650 SS Head

Colorado

Joined
Apr 17, 2012
Messages
21
Can anyone tell me how to easily identify a 650 SS head and how it is different from a 750 head?
 
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...
 
The difference is just the outer four bolt holes. Similar to the difference between a 750 and an 850. Jim
 
"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. ...
 
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.
 
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.'
 
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.
 
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.


650 SS Head


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

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



.
 
Rohan said:
"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. ...
Click to expand...

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.
 
acotrel said:
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 ?'
Click to expand...

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.
 
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..
 
Bernhard said:
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.
Click to expand...

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

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....
 
Rohan said:
No I'm not. For anyone silly enough to actually contemplete doing this
Click to expand...

In the mid 1960s one of the most famous Norton tuners in the USA built up a Norton Dominator 88 road-racer using a 750 Atlas head. That tuner was John Gregory, the builder of the Hog Slayer Norton drag-bike that made T.C. Christenson famous.

Mr. Gregory made his own custom cylinder in alloy to mate the Atlas head to the Domi 88 bottom end. He turned down late 99 pistons to an AMA-legal oversize so he had light domed pistons. He welded the crank up solid into one piece with a new center flywheel that was just a "porkchop" like the outer two counterweights and he used rods from a General Motors Buick V8.

So a lot of work went into the engine and the bike was fast. I talked to both John Gregory about it a few decades ago, and more recently talked to one of it's riders back then, Kenny Hayes. Gregory said the crank was so light that he had to bolt an outside flywheel onto the engine for it to work on long tracks like Daytona. They were timed at Daytona in qualifying going very fast, they claimed over 130mph.

At one point during that Daytona session something in the bottom end came apart and the bike ended up being wrecked. Hayes says he has a photo of the bike but despite a promise he has not yet sent a copy of it to me. I have the old gearbox out of the bike I got from Gregory a few decades ago, it is a regular AMC box with a Manx cluster installed.

Gregory said he thought the Atlas head had some advantage over the 500-650 head, I don't know what it would have been since they were both machined from the same casting any given year, but he was the famous tuner, and if he went through that much work to get that engine together there must have been something to it.

T.C. Christenson ended up taking over Gregory's Sunset Motors Norton dealership and is there to this day. A long time ago I asked T.C. what happened to the 500 racer and he said it was scattered to the four corners after it had blown and wrecked, all that he could find was that gearbox. A sad end to a special bike.
 
One thing is for sure - if racing is involved, someone is sure to have tried it !
Doing a new cylinder gets around the different bolt spacing, thats for sure.

Thanks for that Ben, if you ever get that pic we'd be interested to see.
 
Rohan said:
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....
Click to expand...

Speaking of inaccuracies - Bert Hopwood had not left Norton before alloy heads came out. He actually designed the upgrade to the Model 7 iron head that became the alloy 88. In doing so, it produced a serious oil leak from the head, due to retaining the dimensions of the iron head rocker spindle bore. Alloy expands more than iron, hot oil leaked out and a quick redesign was done to get production back on track. It was an embarrassing episode in an otherwise exceptional career.
 
Bert Hopwood left Nortons in 1949, after designing the 500cc all iron Model 7 dommie twin, and went to BSA.
The alloy heads didn't appear on production (street) bikes until 1954.

Its tough to see how Bert could have had much to do with them ???

Interesting story but.
There is a plate bolted onto the outside of the head, with gasket. Any oil leakage would have all been inside the head ?
All those early twins didn't have pressure feed to the rockers either, it was just a dribble feed bled off from the oil return line to the oil tank.
 
ML, Unusual for Rohan to get something so important, so wrong . Perhaps you should check your facts ?
 
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