For those of you who followed the rebuild of my 500F, you'll know that I promised to start a thread when I had the parts to upgrade the 500cc engine to a fire breathing 695

Over the last few months I've been saving, researching and purchasing parts from around the world. Last year I'd bought a very rusty Niki 650 which I subsequently stripped. Most of the parts I gave away but I kept the engine, drivetrain and a few other bits and pieces. I dismantled the engine and cleaned/soda blasted the main components. I had the head checked and fitted with larger valves. The crankcase was stripped completely, blasted clean and checked for cracks etc.

Because the new 79.5mm cylinders are slightly bigger than the standard 77.0mm 650 cylinders, I had the crankcase bored out to suit. There is plenty of room to do this without compromising the structural integrity of case though I'm told that if you do this to a 500cc crankcase, you'll have to reinforce it.

The new parts I've purchased include -

Pistons/cylinders
Con rods to suit above
Inlet and exhaust valves
Alloy sump
Main bearings
Big end bearings
'Sport' camshaft

Many of the major parts from the 650 engine (eg: crankshaft etc.) were cleaned and checked by a local Engineering firm prior to being packed away until I was ready to assemble the engine. If they were out of tolerance they were replaced.

I'm still working out where all of the gaskets and seals go - I seem to have a set that includes everything for all series of 650 engines. I'm sure it won't be too difficult as I had a late model 650 engine to guide me and I took photos and notes during the disassembly. I also have a good workshop manual.

I've attached a photo of the major parts.

It's Monday night here at the moment and I have a busy week ahead of me, so I won't get around to much assembly before the weekend.

I intend to take lots of photos as I go along, so be warned

Chris

I intend to take lots of photos as I go along, so be warned

Click to expand...

Excellent - look forward to it Chris!

Got home early today so I installed the crankshaft - not really very difficult.

As mine is a late model engine, the rear bearing is sealed using an o-ring rather than the paper gasket present on the earlier models. I coated the mating surfaces with Loctite so hopefully it will never leak

The hardest bit was supporting the crankshaft while I installed both bearings. The bolts were torqued in a radial fashion to a torque of 15ftlb as suggested by my manual. I borrowed a Philips head adapter so I could torque the large cross-head screws.

The actual bearing surfaces were liberally coated with engine oil prior to assembly.

Tomorrow night I'll assemble the pistons, conrods and cylinders.

Chris

Heckle

Joe R

Mmmm, pwetty :yum::yum:

I got a bit of a run on it last night. I guess I can't wait until the weekend and really, it's only an engine rebuild and any competent mechanic would have it done in a couple of hours. I like to plug away at it, taking my time, checking everything as I go and taking a few photos as well.

So last night I fitted the conrods and gudgeon pins to the pistons. The gudgeon pins are an 'interference fit', so the top end of the conrod needs to be warmed a bit until the metal expands enough to easily accept the pin. The pins are fixed in the pistons with a pair of circlips.

The pistons I bought already had rings fitted and all I needed to do was fashion a ring compressor out of an old softdrink can and a long zippy tie, lubricate everything well with engine oil and slip the pistons into the cylinders. I positioned the gaps in the rings so they did not overlap and were away from the areas of the pistons that will take most of the lateral force when it moves up the cylinder during the compression/exhaust cycles.

In my gasket kit I had the choice of a thin, large o-ring or a thick paper gasket to seal the base of the cylinder against the crankcase. I used both, fitting the o-ring to the cylinder first - there seemed to be a small groove for it anyway - then the paper gasket. They will end up being compressed when the head is fitted and torqued down.

Cylinder/pistons were fitted, main bearing caps were lubricated, fitted and torqued to 24ftlb. I'll recheck these tonight before I fit the oil pickup and sump.

The camshaft was next after generous lubrication of the bearing surfaces. I've attached a photo of the cam profiles. The new camshaft lobes are higher and fatter than the old ones so the valves will open further and for longer during the cycle. The profiles are the same for both inlet and exhaust valves.

Timing chain and small crankshaft sprocket went on next after aligning everything - the dots on the sprockets help - and fitting the Woodruff key. The large sprocket was already fitted to the camshaft so all I had to do was gently slip each part down until they seated snugly. The timing chain is quite tight and it took a bit of fiddling to get it all in without damaging any of the camshaft bearing surfaces. This end of the crankshaft is fitted with a distance piece and a large circlipped sealing ring outside that. This setup took a lot of the end float out of the crankshaft.

I put the timing chain cover on just to protect everything. Having already rebuilt the oil pump, I'll fit the crankshaft seal tonight and finish the assembly of that end of the engine.

Next I slowly rotated everything to make sure it would turn and also to check piston movement.

Last thing was to fit a copper head gasket, cover the motor and go to bed. This is the first engine I've rebuilt using a copper head gasket. Normally you would seal around the oil and water galleries when using these gaskets but as this is an air cooled motor with largely external oil galleries, I wonder if I have to do anything but just torque it down. If anyone can give me some advice I'd be grateful.

So far I don't think I've screwed anything up and even though it's a simple engine, it's great fun watching it all come together.

Photos attached - I've got a few, so I've spread them over two posts.

Chris

Here are the rest of the photos.

Hope you guys are getting as much fun out of this as I am.

Chris

Be careful with the rubber O-rings on each end of the pushrod tubes and the top ends of the tubes themselves - you need to line the tubes up as you slide the head down the through-bolts and the head approaches the top of the cylinders - an example of Giacosa's experience in the aero-engine field.

Thanks - I was very careful.

Last night and today I virtually completed the rebuild.

Once I gently lowered the head onto the head gasket, I torqued it down to 24ftlbs. The red pushrod tubes look nice - it's a shame you won't be able to see then when the tinware is installed.

The rocker cover and sump are both aluminium and branded Abarth - bit of a pose, I know. Tappet tolerances were set to 0.15mm (0.06").

Late this afternoon I fitted the tinware, distributor, carby and starter motor. When I mounted the starter, I used a couple of 12mm nuts as spacers to get the correct thickness for the absent bell housing. I turned the motor by hand with the spark plugs out to make sure that it would turn and that nothing was jamming.

I'm currently charging a battery and might try a trial run tonight. If it starts it will be very noisy as there is no exhaust fitted yet

Pictures attached - rest in the next post.

Chris

Couple more photos

Chris

A word of caution - I had a 500F starter motor that sheared the lugs off its mounting on the bellhousing as a result of metal fatigue in the aluminium - they beefed it up on later ones, I think - doing astronomical revs does set up massive off-balance vibrations in this type of twin. In the end I threw the Fiat engine away and mounted a 700cc flat twin BMW engine - an absolute gem of an engine, full of ball and roller bearings, which produced something like 40 horsepower and would cheerfully do 7000 rpm all day. At the time, the Mini Cooper was king of the small cars and my 500/BMW would eat them for breakfast.

Buona fortuna con il progetto. (Off to our Italian home for two months tomorrow, so keeping my hand in.)

babbo_umbro said:

In the end I threw the Fiat engine away and mounted a 700cc flat twin BMW engine - an absolute gem of an engine, full of ball and roller bearings, which produced something like 40 horsepower and would cheerfully do 7000 rpm all day.

Click to expand...

Now you tell me ......

babbo_umbro said:

Buona fortuna con il progetto. (Off to our Italian home for two months tomorrow, so keeping my hand in.)

Click to expand...

Mille grazie. Buona vacanza e buon viaggio in italia.

Chris

Apart from the better balance and more-than-doubled power, the BMW engine also lowered the centre of gravity at the back by a considerable amount, which improved the handling.

Installed the exhaust, connected a fuel line and battery and fired it up. It ran roughly - needs a fine tune - but it did run
After I finished playing I packed it up and shifted it to the floor under a cover until I install it next weekend.
I spent the rest of the afternoon stripping the engine in the car to make it easier to remove later this week.
Pictures attached.

Now where can I get one of those BMW shaft drive engines for my next Bambino ??

Chris

I seems as though the later model 650s (Nikis & 126s) reinforced the starter motor mount by attaching the front of the starter motor to the drivetrain with a bracket - hopefully this will prevent any shearing due to vibration and metal fatigue.

At the moment the complete engine and rebuilt drivetrain are sitting on the garage floor awaiting installation tomorrow.

Chris

Got the engine in today. The only issues were minor.

The studs that hold the rear engine mount are shorter on the 650 crankcase so I changed them for the longer ones from my 500 engine. Fitted perfectly.

The other issue is the cabin warm air supply. Because the starter motor is now mounted at 3o'clock instead of vertically, the first metal pipe will have to have a dent put in it to clear the front end of the starter. I had one like this on my Niki wreck but I gave it away with a whole lot of other parts.

The number plate is a personalised Queensland plate. When the Topolino was superseded the new small cars were called Nuova 500 so I figured that this is a Nuova 695. As close as I could get with 3 letters and 3 numbers was NVA 695. A fitting tribute. Also, in Queensland, the black and white plates were in use in the 1960s and NVA would have been used about 1967. So it's also correct for the period.

I've got a little bit of wiring to do tomorrow and then I'll fire it up and maybe go for a drive Lets hope it goes as well as it looks

The twin pipes look (and sound) great. The reflection in the stainless bumper is the drivers seat. I've got them both out to finish wiring the ignition switch.

Chris

I am following your build and liking it all!! Nice work and systematically done! I have never rebuilt an an entire engine and might find it intimidating, but may well try after seeing your fine results.

Do you have any idea of final horsepower/torque gains? What is used to circulate the air from the engine(looks like large tube of some kind)? Why did you use the carb as shown rather than a Weber sidedraft?

Keep it coming!

Thanks doc - I appreciate the sentiment.

If you have some mechanical knowledge, I'd encourage you to undertake a similar rebuild on your motor. These engines are quite simple yet well built and are not difficult to repair. They are also lightweight so you don't need expensive engine stands or lifting devices. When I built this engine I used the opportunity to take lots of photos, both as a record and in order to help (and possibly encourage) others like yourself who are thinking of doing something similar.

I'm not sure of the final power increase and will have the car dyno tested when complete and road registered. I guess that it may rise to about 30 to 35 bhp at the flywheel. That will be more than enough for me.

Air circulation is standard. From the rear vents, air is drawn in by the large belt driven impeller and distributed across the head and flanged cylinders. Oil cooling is by virtue of a large, ribbed, alloy sump.

The carburettor is a Dell'Orto FZD 32/28. It is an 'inclined' single throat sidedraft (if there is such a thing) and is favoured by tuners of these little motors. As far as I know, it was always a bespoke addition and was never fitted as a standard carby to any engine. I've heard of them being fitted to MotoGuzzi bikes and in pairs to Mini Coopers. Nowadays, they are unfortunately quite rare - I sourced mine from Sicily and it came with a second one for spare parts. Gasket kits and jets are still avaliable with some components shared by the more common (and really good) Dell'Orto DHLA carbies. I went this route because I'd been reliably told that the IMB Webers aren't great carbies and have particular problems with fuel foaming and flooding - made worse if you live in a relatively warm climate. The FZD has a much deeper fuel bowl and a better internal delivery system for the air-fuel mix. It also has an accelerator pump, which is a major advantage over the IMB. My engine starts without using the choke and idles very nicely. I haven't revved it much yet as it is still bedding in and everything will be a little bit too tight for red-lining

At some stage I'll fit the Abarth instrument set (Tacho, Speedo, Fuel gauge and Oil temperature/pressure) and the transformation will be complete. I've absolutely no intention of any deception, it will always be a replica, but even so, it'll be a hoot to drive.

I'll post a few more photos sometime soon.

Regards,
Chris

Bump - for Hamish in NZ

you should of bored the engine out more im running a the 126 motor thats been bored out to an 850 with webers dc40e and some high comp pistons .. the thing flys! I just broke in the motor and i hit 160 eassyy!.. designed to hit 180 lol ... just ran out of road