Dominator Death Rattle

I just thought that I'd offer my recent experience with the infamous Norton death rattle encountered by other Norton twin owners and the topic of several posts on this site.

Having never previously experienced it myself, I was like many others, perplexed as what could be the cause of such a cacophony of offending sounds emanating from the Norton twin engine. Bag of marbles, wild tappets, you get the idea?

Well, having suffered the throbbing vibrations of my 1956 99 fitted with a 650 engine over the last year and 4500 miles I decided that I would transplant a standard 99 engine that I had been rebuilding over the winter months. The only parts that I would need from my 650 engine would be the standard 99 single carb head that I had been using and the push rods. The transplant went reasonably well over a day and a half and after fitting the old 99 head with the SS (fat) push rods (I'm also using a SS barrel on my 99) I came to set the tappets. Daytona cam, so 3 and 5 thou no problems, then a swift kick; oh deary me, what was that? A definite clacking noise.

Could this be the infamous Norton death rattle? Could I have missed looking for worn cam bushes, or is the 4 thou piston clearance too much and creating piston slap, rocker spindles worn, loose valve guide? Perhaps the cam followers are slapping around in the tunnels; they seemed to be a good sliding fit as far as I could remember. I just kept returning to bike and gently turning it over on the kick start trying to convince myself that it would be alright if I just run the engine. The cadence of the 'clack' was entirely consistent with the closure of the LH exhaust valve, so maybe a loose valve guide? Time for a few beers and then bed.

The morning brought a startling resolution; off with the head! I couldn't imagine the engine sounding any better when running than it did just kicking it over. Although a pain to remove and fit, this isn't going to resolve itself, so head off. The cam followers looked fine, no sloppy movement (viewed from the top at least), the valve guides looked sound with no evidence of movement. One last thing, the push rods. Although previously checked for loose caps I didn't check them for being bent. After checking this time I found the LH inlet was significantly bent by rolling it on my surface plate. I hadn't checked it previously because it came out of running engine which although it throbbed, sounded sweet.

After replacing the push rod and refitting the head, the clacking noise disappeared; started the motor and it sounds just great, so job done. The push rod clearances in the Dominator barrels, particularly with the fatter SS pushrods must be so limited that any slight bending can cause the push rods to interfere with each other and cause the ends to become partially disengaged and cause the clatter. I just hope this experience may provide a solution to others afflicted with a similar problem.

Safe riding