I am considering swapping my cross flow engine for something bigger, perhaps a tuned 1600 or a pinto. Can you explain why some models have a different prop shaft and which should I use?
I would always advise using the part that was relevant to the car you are trying to replicate. The are a variety of different propshafts depending upon where your car was built (the English and German gearboxes are very slightly different lengths and they employ a different axle), whether you have auto or manual box, type A (crossflow) or type B (Pinto) gearbox and most notably the engine capacity (cross-flow).
Easiest first, all auto 'box cars have a shorter 2-piece prop with a larger gearbox spline (25 splines as found on the type B gearbox and all 5 speed conversions as opposed to 16 splines on a manual crossflow) I think you can use this prop ‘as is’ with a 5 speed box.
All 1100 (all Manual) cars have a single piece prop, a lot of people prefer a single piece prop but I don’t. They were fitted because they are CHEAP! They increase unsprung weight, (ok, compared to the weight of the axle this is small, but that weight it carried by the universal joints and it shortens their life) and doubtless your bodyshell would not have the mounting for a 2 piece prop (but you can fit one).
1300 manuals have a 2-piece prop with a rubber mounted centre bearing and 3 universal joints. The rubber mounting cuts down on noise and allows the propshaft to slide forwards and backwards as the suspension goes up and down, only slightly but it does and the movement is absorbed by the splines in the back of the gearbox.
For this reason all 1600s (mainly German but all with British axles!) have a CV joint in place of the centre UJ to absorb forwards/backwards movement, the extra torque of the 1600 (and anything bigger for that matter) can cause the splines to lock up, all the forward thrust on the propshaft as your car squats under acceleration causes undue strain and premature failure in the gearbox.
Now lots of people will tell you this is all rubbish but the 2 piece CV jointed prop was designed for a reason, and anyone with a TR4a that has worn splines will agree with me! The key to it is maintenance, the centre bearing can be replaced and the UJs overhauled, if you go to buy one make sure you get the CV jointed prop with a BOLTED CV JOINT (not riveted), these are a sandwich joint and have to be removed to replace the centre bearing/rubber mount (always use a blob of paint on each half to ensure they go back together in the same alignment!). Remember also to check the length/origin of the part you are buying. Finally it is also important that the gearbox is in good condition, a worn output-shaft bearing can give the same symptoms as a badly balanced prop, sometimes only the oil seal is all that keeping things running true (I found this out when I swapped the oil seal).
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