650 SS Head

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650 SS Head

Postby Colorado » Mon Jun 17, 2013 3:10 pm

Can anyone tell me how to easily identify a 650 SS head and how it is different from a 750 head?

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Re: 650 SS Head

Postby comnoz » Mon Jun 17, 2013 3:16 pm

The head gasket bolt pattern is smaller. Jim
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Re: 650 SS Head

Postby Rohan » Mon Jun 17, 2013 3:37 pm

Anyone got any gaskets to show or compare the differences, and where the differences are ?

An Atlas head will very nearly bolt on to a very early dommie 500.
Bolt pattern is only slightly different.
The 4 bolts around the sparkplug are slightly shifted...

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Re: 650 SS Head

Postby comnoz » Mon Jun 17, 2013 3:47 pm

The difference is just the outer four bolt holes. Similar to the difference between a 750 and an 850. Jim
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Re: 650 SS Head

Postby Rohan » Mon Jun 17, 2013 3:58 pm

"The difference is just the 4 outer bolt holes - similar to the difference between a 750 and an 850".

And the difference between an Atlas and an early 500 is just the 4 outer bolt holes.

So does that make 5 different versions then of the 4 outer bolt holes ??

Be interesting to see all those gaskets overlaid on each other. ...

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Re: 650 SS Head

Postby wilkey113 » Tue Jun 18, 2013 7:02 am

If you could post the casting numbers, that would help.
A lot of 650ss heads. depending on the year, had 22707 (and then some letter), cast on the top of the head, right by the intake valve cover.
The 650 heads had larger head bolts spaced closer together, and when the Atlas 750 was introduced, the head bolts needed to be moved out and a smaller diameter head bolt used in order to have room for the larger bore cylinder.
Also, there's an early 650 head that fits over top the spigot cylinder, and then a later 650 head that was used with the non spigot cylinder. Much like the Atlas. So there are a few different versions.
Post some pics and casting numbers and I'm sure we can help you identify it.

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Re: 650 SS Head

Postby kraakevik » Tue Jun 18, 2013 10:35 am

Atlantic Green has an authoritative section on Norton heavyweight twin heads.

AtlanticGreenTechnicalServices.com


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Re: 650 SS Head

Postby acotrel » Tue Jun 18, 2013 12:00 pm

Is the cylinder base gasket the same on the 650SS, Atlas, and Commando 750 ? In other words is it possible to interchange the complete top end without machining ? I would really like to know this, it could give a lot of options. Also which crankshafts and rods are interchangeable ?
Looking for info on the 650SS, I noticed this:

'The Dominator also had a very reasonable engine. Designer Bert Hopwood was an obsessive self-publicist but had worked alongside both Val Page and Edward Turner at Ariel in the 1930s when all three became interested in the concept of neat, cheap to produce, parallel twins. Page penned the elegant Ariel KH, Turner the legendary Speed Twin and Hopwood the Dominator. Naturally, he claimed the Dominator to be far superior to the other two!

The resultant bike was a nice motorcycle by any standards. It handled extremely well, had a sweet, reliable engine which provided a genuine 90mph performance and possessed the best brakes of any contemporary British bike. Only in terms of a leak prone primary chain-case was the Dommi inferior to Triumph’s world-beating range.

Finished in Norton’s classic polychromatic grey colour scheme, the Dominator also looked every part as elegant as its Triumph contemporary and was far more elegant than either Ariels or BMWs of the day.

But it wasn’t oil leaks which constantly forced the Dommi into second place in the sales race. The Triumph factory was modern, well equipped and profitable. By contrast, the Norton works was a model of inefficiency and squalor and suffered from chronic under-funding. At best, the Bracebridge Street works could produce only 200 bikes a week - and that was a rare occurrence.'
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Re: 650 SS Head

Postby Rohan » Tue Jun 18, 2013 3:22 pm

Bert Hopwood was long gone from Nortons before featherbed frames or alloy heads or bigger brakes or poly grey paint ever came out.
Sounds like you have been reading an inaccurate or misguided publicity blurb from somewhere ?
Or crediting the wrong people...

Meanwhile, back to 650ss heads.

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Re: 650 SS Head

Postby beng » Tue Jun 18, 2013 7:56 pm

A few things missed in the above replies, actually there are six different holes, if you count the rear stud and the oil drain hole. Here is a photo of a 650 gasket laid over a 750 Atlas head.


Image

I put up a lot more info on 650 Nortons and Dominators here for Facebook members:

http://www.facebook.com/pages/Norton-Ma ... 1501303123



.

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Re: 650 SS Head

Postby Bernhard » Wed Jun 19, 2013 3:55 am

Rohan wrote:"The difference is just the 4 outer bolt holes - similar to the difference between a 750 and an 850".

And the difference between an Atlas and an early 500 is just the 4 outer bolt holes.

So does that make 5 different versions then of the 4 outer bolt holes ??

Be interesting to see all those gaskets overlaid on each other. ...


you may be right on the holes on the Atlas head, but you are misleading everybody who may be contemplating fitting an Atlas head onto a 500 twin, for a start a 750 has a bigger bore to the 500, so that the spigot of the 500 will be way undersize to the 750.

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Re: 650 SS Head

Postby beng » Wed Jun 19, 2013 4:57 am

acotrel wrote:Is the cylinder base gasket the same on the 650SS, Atlas, and Commando 750 ? In other words is it possible to interchange the complete top end without machining ? I would really like to know this, it could give a lot of options. Also which crankshafts and rods are interchangeable ?'


IF you lay a 650 base gasket onto a 750 crankcase you will see that Norton moved the four rear cylinder studs straight backwards about 1/8 - 3-16 of an inch, also they moved the oil drainback hole to clear the back of the large bore and bored out the cases more for the bottom of the cylinder where it fits down into the crankcase. The Atlas did use the same crankcase and head casting, just machined differently and with a new cylinder barrel casting.

Sure, if someone had the tools and nothing to do they could weld up the rear base stud holes in the 650 cases and machine them into 750 cases.

The 650 was the first production Norton engine with the 89mm stroke and 1.75" crank pins, Norton had them ready and on the sales floor early in 1961. The first engine was serial #93601 and it's crankcases had humps added to the upper back below the cylinder base behind the magneto to clear the new big connecting rods as they swung around, it was tight in there! The bottom of the cylinder barrel also had to be notched to clear the rods in their larger orbit. The later 750 and 850 cranks and rods work in the 650.

The 650 was also the first bike to get the new downdraught cylinder head with the horizontal intake manifold holes and the exhaust ports angled back. For 1960 Norton had introduced a new cylinder head for the Model 99 that had different and larger fins, a bit larger intake ports and gave a point higher compression with any pistons, but it's exhaust ports still pointed more forwards than the 650 head they started to make about one year later. Norton had made the fins on the 99 cylinder larger to match the new 1960 99 cylinder head, but when the new 650 head with it's angled back exhaust came out they had to trim the front of the fins back so the 650 exhaust nuts would clear. So there was a lot going on during 1960-1962 with the Dominator twin.

Norton put the 650 head onto their Domiracer for 1961, and also in spring that year introduced the SS camshaft, tapered pushrods and valve springs that went onto all Nortons for 1963 and later. The 1961 88 and 99 still kept the 1960 style top end parts, but in 1962 the 88ss got the 650 head. The 99 was dropped at the end of 1962 along with the Bracebridge Street works and for some reason was never fitted with the 650 style head, although it is easy enough to swap the parts on, I am sure some have done this.

The 88 and 99 Nortons never got the larger crankpins and rods like the 650, but Norton did considerably strengthen their crankshafts from 1960 onwards by simply making the diameter of the sludge trap much smaller, thus making the wall of the crankpin much thicker, an easy and effective change on the production line. Later in 1961 a small handful of 500cc Domiracer engines were tried with the 650 crankpins, but after AMC shut down the Norton works and Doug Hele left for Triumph almost all development on the Dominators stopped except for the small detail improvements.

So the 650 that came out at the beginning of 1961 really set the pattern for all the 750 and 850 engines that followed, which did not really change much at all except for what was needed to accept the larger bores, tach drive and points ignition.

Doug Hele was the driving force behind all the Dominator twin development in the late 50s and early 60s, he really got things moving by testing the twins for durability and for production races and Daytona and letting the improvements trickle into the machines coming off the assembly line.

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Re: 650 SS Head

Postby acotrel » Wed Jun 19, 2013 10:00 am

Thanks for that Beng. It sounds to me that not much could be achieved with Norton engines by mix and match. With most British bikes the progression through the various models usually allows use of many parts from the previous. I think you would find that a late fifties 650 Triumph will accept 70s 750 parts, and also the very short stroke crank out of the much later 650 Thunderbird. The Japanese seem to often completely re-engineer their bikes as the models progress, and often nothing from a later model fits an earlier model. There is one notable exception which is important to Australian historic racing, the six speed box and clutch from the GPZ900 Kawasaki fits the earlier Z900 which was five speed. I believe the situation between the GSX1100 Suzuki, and the GSXR might be similar, and some GSXR models had close ratio boxes..
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Re: 650 SS Head

Postby Rohan » Wed Jun 19, 2013 3:36 pm

Bernhard wrote:you may be right on the holes on the Atlas head, but you are misleading everybody who may be contemplating fitting an Atlas head onto a 500 twin, for a start a 750 has a bigger bore to the 500, so that the spigot of the 500 will be way undersize to the 750.


No I'm not. For anyone silly enough to actually contemplete doing this (why would you, 4:1 compression ??!), the later Atlas heads are spigottless - so you'd have to machine off the 500 spigots, to match. From there, its nearly a bolt up fit. Apart from the 4 bolts that don't line up, that is. This is without investigating what the valves would be doing either...

The point was that the bolt dimensions had not actually changed that much between early 500 dommie and Atlas.
Surprising little, in fact, to me anyway.

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Re: 650 SS Head

Postby Rohan » Wed Jun 19, 2013 3:39 pm

acotrel wrote:Thanks for that Beng. It sounds to me that not much could be achieved with Norton engines by mix and match. .


Bear in mind here that Commando engines will go close to bolting into a 1930s Norton chassis, so depends on what you mean by mix-n-match.
By the same token, that could give you a 1930s engine in a much later frame, so we could claim that Nortons did a featherbed in the 1930s... !!
Only if we were wearing our rose-tinted specs though....

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