassis, complete with 40,000 pound capable hitches front and back. The tug is in rattle bomb self etching green primer and still has a few minor bug. For the most part, the tug is ready to be put into service. Just in time. Today, Bill Foraker and I were invited to work the Doolittle Tokyo Raiders Reunion at Grimes Field in Urbana, Ohio on April 15 and 16.

1942 Clarktor 6 aircraft towing tractor in primer.

March 2010

John Watler was kind enough to get his buddy "Smoker" to locate, mill and tap holes for the 11 inch clutch pack onto the new, correct size but wrong bolt holes flywheels from VPW. They fit beautifully!  Jeff Wellum and I re-assembled the flywheel and clutch assembly, the rebuilt starter and all the associated parts and the tug was again ready to roll.  I installed a new battery and hit the switch. The tug starts easily and runs beautifully at speed.  However it still wouldn't idle. We took the carburetor (Carter Ball & Ball 700s) apart and tried to make sure all the circuits were open. We found a couple passages blocked and a lot of grime in the "rebuilt" carburetor.

We also retrieved the untouched bumper plate from the machine shop that had it for 4 months and started looking for a new place to get it straightened and the extra holes welded shut. I asked my friend Jordan Brown who owns J&N Metal Products, an aerospace products machine shop if he thought he could straighten it. He said surely that he could, and asked if I had a drawing of the front bumper plate. He said he could make a new one easier and better than we could straighten the old one. Fortunately, Joe the moderator on Clarktugs Yahoo group has provided technical drawings of almost every clark tug part that is out of production. Jordan looked at the drawings and said it took him about 40 minutes to make a 3D rendering of the bumper plate. Bill Foraker and I went to J&N Metals for a tour and to watch the plate being fabricated, along with a new rear hitch mounting plate and doublers for the front bumper plate (to eliminate the lead weights on the tug fenders). In a little over an hour, the laser had cut all the parts, they formed the 45° bends on the "wings", and welded the fender mounting angles on the 1/2 inch steel plate. Man the thing is a work of art!

J&N Metals laser cut, formed and welded a new front bumper plate for our Clarktor 6 aircraft tug.

The rear pintle hitch attach plate was originally square and made from 3/4 inch plate steel. Since we were burning a new bumper plate out of 1/2 inch steel, it would be easy and practical to set up the rear mounting plate on the same burn and just use TWO each 1/2 inch steel plates welded together. It's pretty beefy. We also weren't sure what height to set the hitch, so we made several position options to set the hitch between about 12 and 18 inches off the ground.

February 2010

Jeff Wellum and I pulled the clutch assembly and flywheel out from under the clutch housing today. Thanks to John Watler and Bill Foraker for getting the transmission and propeller shaft out of the way. All Jeff and I did was release ALL the bell housing bolts and then pull the housing slightly aft. Then all the parts came right out the bottom... after removing the 8 shoulder bolts that hold the 11 inch clutch assembly from the Chrysler Industrial 230 cid engine. Turns out that the 10 inch disc that I ordered from Vintage Power Wagons was wrong. And the original starter ring gear teeth were not only damaged, but the flywheel was broken. The should that the ring gear seats upon was partly fractured off and the starter ring gear was flush on the face of the flywheel. The whole thing is trash. Now I have to ship 30 pounds of flywheel back to Iowa, and order the much more expensive 11 inch flywheel and ring gear.

December 2009

Jeff, Jeff and Bill worked on the tug while a few others of us worked on the Rocket airframe. We flushed the radiator before we removed it. Bill and Jeff Tucker got the battery box/seat mount hinged to position. The tug started pretty easily... even though Jeff Wellum determined that two plug wires were swapped. We didn't get much of a chance to run the tug after figuring out why the damn thing wouldn't run very well, but we did run it for a few seconds and it's MUCH better.  We keep making little improvements to the tug, trying to get it ready for work early in the Spring, 2010.

Most of the tug in green primer:
Jeff Wellum is on the other side turning the distributor..

The First Part of the Story.....

I was approached by Keith at Muncie Aviation about a Mill-44 aircraft tug they wanted to sell. It had been in a hangar (barn) for quite some time. Apparently it had been used extensively by MAC after the tug retired from military service.

The tug was rought, but it ran. A few parts missing, but a solid project to work with.

The engine was reported to be a Chrysler flathead 218, which is a 6 cylinder engine. This one is an industrial engine and a data plate shows it was rebuilt in 1983.

The tug has a couple hitches. Neither is original, or in very good shape. The bumper plate is bent quite a lot, but should be repairable. I want to have a working tug that is as original as possible. This bumper plate is a keeper.

There's a lot of surface rust. There's a lot of steel!  But I think that everything is workable, including the wheels.

There is a serial number stamped into the frame in this location. It shows this tug is #H-1583.

The data plate has been moved to the top of the hood for some reason. It's very hard to read. At least we know it says it's a MILL-44 and has a drawbar pull of 4000 pounds.... according to the plate, anyway.

It's a shame that someone drilled teh brass placard and painted it with texture paint. Hope we can fix that.

The seat is missing. There are none available as new. But there are "blue prints"  of the seats. In fact prints and plans are available for many parts of Clark tugs. Clark is still in business, and evidently they have kept just about every document they ever used or created.

The seat mount is the top of the battery box. The hinges are shot, and some extra holes have been drilled through the box over the years. But there's a bunch of storge under there, and I'm going to try to take advantage of that.

This tire looks a little fuzzy. It's barn rash, not rot. The tires are actually in quite good condition... just squared from sitting flat for a long time.

There's a little splooge on the rear end. That should clean up. It's not leaking TOO badly.

The plastic covering of the steering wheel is long gone. New hand wheels are available from The Berns Corporation in California. I could also have this one restored for about 4 times the price of a new wheel.

I bought the tug and we loaded it up on a 7 ton car hauler.

It's about all my C1500 wants to do to pull this trailer and a 5000 pound tug.

Bill Foraker sure was excited to see the tug on the trailer. He wants it bad.

We made it home and parked the tug next to my wrecked F1 Rocket fuselage.

A little paint stripper tells more of the story.  My tug was refurbished by the Jeffersonville Quartermaster Depot right here in Indiana back in 1951. We assume that was when the engine was changed out, and the paint was stipped from Air Corps olive drab to Korean War era traffic yellow. There's LOTS of yellow showing under the Muncie Aviation Blue.

I drove the tug the next day. Double clutching is nearly impossible, second gear is missing, and there are no hydraulic brakes. Note that I did go to Tractor Supply and bought a temporary drivers seat.

Second gear was not actually missing. It was just being shoved out of the way by the shift handle because there is a retainer clip missing. That clip is supposed to hold second gear stationary and the other gears are shited into and away from second. The Berns Company still has a few Clark transmission parts.

The drive shaft and propeller are grimy from 67 years of use, but fairly tight and quite usable.

The fuel pump was disconnected. We assume it doesn't work at all. They are still available brand new!

The distributor needs points, condenser, rotor and dist cap. The Berns Company sells them... Hope to get NAPA or Autozone conversions right quickly..

Jeff, Jeff and Scott helped remove the bumper plate. It's pretty heavy.

Underneath the back "girder bumper" there is a wound screen contraption supported by a steel rod frame. There was a piece of exhaust pipe stuck inside of it, and rusted to pieces. I take it that this thing is either a spark arrestor or a noise/gas diffuser. No one seems to be familiar with it....

4/2011  Engine Ring and Bearing Job

The T116 230 cid L head ("Flathead") Chrysler Industrial engine on the tug has great compression and runs well, but smokes terribly and has very low oil pressure. We decided it was time to do a ring and bearing job on the engine to try to reduce the oil smoke and bring up the oil pressure. Bearings may not be enough to pump up the oil pressure, so we may need to look into a new high volume pump. But first things first.

 I started shopping for parts. VintagePowerWagons.com has all the engine parts we need, but the total price was around $500. I shopped on eBay and found a company in Sioux City, IA that sold me rings, rod and main bearings, head and oil pan gaskets all for less than $300 shipped.

A shot of the head to help show where stuff attaches.

I removed the hood/gas tank and some of the accessories from the top of the engine. So far, so good. Removing the head on a flathead is about as simple as it gets. Out with the head bolts and off with the head!  I didn't drain the glycol from the block. What a mess.

Head gasket and view of cylinders with head removed.

The pistons are in relatively good shape, but there is oil and soot everywhere. Wellum, Foraker and I dropped the oil pan and removed the pistons and rods through the top. A couple of the cylinders are gouged, but it doesn't appear recent. In fact the cylinder wall are very clean and smooth. The rings on the pistons were free and looked very clean. However, they also looked to be all chrome. We think perhaps they never seated since they were chrome. When we pulled them out, they slipped out very easily, with very little resistance from the 4 rings on each piston. BTW, these pistons are standard size and the bores checked out to also be very close to spec.

Jeff Wellum pulled out some of the main bearings for inspection. They weren't too badly worn, but they were ALL corroded. It appears that some moisture got into the engine and it looks as though it took it's toll on the bearings. Fortunately the crankshaft appears not to be that badly affected, so we'll just throw in the new bearings and call it good. We confirmed that the main and rod bearings were in fact .030 undersized as was indicated on the overhaul data tag on the engine. From 1981.

Jeff noted that a couple of the valve guides were a little sloppy, but not terrible. He also noted that the valves appeared to seat very well and uniformly. We'll leave the valves and guides for another day (hopefully not in my lifetime...).  All in all, this thing isn't in too bad a shape!

Next step: hone the cylinders with a flex hone and then clean everything up and get ready to install the new parts.