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Old 2 Weeks Ago   #1
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704cc 'HOT' Engine Build

Greetings All, I'm raising this thread to document the build of a 704cc engine. The parts have come from a variety of sources, but suffice to say it's a collection, and instead of having a pile of spare parts laying around I'm gathering everything into what I hope will be a hybrid of 500 and 126 engines
I'll start with the assembly of a 'short engine' that is assembled purely for the purpose of balancing and then I'll run through the different areas and what I have done to modify things.
I have a late 80's 126 crankcase that has needed a lot of cleaning prior to starting assembly and as I'm a little manic about cleanliness the need for everything to be spotless will be noticed. The reader will have noticed that the capacity of the engine will be 704cc this is using an 80mm bore (VW sourced barrels) and stroke of 70mm from the 126 BIS. I have also used a BIS crankshaft that has needed some work to make it acceptable, both the main bearings (+0.4mm) and big end bearings (+0.01mm) needed regrinding and to clean the crank properly the core plugs were removed and the difficult job of removing a great deal of muck from the inside gallery began. Because the gallery is not straight black muck builds up in the corners so my engineer used small stiff brushes to get into the corners. The crank was then washed out. I will add that this crank was removed from a serviceable engine and as it was largely an unknown needed careful preparation. The core plugs were replaced and spot welded to prevent them from blowing out
I'm using copper/bronze bearings (hi quality) from a performance application because they can withstand greater heat, stress and lower oil pressure for longer, but the downside is the price It's a simple job to assemble everything once the engineering work is complete. The flywheel is now 4.56kg and the clutch pressure plate is part of an uprated unit. The rest of the rear of the engine goes together as standard, but I think the crankshaft backlash will need checking after balancing as it seems a little tight
The bearing journals have been lubricated with Graphogen which is a very good engine build paste.
The remainder of the balancing build-up is to have the pistons running in the bores without rings, The max speeding rods are fitted with ARP 2000 bolts, but these will be replaced as the past fitment is unknown and any stretch will be unknown also. The barrels will be clamped down and an original sump fitted so that the assembly can be dynamically balanced by spinning it all at 270rpm on a balance table that detects out of balance forces, as the force is linear it will all be the same at 10,000rpm but I have no intention of going that far even if the bolts can take 220,000psi tensile loading. I'm not sure how long the balance will take, but I'll get back with the result and progress when I can.
Ian.
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Old 2 Weeks Ago   #2
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Re: 704cc 'HOT' Engine Build

... (speechless)
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Old 1 Week Ago   #3
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Re: 704cc 'HOT' Engine Build

Hi Ian , that all looks and sounds very impressive. Is this going to be the next generation of tuned engine for your car? I guess that you have been planning this for a while. If this is a 'HOT' engine then I have been planning a slightly 'WARM' and far more modest engine project for a while as a winter project to make use of some of the parts I have here. I am starting with a clean bare 499cc crankcase to which I am going to fit one of the already reground crankshafts I have and new bearings of course. I have assembled the new 540cc high compression pistons and barrels I have with 126 con rods to get the double oil squirt onto each bore. They will fit along with a late 126 camshaft and new timing chain kit. Will also use a 126 timing chain cover to get the benefit of the larger oil pump and a Nanni alloy sump. Yet to make a final decision on the cylinder head but thinking of using the Weber 26IMB5 carb I have which is the same spec as the original 500 Sport carb. Just doing it for fun really and to bring together some interesting parts
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Old 1 Week Ago   #4
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Re: 704cc 'HOT' Engine Build

Hi Dave, Yes I suppose it is a step up, but like you I have managed to collect all the pieces of another engine and instead of having some spares I'll assemble them all together.
I don't want a race engine just a good useable road item. It will have a better cam and carb, and I will probably 'borrow' the alloy fan from my present engine. The big sump and oil filter + cooler system and exhaust will also swap over. I am concentrating on getting the bottom end as good as I can afford (balancing) as I feel that most if not all of the aftermarket kits for these engine only focus on the top end at the expense of the rest.
Ian.
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Old 1 Week Ago   #5
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Re: 704cc 'HOT' Engine Build

Well here it is all ready to ship off to the balancing man, I've only to find some wood bits and pieces and test my carpentry skills to crate it all up

Ian.
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Old 1 Week Ago   #6
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Re: 704cc 'HOT' Engine Build

Very interesting Ian---I am following your progress with great interest. Who is doing your balancing for you. As I have advised you, Oselli, despite rumours to the contrary, are still able to balance the 500/126 cranks, something they have a lot of experience doing,so it would be interesting (if it all goes well) to have another 'arrow in the quiver' with regard to crank balancing.
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Re: 704cc 'HOT' Engine Build

Quote Originally Posted by the hobbler View Post
Very interesting Ian---I am following your progress with great interest. Who is doing your balancing for you. As I have advised you, Oselli, despite rumours to the contrary, are still able to balance the 500/126 cranks, something they have a lot of experience doing,so it would be interesting (if it all goes well) to have another 'arrow in the quiver' with regard to crank balancing.
Hi Tom, I'm going to go with Steve at Vibration Free, It seems to me that the 'Dynamic' balance method is more accurate with these Type 2 crankshafts, than only having the crankshaft assembly and working out the balance factor. I will see how it all goes and report back - hopefully with good news
Ian.
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Old 1 Week Ago   #8
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Re: 704cc 'HOT' Engine Build

Quote Originally Posted by Bleeding Knuckles View Post
Hi Tom, I'm going to go with Steve at Vibration Free, It seems to me that the 'Dynamic' balance method is more accurate with these Type 2 crankshafts, than only having the crankshaft assembly and working out the balance factor. I will see how it all goes and report back - hopefully with good news
Ian.
I wonder what adjustments will be needed given the BIS crank was designed to be used with pistons moving in a horizontal plane?
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Old 1 Week Ago   #9
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Re: 704cc 'HOT' Engine Build

The VW barrels...
I presume the bolt pattern is different. Did you need to modify the crank case to fit them?


I had asked about the larger barrels available from 500sport and understood that due to the larger diameter skirt that fits into the crank case needs to be modified to suit this, I presume this is also the case with VW ones, although I have never seen a set in person.


I had not considered how much difference a thorough cleaning would make. I will have to add this to the list once my engine mods begin.


I have been looking into knife edging the crankshaft
https://i160.photobucket.com/albums/...boxedcrank.jpg


The centre of mass of the bis crank is closer to the axis which helps it spin faster. Also the profile is less blunt which allows the crank to punch through the oil in the sump a bit easier.
Knife edging allows the crank to cut through the oil to a certain degree. This can be carried out on an aircooled crank.


The trade off as always is less mass = less torque


I will be reading this thread with continued interest!
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Old 1 Week Ago   #10
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Re: 704cc 'HOT' Engine Build

Quote Originally Posted by fiat500 View Post
I wonder what adjustments will be needed given the BIS crank was designed to be used with pistons moving in a horizontal plane?
As to why the Giardiniera and Bis engines create such an out of balence force just because the cylinder plane is moved from vertical to horizontal is totally beyond me but with both of those engines the balence is maintained by the loading on the flywheel and crankshaft pulley. The Bis crankshaft itself is balenced and is seen as a good upgrade without spending a 4 figure sum
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Old 1 Week Ago   #11
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Re: 704cc 'HOT' Engine Build

When I was at 'Radbourne Racing' we fitted "Nardi" 650cc kits to the 500s. If my memory serves me right, the barrels supplied were VW based---I seem to remember them still having a VW part number cast into them. The crankcases were stripped to 'bare' and then sent away to have the barrel aperture increased. We did it this way so that the original engine number stayed with the car. The old VW 1300 and 1600 barrels are, as far as I can see, of the same external dimensions--the 1300 has thick barrel walls which are bored out to give a 1600 capacity (an extra 75cc per cylinder).
As to the cleanliness of the crank-case, I get all my aluminium parts "aqua-blasted" (aka, vapour blasting). The beauty of this process is that as the abrasive medium is carried in high-pressure water, it leaves no 'pock-marks' on the gasket surfaces, which makes for much easier preparation. "Aqua-blasting" is also a good way to get complicated-shape non-ally parts de-painted ready for re-painting (fan and heater shrouding being such examples).
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Old 1 Week Ago   #12
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Re: 704cc 'HOT' Engine Build

Quote Originally Posted by Toshi 975 View Post
As to why the Giardiniera and Bis engines create such an out of balence force just because the cylinder plane is moved from vertical to horizontal is totally beyond me but with both of those engines the balence is maintained by the loading on the flywheel and crankshaft pulley. The Bis crankshaft itself is balenced and is seen as a good upgrade without spending a 4 figure sum
I'm guessing that the problem with a horizontal stroke is that gravity is not aligned with the piston movement in the way it is with the vertical design and perhaps that puts in an extra wobble?

...short memory on me...I see we've discussed this before.

https://www.fiatforum.com/500-classi...1=#post4015095
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Last edited by fiat500; 1 Week Ago at 17:30.
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Re: 704cc 'HOT' Engine Build

So what do you guys think is the right timing advance at idle and at 3K rpm for this engine? I have a similar 700cc build and am trying to work it out (but still trying to get the carb jetted properly first).

I have a full 123 ignition and electronic coil setup if that will help. I have posted previously, but didn't get any insight from others other than to use the values for the 126 BIS engine (but I can't find those values).

Thanks, and happy holidays!!
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Old 4 Days Ago   #14
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Re: 704cc 'HOT' Engine Build

Evening Dax;
There are so many things that can affect what timing is required, including altitude and what fuel is in the car (I use 98 octaine in my engine) that all I can give you is the (652cc) 126 basic timing, which is:--10deg at idle (700rpm) + 14deg at 3,000rpm + 21deg at 3850rpm--all BTDC. I am still to fit my '123' system, so I would also be interested in which setting people who HAVE fitted (and using) the '123' system are on.
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