Technical Which gearbox
- Thread starter JonPiz
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Technical Which gearbox
smart51
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The 500R didn't have the synchro box. I got used to mine very quickly so there doesn't seem like any point in swapping.
Similarly, the 650 engine only has 1 BHP more than the 595. You could get more than that just tuning up what you've got. Or do you plan to fit a tuned 650?
Similarly, the 650 engine only has 1 BHP more than the 595. You could get more than that just tuning up what you've got. Or do you plan to fit a tuned 650?
Ive rebuilt a 650 engine with no upgrades apart from larger exhaust valves in the head. Can you just drop the Weber 28 on the 594 engine or do you need to open up the inlet in the head to match the bigger carb
smart51
Established member
My 500R came with an 28 IMB fitted by a previous owner. The 594cc head has the bigger diameter carburettor port already. It should just be plug and play. Has your car still got the 24 IMB?
Not sure, I bought it yesterday and collect it next Saturday. I have a 28 IMB I can put on it
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I thought the R did get the synchro box?
You’ll soon find out when you pick it up, either you’ll need to double de-clutch the downshifts or you won’t!
I believe the 500r and 126 use the same gearbox bell housing, with the side mounted starter (as opposed to top mounted on the un-synchronised 500cc gearboxes).
If my understanding is correct, then the 650cc engine is a straight drop in
You’ll soon find out when you pick it up, either you’ll need to double de-clutch the downshifts or you won’t!
I believe the 500r and 126 use the same gearbox bell housing, with the side mounted starter (as opposed to top mounted on the un-synchronised 500cc gearboxes).
If my understanding is correct, then the 650cc engine is a straight drop in
smart51
Established member
My 500R has a non-synchro box. They do have the 126 bellhousing, with the starter motor on the side. It's quite handy when working on the engine by yourself, as you can push the starter motor arm with a long stick to turn it over. It does mean you can swap in a 126 gearbox and "all" you have to change are the half shafts.
smart51
Established member
Check the jet sizes. Mine is currently running with the mixture screw turned out by 2.75 turns. Any less and if I press the clutch with the engine doing 3000 RPM or more, the revs drop to zero and the engine stops. 3 turns out is the max. If you need more, you need a bigger jet. I have a bigger idle jet, I just haven't fitted it yet.
lazylobster
Established member
I have a 500R. Yes, 28 carb fits no prob.
I also have a sync gearbox which is pretty fab. I had it fitted. I use my car a lot and do lots of miles, so double de clutching was not really an option I wanted to live with.
your car, your choice.
I also have a sync gearbox which is pretty fab. I had it fitted. I use my car a lot and do lots of miles, so double de clutching was not really an option I wanted to live with.
your car, your choice.
smart51
Established member
Maybe cars for NZ had the 126 box. It's not uncommon for different territories to get different specs of car.
Yes that may be possible but unlikely I would think as only a little over 100 Fiat 500R cars made it to NZ as opposed to the earlier models that were part assembled there and all had the original non synchro box.
Looking for other details in the book, "La Guida", that was given to me some years ao by a generous forum member, I came across the sentence, "The 500R remained quick-engaging, but not yet synchronized".
But that was over fifty years ago and anything could have happened since.
Just checked an it still has the 24 IMB. I drove it home yesterday from the people I bought it from and it did go OK so I look forward to the power improvement with the 28 IMB
the hobbler
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Try "lucasz" at L.P. Garage in Sudbury, Suffolk. He strips126 cars and occasionally has a 126 box for sale. I have bought 2 from him with no problems, but I will admit, it is always a risk. But why change to a 126 box? The 500's box is actually the better box and all one has to do is to learn how to double-de clutch. Don't forget, if you are going to use a 126 box in a 500, you will have to fit 500 drive-shafts---the 126 shafts are too long. It is not a difficult job, just a bit tedious.
Ant Knox
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Worth noting also the the 126 gearbox has no sychro on first gear too, which is the gear that's arguably most difficult to mesh in both types of box and should be done when the car is stationary.
I go through phases of wanting to swap out for a sychro, but i'm actually starting to enjoy the challenge of the original setup.
I go through phases of wanting to swap out for a sychro, but i'm actually starting to enjoy the challenge of the original setup.
lazylobster
Established member
All good points re: the original box. But I still rather have my 126 sync gearbox. Depends on your OP's use case.
