D-Rods, Demons Be GoneTech Talk Page


Many late 850 Commandos, (January 1974 Onward), that came out of the Norton factory were fitted with what are known as D-Rods.  For those that don't know, these are conrods that have the letter "D" stamped on them inside a circle.  D-rods look harmless enough and to all intents and purposes, to the naked eye, they look like any other conrod.  But the problems associated with them are not visible to the naked eye.  It is the way that a D-rod is made, that makes it so much more likely to snap than a standard conrod.  When a normal conrod is made, the rod is stamped once for the whole part of the conrod main body, but a D-rod was stamped twice, once for the little bit on the end and once for the rest.  This was introduced as a cheaper way to produce conrods (probably took less complex tooling I can only presume).  Unfortunately, the D-rods turned out to be prone to premature failure down the invisible stamping line where the two stamps met.  Failure often occurred between 18000 & 22000 miles (this was usually well outside the manufacturers warranty period when the bikes were new), but failure can occur at any time.

The Demon In Question
Notice The D's In The Circles, There Are Two In This Picture

Here are a couple of photos of what you will probably be left with after a conrod failure.

If we have your bike in for a top end over haul, we will advise if D-rods are found and a photo of the D-rod with your engine number visible will be supplied.  You will then need to decide whether to proceed to have the engine cracked open for conrod replacement or take your bike away for rebuild elsewhere.  For safety reasons, Norvil Motorcycle Company WILL NOT rebuild any 850 engine where D-rods are found unless they are replaced with new conrods.  After replacement rods are fitted, the D-rod/s may be destroyed by us.  We don't keep vast stocks of conrods in stock but we can source them for you if required.

Page last updated 27/06/07