Norton Mercury restoration Part two Messenger of the jods...
I UNEARTHED THE HEAD FOR INSPECTION AND WAS horrified at what I saw. Not only was there a broken valve guide but the seats were severely worn, to the extent that the combustion burn had crept beneath them to the head itself. It went over to Len Paterson at The Cylinder Head Shop for a complete overhaul, including new seats, guides, valves, flowing et al. Expensive but necessary. Len reckoned he’d seen few heads as bad. It transpired that the Mercury cylinder head had been factory-fitted with slightly larger inlet valves. Len sourced from his stock a suitably-sized head, but the stems were slightly too long. I took the head to Jeff, who duly shortened the valve stems and supplied a pair of lash caps. For those who may not know, these are tiny caps that fit over the head of the stem – in this case because the case hardening may well have been compromised by the shortening process – onto which the rocker arm bears, instead of directly onto the stem. Before I built up the rocker gear into the head, I gave it a tidy-up in the blast cabinet with a very gentle cleaning medium and it came up a treat. Once cleaned out thoroughly, the rebuild process went uneventfully.
The carburettor resulted in more work, as there was a noticeable crack in the body. After a thorough clean-up, further inspection just compounded the disappointment. It had seen some serious abuse and was worn out, so the simple answer was to replace it with an Amal Premier Concentric. Compared to the concentrics of old, this is indeed a superb piece of work, precise and beautifully finished with a hard anodised slide. Ordered as per catalogue specification, it was simply a case of fit and forget.
Returning to the frame, I
