New color on the Fiat 850 engine

The gray primer that I put on the engine during the mock-up phase looked acceptable but I wanted something different. After much deliberation I have finally decided what color the block will be. White! You don't see it very often and of course there is a chance of discoloration, but with white heat-resistant paint I am willing to accept the risk.

850 motor links

850 motor rechts

The 4-in-1 exhaust manifold was sprayed in heat-resistant dark gray paint and then "baked" in the oven. The damper will be welded when the block is mounted in the car to make sure that everything is straight.

New throttle mechanism for the Fiat 850

For the new engine for the Fiat 850 I bought a nice valve cover from Abarth Online in Germany. Because there were problems with the production, I did get the valve cover but not the accompanying bracket for the throttle mechanism. And it's still unavailable 6 months after purchase.

850 kleppendeksel plaat

This is one of the reasons the engine was kept in my workshop. While waiting I tried everywhere to get such a bracket, but they turn out to be extremely rare. Making my own seemed to be the best solution.

In my search I came across several examples, but it was only since mid-July that I had a clear picture of what it should be. I bought a piece of aluminum 80mm wide and 3mm thick through a local supplier. Strong yet fairly easy to shape. From an old valve cover I took the bracket and from that the guide for the throttle cable.

Fiat 850 plaat voor gasmechanisme

From there I kept myself busy measuring, drawing, sawing, drilling and filing. The pivot shaft for the mechanism was an 8mm stud from which one piece of thread was sawn off. The groove for the circlip was made with the stud in the drill press and holding a new saw blade against it (not really very safe....). And while it took me half a year to figure out, it was ready in a few hours.

Fiat 850 plaat voor gasmechanisme

Fiat 850 plaat voor gasmechanisme gemonteerd

Fiat 850 plaat voor gasmechanisme met gasstang

The Weber DCD carburetor now knows how much fuel to deliver. I'll finish it off later with the correct spring for the 0 position and then I am one step further towards putting this engine in the 850.

ARP head studs in my Fiat 850 engine

ARP studs are a way to avoid having to install new head bolts every time your cylinder head has to be taken off the engine. It's a fairly expensive solution. But especially if you mount a separate intake manifold, it is the only safe way to get longer bolts / threaded ends. An alternative of course is to drill the block and head from 9mm to 10mm and use thicker head bolts. But this also costs money.

You can recognize ARP threaded ends by an hexagon hole in the head. The other end is machined flat and usually has a raised edge at the end of the thread on that side.

850 arp boven 850 arp onder 850 arp

Additional installation instructions apply for the use of ARP threaded rods for the cylinder head:

  • For example, ARP Thread Sealer must be used in the threads in the block. This is to prevent coolant from creeping up when the engine is warm and not running. I wrote an article about it before (thanks to Paul Vanderheijden).
  • In order for this paste to work properly, it is highly recommended to thoroughly clean the threaded passages with an M9x1.25 tap. If you can turn the tap in and out by hand, the screw thread is clean enough.
  • Then brush out the last bits of oil / grease with a round brush and brake fluid and dry the threads, preferably with compressed air.
  • 850 opbouw (12)850 arp schoonmaken 1
  • Next the threaded ends have to be thoroughly brushed clean in a warm bath with plenty of soap, rinse with water and rub dry.
  • Now coat the bottom half of the wire with Thread Sealer (or an alternative, for example LOCTITE 242 Blue Threadlocker). This should be a thin layer.
    Tip: do this with two studs held together and rotate the greased parts against each other so that the thread is filled with a thin layer.
  • 850 cilinderkop montage (1)
  • Ligthly tighten the studs into the block and use an Allen wrench to tighten them just a bit more.
    850 cilinderkop montage (2)
  • Remove excess Thread Sealer from the studs and the engine block.
    850 cilinderkop montage (3) 850 cilinderkop montage (4)
  • Clean the deck of the block and the cilinder head with brake cleaner or a similar fluid (do not use benzene or a paint thinner), and put the head gasket in place.
    Avoid to touch the cleaned surfaces and place the head.
    850 cilinderkop montage (7)
  • Lubricate the washers on both sides with ARP Thread Lubricant put them in place.
    850 cilinderkop montage (9)
  • Lubricate the nuts an tighten them by hand. Next, tighten them with a torque wrench. This is done in 3 steps:
    For a 9mm stud in highest quality (ARP-3, my definition) the end torque is 65Nm. These steps are, for example, 20Nm, 42 Nm and 65Nm.
    This is a bit lower than the recommende torque of 69Nm applicable for an A112 engine. Please note: ARP nuts have a Torx head. I had to use a 7/16" socket for this:
    850 cilinderkop montage (15)
    Have a look at the graph I made using data from the ARP manuals
  • Done:
  • 850 cilinderkop montage (14)

My Fiat 850 engine, from mock-up to building phase

After a few weeks of anticipation while waiting for crucial parts, these finally started to arrive last week. The longer ARP studs for the intake manifold, the thread sealing paste and lubricant for its assembly, plus the crankshaft pulley and crankshaft locknut. The dowels for the cylinder head and the gearbox were also supplied.

Why should I (and you) use a thread sealing paste when using ARP studs? I received a very good explanation from Paul Vanderheijden:

In Fiat 850 engines (and their derivatives) the head bolts are in contact with the cooling water channels. These head bolts are tensioned in the block. When the engine is running, the oil pressure (350 to 550 kPa) provides enough pressure in the bolt hole to prevent coolant from creeping up through the threads. When you switch off the engine, the oil pressure drops and the pressure from the cooling system gets the upper hand. This will cause coolant to want to flow up the thread. If head bolts are mounted, you have the washer and the bolt head to generate enough pressure.
When you use ARP studs, they are not tensioned in the block; they are hand tightened. As soon as the oil pressure drops, the coolant will certainly creep up and mix with the engine oil, resulting in a "nice" sludge. That's why you should always use ARP Thread Sealer (or a comparable product) with ARP studs. The Fastener Assembly Lubricant is put on both sides of the washers and the bottom of the nuts; when tightening, no friction is created that affects the stretch of the stud required to achieve the correct torque.
The advantage of the Thread Sealer is that it does not harden and always guarantees a good seal.

850 arp thread sealer

Of course you can use other sealers (Loctite). However, most of them only reach their effect when they are tightened. This does not work with ARP studs because thethreaded end in the block is not tightened.

The intake manifold studs that were part of my original order were 15mm too short. Without the longer intake manifold studs I couldn't mount the cylinder head as they need to be secured as 5th and 6th. Since ARP's advice is to lubricate all studs with thread sealer, tighten them slightly and then thoroughly clean the top of the block before the head gasket and cilinder head are placed I had to wait until I had everything delivered. Fortunately, Michael from Abarth-Online quickly (within 3 days from Germany!) arranged two longer ones. Now I have enough thread to tighten the intake manifold as well.

850 kopbouten volgorde 850 opbouw (11)

When assembling the front of the engine I got stuck due to the lack of slip rings I thought I needed. On the original 850 engines these are fitted as part of the centrifugal lubrication. I had enough rings in stock, but all of them with an inner diameter that was too small.
850 krusasringen

I assumed these rings were needed on all A112 engines; in the 903cc engines they are, according to my parts book, but in the 965cc and larger they appear not to be necessary. Since no oil flows from the pump to the first main bearing bracket, I have no problem leaving these rings out.

I have quite a lot of crankshaft pulleys in stock, but they all are for engines with centrifugal lubrication. One of them had the correct connection to the crankshaft, but then the crankshaft nut did not fit properly.

Luckily Roel, the one where I bought the engine and the first set of parts, still had a pulley with nut AND he had the sandwich plate for the oil cooler which he had no use for. So I drove to Amsterdam again to pick up the parts and talk about the project. With some insider tips because Roel has built many of these engines!
The sandwich plate for the oil cooler with the longer mounting pipe and hoses are not immediately necessary, but it is nice that I have them already.

850 buit binnen

Since I have chosen to mount the oil cooler, I am not going to use the heat exchanger. It will be for sale later on.

So now I have finally switched from the mock-up phase to the construction phase, although it is getting too cold in my workshop to be working there for a longer period.

The first step was the final assembly of the timing chain and the timing cover (the interior of the engine is already finished). To tighten the camshaft gear you should do the following: mount a ring and a locking ring with a tab that fits into a hole in the sprocket. The other hole fits over the pin in the camshaft:

850 distributietandwiel

My camshaft sprocket has only one hole: for the pin on the camshaft. I tried mounting the washer in various ways and finally came up with the following solution:
In several Fiat 850 engines an "eccentric bush" is mounted on the camshaft. Probably as a counterweight to the drive cam for the fuel pump on the camshaft.
At first I put the washer between bush and camshaft (see top right) but that was not correct. Then I put the ring inside so that the tab fell through the hole (below).
The lip now fits into the hole in the sprocket, after which I could tighten it with 49Nm of torque.

850 nokkenasbus 850 opbouw (5)

It is obvious why the eccentric bush has been given its name.

After that the timing cover with PCV breather can be put on, followed by the crankshaft pulley with nut. At the rear, the cover plate of the cooling system is put back on (with a Staal dealer sticker) and I am ready to mount the flywheel as well.

850 opbouw (6) 850 opbouw (7)

850 opbouw (10) 850 opbouw (9)

As soon as the temperature in my workshop is acceptable again I will continue with the studs and the cylinder head.


Engine-porn in my Fiat 850

Today the last Abarth-Online shipment finally arrived: a set of ARP heard studs with washers and nuts plus the crankcase breather. Of course I immediately started cleaning all ARP parts. According to instructions, this must be done in soapy water; brush everything clean, rinse and dry thoroughly. Earlier I had cleaned the mounting holes in the block with a series of M9 taps so that I was sure that there would be no influence on the torque due to dirty screw thread. Of course I immediately mounted the studs and this really is engine porn!

850 arp set 850 arp schoonmaken 1 850 arp gemonteerd

The crankcase breather replaces the mechanical fuel pump (I use an electric pump) and just because I did not feel like mounting a cover in this place. I did not have an 843cc housing, but did have one of a 903cc engine. I did have to drill an extra hole in the flange because the original hole did not match with the flange on the distribution housing. This looks much nicer. And mounted it even looks better.

850 breather 0 850 breather 1

As last job of the day I made a small adjustment to the cylinder head; a development by Hakan Leppens that was passed on to me by Joop van den Einde. Where the push rod of the inlet valve of the 4th cylinder is located in the cylinder head, no oil can flow back from the top of the cylinder head to the cam follower. This is now made possible by milling away a small piece. A small job with good results.

850 cilinderkop gleuf 0

850 cilinderkop gleuf 2

Compression ratio A112 engine for my Fiat 850

While I was still able, I determined the compression ratio of the A112 engine after all the work I did. With a little creativity it was possible to measure the size of the combustion chamber, the rest was just using old math knowledge.

To determine the size of the combustion chamber I greased a CD with petroleum jelly so that it stuck to the head and no water could leak out. Then I filled the combustion chamber with a large and a small syringe until the water just entered the opening of the CD. After multiple filling / cleaning / filling sessions the size was found to be 20.5 cc. The other details are:

 850 compression ratio850 cr

I am satisfied with a 9.7 compression ratio. My intention is to build an engine for a Fiat 850 that can easily keep up with all sorts off traffic, not a racing monster.

New engine for my Fiat 850: the mock-up

Just before Christmas, the modified engine and cylinder head for my project were ready at the machining company. Because I have no workbench and no light in the garage where my Fiat 850 project is located, it seemed sensible to assemble the engine in my small workshop at home. So also moved all necessary parts from my stock there and it is now nice and full.

The block was sprayed in primer and then I started building it up; I do the "intestines" first and then the superstructures. The crankshaft and connecting rod bearings had already been checked for size by the machineshop, so installation started easy, although the correct alignment of the front camshaft bearing was a bit more difficult than expected. After an hour everything was correctly in its place, including the 296° camshaft purchased from Abarth-online.

850 lagers 2

850 mockup 2 850 mockup 1

850 mockup 4 850 mockup 4a 850 mockup 5

850 mockup 6

At the workshop, the cam followers were ground and the crankshaft / flywheel combination was balanced (after the flywheel had been machined to reduce the weight). The flywheel now weighs 4435 grams, compared to 5100 grams for the standard flywheel. Maybe too conservative with turning, but it still is old cast iron.

850 vliegwiel

The cylinder head has been thoroughly overhauled: new (larger) valves and seats, inlet and outlet channels made larger and of course the surface was milled, just to be sure. The valves are 1.5 mm larger than standard, which results in a 10 to 15% greater flow. This is also quite conservative, but the seats are now very close to the edge of the combustion chamber; one has to be satisfied at one stage.

850 cilinderkop klaar

850 kleppen

The oil-pump was also purchased from Abarth-Online; and is driven by a shaft that is slightly longer than standard:
850 pompas

The next step is to see I will do to the front of the engine: Timing chain or Triger belt set ..... Both I have in stock, but what is the best decision? Various opinions on various forums. Who can help?

850 mockup 7


Overhauling the engine for my Fiat 850

The first work on the A112 block for the Fiat 850 at Broos Revisie in Breda has started. After a thorough cleaning, the block was bored to 67.8mm (3rd oversize) and skimmed slightly. The crankshaft, connecting rods, pistons and bearings will also be installed after all rotating parts are balanced.

And for the main bearings, they are "back home" again: my father once sold old stock to Broos and he now installs the main bearings from that stock in my engine.

850 blok broos 850 lagers

I had bought the original connecting rods with the block. Because the Autobianchi engine has press-on piston pins and the pistons from Scuderia Abarth use pins with clips, there was some room between the eyes of the connecting rods and the piston pins. That is not really conducive to a long life. This is solved by machining phosphor bronze bushings:

850 drijfstangbus 1 850 drijfstangbus 2

The cylinder head had suffered quite a bit from the standard ailments of the 850 engine: lean mixture in the outer cylinders and excessive heat: quite a bit of pitting at the valve seats. Slightly larger valves than standard have been chosen for the head; exhaust 27.5 instead of 26mm, inlet 30.5 instead of 29mm (valves of a Fiat Seicento Sporting have the same length and stem diameter. And one groove) and, of course, also new valve seats. This means that a large part of the pitting has disappeared immediately.

850 kop broos

The setup for the cylinder head to be overhauled. And this is the head (almost) ready for use:
850 cilinderkop klaar

Inlet and outlet channels have been milled a bit and everything neatly installed.

The camshaft has also arrived, a 296° one from Abarth-online / Scuderia Topolino. The cam followers I had in stock look good, they are only polished a bit. And this is the new camshaft housing:

850 nokkenas nieuw 850 nokkenaslagers nieuw

Plus some weight has been removed from the flywheel.

Fiat 850; Block 2 - Update

Block 2 has stayed at the machine shop, Revisiebedrijf Broos, for a few weeks and has been through quite a bit there. The intention was to drill 0.6mm over, machine the flywheel, balance the crankshaft and flywheel and install larger pistons and piston rings. After that I would rebuild it myself. That was the plan, but unfortunately it turned out not to be that easy.
After cleaning and drilling I got a call: two pistons had been installed and they did not get where they should be: at the top of the block. Block 1 inspected and the block height compared with block 2. Being a Seat block, there was quite a difference, almost 5 mm. Here's what that looked like:
Fiat 850 motorblok
How did we fix this? Of course with a lot of measuring. With that we arrived at the following solution: the oversized pistons would be transferred to connecting rods that I still had; these were 2.5 mm longer than the ones first used. All other dimensions being the same, I could use the new bearings. After that everything was built up and measured again; we were still just under 2.5 mm short. The decision to machine the engine block and polisch it afterwards was an easy one. Naturally thought about the consequences of head bolts, pushrods and ignition shaft length. Would all of that still fit? But doubt is for wimps, so on to the milling machine with this block. Last week I picked up the whole assembly and I have to say: they have done a great job!

Fiat 850 motorblok nog vet

Today I started with the build-up: degrease, spray wash primer, spray primer and then a nice layer of dark gray.

Fiat 850 motorblok in washprimer

Fiat 850 motorblok in Speedprimer

Fiat 850 motorblok grijs gespoten

The cam followers (nicely polished) installed, the camshaft and the oil pump installed. I had a new pump, only the pressure relief valve was transferred. Then started the next fun job of the day: assembling the Triger kit
Fiat 850 motorblok met nieuwe Triger set

Fitting this kit was simple (the manual in Spanish was more difficult) and completed within half an hour. One problem: the original crankshaft pulley of block 2 does not fit because it touches against the bolt of the camshaft gear. And I do not have a suitable crankshaft pulley in my stock.

Today's final score: block finished, Triger kit installed, oilsump mounted, head placed, complete with rocker shaft and the ignition is put in. Everything fit perfectly, we have not found problems with the 2.5 mm milled off the block. There are still some minor work on the head and the carburettor. The gearbox is waiting to be assembled and then everything can be put back in the Fiat 850.

Fiat 850 motorblok met nieuwe Triger set

Block 2. A new engine for my Fiat 850

Block 1 is almost ready to build. But thinking ahead, and also using the experiences of the technicians on the (now extinct) forum of via850.nl, I felt more in favor of subjecting block 2 to further research. Is it an alternative to block 1?

Block 2, bougt a long time ago, is a Seat 133 block (100GL) of 843cc. Such a block has a normal oil filter and better oil flow than block 1. If I want to install the Triger-timing belt kit that I still have lying around, I cannot do that on block 1 because the centrifugal lubrication will then be canceled. Time for disassembly and inspection. Before doing that, IU first checked that everything turned freely. It did and very smoothly too.

blok 1

blok 2

De krukas en de lagers zien er goed uit, vrijwel geen zichtbare slijtage; twee zuigerveren zijn gebroken en hebben ondiepe groeven in de cilinderwand gesleten. De zuigers zitten vol kool maar aan de kop is dan weer niets te zien. Wel blijken de koelkanalen nogal vol met ketelsteen te zitten.

blok 5

The block was sent to Broos, a local revision company, for cleaning and technical advice.

Malheur !

That's what is said in Belgium when things go horribly wrong. Today the engine was to be prepared for installation. And that's where it stopped.
Turning the crankshaft, there appears to be a tight spot somewhere. At first glance, I had no explanation for it, so I decided to remove the cylinder head, to see a bit more. The problem occurs when the pistons are at (roughly) the same position.
I bought the engine from the estate of an overhauling workshop whose owner had died. Engine looked perfect on the inside. Camshaft and oil pump appear to be new. That is why I am confident that it was not overhauled cheaply and that the assembly of the rest of the parts is also to be trusted.
Still, I don't want to install the engine like this and will take it to an overhaul company in the area shortly. Hopefully they have a quick fix, otherwise I'll have to overhaul my spare engine.

Heads up! The cylinderhead back on the Fiat 850 engine.

This weekend finally some noticeable progress was made. A few weeks ago I had already sanded and sprayed the new water pump. Then the freshly sprayed pulley mounted and everything (temporarily) attached to the engine.
Yesterday I put the head on and built it up, the ignition parts, old and new, were cleaned and built up. But it only works after the engine has been installed. The valve cover was prepared for spraying and that is now back to beautiful black.



Testata come nuova. Fiat 850 cylinderhead revision

Today I made a trip to Roosendaal to have the head checked and machined at the AVT workshop. Mano helped me in very friendly and professional way and within an hour and a half I was on my way back to Breda with a shiny cylinder head in the back of the car.

As you can see the head was pressurechecked, the valves were vacuum tested, sanded and then everything was cleaned before machining. I am super satisfied. If the head gasket arrives in time, I can continue. "Le mani in aria per Mano!"

850 cilinderkoprevisie AVT


Enginejob for my Fiat 850

Because the sheet metal worker is not yet available, we started working on the engine again. Today's intention was degreasing, sanding, masking and spraying dark gray. Then mount the crankshaft pulley with the new nut. Finally, I would mount the extra oil filter. For this I have found a reducer nipple from original stock. Also ordered an oil filter so that should be easy ..

The first plan worked, the second failed. The nut that came from my father's secret stash turned out to have too long a shank so as soon as it was tightened the washer remained loose. The solution is to have it shortened by a few millimeters, but that again means some delay in progress.

Plan 3 already ended with the oil filter supplier. The nipple had too small a thread so the filter will never fit. Tried all kinds of filters in his warehouse but no success. A new nipple is also running late for this because I want that filter on it.

The results of plan 1:

Na schoonmaken en schuren Na schoonmaken en schuren

Gespoten Kon het niet laten

Soon the head goes to the overhaul company and hopefully the sheet metal worker will have time again soon!

New engine for my Fiat 850

Last Saturday I worked on the block together with Yorn. First dismantled and cleaned the centrifugal filter. It contained about a full coffee cup of sludge. It seems that such a filter is often forgotten. We will at least add an external filter (on the side of the block there is a mounting option: see the photos in an earlier article) so that the oil remains in good condition. The necessary parts are already in stock.

Then disassembled the timing cover of the old block after which we were confronted with this:


This has had its day, even links are defective. Fortunately, the new block contains a new distribution set.
The rest of the block didn't look much better, although the crankshaft still looks neat.

Here the old and the new intestines:

Het oude blok 

When we wanted to reassemble the centrifugal filter, it turned out to be impossible to tighten the central nut (on the crankshaft) without "fixing" the pulley. The nut has a short edge that sits in the oil seal against the head of the crankshaft. Unfortunately, the rim was too short and did not touch so that the rear of the pulley was against the timing cover. Result: a crankshaft that could no longer be rotated.

Fortunately my father had a longer nut lying around but I can only install it later.

While I was busy cleaning loose parts, Yorn degreased, dented and sanded the crankcase after which it was neatly repainted. First filling primer and then chassis paint.


The Marbella cylinder head has been checked for flatness and is very tight. The old rocker shaft fits well so I will use it again after cleaning and reassembly.
In the meantime I am looking for a nice carburettor, something in the order of 32 or 34 mm.

For the time being we still have plenty of work to finish the new block neatly. As mit is, little will be done to the bodywork because unfortunately for us our sheet metal worker has bought a damaged car himself and is therefore unavailable until mid-January.

Round trip to Belgium: picked up the Fiat 850 engine

Just back from Belgium where we picked up the block. Has been shelved for years at an overhaul company in Maastricht. The photos I collected from kapaza.be do not do it justice! It looks beautiful.
When the owner of the overhaul company died, the current owner bought it (along with many other parts). He couldn't use it because he's only interested in vintage motorcycles.

Almost everything is new about this block:

  1. Drilled and new pistons (65.58mm) and springs (yields 15 cc)
  2. Crankshaft ground and new bearings
  3. Seals and gaskets.
  4. Oil pump and camshaft look new and I will check the timing chain tomorrow.

All parts were nicely oiled so everything was rustfree and spotless. The crankshaft can be turned by hand. So my weekend was a complete success. Today we also had a few hours of sheet metal work. The right inner sill is now almost ready. Photos will follow later


Head hunting. Taking of the Fiat 850 cilinderhead.

Last week, an inspection with an endoscope showed that the 2nd and 3rd cylinders were full of gunk. So there was only one thing to do: take the cilinderhead off. This afternoon we did just that. A small job. Finally the motor stand (Winntec 500) that I once bought second-hand came in handy. Too bad about the "extra capacity" because that thing can safely handle 500 kilos and an 850 block you can easily manhandle yourself.

Within half an hour the head was off and we could finally see what was on the pistons. It looked like mud. Anyway, cleaned it well and check if there is any damage to the cylinders. We hope it will not be too bad. You will find a small report here

Diagnosis of the Fiat 850 engine

Last week it was found that the compression of the 850 was bad.
Just inspected the engine with an endoscope from work. Not good news because the second cylinder had "snot" on the wall, the third looked like a dripstone cave; the first and fourth were reasonably clean. So I am thinking of a broken head gasket between the second and third cylinder. We'll disassemble the head soon and see if more misery surfaces.

The engine is out of the car!

Last week we tried to start the engine but that wasn't much of a success. We had both spark and fuel so one would think it could start. Compression test done (2 times) and that didn't seem right. Compression test ticket will be posted here soon. The reason was not clear and with a built-in engine with an endoscope looking inside is a bit difficult with an 850. We were planning to make the engine and the engine compartment beautiful again, so immediately decided to disassemble everything under the hood. Because we were busy anyway, Yorn was explained how to set valves.

Today the engine has been taken out. Everything neatly disassembled and labeled and a collection of photos made so that Yorn can assemble everything again based on the photos. After a few hours of relaxed tinkering, the block was out. Next week the endoscope from my work will be used to see what is going on internally.

This week we also ordered some brake parts and serviceparst from Martin Willems. As always fast delivery. Still trying to buy a front suspension of a Coupé so that we can install disc brakes. Short report is available here