Technical Fiat 500N Engine Rebuild - Pistons?

[Mferg]

I am into the engine rebuild of the original 479cc engine of my 1958 500N with 66.0mm pistons. My cylinders are showing a slight taper, so my machine shop wants to go to slightly oversized pistons. I cannot find any 66.2, 66.4 mm etc. pistons available anywhere. The closest size appears to be the commonly available 67.4mm pistons. Questions:

1. Does anyone know a source for oversized 66.2, 66.4 etc. mm pistons/rings that would work?
2. Will the 67.4mm pistons work in the original 479cc cylinders, or is this too much of a jump (1.4mm oversize)?
3. Other ideas? My original pistons cannot be reused in any instance, as one of them is damaged.

Thanks for any help.

 

[Bleeding Knuckles]

I am into the engine rebuild of the original 479cc engine of my 1958 500N with 66.0mm pistons. My cylinders are showing a slight taper, so my machine shop wants to go to slightly oversized pistons. I cannot find any 66.2, 66.4 mm etc. pistons available anywhere. The closest size appears to be the commonly available 67.4mm pistons. Questions:

1. Does anyone know a source for oversized 66.2, 66.4 etc. mm pistons/rings that would work?
2. Will the 67.4mm pistons work in the original 479cc cylinders, or is this too much of a jump (1.4mm oversize)?
3. Other ideas? My original pistons cannot be reused in any instance, as one of them is damaged.

Thanks for any help.

Hi Mferg, Go to the RICAMBIO INTERNATIONAL website. they are based in London. They list a piston and ring set of 66.2mm for your engine. The web site says out of stock, but you can order or ask a question and they will let you know the availability, good luck.
Ian.

 

[Mferg]

Hi Ian,

Thanks for this. I actually contacted them some months ago and they were not able to find anything in the 66.xx size. I sent them another message yesterday to see if anything had changed. I will post back as soon as I hear from them if they find something for me.

 

[Franko500]

I think you should be fine going up to 67.4mm


just think of the extra power!

 

[Bleeding Knuckles]

Hi Ian,

Thanks for this. I actually contacted them some months ago and they were not able to find anything in the 66.xx size. I sent them another message yesterday to see if anything had changed. I will post back as soon as I hear from them if they find something for me.

Hi Again Mferg, alternatively try FD Ricambi in Holland part number MO1318 a set of pistons and rings to 66.4mm
Ian.

 

[Mferg]

Hi Ian,

Thanks again. You must be reading my mind. I also contacted FD Ricambi some months ago and again yesterday, as they still show everything out of stock. Hopefully someone will have something for me..

 

[Mferg]

Sean - the extra power scares me - I can only imagine the acceleration and top speed with such a change.

It seems that the 67.4mm might be where I end up - no one seems to have anything smaller at the moment, and I think the Sport version of the N used 67.4mm pistons in the same cylinders, so they should be able to handle it...

 

[the hobbler]

Are you aware that one of the standard Lambretta piston sizes is 66mm, also available in 66.2/66.4mm It might be that those pistons can be modified (machine top of piston to give a flat top to the piston) to fit?

 

[Mferg]

I was not aware of that, interesting idea. Thanks for the tip, will look into it.

 

[Bigvtwin996]

I think you should be fine going up to 67.4mm


just think of the extra power!

What the eye can't see... MORE POWER!!!

you can never have enough power...
especially with 15mm drive shafts!

Thin end of he wedge!!! thin end of the wedge!!!!

 

[Mferg]

I've heard rumors that one can move to the larger drive shafts on the N version, but I must admit I have not had time to look into this yet.... One bit at a time...