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Dominator cylinder heads

Submitted by howard_thompson on Thu, 17/05/2012
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Heavy Twins

Having recently acquired a Dominator 88 I'm currently trying to make sense of the seemingly impenetrable world of cylinder heads. A bit of internet research shows me that there are at least four different types, possibly more, but whether or not they are interchangeable and, if so, to what extent, isn't apparent.

My 1958 bike is fitted with a 1960 engine, the cylinder head of which is marked 'T2225 BA' and, as it has a couple of broken fins, I've just bought, from NOCshop, a replacement which is clearly a different type and bears the mark '22707' followed by what looks like an upside down letter Y.

A couple of questions:- firstly, is 'T2225 BA' the correct head for a 1960 88 and, secondly, is the '22707' head interchangeable or do I need to send it back? If it can in fact be used on my engine, would the existing pushrods fit or would it require a different type as, I gather from exchanges on here, that the pushrods too come in various flavours, steel, alloy, straight, barrelled (any more?)

Submitted by benjamin_gradler on Mon, 21/05/2012

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I would say that the 22707 head has a much greater chance of being the correct head for a 1960 Dominator. The 1960 Dominator head had more and better finning than the earlier heads, and the vertical distance between the intake manifold bolts was increased from 1.5" to 1.625".

If your bike had a head with a t2225 casting # it sounds as though at some time in the past someone swapped in a set of later cases but kept the 1958 head etc.. A later head will work with the older pushrods, it is when later, fatter SS type pushrods are used on earlier heads and cylinders the clearances should be checked, but anyone putting any engine together at all should always check all the moving bits during assembly to make sure they all clear.

So the 22707 head should replace the t225 head just fine except you might need a later matching intake manifold if it is the one with the different stud pattern. The later head with the 1.625" vertical spacing for the manifold studs is also supposed to bump the compression up about one point and have a hair bigger intake valves, so it might give the bike a little more power if it is that type.

All the 500-600-650cc Dominator heads can be swapped for one another as long as a careful mechanic does the work correctly and the matching intake manifolds and exhaust pipes etc. are handy.

Submitted by howard_thompson on Mon, 21/05/2012

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Very many thanks Benjamin for an extremely helpful and comprehensive answer. This is exactly the kind of detailed and knowledgeable help that makes such forums as this so invaluable, rather than as an excercise arena for personal hobby-horses which is, unfortunately, too often the case. Again, many thanks.

Submitted by howard_thompson on Tue, 22/05/2012

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I still have a couple of questions that I need to resolve before deciding whether or not I should keep the 22707 head that I've just got from NOCShop.What I now need to know is if the rocker arms, spindles etc from the T2225 head that's presently on the bike can simply be transferred to the 22707 head or if in fact the later head uses rockers and spindles of a different design. I see from Benjamin's earlier information that this head uses larger inlet valves so, obviously, new/replacement ones will be required, as will valve guides as only one remains in the head as received. All/any help greatly appreciated.

Submitted by howard_thompson on Sun, 27/05/2012

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Many thanks Skip. A very useful link. I'll contact him, as you suggest, and let you know what I find out.

From the otherwise deafening silence on the subject it does look as though I'm not alone in my lack of knowledge in heavyweight cylinder head matters.

Howard

Submitted by benjamin_gradler on Mon, 28/05/2012

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All the Norton heavy twin rocker arms will interchange as long as they will fit into the head. On later bikes at some point after AMC took over Norton production they made the rocker arm pivot area narrower, so the early rocker arms will not go into a late head and the late arms will not go into an early head, unless of course you are an engineer/machinist and have the will and skill to modify the head or make spacers etc.....

Submitted by howard_thompson on Mon, 28/05/2012

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Once again Benjamin, many thanks. That's exactly the info I needed and in the light of it I'll keep the replacement head and at some as yet undecided point in the future I'll pull the existing head off the bike and take both of them to Tony Hartlen for the necessary engineering input.

 


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