Where can I get new Conrods ?

All 500 and 600 cc Norton twin conrods are the same spec.  I bought a pair of CNC milled conrods for my Model 88 from Thunder Engineering of Leicester.  The are of similar weight to standard ones (I think they are about 25grams heavier, but forget which end) much stronger, and finely made.  They are exactly matched to each other and can be installed without rebalancing.  Price three years ago was £320 inc VAT and post.

Disclaimer, I have no connection with this firm other than being satisfied with doing business with them.

Paul

I have just tried the RGM catalogue, and they are the Thunder Engineering conrod.  The asking price is £347 if you add the VAT.

You obviously need a small end bush if you have steel conrods.  It is perfectly respectable engineering to run the small end directly in an alloy conrod.  It's stronger, and simply does not wear.

I bought my rods direct from the owner of Thunder Engineering.  He told me that the rods could be fitted as is, without any modifications, and so I found - I had no clearance issues at all.  The two rods were EXACTLY the same weight.  I used digital scales measuring to .5 gram, and I could not detect a difference between them. Considering the change in weight if you fit different pistons (the modern GM ones for our bikes are VERY heavy) I don't think this difference is worth worrying about much. 

However, you have a 600, and the greater stroke may well cause clearance issues, within the cases (check carefully at the upper back) and at the bottom of the sleeves.  I just spoke to the boss at RGM, and he had not fitted the rods to a 600, so he could not say if there were definitely clearance issues.  But that statement on his web-site covers him in case you do not have clearance

For a definitive answer, I rang Thunder Engineering.  0116 283 4640.  He says that you are unlikely to have a clearance issue with a 99, but of course, CHECK as you do the build

I have original-fit Hepolite pistons which were put aside in 1962, having worn out the bores in a 1956 Dominator, and sat on a friend's garage shelf until the mid '80s. They had light scuffing, and no ring-land wear.   I was needing to get my barrels sleeved, and at that time, in New Zealand, you just could not get pistons for the bike.  Or conrods.....  mine were bent, which is why I ended up buying the Thunder rods.  My engine is very smooth compared with a bigger one like yours....

Paul