Hey all,

So I have started out on my power train build for the locost, as some might have seen I am exploring something different as usual. I have a 2.0 Fiat coupe 20 valve turbo, and if that wasn’t enough I’m taking it further by hopefully building it into a 2.5 litre using the Stilo 2.4 bottom end and some piston reworking to allow a lower CR and boost it. To compliment this fine engine build, I’m looking at a closer ratio gearbox, with 6 speeds.

Now last month I bought off eBay a Stilo Abarth “6 speed” box, now from my research I didn’t think they did one, but the seller was sure it had forward 6 cogs in it, well it didn’t, so long story short I had a refund and he didn’t want it back. So, what’s the next step. Well I’ve read up as much as I can about the Alfa/fiat C family of boxes and from what I have learned this C514.5 from the Stilo is very similar to the late spec coupe box I already have and the Alfa Romeo C630.6 gear box from the 3.2v6 and 1.9 16v diesel as found in the Alfa GT.

Now, the ratios in the V6 are very similar to the Stilo and coupe, 3rd and 4th are identical. But a v6 box is rare and expensive. So I’ve ordered a C630.6 from the diesel GT (£120), should be here next week. Now, not sure if it’s going to be possible, but I think I should be able to switch the gears from the Stilo box I have into the new Alfa GT box replacing 3rd-6th with cogs from the fiat box. With the lower final drive as a pose to the coupe box I have calculated at 6000rpm my gearing 1st to 5th could be a lot closer then I would have a 6th gear which I could tune to be a little taller for cruising.

So I’ve started stripping the Free Stilo box, plan to use the bell housing as it has an internal clutch release mech and the diff casing hast got the speedo gear, so can delete that using that casing.







Might all be a waste of time, but learning a lot about gear boxes and I have 2 other spare coupe 5 speeds if it all goes wrong.

From what I have learnt, this box is pretty strong, maybe not as strong as the F40, but better bearings than the M32. And in a light weight car, 410Nm (the max rating of that box) it should all be pretty interesting.

If any one has any experience on these do please comment, I’m learning as I go. This Stilo box is in really good condition, no wear on the synchros or gears, so it’s a good sign that my 2.4 litre bottom end should also be reasonable as it came off the same engine. I need some new pullers I think before I go ahead and remove the gears, but if I have both gear sets side by side, I am confident I can make it work, lot of the part numbers are the same.

Rob

Learning as you go with gearboxes is certainly brave, I'll give you that. Confident I could dismantle them, but reassembling one froma variety of bits and having the confidence it's going to work is beyond my knowledge / skill level. Still, you'll have spares to fall back on!
Having built the car from scratch swapping out a gearbox shouldn't be too much of a task if you need to in the future - make sure there's clearances for getting the old one out and the replacement one in.

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Got the Alfa 6 speed stripped and set out side by side the 5 speed fiat box. Both boxes in great condition and my research seems to have paid off, think I can do what I want. Need to order some new tools next week. Going to clean up the casings next job, but I have tried the full gear set in the casing. All fits.

Really pleased with the progress so far.

Rob

I think the trickiest bit of the reassembly will be getting the reverse spindle realigned to bolt up.

I’ll post the ratios I’ll achieve once I’ve got the gear set split.

But from my research and calculation, if I can achieve my goal, I should end up with a box similar to the 3.2 V6, but 1st and 2nd will be slightly lower ratio and 6th will top out at about 136mph @6000rpm, compared to the coupe box @160mph in 5th. Should be perfect mated to my 2.5 turbo build.

I’m excited. Cost wise, this is working out much cheaper than a coupe or V6 6 speed, so happy to throw the money at it just for the learning.

Once you have done it or even before would it be possible for you list all the tools you used to carry out the task i.e the kind of hydraulic press you use and if any testing rig you have built up. thanks.

Yes I’ll share all the details as I go. No problem. It’s all experimental, like said earlier, there isn’t much info out there on this kind of conversion.

It is it the conversion , but the general know how to pull
Off or press out the gearing: circlip removal re- assembling : ways of testing before putting back together.

It’s the expense of the tooling required because as these gearbox age only Cheaper way really would be to diy.

I can build my type of engine but I had a look at the gearbox and just threw it away lol

The stripping of the two gear boxes is nearly done..... been a little frustrating, the 5th gear on the Stilo box was solid, my 6ton press has struggled to to get it shifted. So I cut it off and had it on the lathe. It’s in the freezer to chill over night and I’ll try again tomorrow with some heat.

Learnt a fair bit so far.

Once all stripped am going to do some measuring and calculations, then I’ll post my final achievable ratio choice.

Rob

My locost ratios are highlighted in Blue.

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More updates to come soon as I will be starting the rebuild.

Rob

So bought a 5th gearbox, this is the 2.5 Alfa V6 box, wanted it for the 6th gear, going to use that on the rebuild rather than fabricate my own custom 6th.....







So now I have two spare 6 speed shafts and extra gears. Interestingly this box had done 104k before the diff let go destroying the bell housing, but the condition of the synchros and selector folks are in pretty poor condition in comparison to my 80k mile diesel GT box.

Also, there are additional strengthening braces on the GT box, so I think I am building the strongest possible option. 3 boxes to build one, cost wise with the little odd replacement parts I’m still under £300. And in the future should I have a failure I should be able to rebuild it.

The casing has now been cleaned in the dish washer, it’s looking pretty clean now.

I will do a detailed post when I come to assemble it, next job will be to remove the V6 6th gears and clean those. Then paint the casing. I want to restore all the fasteners too, so I may want to re-plate them, another interesting process to learn and master.

Rob

[Edited on 26/6/22 by b14wrc]

Afternoon all,

So I have been so busy of late I haven’t had time to get on with putting the gear box back together. Managed to have a couple of much needed hours last night and this morning to start the assembly now I have all the parts I needed. Gone back together reasonably well, I’ve added new bearings and everything internally has been cleaned and checked. I chipped a couple of teeth on my 4th gear on disassembly, so replaced that with a new one for peace of mind. All synchro’s are good and no damage or wear to the main component. I think I’ve used the best and strongest standard parts I had available. So as far as a quality budget build goes, I’m pleased. Should have a nice short ratio box for track use and then a longer 6th gear (160mph) for road use, at 70mph the engine won’t be reving that hard, so I think it’s turned out well.

Still the diff to do, and clutch slave cylinder and seal, the selector needs a rebuild and clean. But it’s coming along.