A Bigger Engine and 126 Transmission

Old 500 Engine and Transmission Removed



New 126 Transmission

The original transmission was uprated with a 126 version imported with the engine from Italy. This is required, as the 650cc engine from the 126, has different mounting face from the 500. I have also installed  new Abarth racing spec drive shafts (on advice and supplied from Middle Barton), and shown in parts area (Part 1).



The later 126 transmission designs are based on the original 500 layout, but with several improvements on the weaknesses inherent in the 500 designs.The 126 gearbox provides a good next step and will take double the torque of the 500 with these mods.

The original Fiat 500 had a non-synchromesh (crash) gearbox, so installing the 126 4-speed, synchromesh, manual transmission was going to be a big improvement. The 126 gearbox, has synchromesh on second, third and fourth gears, is an easier gearbox to use, and has a higher final drive ratio (ideal for running 13” diameter wheels and tyres), so it's more relaxed.

Both the 126 and later 850s still suffer from a fragile differential.... though stronger than the 500. Its something you need to check for fatigue cracks and wear regularly. Luckily, the differential is showing no fretting and less than 10 degrees of backlash (measured at tyre). The diff is noisy in operation, even when in good shape. And its well worth experimenting with oils for a longer quieter differential life. I have gone with Hypoid Gear Oil - SAE 90 or 85 W 90.

The Ratios are 3.25/2.07/1.30/0.57 with a final drive ratio of 4.88.
(N.B. To calculate the gear ratio of an 18/34 gear set, divide the 34 by 18 i.e 34/18 = 1.88:1).


Clutch
An uprated clutch that bolts straight in was installed. It is more reliable at higher power outputs, its pressure plate will take up to about 60bhp and equivalent torque, while the diaphram will help provide a smoother change with a better thrust bearing.


Engine
Initially I have installed a lightly modified single port Fiat 126 engine, delivered used from Italy, but was overhauled and rebuilt from bottom end up, with new gaskets, rings, etc.. A new single-port cylinder head was imported from U.K. and installed after free-flowing and porting. At the time of engine installation, new engine and transmission mountings and bushings were installed, along with a tuned, free-flow muffler being constructed. This was done to first satisfy me that the car was sorted out, with the correct braking and handling setup. Afterwards, I will then choose which way to improve the motive power.

A big advantage of this engine was the electric, push-button starter (previously a cable pull), and the upgrade to an alternator instead of an antiquated dynamo, for electrical charging.


   
Rebuilt 126 Engine below :



Ready for engine/transmission installation (note the new coil springs and dampers already installed).




Later options could be

•   modify the 650cc engine into a big-valve, dual-port, Dell’orto carburettor, screamer
•   modify it into a lower-rpm, single-port turbocharged brute
•   or, convert to an EV (electric vehicle); a good idea in these ecology-minded days.

It's running really well, and the 650cc engine makes a surprising difference over the original 500cc (but certainly no speed demon).