235 XXX Engine Number - Short Stroke?

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timsha

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Hi,

i recently purchased a Norton Commando Roadster which was manufactured in 73 but first registered in 74.

It has the number 235636 stamped on the Engine and Gearbox. Could this be a short stroke motor? If so, is it possible to tell the difference without taking the engine apart.

I have not been able to ride her yet, as the gearbox urgently needed overhauling - at the moment its open and im waiting on a new layshaft. The old one was bent by about 1 mm...didnt believe my eyes at first so put it on a mates lathe to check i wasn't seeing things.....can anyone explain how you bend a layshaft without causing any damage to the gears themselves ?

Cheers

Tim
 
Welcome, Tim.

timsha said:
i recently purchased a Norton Commando Roadster which was manufactured in 73 but first registered in 74.

It has the number 235636 stamped on the Engine and Gearbox. Could this be a short stroke motor?
Click to expand...

Probably not. Although there were 235 series short stroke engines, we do know that a considerable number of standard stroke 750 Commandos (and a few '74 850s) were built that also had 235xxx series numbers.


timsha said:
If so, is it possible to tell the difference without taking the engine apart.
Click to expand...

Take a spark plug out and measure the stroke using a rod or pencil etc.. Short stroke is 80.4mm and standard is 89mm.
However the short stroke 750s were short stroke versions of the 850 engine so have the 850 pattern through-bolt style cylinder barrels.

We know from a previous discussion that 235638 is a standard 850 Mk2A.
 
Could be any reason for the shaft to bend. may a PO had renewed some of the gears and not the layshaft. I do recommend you replace any gear pair where the hardening has come off or you will end up with a screaming gearbox. [ personal experience here.] Maybe the bent shaft is the cause of so many gearboxes kicking the kick starter back on harder acceleration. I see it often, and it does it on my 850. I am waiting on new gears to arrive prior to redoing my box.

I understand Hobot has straightened one of his shafts. I wonder if that is the right thing to do. I wonder how long it lasted as well.

Dereck
 
Bent mainshafts are pretty common, bent layshafts less so. Most likely reason is prior gearbox blow up, but kept layshaft because it looked ok.

Like LAB said, very unlikely to be short stroke. As far as I know, no one has been able to verify a factory built Commando with short stroke 750, other than the ones built for show and display. On the other hand, if the title plate says 750, and the engine has the 850 style cylinder, and the numbers match, and the cylinder head has RH 7 stamped on it, and it has 33 mm Amal carbs, you would have a very rare and valuable bike.

Ken
 
lcrken said:
and it has 33 mm Amal carbs
Click to expand...

What is a 33 mm Amal carb, and how would you recognise one ?
Are they numbered differently, or did someone just lean on the boring machine when the choke size was being set ?
 
Rohan said:
lcrken said:
and it has 33 mm Amal carbs
Click to expand...

What is a 33 mm Amal carb, and how would you recognise one ?
Are they numbered differently, or did someone just lean on the boring machine when the choke size was being set ?
Click to expand...

The factory offered the 750 short stroke for racing with 33 mm Amal concentrics and a megaphone exhaust. They were 32 mm Amal bodies bored out to 33 mm and stamped 33 on the side. Back when I first started racing, I had a set of 32s that had been bored to 33.5 mm. I think that was as large as you could go with them.

Ken
 
lcrken said:
Bent mainshafts are pretty common, bent layshafts less so. Most likely reason is prior gearbox blow up, but kept layshaft because it looked ok.

Like LAB said, very unlikely to be short stroke. As far as I know, no one has been able to verify a factory built Commando with short stroke 750, other than the ones built for show and display. On the other hand, if the title plate says 750, and the engine has the 850 style cylinder, and the numbers match, and the cylinder head has RH 7 stamped on it, and it has 33 mm Amal carbs, you would have a very rare and valuable bike.
Click to expand...

Hi Ken and LAB,

thanks for the information...unfortunately it has neither 33mm Carbs, an 850 Barrel nor anything stamped on the head. :(

Strange though that the Andover Norton who have access to the norton factory records say, that the very last 750s still had the 230 prefix and the 235s were short strokers. Obviously those who wanted one could still order a standard 750 right up till the end of the 235 batch although there appears to be no information whatsoever to back this up.
 
by the way, the frame is an 850 Frame - the number starts with 850 F and there was no red number plate on the headstock. I believed, that someone had had the frame restored without replacing it, so i have since put one on it :oops:

In the post dealing with this subject which i just found (850-vin-numbers-t12674.html) Reryder refers to "VIN stamped vertically on the RH side of the steering head". Which got me thinking about another commando which i own - its a 72 Combat which was first registered in the UK. It also has the VIN stamped in this manner (with the numbers stamped one above the other on the right side of the headstock). It does also have a red VIN plate with the month and year of production stamped, but with no VIN stamped on it.

Has anyone else come across this on 750s?

I
 
timsha said:
Strange though that the Andover Norton who have access to the norton factory records say, that the very last 750s still had the 230 prefix and the 235s were short strokers.
Click to expand...

Who were you dealing with at Andover?
Andover Norton holds some of the factory records, and their M.D., Joe Seifert (member 'ZFD' here) has contributed to a number of previous "235" discussions as we've had quite a few (heck, yet another in the last few hours :wink: ) so he must obviously be aware of their existence-but perhaps he needs to update his staff?
 
Hi LAB,

i spoke only yesterday to Simon at Andover who said he would refer it to Joe for further information.
 
Richard Negus the ex managing director of Norton Motors, now part of Andover Norton (not Norton Motorcycles) told me that the last 750 Commando's produced had the 850 through bolted type of barrel. As a designer and draughtsman at Norton, he would know.
 
I thought that the 750 short stroke cylinder was identical to the 850 - less one fin as it is approx 9mm shorter, standard cylinder has 9 fins therefore 750 short stroke has 8 fins?? therefore no need to shove calibrated sticks/pencils through spark plug holes.
 
gripper said:
Richard Negus the ex managing director of Norton Motors, now part of Andover Norton (not Norton Motorcycles) told me that the last 750 Commando's produced had the 850 through bolted type of barrel. As a designer and draughtsman at Norton, he would know.
Click to expand...

They have been discussed somewhere here before, recently.
Someone showed an example ?

They would appear to be extremely limited in numbers ??
 
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