Compression height of 500 twin flat top pistons.

Whats the measurement of the pin center to flat top piston crown of the Norton 500? Were there different options with the flat top pistons? And what were the actual compression ratios? Photo's of the piston tops and valve pockets would be appreciated.

I never measured the cr. I just thrashed it! piston ID and part number visible on picture iii.
Pin center to top of crown = 42.2mm
pin center to top of contact with cylinder bore = 37.8mm

Hybrid racer - thanks for those specs.

you say yours are 42.2mm/ 1.66" from pin center to flat crown.
I have one on the shelf that is 1.50" from pin center to flat crown. Another 500cc twin owner said his were the same.
I got specs from some else saying 40.50 mm (1.594”) from pin center to top of flat crown.
I've made them up to 1.75 from pin center to top of flat crown with 10.5 C.R.
Now I need to know what to use for a 8.5 C.R. street bike. I've done the calculations but would like some verification.

Both the 1.5" and the 1.594 crown owners said the C.R. was 7.5 which doesn't agree.

I did a few calculations and if you are correct about 10.5 : 1. at a distance of 1.75” then a distance of 1.5” gives about 6.5 : 1 which would be the model 7 spec piston. My pistons calculate to around 8.5 to 9 : 1 leaving the 1.6” pistons at 7.5 : 1.

Great. That's exactly what I needed. Much appreciated.
Which one is the model 88SS ?

I’m not sure because the book “Norton twins” by Roy Bacon gives cr values of 8.5, 9.0 and 9.5 : 1 for the 88ss
For the cr you are after you can’t go wrong with 1.66”, or whatever you can find close to that

Both Gandini and JP have this info published on their sites. They both list the 88SS spec for 9.45 or 9.5:1 as having a height of 42.069mm/1.656". Gandini list a piston with a cr of 7.5/8.5:1 (presumably the difference being the head used) having a height of 40.5mm/1.594", and JP list a 7.8:1 as having a height of 1.5937".