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Old 1 Week Ago   #1
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479cc to 499cc help??!

Hey all! I'm currently working on rebuilding my engine and trying to figure the best approach. I'm likely going to get new pistons and rings, as its affordable and seems to solve my compression issues, however I don't think I want to use my liners as they are, being they're likely well worn.


My two main options are

1.bore out current liners to fit 499cc pistons
2. Get 499cc liners and pistons and very slightly bore out the case.

I've asked the guys at FD Ricambi the OD of their 67.4mm liners, which they said 75mm. My current 479cc liners are 73.8. So there is a small difference.

Has anybody done this? Have any suggestions?

I am aware if I'm doing this kind of work, I could get much bigger pistons for better performance, but my head work was already done, I have new exhaust already and my carb is fine. I don't need a hot rod, I just want it to function as it should!

Thank you!
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Old 1 Week Ago   #2
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Re: 479cc to 499cc help??!

Quote Originally Posted by ChiapC View Post
Hey all! I'm currently working on rebuilding my engine and trying to figure the best approach. I'm likely going to get new pistons and rings, as its affordable and seems to solve my compression issues, however I don't think I want to use my liners as they are, being they're likely well worn.

My two main options are
1.bore out current liners to fit 499cc pistons
2. Get 499cc liners and pistons and very slightly bore out the case.
I've asked the guys at FD Ricambi the OD of their 67.4mm liners, which they said 75mm. My current 479cc liners are 73.8. So there is a small difference.Has anybody done this? Have any suggestions?
I am aware if I'm doing this kind of work, I could get much bigger pistons for better performance, but my head work was already done, I have new exhaust already and my carb is fine. I don't need a hot rod, I just want it to function as it should!
Thank you!
Hi, I have had to bore and hone my cylinders too in the past, but, much larger parts from a 126. Because the difference is so small you may get away with a good hone of the barrels to fit the new pistons, otherwise get your machine shop to advise if boring is ok as the honing will reduce the amount to be removed. Alway accurately check that the barrels have parallel bores too. Otherwise the engine has to come apart to do the work on the crankcase spigot area!!!
Ian.
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Old 1 Week Ago   #3
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Re: 479cc to 499cc help??!

My suggestion would be to strip your engine completely, get the crank-case machined out to accept the slightly bigger barrels and then fit 540cc barrels and pistons. They have the same external diameter as the standard 499cc barrels (and are sold on the basis of being a 'straight swap'). When re-building the engine, fit new bearings, gaskets and seals, as you would with any re-build. Fitting a later, but standard, 500 cam might also be beneficial. Doing it this way, the engine will look absolutely standard, but give you a bit more performance which will make coping with modern traffic a bit easier. It will also retain the car's original engine number---very important to some people.
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Old 1 Week Ago   #4
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Re: 479cc to 499cc help??!

Found this interesting as I had not realised that the 479cc crankcase had smaller cylinder locating bores than the 499cc so it got me measuring. So the base of the 479 cylinder with a 66mm bore and o/d of 73.8 has a wall thickness of 3.9mm. The base of the 499 cylinder and 67.4 bore, o/d 75 and a wall thickness 3.8mm. I have a 540cc kit here with a 70 bore, same o/d as the 499 and wall thickness of 2.5mm so if you rebore the 479 to 499 you get a wall thickness of 3.2mm. That sounds doable to me but worth chatting with your machine shop.
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Old 1 Week Ago   #5
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Re: 479cc to 499cc help??!

Quote Originally Posted by Toshi 975 View Post
........ That sounds doable to me but worth chatting with your machine shop.
It is what I would advise....
the 500 N Sport was a 479 bored out to 499
even 479 power is sufficient to snap shafts on an N so drive shafts need to be upgraded to the N specific 25mm ones..

So for you people who worry about the rubber couplings on F/L/Rs.... remember N ones are smaller and without changing the wishbones that's what we are stuck with...

so whilst 540 would be nice it brings more complications....
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Old 6 Days Ago   #6
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Re: 479cc to 499cc help??!

I never got notifications of the most recent posts here! Sorry for not responding!


So I'm still working on what I want to do here. I found a shop that will bore out the case as the hobbler mentioned. This would be to just fit the 499cc liners. I really don't need to snap the drive shafts, even though I do have a set of later F or L shafts here, I'd rather not mess with it as the car won't be with me forever.


My machine shop is comfortable turning my liners into 499cc. Their setup/machine work for that is the price of new N liners (If I could find them, which is another story.) They're working on evaluating my current liners to see if they could hone out and a new set of rings would be acceptable to get my compression back. Once they report back I'll have a better idea.


A few other points of interest.... While looking for pistons/rings/liners, I found some "stock N pistons that had another piston ring below the pin? And some of the ring sets list 6 rings, where my pistons only have 4, which I found odd. Are stock N pistons supposed to have more than 4 rings?

I also searched the entire internet for two N liners. I found one. On fiatparts.de. For the life of me, I couldn't find another. (That's a challenge for you all )


On top of the standard part suppliers, I searched ebay.it, ebay.pl, ebay.nl.... you name it. I'd much rather buy new N pistons, liners and rings and drop em in, but being as though I want to own one of the early rare ones, i have to deal with the lack of proper parts supply!


I'll keep you updated! In the meantime.... here's a pick of my block vapor blasted! I love it!
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Last edited by ChiapC; 6 Days Ago at 14:45. Reason: removed computer jibberish
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Old 6 Days Ago   #7
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Re: 479cc to 499cc help??!

Firstly I think we have to differentiate between Barrels and Liners....
Liners can either be wet or dry
Wet liners are inserted into a block and come directly in contact wt coolant, dry liners are not in contact with coolant, in addition, dry liners can be pressed into a block, sometimes to return a block that has been over bored to it's maximum....
Barrels are more of a description of a single or multiple cylinder of an air-cooled engine...
So boring Barrels is different to discussing liners......

May be just words but it is very confusing...

Well had some word back from the people in Italy, they would opt to rebore teh original Barrels to 67.4mm, any engine shop should do this easily, and believe it or not a motorcycle engine shop may be more confident and cheaper as basically a Fiat 500 Barrel is very similar to a motorcycle one....
The logic bing, the pistons are easily obtainable and it is what fiat did for the sport..
The second is...
accidents can happen.. perhaps a tool shatters... Boring the crank case on an N would be needed to fit the later barrels.. and what happens if something goes wrong... N cases are not falling out of trees....
but if something happens with the a barrels ... well you can actually have 499 ones machined down to fit the N Case... Thus keeping the N as safe!!


Also fitting 67.4 pistons and re-boring the 479 Barrels is probably the cheapest option..
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Old 5 Days Ago   #8
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Re: 479cc to 499cc help??!

Spoke to one of my Motorbike mates...
He said Machining Fiat Barrels wasn't that difficult...
he reckoned about 30-40 per cylinder
A good shop would Machine based on the Pistons...
Clearly there would be some Manufacturer tolerances listed somewhere, and it would be easier to supply the shop with them,,,

Next the interesting bit...
The barrels should be machined from bottom to top... don't ask me why!!
the final few thou taken out by honing..
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Old 4 Days Ago   #9
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Re: 479cc to 499cc help??!

Quote Originally Posted by ChiapC View Post

I also searched the entire internet for two N liners. I found one. On fiatparts.de. For the life of me, I couldn't find another. (That's a challenge for you all )


I'll keep you updated! In the meantime.... here's a pick of my block vapor blasted! I love it!
Having seen a picture of your crankcase, which looks awesome, I can see why you want to go with original parts. Sometimes these things transcend common or economic sense, just down to the dream and the passion.
You can be sure that somewhere in the world those parts exist , it is just a case of finding the damn things. I spent months trying to get some piston rings for an engine I was restoring. I eventually I got them via ebay from Athens, Greece from an outlet that have loads of old stock. As you may know many 500s were part assembled and sold in New Zealand. When I visited the Horopito Motor Wreckers yard there a couple of years ago there were 5 Fiat 500s there including a couple of almost complete N models. It is like no other place on earth and they have huge barns full of old parts, used and NOS. Also the guy who has the greatest stock of 500 parts is located in Auckland , New Zealand. I have pinged them all emails as that seemed easier than passing all the details on to you. If I get any response I will let you know
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Old 4 Days Ago   #10
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Re: 479cc to 499cc help??!

Totally appreciate the help and follow up! Let me know if they come up with anything. I'm trying to find parts stores based in NZ or AU, but nothing really popping up yet!
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Old 4 Days Ago   #11
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Re: 479cc to 499cc help??!

Quote Originally Posted by Bigvtwin996 View Post
Spoke to one of my Motorbike mates...
He said Machining Fiat Barrels wasn't that difficult...
he reckoned about 30-40 per cylinder
A good shop would Machine based on the Pistons...
Clearly there would be some Manufacturer tolerances listed somewhere, and it would be easier to supply the shop with them,,,

Next the interesting bit...
The barrels should be machined from bottom to top... don't ask me why!!
the final few thou taken out by honing..
Good info here! I've to to try to find manufacturing tolerances! Peter, do you happen to have the part number for the proper 479cc barrels? I may get lucky if I use that to search!

Thanks!
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Old 3 Days Ago   #12
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Re: 479cc to 499cc help??!

Quote Originally Posted by ChiapC View Post
Totally appreciate the help and follow up! Let me know if they come up with anything. I'm trying to find parts stores based in NZ or AU, but nothing really popping up yet!
Just looking on ebay for 66mm pistons or rings and a set of rings popped up and they are in the US. Item number 372798579209. Titled "Fiat 500 classic 2-cylinder standard piston rings. I think they are $22. Reckon they might be worth having in your locker.
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