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1923 Metallurgique Gearbox


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I have just pulled the engine and gearbox out of my 1923 Metallurgique to try to eliminate a loud knocking coming from low in the engine from the spiral gears which drive the overhead camshaft and magneto / waterpump but more on that later.

The gearbox in this car is a four speed crash box and while it is out I have cleaned it down and am in the process removing the gears and shafts to replace all the bearings and to try to some how stop the oil weeping past all the shafts and bearings where they penetrate the casing (no seals originally of course).

I have noticed that there is no provision for a vent in the gearbox anywhere and thought that maybe I should drill a small hole in the case somewhere near the top as maybe that might stop pressure build up in the box when it is hot and possibly decrease the oil pushing past the shafts etc.

What do others think and if you agree, how big a hole do you think I should drill.

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  • 2 weeks later...

Too bad, no response to your question yet. My only 2 cents to offer is how Harley used to vent their gearboxes by using one of the cover screws appropriately drilled about 1/16" hole vertically along the axis of the screw but not through the head and then horizontally across the head of the screw to match up. Certainly not as large a box on your Metallurgique but maybe some food for thought for you rather than drilling the box itself. Sounds like a very cool car, how about a picture here for us ?

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Thanks for your thoughts Barry.

Since posting my question I have thought that maybe drilling and tapping the top cover plate and installing a vent cap off a diff might work OK as long as it didn't spit oil out.

When I saw your idea, I had a look to see if I could use that somehow but unfortunately the hold down bolts on the cover plate are actually studs and nuts so no luck there but you wouldn't believe it, it has a bolt in the top of the bellhousing above the flywheel/clutch drilled exactly as you described. What it does there, I have no idea as although the area is fully enclosed it has a hole about a third up from the bottom where the clutch pushrod goes in so there would be no pressure build up inside.

Maybe it bleeds off hot air from the clutch and generator which is also in there.

This is the car before it was dismantled but is now in many pieces however I will get some photos of the engine etc as it goes back together.


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You might talk to Barry at Berwick Vic (03) 97071994. He and the boys have mostly been restoring and running veteran Met.s of different sizes, but is probably running at least one like yours. There was an exhibition of vintage cars at the Olympic Pool venue in 1960, where his restored engine of the first was displayed.

Nanette Polard had one in Brisbane for years. The engine had been largely rebuilt by someone; and largely I think because she and he husband had been abandonned high and dry by the man they had been helping and reliant upon on the 1970 FIVA International Rally from Sydney to Melbourne she asked me to complete unfinished details. ( They finished the event with me in the 1918 Mercer, and I left the booked accomodation to them.) Your car may or may not be the same one.

I do not recall anything suspect about the vertical drive gears, but one thing I did pick up was that the main bearings had been line-bored without the block bolted down, so that the centre main was out of line by more than the thickness of the oil film. The crankshaft would have bent with every rev., but fortunately it had not been run.

The generation of heat in a gearbox is much to do with the gears churning heavy viscosity oil. If you have good bearings, and seals that will keep the oil inside the gearbox, you may be able to run gear oil light enough to turn little horsepower into heat, yet still protect everything perfectly. One man near here has a highly developed V8 Chev engine in a cut-down Stuart tank, and with ATF in the transmission it will accelerate to 50/60mph within yards, and then climb a wall.

In the beginning of the war, Bob Chamberlain of Rolloy Pistons and Chamberlain Tractors was sent to USA fro various reasons, and was on the committee responsible for tank design, with Walter Chrysler among others. The first Medium Tanks, 27 ton Lee, Grant, and Sherman and the AC1 Australian derivative, had basically the same transmission. When the first ones were tested, Shock, Horror, the transmission within half an hour became far too hot for the health and procreational viability of the driver sitting astride it. Everyone except Bob blamed the transmission steering brakes and thought the concept doomed. After some argument, they consented to take the test vehicle to a place where they could drive it in a straight line, without touching the brakes, for half an hour; thus proving that the gears churning the large volume of high viscosity oil was what really generated most of the heat. Re-designed with a driven oil pump to send it in sensible quantity to everywhere it was needed, and with the filler neck and dipstick shortened so there was only a couple of inches oil depth in the bottom, the overheating vanished. Doubtless the performance and economy also improved remarkably.

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