http://www.athenaparts.com/files/pdfs/Big_Bore_FIAT_500_web_eng.pdf

Hello Gents

Can someone please comment on reason for the 2.5mm spacer plate between block and barrels?

When fitted now pistons at TDC sit below top of barrels by same amount , 2.5mm? All I can see this doing is reducing compression. Is it for valve clearance perhaps? At a loss if I need it or not. Appreciate all input in advance.

Cheers

Hugh

My engine builder asked the same question when using the Athena kit.
It was discarded and I run a 10.5:1 C.R.
It is most likely that different versions of the crank case have different barrel mounting heights.
I also do no run a head gasket.
You need 0.7mm between the top of piston and the top of the barrel

Makes sense, cheers for the insight.

Hi Hugh , I'm not familiar with the kit you have mentioned but looking at the link it is not clear if it is an upgrade for a 499ccs engine or the 652ccs. The original engine has a 10 mms longer barrel than the 126 engine so generally when upping the capacity on a 500 crankcase which has to be bored out a 10 mms spacer is used so the 2.5 mms spacer is a bit of a mystery although those barrels are also a special. Also sometimes the spacer has been described as a strengthening plate.

Thank you Toshi, yes I am using a 126 650 cc engine as starting point, I removed the 2.5mm spacer and all is okay, apparently some need and some do not.

At some point (time permitting) I will post a thread of my project also.