Standard tappet clearance for 62 Dommi 99?

The Norton Motors Maintenance manual for 1963 models and earlier covers your actual model.

It recommends clearances Inlet - 0.003" and Exhaust - 0.005.

This is of course assuming that your engine is still running with the factory fitted camshaft, which was probably the Q.R. version fitted from 1959 to 1962. The profile of this camshaft is quite close to that of the SS camshaft fitted to the 88SS, 99SS, 650 and 750 engines, so a thou wider for each valve would not be a problem.

Previously jason_jordan wrote:

Hi folks

Different texts seem to have different info.

I have 3 books with clearances ranging from .002 inlet - .003 exhaust, right up to.006 inlet - .008 exhaust.

I have previously been running the wider settings but it does sound rattley as hell. This is however the only Norton I am familiar with and from what I have read they possibly all sound like that.

Sound advice from anyone familiar with the standard spec 600cc 99 (1962) would be appreciated.

Apologies if this has been covered before. I did spend a while looking through previous threads but without success.

Much obliged as always,

Jason.

Hello you will be better off with 6and 8 thou has the SS models were engine get that bit hotter runningon ethanol fuels there less dense to older fuels that why everyone having carb problems yours anna j

A bit of a red herring regarding fuel density. It hasn't changed significantly. Phil is absolutely correct, .003" and .005", an extra .001" wouldn't hurt.

Does anyone know if the increases in or around the early 60's due to the SS camshaft or the alloy push rods? I can't work it out from the various books. I suspect I might have the earlier cam but I have alloy rods so I might try smaller gaps. But don't want to have to reset them at the roadside.

With alloy pushrods, and alloy head, there should be no problem. However, fitting alloy rods into an early motor, with iron head, DOSE cause headaches! The alloy rods expand more than the old steel ones. If tappet clearances are set "according to the book", the engine will start, and run perfectly for a few miles. Power will the fall away, the engine will overheat, then stop. Tappet clearance will be lost, and, particularly the exhaust valves will not fully close. I KNOW!

The pushrods changed to alloy shafts at the end of 1956. About the same time that the Daytona camshaft was being fitted to all the engines. Prior to that the pushrods had hollow steel shafts. These, combined with the alloy head, gave a nice rattly motor once it got hot. The very first Model 7 engines had solid steel shafted pushrods.

The much wider clearances were needed when the Norton Twin engines were given the SS camshaft and SS cylinder head along with the shorter but stronger valve springs. This affected most big twin engines from 1960 onwards.

The oddball being the 99SS which kept the old style cylinder head but used a special twin carb mounting block bolted on the back of the head where the single carb normally sat.

The extra clearance stopped the SS camshaft from lifting its valves too early or letting them close too late when used with the flat followers. Thus messing up the important 8* lead of the inlet opening before the exhaust closing.

Of interest, to some owners, is the PW camshafts which open very early but without the huge lift of most race cams.