Without photos, it never happened so I revisit the JATCO 4N71B adaption project to show what the transmission looks like bolted up to the Willys 4 banger engine and also the progress made on the flexplate adaption. A lathe mishap delayed this and other projects while I tracked down and purchased replacement parts for the cam lock mechanism that holds the chuck in the lathe spindle. Twenty years of wear and my ham-fisted attempt to force a replacement chuck to fit resulted in the lathe expelling the chuck, bringing machining of the torque converter locating spigot bush and reinforcing plate to a halt until just before this column was due. That also halted truing up the tool used to locate the bellhousing under the milling machine spindle. Turns out my 20-year-old lathe is a Chinese copy of a Taiwanese one that in turn was a copy of an American one, or was that a British one? Didn’t matter in the end for the worn cam-lock devices, used to secure the chuck to the lathe spindle, are a smaller diameter on mine compared to the standard USA spec D1-4 Camlock system used by most Asian manufacturers of imported lathes. Of course, the online suppliers only listed the standard sized spare parts and when I did find a supplier with a stock of the correct ones they were on the other side of the city and another ad-hoc COVID lockdown was in force. Also, I am still trying to find a supplier, with stock, of the 3mm wide Woodruff key cutter needed to progress the twin-supercharger project but that is another story.
Again, as explained in the ASR370 column, this is a report on what I am up to and not offered as a full on how-to article on how everyone else should be doing a transmission conversion. Also, I should clarify I do these conversions as a hobby, just like with this column, and don’t have a budget to engage outside CAD or CNC services or to pretty things up for photoshoots. As always what you see is provided for inspiration to try your own home brand conversion or just for amusement.
At least my TIG welder behaved and welding the tabs on the bell housing to line up with the mounting ears located either side of the engine block was a straight forward operation, as was weld filling one bolt hole and reinforcing around the edge of another. The aluminium VL Commodore 4N71B bellhousing has a nice ring to it, when struck, indicating it was heat-treated during manufacture for increased strength, so I was careful not to get it too hot during welding to avoid reducing its temper. Also, let it cool down slowly after welding for the same reason. If it had softened during welding or cracked during cool down the ring would be duller or non-existent but it still chimes nicely, indicating the procedure worked. The weld deposits were dressed down using an end mill while the bell housing was clamped to a rotary table and turned. For now, only enough material was removed to allow it to sit flush on the drilling jig so the two dowel holes could be located and drilled undersized, along with the other two upper bell housing to engine block bolt holes. I’ll give it a final fly cut before fitment to the engine. Reason for under-sizing the dowel holes is that, as with all early engines, the crankshaft centreline is not always where it is meant to be due to the manual machining procedures and tolerances in play at the time of manufacture, or line boring of the main bearing tunnels during a subsequent engine recondition. The latter example particularly when babbitted in place main bearings are involved. For this conversion,the dowel holes will be final sized using a “D” drill bit and reamer after a dial indicator, attached to the crankshaft flange, has been used to clock the opening at the rear of the bell housing into alignment with the crankshaft centreline of the recipient engine. This “clocking” to avoid misalignment isn’t as critical with early non-synchromesh gearboxes but is best practice when adapting a modern synchromesh equipped gearbox or automatic transmission to an early engine. More modern engines manufactured using automated machinery generally are held to closer tolerances, but “clocking” should still be checked when fitting up an adaption.
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