Sandstone Heritage Trust - News

HTN 144 - Chris Wilson Reports on the Marshall MP6, the Allis Chalmers B & the Fordson Aircraft Tug- 9th October 2006

10th October 2006

Work continues on the Marshall MP6.
The main frame has been thoroughly sanded & cleaned – photo 100-0592.

Having got the engine assembled to the point where it is ready to fit into the frame, the next task was to check the transmission.

Firstly the remaining oil was drained – photo 100-0589. As can be seen, what little oil there was was not in good shape- years of condensation & sludge had accumulated in the bottom of the casings.

The MP6 has various drain plugs for all the compartments, and good sized inspection covers on top to allow for thorough cleaning – photo 100-0597.
At the same time it was possible to check the brakes. These are massive constricting bands, oil immersed, and because of the diameter of the drums are extremely efficient, while the oil gives excellent cooling & durability. The linings were in good shape, and there is plenty of adjustment. The bands are centralized by bolts protruding from underneath.

The all important crown wheel & pinion was found to be in excellent shape, with the correct amount of backlash etc – photo 100-0594.

A problem with the gearbox had been identified while towing the machine – it was obviously jammed in one gear. Removal of the gearbox cover revealed a misplaced selector. At the same time much superficial rust caused by condensation could be seen – photo 100-0597.

Since there had been a problem and also due to the presence of rust it was decided to remove the selector assemblies, check, repair & clean – photos 100-0596 & 0597. A small amount of wear was rectified, but it seems that the main problem was due to the cover having been removed and misplaced at some time.

The gears could be properly inspected at this stage, and apart from some staining are in good condition. The second & third motion shafts were correctly set up, but excessive end float on the first motion (Input) shaft was evident.
photo 100-0596

That this was an old problem could be seen from the fact that the clutch brake disc had been rubbing on the retaining bolts. However it was decided to get the setting right (.010” - .015”). This entailed removing the brake disc, and this revealed a surprising modification. Obviously at some stage the disc, which transmits all the engine power, had come loose and damaged the splines on the main shaft. To effect a repair the shaft had been machined down to a square, and a corresponding square boss welded into the disc.
photo - 100-0605.

This appears to have been done professionally, but nevertheless it is unusual to say the least to see power transmitted through a square drive, although come to think of it early heavy duty PTO drives were similar.
Great care will be taken to eliminate play using a high grade loctite. It is to be hoped that the shaft has not been weakened in the process.

Another discovery was that an important spacer between the disc and front bearing had become worn, presumably when the disc ran loose, and was also cracked – photo -100-0606. This had been welded, but had re-cracked. A new spacer is under construction.
A seal runs on this spacer which will also be replaced.

To obtain the correct end float shims had to be removed – the discarded shim pack can be seen in the picture.
The front axle and steering appeared to be ok, but checks revealed problems in the steering box and one front bearing, which fell out in bits on disassembly - photo -100-0609. One hub has broken or missing studs, and is having new studs & nuts made up. New bearings have been sourced. The kingpins are mounted on cup & cone bearings – a vast improvement on the usual bush arrangement – and even today usually only found on 4wd tractors.

The steering box has suffered from years of water ingress to the detriment of the shaft bearings. This type of specialized bearings can be difficult to find; fortunately they are identical to those used on John Deere 2cyl rowcrop tractors, and the bearings are readily available. photo -100-0607.
The steering draglink ends are worn, and this has been sent in for the end joints to be re-packed with high grade nylon.
The standard agricultural drawbar had long been discarded in favour of a straight pull from the rear housing. This had put serious strain on the side plates, which have been replaced – photo -100-0610.

A new drawbar tongue and securing pin under the belly have also been fabricated, photo -100-0611, and when these are in position the rear swinging bracket can measured and restored with it’s locating holes.
Allis Chalmers B
With rebuilt carburetor & magneto, repaired oil filter assembly, and attention to valves & oils, it was time to test the tractor. A suitable crank handle has been modified to fit, and a temporary fuel system rigged. After a considerable amount of cranking the engine burst into life. photos -100-0585 & 0586. Without a cooling system it could not be run for long obviously, but long enough to check oil pressure, which is good, and clutch and gearbox, which seem fine.

However a major oil leak showed up from the front crank seal. This was removed and replaced – photo -100-0587.
One thing leads to another, and during the stripping process it was discovered that the front axle mountings, which screw into the block,
were stripped. The holes have been enlarged and re-tapped
to 9/16” NC. – photo - 100-0588.
Fordson Aircraft Tug
Work on this has focused on removing years of grime and rust, treating rust spots, and sourcing spares –photo - 100-0612.