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differences in RWD A series gearboxes

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Keith Bennett

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Re: differences in RWD A series gearboxes

Post243102UTC FriUTC2018-05-11T14:20:10+00:00 2018...17.52

Hello Paul, and a warm welcome to our forums. I myself aren't an expert on such mechanical matters but I know there are several inmates on here who will soon be helping you. A40 owners are not thick on the ground in New Zealand although we do have a Club member down in Invercargill. Thanks for taking on an A40 - is it a saloon or Countryman model, and what year?
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dave the rave

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Re: differences in RWD A series gearboxes

Post243104UTC SatUTC2018-05-12T16:04:16+00:00 2018...17.52

Being a Marina that'll have the Triumph gearbox. That's why you've been told such. Probably a better box as it has synchro on all gears. Not au fait with them myself, but it sounds like they're a bit bulkier. Be a LOT easier if you can get a Midget rib case box. With a Midget 1275 backplate its a direct fit. No mods required.
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johnsearby

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Re: differences in RWD A series gearboxes

Post243104UTC ThuUTC2018-05-17T16:33:04+00:00 2018...17.52

Marinas have Triumph box, so you will need to get a propshaft made and modify the gearbox tunnel. 948 engined cars have a smooth case box and 1098 cars have a ribbed case box. Both have brass bushes on the mainshaft gears. 1275 Spridgets have a ribbed case box, but they have roller bearings on the mainshaft so are much stronger. They are however quite rare now. If you fit any of the Austin/ Morris/ Spridget boxes you will need the backplate and flywheel to match. As far as I rmember the Marina has a 6 bolt crank like the Spridget so a Spridget flywheel will fit but the smaller engines have a 4 bolt crank. You therefore need a Spridget flywheel and backplate whichever box you use. Don`t forget to have the crank, flywheel and clutch balanced as a unit. It might be simlpler to spend the money on tuning your existing engine; you can make a 1098 go quite well.
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dave the rave

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Re: differences in RWD A series gearboxes

Post243112UTC FriUTC2018-05-18T12:02:19+00:00 2018...17.52

Ah John......"Midget flywheel will fit"......NO it won't, the Midget crank has two diameters on the end, the larger one, ( same as Marina ), tapering down to a smaller diameter. Ergo, the Midget flywheel has a smaller hole that fits the crank. The Marina crank is a uniform size.

Marina diameter is 3.131"
Midget " " is 3.131 initially, then the tapered part, and finally 3.031"
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johnsearby

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Re: differences in RWD A series gearboxes

Post243109UTC SatUTC2018-05-19T09:11:49+00:00 2018...17.52

Had forgotten that, thanks for pointing it out.
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dave the rave

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Re: differences in RWD A series gearboxes

Post243101UTC SunUTC2018-05-20T13:19:38+00:00 2018...17.52

If deciding against the Triumph box, ( which i would ), there's two ways round it. Fit a Midget crank, ergo then you have Midget flywheel and clutch and box all matching. THOUGH will need Midget conrods, as crankpin on Midget crank is smaller, 1.625" as opposed to Marinas 1.750". Plus pistons are press-fit on the rods, so if they're damaged being taken off, new pistons needed. Cranks are not too difficult to locate, conrods perhaps a bit more so.
The other way is to have the back of the Marina crank turned down to suit the Midget flywheel. Of course, could use the Marina clutch & flywheel, but i think the flywheel is a bit too big for the bell-housing. And, the clutch plate will undoubtedly NOT fit the Midget gearbox input shaft.
So, yer pays yer coin and takes yer choice. Either way, looks like an engine strip.

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