Morgan transmission chain, and sprockets
All Morgans , 2 SPD, 3 SPD & F TYPE Left the works fitted with ¾ pitch,7/16 wide Reynolds roller chain. Originally known as 6R chain, today is Designated as 12-b-1 to ISO 606, or DIN8187.
Any Morgan fitted with a sprocket/brake drum, MUST use this chain, more modern design O ring chains have larger side plates and so the chain rollerdoes not sit correctly in the sprocket, causing excessive wear, and broken teeth.
3 Speed & F Types left the factory With a rear wheel sprocket/drum of 38 teeth, and a gearbox Xshaft sprocket of 17 teeth. With 1930’s roads and no interstates, this was fine. Today this gearing , with Morgan gearbox internals, is too low for modern roads. It seems best to run mostly with a 20 tooth gearbox sprocket, dropping to18 for trips around the hills. Many use a 19 tooth sprocket, but you should only use this for competition, and only for short periods. With the 38 tooth rear sprocket and the 19 tooth gearbox sprocket the chain never progresses around the sprockets, so any damage to the rollers will damage the sprocket/drum. BEWARE, some gearbox sprockets made in the 1970’s had the wrong spline in them and the X Shaft can be damaged. If the sprocket does not have 2 3/8 BSF extractor holes in it there is a good chance it is one of these.
Conventional wisdom says that It is normal practice to use only one split link in the chain. You should use 2, or 3. Setting the rear wheel position with the smallest sprocket on the X Shaft, (that would be 16 teeth) making sure that the open end of the link faces the rear of the car.
Set the chain length so that you have 2 rollers between the split links. With the bottom run of the chain tight you need around 1 ½ inches of play in the top run. Adding 1 tooth to the front sprocket requires a bolt adjustment to the rear axle. By changing sprockets in 2 teeth increments you can change the chain length by adding or subtracting one roller for each two teeth without adjusting the wheel position. Cranked links (3 rollers) are available so thatyou can have short sections in the sprocket box to quickly change gearing.
DH and K- 2017