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I've not done this particular convo, but doing mine, i've found that old engineer's maxim of "if it LOOKS right, it IS right!" is your friend.
A lot depends on the design of the front (gearbox end) prop joint.
When building the Carledo, I utilised the rotoflex style joint as used on the Carlton. I'd already fitted and leveled up the engine (like you it had a factory list to the left, in my case 7 degrees) and fore and aft it looked about level and I'd taken pains to get the extended centre line of the output shaft (the Vaux gearbox is beautifully short) dead centre in the tunnel. But when I took the stock prop to be adapted to the rubber coupling, the guy at Proptech told me it should have no more than 1 degree of runout between crank line and the angle of the front prop. Or it would destroy the coupling in short order. Since the engine/gearbox was already settled in the ONLY place it really fitted and I only had limited adjustment available by shimming the centre prop bearing, I took a chance and fitted the prop where I'd designed it. 10 years and a thousand storming starts and linelock burnouts later, the same (2nd hand) rubber joint is still there and shows no signs of damage or imminent failure. So I either have a good eye or am extremely lucky. Since i've never won the lottery, i'm tentatively eliminating luck!
On the other hand, if you have a universal joint at the front of the prop (which I believe is your case) it's the other way round. With a UJ, the LAST thing you want is for the crank/gearbox mainshaft line to exactly match the line of the prop front section. It not only leads to accelerated wear on the UJ, it can also introduce a lot of nasty harmonics and vibrations into the driveline. This is why the Sprint carries it's centre bearing cockeyed with one nut tag above the fixing bracket and one below. One or two people I know have "corrected" this "mistake made by a previous owner/mechanic" then come to me to sort their driveline vibe!
For a UJ, you should be looking for a minimum of 1.5 degree variation and practical max of up to 5 degrees, 3 is about optimal.
Or are you using a single piece prop? If so, put it wherever you like! Just avoid that straight line in the normal running position!
Steve
Steve,
Sorry abut the late reply, I have been away for a few days.
Yes, I like that maxim. I first heard it only a few years ago (which is surprising, as I am getting on a bit now) but it does hold true with so many things, even aesthetics.
That's very interesting about the prop-shaft ideally not being directly in line with the gearbox. If you hadn't mentioned this, I would have been trying my very best to get it directly in line.
I am using the TX1 prop-shaft, shortened by about 6", with a modified Sprint diff flange. It is a one-piece prop-shaft and it has a U/J at the front, with a splined sliding joint on the gearbox. So I will aim for about 3 degrees off the gearbox line, with the car sat on the ground. I am hoping that with engine level in the car this will be achieved vertically but we will see.