Seems like a 750 serial number on an 850 (2008)

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So L.A.B., then should raise approximately 89mm for a stock 850 and 80mm if it is a short stroke; correct?
 
One other question: On these short stroke Commandos you are seeing photos of, do they have the 850 style crossover exhaust pipes?
 
Yellow_Cad said:
One other question: On these short stroke Commandos you are seeing photos of, do they have the 850 style crossover exhaust pipes?
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No, they don't. I'll post some brochure scans later so you can see the beast.

Although they're scarce, the reason for that seems to be that the racers didn't want them. The long stroke 750 was apparently easier to ride.
 
What is the consensus: would a short stroke 850 be a good thing or a bad thing. Kommando thought it would be a good thing. I am going to try and measure the stroke tonight.

Also, it has some type of electronic ignition added (owner still has the stock points and cover). The new cover has a flat face the same diameter as the base of the cover and it all protrudes further than the original points cover. Any ideas as to what type of electronic ignition this would be? The electronic ignition would be at least ten years old if not twenty.
 
Whether the short-stroke 750 is a good thing or not, depends on your reasons for wanting it. It was sold as a tuned engine (4-S cam etc.) The 750 capacity was fixed because of the then-current restrictions for racing.

It is undoubtedly a stronger engine that the long-stroke 750 (it has through bolts so it shouldn't pull the cylinder flange off). I have heard that it lacked the grunt from low revs that the older engine had and generally wasn't as sweet to ride - It still didn't rev like the Japanese.

Generally, if the seller knows what he has then you'd expect to pay more for rarity (you're up against the collectors) and you will find parts harder to obtain and probably dearer.

If you want a fast Norton and have no artificial capacity limit then a large bore engine based on the 850 is probably a better bet.

The ignition system it has will probably be the Lucas RITA (is it a rather flimsy spun cover ?) There are two versions, the earlier with a finned alloy ignition box was a bit power-hungry, the later less so. It's a good system without the Boyer low-volt problems. I don't know how it compares with the latest state of the art units. It is no longer made but I believe that servicing is available.
 
Seems like a 750 serial number on an 850 (2008)

750 Short stroke illustration taken from the late 1973 850 brochure.
 
Well I never ! :idea: Well spotted that man ! That's it for sure

I had been unsuccesfully trying the count the fins in the brochure picture.

The Roadster picture is the same as on Roy Bacon's book and would seem to suggest that the 'Short-stroke' decal might just be a figment of somebody in Rugeley's fertile imagination !
 
Well, I visited this Commando one more time and here is what I learned:

1) The stroke is that of an 850

2) All three numbers (plate, motor, and gearbox) all match (235565)

3) The number on the motor has a little round symbal before and after it and after the round symbal after it is the number 1 and then another little round symbal

4) There is smaller than normal (not much space at all) space between the top fin on the barrels and the lowest fin on the head

5) Many years ago this bike blew a head gasket. This was repaired but the silver paint on the head is very thick and almost certainly brushed on. This made me think that it might have been originally polished and painted during the repair.
 
Stolen??

You could also be in the presence of a stolen bike renumbered for resale. My brother bouht a 750 Atlas and we later learned the serial numbers had been tampered with, kept quiet bout it then and sold it later. Even the police could not see the serial number had been changed when they started to add their own punces to keep bike theft down.

Jean
 
L.A.B. and 79x100, please let me know what you think of my most recent findings on this bike especially the number 1 just after the serial number on the crankcase and the high compression part all coupled with the three matching 235,xxx serial number. As you have said, maybe just an odd numbered 850.
 
I don't know. All the reference sources suggest that it is too high a number for the 200000 series 750 engines and yet also not correct for a 300000 series 850 motor.

The Vintage Motor Cycle Club in England have the surviving factory ledgers but there are odd gaps. I found neither my '72 750 nor '75 850 in the books which is strange because I know from the Registration records that both were UK market bikes with traceable histories and I do not recall any blocks of numbers out of sequence. Perhaps worth sending them an e-mail. I don't think it will bring anything to light though.

Has the owner let you take photographs of the numbers ? We could perhaps form a view as to whether this was an important (to us numbers nuts) discovery or if it looks to have been tampered with.

I am suspicious of the number 1 after the main ciphers. I have seen a quantity of pre-production cases and things showing casting oddities to back it up but they have never looked like proper production numbers.

The idea that it was an 850 number seems odd as that should not be before 300000 and not be higher than 325000 as the Mk111s started then.

If the frame paint is original, you should be able to see a number begining 'F' stamped beside the red plate and this may give a clue to where in the sequence it comes.
 
Yellow_Cad said:
All three numbers (plate, motor, and gearbox) all match (235565)
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I really have no idea why this particular Commando has such an odd serial number, or why there is an extra "1"? As all three stamped numbers are the same, the engine has the (presumably genuine?) circle stamp limit markings, so it could have been produced as some sort of special, rather than it being any attempt to hide an original identity if there's no evidence of any over-stamping or metal being removed that would have obliterated any original stamps?

Yellow_Cad said:
4) There is smaller than normal (not much space at all) space between the top fin on the barrels and the lowest fin on the head
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The head may have been skimmed then? Was there an "RH number on the head?

As 79x100 has suggested, it could be worth approaching the VMCC, or the UK NOC to see if anything is known about it, but many of the factory production records from 1973 onwards are incomplete.
 
I was a tooling machinist for a lot of years, I have stamped a lot of things and seen a lot of things stamped, and I don't have any doubts that these numbers were done by the factory. Out of curiousity, I will email the sources you suggest L.A.B. and send them the link to this post with a question from me to them. I'll let you know what I find out.
 
It's sounding more and more like this could be a short stroke 750. I'm not sure measuring the stroke through the spark plug hole is very accurate due to the angle.

The short stroke should have an RH7 head which would have been milled to achieve 10:1 compression so would have a visibly smaller spacing between the last cylinder fin and the first head fin.

It also would be logical (can I use that word when speaking of Norton?) to have numbered them after the MkV 750 but of course prior to the 30xxxx series of the 850.

Les has the right idea. What is the RH designation on the head?
 
Unlike Ron L said there should not be a visibly smaller spacing between the last cylinder fin and the first head fin as the RH7 head isn't milled to achieve a higher compression. This is done by using high compression short-stroke Omega pistons with valve-cutaways. So if you can see (or feel) a cutaway through the sparkplughole you will know its not the regular flat piston crown of the standard engine.
 
Unlike Ron L said there should not be a visibly smaller spacing between the last cylinder fin and the first head fin as the RH7 head isn't milled to achieve a higher compression
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Really? I had never heard that. I wonder then what is the difference in an RH7 head and an RH4?

I also was under the impression that Norton did not recommend domed pistons for compression increase due to poorer gas flow.
 
Yellow_Cad said:
I was a tooling machinist for a lot of years, I have stamped a lot of things and seen a lot of things stamped, and I don't have any doubts that these numbers were done by the factory. Out of curiousity, I will email the sources you suggest L.A.B. and send them the link to this post with a question from me to them. I'll let you know what I find out.
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Good thread here, just catching up.

Yellow_Cad, can you educate one just why you have no doubt the numbers were stamped by the factory? As a machinist you have a particularly valuable insight into the process. I ask because the bike I bought was sold as a earlier 750 model, but I later learned it had an 850 frame, most likely made in Italy. I don't think this is a particularly bad combination, but it was presented to me as otherwise. I've been wondering ever since if the engine stamping was tampered with and I'd like to know what to look for.

Cheers--

wrench
 
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