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I have an old SWB 1300 Marina based roadster. The 1300 engine & gearbox were long past their sell-by date and I intend to replace them with an Alfa 1750 engine & 'box. I was hoping to mate them to the existing marina diff. Can anyone who has done this modification please advise me as to the best way to successfully modify the hybrid 2-piece propshaft? I am assuming that the central Alfa propshaft bearing must be retained.
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Re: Alfa Engine swap SWB roadster
I have not done this mod but here are a couple of things that you may want to consider.
If you have the rubber donut antivibration UJ, with a shortened prop it will be working through a larger angle than originally intended. I suggest replacing it with a new one or perhaps replacing it with a standard bearing unit.
The 1.3 diff will in all probability have a 4.1:1 diff centre and if 'past its sell by date' may not like the higher power. Even with an overdrive 5th gear the engine may over rev for the road speed. I suggest replacing the diff centre with a 3.63:1 or if you are planning further tuning fitting a 3.45:1 Dolomite Sprint axle. -
Re: Alfa Engine swap SWB roadster
Thanks Steve, I take your point about the diff ratios but I thought it might be possible to retain a shortened front half of the Alfa propshshaft with its supporting central bearing which would ensure that the run of the front half of the propshaft was straight & level to the doughnut which is on the rear of the gear box. The connection to the rear of the central bearing is a conventional Hardy-spicer type UJ leading to a splined connection which matches the splines on the front of the Marina propshaft. Is it be possible to shorten both propshaft tubes sufficiently to retain this setup in the space available?Comment
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Re: Alfa Engine swap SWB roadster
Ah... I was forgetting the standard Alfa prop setup, with a splined adjustment section on the rear portion.
I think that whatever approach you take, the least angle that the UJ has to cope with must be best.Comment
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Re: Alfa Engine swap SWB roadster
Try, search the forum with "fitting a twin cam"
See entry by robert(honiton) 15 Nov 09
Ben Caswell probably not the last word on anything here!!Comment
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Re: Alfa Engine swap SWB roadster
I replaced the 1300 engine in my SWB roadster with a 2 litre Alfa twin cam some years ago but the difference was that I mated the engine to a Sierra gearbox. However, I retained the Marina axle but replaced the 4:11 diff with a 3.62:1 from an Ital. The propshaft is the original Marina cut down one piece but with the gearbox end u/j replaced with the sliding splined u/j used with the Sierra box. Not sure if this is any help to you due to the fact you are using the Alfa gearbox.Comment
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Re: Alfa Engine swap SWB roadster
I replaced the 1300 engine in my SWB roadster with a 2 litre Alfa twin cam some years ago but the difference was that I mated the engine to a Sierra gearbox. However, I retained the Marina axle but replaced the 4:11 diff with a 3.62:1 from an Ital. The propshaft is the original Marina cut down one piece but with the gearbox end u/j replaced with the sliding splined u/j used with the Sierra box. Not sure if this is any help to you due to the fact you are using the Alfa gearbox.Comment
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Re: Alfa Engine swap SWB roadster
Thanks for the input folks. It looks like I'll have to "suck it and see".
I remember, way back when Adam was just a boy, that the Marlin demonstrator roadster at kit car shows did in fact have an Alfa twin cam power unit but I can't remember the drivetrain setup. Does anyone remember this? Does the car still exist?Comment
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Re: Alfa Engine swap SWB roadster
Re an Alfa engine, I had the first one built by the factory after the factory demo. I used a 1750 with the alfa 5 speed box and a 1.8 marina TC axle with aa alfa prop shortened down. My red one appeared in Kit Car magazine as a full road test. It was sold to the Isle of Man, would love to know what happened to it and buy it back !!!!!Comment
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