Cylinder head

Two possible answers Pete. Check out below for options. Dial into http://www.Atlanticgreen.com for photos.

The fifth generation of the Norton twin cylinder head arrived in 1959 and was fitted to engines produced until the end of 1961. It has slightly increased finning all over but especially in the exhaust area. The finning pattern in front of the spark plug was now all-horizontal. Between the two exhausts ports, the finning was also more substantial and no longer stepped. A very noticeable feature of these heads is a line of raised cross ribbing between the two rocker spindle covers. The head has a casting number of 22707K or M, again, located above the intake rocker box cover. These heads also received larger inlet valves of 1.406â diameter and the compression ration had risen from 7.4 to 8.2 on standard pistons. Stellite-tipped valve stems were also now the norm. The 1959-61 head also had carburettor manifold mounting studs with 1 5/8" vertical centres as opposed to the earlier 1 ?â of the earlier versions.

In 1960, the first versions of the legendary semi down draught SS cylinders heads appeared. These were significantly different from the earlier heads and cause much confusion in the chronology of Norton engines. They first appeared on export-only 650 engines and later on the 88SS bikes. However, they were not standard on the 99SS bikes, early 88SS bikes or any of the Nomads. The two most radical changes were the shape of the exhaust ports and the carburettor manifold mountings.

These heads had re-angled exhaust ports at 80? included angle or 40? each from straight forward. The changes improved both the internal combustion process and cylinder head cooling, resulting in dramatic increases in performance when combined with the new SS camshaft, flat-based followers and bigger twin carbs. In fact the power increases were too much for the early engines, which subsequently suffered from piston, barrels and crankshaft problems.

Strangely, despite being quite different in shape from the previous model head, the SS version kept the same casting number of 22707. Usually, this is found on top of the head with the suffix W. It additionally, sometimes had the casting number of 23166 on the underside of the head. This 23166 casting number was also used on the early Atlas cylinder heads Butthese have adifferent head bolt spacing, which does not help when looking for a replacement.

I have 3 heads marked 22707Y. All are the first type that Phil has described and were fitted to 99 engines.

And I have some downdraught heads that are marked 22707 "S" and "J" among others, so no one can state that heads were all marked with any specific letters. It is common for foundries to put various letters and numbers on castings to show the date and shift they were produced on, so maybe something like that was going on.

The heads with 23166 on the bottom can be found in the old vertical manifold-stud style and also cast with the down-draught ports and horizontal manifold studs machined to fit the late 88ss, 650 and 750 engines. The "22707" casting number and it's various Letter suffixes on the top disappear quickly after 1962 along with the original Norton works.

This shows that casting numbers can not be used to positively identify a Heavy Twin head, they are just one clue needed along with how the head is actually machined before one can tell what model Norton it might have been supplied on when it was new.

The example of the T2225 head described on the Atlantic Green site denotes it as having small inlet valves and vertical manifold spacing of 1.5". The head on my own Model 99 ismarked T2225 yet it has the larger inlet valves and vertical manifold spacing of 1.625". Not a particularly useful response to Peter's original post, but it would suggest to me anyway that heads were perhapscast with their numbersbefore some machining was completed, which would tend to lend weight to Benjamin's comments above.

The castingletters on the 22707 heads do not appear to follow any logical reasoning. Neither does the use of 22707 for two different heads. These aretypical ofNorton mysteries which need an explanation and I am sure this will eventually happen. For example we know that alloy heads were cast and used from the early 1950s for competition use. But.......what casting numbers and letters did these heads have?

One ex-foundary worker I talked with suggested that the letters were indicators of a particular section of a foundary works; thus enablingany problems that arose with anycastings to be narroweddown to one processing line and even ashift. This would agree to some extent with Benjamin's comments except that almost every letter in the alphabet appears to get used. I can not believe that there was that many production lines for Norton Twin cylinder heads.

The T2225 marking do generally tend to indicate the earlier heads with the smaller valves. I am wondering if Martin has managed to get his hands on an ex-works head made for competition use.

I believe that Dave Comeau put the Atlantic Green site togetherto try and help Norton big twin owners work out which cylinder head they had crowning the barrels of their bike. It is not 100% correct with regard to detail butis updated as and when new information turns up.A version of this site, for Dominator engines,should also be appearing in the February 2013 Roadholder.

Pete, could you post a photo of this head?

Per D"Dyno Dave Comeau" :

The id # are mould ID numbers and the top has a # and the bottom has another # or version and the combination of the 2 makes the head what it is.

Skip Brolund

The same complete head casting was machined differently to make both 500-650cc heads and 750cc heads, which as I already stated above means that casting numbers alone are not all that is needed to I.D. heads......

Previously wrote:

hello, i would like to know if anyone can help with cylinder head identification i have recently found one in a shed with the casting number 22707 Y.

is this the downdraught head maybe?

regards pete

Previously wrote:

hello, i would like to know if anyone can help with cylinder head identification i have recently found one in a shed with the casting number 22707 Y.

is this the downdraught head maybe?

regards pete

Pete - The most obvious feature of the so-called downdraught head is that all the carb/inlet manifold mounting stud holes are horizontal. Cheers, Howard