Can anyone tell me the exact size that a lightweight con rod big end eye should measure?
I cannot tell you the size of the con-rod eye itself but the big end size is 1.5 " and re - grind is in 0.010" steps, this should be stamped on the appropriate bob weight edge. (i.e. 10, 20 or 30). I cannot measure a con-rod eye at the moment, the garage is in turmoil as it's having a new roof on Thursday but will measure one as soon as possible if you can wait.
Attachment contains Technical Data
All good info Phil but does not contain what Barrie needs. My own experience of rod ovality came when I fitted new std shells to a well worn std 1.5" 99 crank. I was expecting that the assembly would be a bit looser than ideal.But found that I rod would not fall under its own weight. I polished the crank journal with emery tape in a bandolier fashion and it then fitted fine. I was not really expecting it to last but it has. 25years on with regular classic use and plenty of 65mph cruising and short blasts up to 80 . Norton bottom ends are strong and tollerant of wear,especially strong on the lightweight. If you can get the rod re-sized ,good but as long as it all turns freely without any play and you have a good pump I would not stress over it.
Thanks Philip,I have that info but there is no spec for the rod big end unfortunately. Thanks Peter, mine measure 1.600" and 1.626" with a digital vernier but to be dead accurate would probably need a bore gauge. Thanks for info Robert,I need to check for ovality too.
I intend to race this engine so want it to be near to factory spec as possible, but cannot find spec for rod big end anywhere! Is it same as 500 domi? When I put a 885 crank in my 750 Triumph triple race engine there were 4 different shell sizes depending on grade of rod ie. rod big end bore, and then had to check big end clearances with plastigauge, I know my Norton engine won't be to that tolerance but am aiming high. Looking at Commando spec with 1.750" crank journal, rod big end bore should be 1.8950 - 1.8955. This is the info I need for lightweight twins.
If checking for ovality then without a size just go on the difference between 2 measurements at 90 degrees apart, if it shows as oval does it matter what the size is as you need a new rod as you are going racing.
Its the same size big end on Lightweights as for Domi 88/99 - if that is of any help