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Fiat 500F Engine Rebuild.

Building a Fiat 500cc 2-cylinder Fiat engine.

The Beginning

Our first experience with a rebuild of a Fiat 500F engine. It was April this year (2019) when Rob limped his award winning 1969 Fiat 500 into the workshop. The engine sounding like a twenty year old Victa lawnmower that had never received a tune-up. Though it certainly did look brand new.



An Italian icon and classic. This 1969 Fiat 500F 500cc engine rebuild was the biggest project of the year and it only has 2 cylinders!


Rob had owned the car for roughly 2 years. Purchased off a Fiat restorer, this car had recently undergone a full restoration. Completely stripped, all rust repaired, new paint, suspension and steering components. No bolt was left un-turned, except for the engine.

Upon completion, it was entered into various classic car shows and won several awards. This is where Rob first saw the car and instantly fell in love with it. A deal was done, a cheque was written out and the Fiat now had a new home.



Fiat 500 500cc 110F engine bay

The Original 110F engine in the bay of the Fiat when it arrived at the shop.


It looks great and has never been out in the rain, nor washed with water since it was restored to be sure no rust reappears. “These cars are renowned for rust and don’t have great drainage systems” explained Rob after he had given us strict instructions to not wash the car.

It was clear Rob had a love for this car that we did not yet share with him, but it was sure to grow.


The Issue

Rob explained  to us that the car never seemed to run correctly since he first purchased it and the problem gradually worsened with each drive. He had replaced  various parts tryin to fix it without any luck.

A one-way valve was installed Into the fuel line to prevent fuel leaking back to the tank when parked for a period of time and a new fuel pump was fitted at the same time. The original ignition system with points style distributor was replaced with a new “123ignition” electronic item and the coil, leads and plugs were also replaced to eliminate any possible spark issues. A new, original “Weber 26IMB” carburettor was also installed.

Even though these upgrades didn’t fix the problem, they were certainly needed for what was to come. The other upgrades that Rob had already carried out and would be needed were an all new synchronised gearbox and sports clutch and even though still in standard form, the entire 4 wheel drum braking system was overhauled with all new parts. Even though it still uses factory drums and has no help from a vacuum assisted booster, it was certainly an upgrade from the old, rusty setup.


The Diagnosis

After chatting for a while, we proceeded to look over the car in the hope of diagnosing the issue. After getting the little 500cc running, it was clear that Rob’s diagnosis was correct. There certainly was a misfire, but it wasn’t an electrical one, nor was it a fuel/air mixture fault. A compression test confirmed the worst; cylinder 2 showed no signs of holding any air let alone compressing it.

This now meant the head had to be removed to be able to find and fix the issue and after hearing the news and looking upset for no more than 5 seconds, Rob told us to get it fixed, no matter what the cost. He also wanted us to give it a bit more power if possible.

A quick overhaul to freshen it up, with the addition of a sports camshaft for some added performance would have all the issues sorted quickly and easily. Well that was the initial plan anyway.

This project just became the biggest job for the year, and with it having only 2 cylinders, we never would’ve guessed it. We had only 3 objectives to meet: Make it reliable, give it some more power & keep the engine and the car looking factory.



Fiat 500F cylinder head removal

The cylinder head was removed to find the cause of the misfire.


“These little 500cc powered cars were designed for city driving and only produced a tiny 16.2kw(22hp) and 35.3Nm of torque when delivered from the factory. Their top speed peaked at 95km/h. Not the kind of car you’d wanna be in whilst travelling on a highway with a semi-trailer roaring past you.”



A badly burnt valve was clearly visible with the head removed.

The Research

With the cylinder head removed, it was clear that the cause of the misfire was a badly burnt exhaust valve. The engine was then completely removed and further disassembly showed more excessive wear and internal damage, including broken compression rings on both pistons. There was also evidence of a previous timing chain failure thanks to the score marks that were evident on the inside of the timing cover. How did this car make it to our workshop running on only one cylinder and with broken piston rings? We will never know but we suddenly had a lot more respect for this tired little engine.



Fiat 500F Engine Removal

The engine was removed to receive a complete overhaul.


With the internals looking very tired and the little oil that was left in the sump looking more like a thick sludge, it was apparent that this was going to turn into more than just a reconditioned cylinder head and a quick overhaul.



Poor oil quality Fiat 500 1969

The thick sludge of oil found in the sump and blocking the pickup.


From that night onward for the next month, we spent many late nights researching and studying the 110F series engine, which at this point, we still knew nothing about. Whilst searching for kits to carry out the rebuild, we were shocked to see the massive amount of parts available for these cars straight off the shelf. Of course none were in Australia, but around the world there was a huge love for these cars and around 95% of parts for the classic 500 were still being re manufactured by several companies. This included each and every bolt found around the body.



Fiat 500f engine rebuild

Further dismantling of the engine found more badly worn parts and broken piston rings.


Even more surprising, was the ridiculous amount of performance enhancing parts available. Not only that, but a kit, with all the parts required to turn a Fiat 500 into a complete race car including 4 wheel disc brake conversion, racing harness and engine bits to build it into an 800cc monster, were readily available and not at a ridiculous price you would expect to pay if doing the conversion on any mid-sized vehicle here in Oz.

We decided get in contact with some specialised Fiat 500 engine restoring companies to get some advice on which way to go about things, and after sending many emails, we had replies from USA, England and of course, Italy. We also read many forums and posts by people who had done it all before and learnt the issues they encountered and how to overcome them. Eventually, it was decided that the only way to get enough power from 2 cylinders in order to be able to even notice a difference yet still maintain excellent road manners, would be to increase its overall capacity.



Fiat 500 126 oil pump bad wear

The wear on the face of the oil pump meant it definitely required replacing.


Badly worn camshaft support 500cc crankcase

More wear found in the camshaft journal bearing within the crankcase.



The Plan

Seeing as though Rob had already upgraded to a newer, better gearbox and clutch combo, and the new electronic ignition system was good for anything up to a 700cc engine combo, we decided that upgrading to a 652cc combo would be enough of a power increase while still keeping it reliable enough to drive on a summers day without having to stop every few meters to check the oil or let the engine cool down.

Another bonus was that the parts that would be required are the same ones found in the later Fiat 126 that came standard with a 652cc, and an engine that enables you to swap cylinder bores and pistons by simply lifting them out and sitting new ones in meant fitting a larger size was as simple as slightly honing the crankcase enough to enable the larger bore sleeve to slide in…. Well at least we had read of it being done on the forums.

Finally, we had a plan, an estimated power increase figure and a total to put forward to owner, Rob. He giggled at the thought of the upped power figure, a total of 19kw and 41Nm of torque. (In a car weighing less than 500kg, this is a good increase). Then with excitement, he gave us the go ahead.


The Parts

It was now time to compile a list of all the parts we required, including anything that was worn or close to worn. Rebuilding a 500cc 2-cylinder Fiat engine whilst increasing its size requires patience as we found out. Everything had to be new or near new, and dimensions and angles of one part had to match those of another part in order for it to run correctly and efficiently whilst being reliable and looking as close to factory as possible.

The next month consisted of more late nights contacting various parts suppliers. Some required the aid of Google translate which got too complicated, others took days to reply if they replied at all. Most did not ship to Australia. Either way, we managed to compile a list of components we would require and before ordering, we contacted our engine machinist, Graham from Hi-Torque Engines, and handed him the list to see if he would require any other bits as he would be doing the machine work.

With the list finalised, Rob gave us the details of the supplier he had previously purchased his parts from. We decided that if Rob was happy with this particular supplier, then we knew we could at least rely on them shipping the parts without stealing our money. From the initial contact right through to the final payment and shipping requirements, David from MrFiat.com in America was extremely helpful and even went out of his way to quickly source the pistons he had run out of from another supplier in order to get the parts shipped to us as quick as possible.

With the parts now on their way, the excitement began to grow and by now, almost 3 months since it first drove in, our regular customers knew the deal with the Fiat and would ask for updates when they came to visit.



The Headache

The parts arrived within one week and it was like Christmas had come early the day the box showed up. We giggled at the small size of the box as the delivery driver sat it on the floor without breaking a sweat. Don’t forget, this box contained almost a complete engine and entire sports exhaust system.

Fiat 500 parts

The day the box of parts arrived

The following day, Graham came past to collect the cylinder head, crankcase and a handful of parts he required for measuring in order to machine the crankcase accordingly. We sat a new piston next to an old one and again started laughing at the size difference, all of us except Graham. He had a confused and worried look on his face as he carefully looked at the parts we had received.

With a new and old cylinder bore placed on the bench beside each other, and the crankcase placed gently on the ground, he started to point out his concerns. Whilst the overall height of the bores, from top face to the bottom of the sleeve, were exactly the same, the lower face of the new bore sat 9.5mm higher than the old one. This meant a few things.

First, the sleeve of the cylinder would need to sit further down into the crankcase which would obstruct the counter-weight of the crankshaft as it spun. It also meant, due to the fact that we were using the original rods as they were ok, the piston would no longer finish flush with the top of the bore at the highest point of its stroke, but 9.5mm above it. Finally, due to the tapered shape of the cylinder sleeve, the crankcase would not be able to be machined enough without it losing its strength and breaking within moments of the engine firing up.

Surely this couldn’t be a complete disaster. How have people successfully carried out this conversion before? We needed a solution and fast. This meant more researching.



Fiat 500F 500cc pistons next to 650cc piston

The size difference between the original and new Pistons.


Classic Fiat 500F cylinder bore sleeve 650cc

Overall, the height of the new and old cylinder bores were exactly the same. Though the mating surface at the bottom of the new bore sat 9.5mm higher than the original.


The Solution

Another late night searching the net for a solution answered our questions.  How did we end up with this issue? And how do we rectify it?

During our initial research for parts and reading forums, we missed a vital piece of information. Yes, many people were upgrading 500cc to 650cc, but they were either swapping a complete engine with that of a Fiat 126 or modifying a 126 500cc crankcase. We learnt that the 126 crankcase was stronger and could be bored out without compromising strength. This was due to only one reason,  the top of the 126 crankcase was 9.8mm taller.

Swapping to a 126 crankcase now was out of the question as the fact that the crankcase was taller meant that the gearbox bell housing was different to the smaller 500 one. This would mean the new synchro gearbox recently installed would be useless.

Another few emails were sent to David who had 2 solutions available. He first offered a set of shorter con-rods that would help with the height issue. But this wouldn’t stop the counter balance of the crank smashing the lower section of sleeve to pieces as they would still sit too low, it would also reduce the engine size to roughly 623 Cubic Centimetres (CC) due to the shorter stroke. His next option was perfect! A solid steel spacer plate with 650cc sized bore holes, the outer edge perfectly matched to the shape of the crankcase and a thickness of 9.75mm and ready on the shelf to be shipped. The remaining height would be taken up by using copper gaskets to seal the contact areas between the plate & crankcase and also plate & cylinder bores. This would also help strengthen the crankcase dramatically.



The Machine Work

Unfortunately the spacer plate was shipped with regular postage. An unfortunate mistake we made during checkout when we finalised the sale online. This meant three more weeks passed before the spacer arrived and pushed the build back a lot more.

More than 4 months into the project and Graham was only just about to start measuring and machining, but at least we were moving forward. Once the plate arrived, Graham was still slightly concerned with the integrity of the crankcase as he had to still had to remove 6mm from the diameter of each bore hole. So instead of just machining the holes, he very carefully machined a step into the crankcase that would match the profile of the new bore sleeves. This created a very snug fit and the step would reduce any gaps between the sleeve and crankcase, again helping to strengthen the complete unit.

He also filled in a void at the rear of the crankcase with alloy weld to prevent the thinner rear wall from cracking under stress. At this point, an unfortunate family emergency meant Graham had to be off work for 2 weeks and again push the project further back.

Upon his return to work, he did an amazing job, finishing off the crankcase, linishing the crankshaft and measuring all the components including the new camshaft for correct valve lift and duration. This would help him to be sure that the larger valves we insisted he install into the cylinder head, wouldn’t contact other components or each other. The cylinder head was then heavily ported and carefully finished off by matching the size and shape of the ports with those of the new carby manifold and exhaust tubes. He then shaved as much as possible off the face off the head to help raise compression slightly.



Classic fiat 500f engine rebuild

Perfect view of Graham’s amazing work. Here you can see the perfectly shaped exhaust port and also the void he filled with alloy weld to stop the rear of the crankcase cracking under load.


New hardened valve stems and seals were installed to suit higher octane fuels, the seats were 3-angle cut and larger intake and exhaust valves were fitted with new heavier rated, dual valve springs.



Fiat 500F 110F rebuild enginebspacer plate

The crankcase and spacer plate were carefully stepped down to match the profile of the cylinder bore sleeve.


With the cylinder head completed, Graham returned everything to the workshop and gave as the measurements of which size bearings would work best and insisted on a “dummy” build. This is a build using either old, good condition gaskets or new, cheap versions of them and building the engine using only the required moving parts. This allows you to rotate the engine by hand and visually check for any clearance or contact issues.



Fiat 500 engine rebuild

The cylinder head was shaved as much as possible to help raise compression slightly and larger valves fitted to allow better air flow.



The Build

With the parts cleaned and neatly laid out on the bench, we slowly pieced together the rotating pieces of the engine. Enough to enable us to visually inspect the clearances and be sure no contact will occur during engine operation. With everything together, timed correctly and valves adjusted to spec, we turned the engine crankshaft and watched everything move in harmony with one another. It was perfect. But now we had to strip it all down and do it all again, only this time with all the pieces, all new gaskets and all seals.



Fiat 500cc engine rebuild

The engine was “dummy” built to ensure all clearances were exact before being pulled back down and built again with new gaskets and seals.



The 110F engine rebuild included a huge list of new parts including:

  • New crank support bearings
  • New big end bearings
  • New 40/80 street/race camshaft
  • New head stud and nut set
  • New rocker shaft and cover stud kit
  • New engine gasket kit
  • Copper head gasket
  • New forged lifters
  • New polished aluminum pushrod sleeves
  • New oil pump
  • New fuel pump pushrod
  • New carburettor manifold (bakerlite)
  • And a brand new, genuine “Weber” 26IMB carby


The engine was then timed correctly using brand a brand new timing chain and gears. As most of these parts were suited for the later Fiat 126, it meant some modifications were required, like notching out the new carby manifold to clear the rocker cover. Nothing to hard, just required patience to get it right.



The crank and cam installed using a quality assembly lube


A new intake elbow was also fitted to match the top of the larger carby and help suck in more air while a new sports exhaust with 50mm tuned pipes was bolted up to help get the burnt gases out. This was coupled with a anti-vibration style bracket to reduce extra unwanted vibration through the assembly.

The surrounding tinware was then fitted up and was not as easy as expected. The tinware that surrounds the engine plays a vital part in keeping this engine in good order. As it is an air-cooled design, there is obviously no coolant to help keep things cool. Instead it uses an old Porsche/VW setup from the same era.



The finished 650cc engine ready to be installed.


The large round section of the tinware, behind the dynamo (old style of alternator) encloses a large fan that pushes air around the motor and through the cooling fins on the cylinder head and bore sleeves. The square section on the opposite side contains a thermostat connected to a rod that is hinged to a flap at the bottom. When the engine reaches a certain temperature, the thermostat opens the flap and allows the hot air to rush out.

For this system to work correctly, the tinware must be fitted correctly and doing this certainly requires patience. Aligning the tin correctly ensuring no gaps are left and so that the dynamo and fan are correctly adjusted as to not scrape on the inside of the tin, took several attempts. But it paid off in the end. A new fan belt was then fitted and adjusted to original specifications.



Fiat 500cc engine rebuild

Finished 650cc engine


The final part of the Fiat 500cc engine rebuild was the addition of a fuel return line. The new carburettor required the use of a return line to prevent excess fuel pressure from flooding the carby. The original, smaller 500cc carby did not have a return line.

Thanks to reading the forums at the beginning of this project, we knew this was the case and prepared for it by ordering some new genuine style clear Cavis fuel hose. This replaced all the old fuel hose and also to create the return line which ran down behind the cooling fan housing and joined back into the existing fuel line using a ‘T’ piece. The engine was now ready to be installed.



The install and initial start

By now, it was almost September. Nearly 6 months since we first began this project and after finishing off all the other jobs that had gotten in the way of this one, it was time to finally get the Fiat finished. Installing the engine was relatively easy. Being so small you could almost lift it into place with just your hands. After sitting it in and reinstalling the rear bar, which also acts as the engine support, we phoned Rob to let him know that his pride and joy will be ready to turn the key for the first time by that afternoon.

The engine was filled with a thick run-in oil and just as we were finishing off the final bit of wiring, Rob walked in the door. We gave him the honour of cranking the engine for the first time. After adjusting the carby and timing slightly, the little 650cc roared to life and with a few more minor adjustments, was running perfectly and with a nice exhaust note that put a smile on Rob’s face once more.

With everyone satisfied with how well the car was running, we let it run-In for an hour on idle while keeping an eye on everything.



The Final Touches

With the engine idling away, we noticed the oil pressure warning light coming up on the dash. We decided to shut it down and not risk any engine damage. We also found that the new exhaust created an amazing amount of heat in the engine bay which was a great concern seeing as though it was only air-cooled.

With the Fiat so close to being on the road again, we were eager to see it finished and back with its owner. We suspected the low oil pressure to be caused by the now worn off special coating used on the new camshaft and lifters. We were expecting it to occur, just not this soon. We drained the oil and removed the sump and surely enough, the cam and other parts had worn in.

The parts were actually wearing in perfectly which was great news. We cleaned the centrifugal oil filter out, added fresh oil and let her run again. After 20 minutes, to our disbelief, the oil pressure,warning light was glowing again. We shut her down again and this time swapped the oil pressure sender for an oil pressure gauge. Surely the sensor had to be either faulty or the heat generated by the new exhaust was causing it to play games.

With the gauge fitted up, the car was running once more. Though this time, while keeping an eye on the gauge, the engine suddenly died and refused to start again. We still had no idea if the oil pressure was dropping as it hadn’t ran long enough and now we had another issue. This was starting to dampen the excitement of the Fiat engine rebuild. But we had to sort it out, and fast.

We eventually found that the mechanical fuel pump was not strong enough to pull fuel from the tank at the front as well as push enough fuel through the carby and back around through the return line with enough volume. This was causing air-locks in the system. There was only one way to solve this and keep the bay looking as original as possible. We looked for and easily found the smallest electric fuel pump we could find. It was a “Derale Performance” 2.5psi in line, low pressure item and also had a small in line filter to suit. We custom made a bracket and fitted it up front as neatly as the tiny space would allow and neatly wired it up. It wasn’t factory but still didn’t look too out of place.



Fiat 500cc engine rebuild

A  “DERALE Performance”  2.5psi electric fuel pump was small and solved any future fuel delivery issues.



The mechanical fuel pump is still in its normal spot and helps send fuel upwards to the carby. With this system in place, we were able to completely hide the return line without having to worry about air locking in the future. We also were able to delete the fuel filter from the engine bay.

With the car now running again, and perfectly, we managed to find that the oil pressure was in fact correct and a dodgy sensor was replaced with a new one to sort out the warning light issue. The last thing to do was heat wrap the exhaust at the request of Rob to help minimise the heat in the bay. We backed his decision and we are glad he made it. The wrapped exhaust dropped the temperatures dramatically and also deadened some of the noise into the cockpit. Unfortunately, the exhaust is the only thing giving away any signs of this setup being slightly more than just a normal 500cc and we’re happy Rob allowed it. We think he is too. 🙂




Fiat 650cc engine rebuild

The finished product ended with the exhaust being the only thing not keeping this 650cc a secret.



The Result

Even though we had never sat in one let alone driven one, it was a massive surprise when it came time for the road test. Besides the pedals being extremely close together, it was great to drive.

Power was nice and smooth. Acceleration was no issue no matter what gear we selected. The car pulled up the hills with absolute ease and at every turn people would just stop and stare. The Fiat 500 was never fitted with a radio, but now, it wasn’t needed as the sound of the exhaust, even though it wasn’t load like the V8’s we love, was very enjoyable and let off a slight burble each time you released the accelerator to select the next gear.

During that test drive, we realised we too had fallen in love with this car. It is tiny, and you couldn’t fit too many of your friends in it, but you could certainly enjoy it, on your own.

The big test was going to be Rob’s first drive and we were eager to see his reaction. He was gone for no more than 15minutes and as he pulled back in the driveway, we could see him laughing and then heard it as he shut off the engine. His laughter almost uncontrollable and we waited suspensfully for him to tell us what was so funny.

Finally he said “this thing is amazing, I can actually overtake people now”, still struggling to stop himself laughing he then added, “i Don’t need my other cars anymore”. What a relief. He was extremely happy with the final product and we were too. It was certainly a different project to what we were used to and yet this Fiat 500cc engine rebuild was an absolute success.

Would we do another? Yes, of course. With the knowledge we have gained from this build, the next one will be done in less than half the time.

We would like to thank Rob for his patience, his gratitude, his amazing attitude and friendliness throughout this project. We also thank you for trusting us with your pride and joy. Enjoy that beautiful little beast.










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