Please help me identify my frame

So this started a few days ago as a thread about how to remove the lock from the yoke of my '1974' 850. Along the way it seems I might have a 750 frame on the bike. I'd really like some help identifying this. Yes, I've read as many old threads on the subject as I can find, but it has left me confused. Here's what I can tell you:

1)The bike is registered as a 1974 850 Commando.
2)the upper and lower yokes appear to be 750--though the bike seemed to handle very well--though I'm not very experienced.
3)the serial plate riveted to the front tube lists it as manufactured in ' 3 74'. That puts it as 'early' '74. Presumably March
4)The serial number on that plate is 313811. It is the same number as both the engine and the transmission
5)I've checked the leading edge of the left (and right) front gas tank bracket of the frame (and the trailing edge too) for a number. Nothing. The paint is peeled there so I can see. There is no number.
5)I cannot find any other numbers stamped into the frame.
6)The central frame tube is 57 mm O/D
7) The front of the swing arm has a heavy boxed gusset on the crossbar just ahead of the wheel (I understand this can be a clue, though the swing arm is obviously not a part of the frame)
8) The bike seems to be complete and looks like it has enjoyed an easy life. A local Norton guy told me that he thought the 12,000 miles showing on the odo was probably correct.

I understand that it may be possible to tell an 850 frame by the shock mounts. Hence the attached photo.

Nielsen,
It looks like a 73-4 850 frame. It also looks like the spring top collet is striking the gusset. I would investigate the upper bushes in the shock. They should have some space between the top spring support and the gusset. Are your springs stock?
Cheers,
Thomas
CNN

Thomas: thanks for the heads-up. I'd never noticed that! I have no idea whether the springs are stock. What is it about the photo that makes you think it is an 850 frame?

Nielsen said:

What is it about the photo that makes you think it is an 850 frame?

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The inboard gusset is what tells me that it is from 73-74. On an 72 frame these gussets would be identical to the outboard one in your picture. I believe that this was changed to help alleviate the rear hoop from bending down when riding two up on earlier bikes.
Cheers,
Thomas
CNN

850 frame for '73-early '74 will have the fame part number 06-4140 stamped on the left front gas tank bracket looking from the front.

illf8ed said:

850 frame for '73-early '74 will have the fame part number 06-4140 stamped on the left front gas tank bracket looking from the front.

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there are no numbers on that bracket unless they are underneath the bracket in the area covered by the bracket for the coils which is bolted to the gas tank bracket. I haven't taken that coil bracket off. Should I? I thought I understood that the numbers were on the leading edge of the gas tank bracket--and there's nothing there.

Nielsen said:

illf8ed said:

850 frame for '73-early '74 will have the fame part number 06-4140 stamped on the left front gas tank bracket looking from the front.

Click to expand...

there are no numbers on that bracket unless they are underneath the bracket in the area covered by the bracket for the coils which is bolted to the gas tank bracket. I haven't taken that coil bracket off. Should I? I thought I understood that the numbers were on the leading edge of the gas tank bracket--and there's nothing there.

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The stamped numbers are on the front of the vertical portion of the left gas tank bracket, would not be covered by the coil bracket. 750 frames have no stamped numbers. Check Dave Comeau's atlanticgreen.com site or google "Norton Commando frame dimensions"
750 frames have a narrower rear loop than the 850 frames. Dimensions are on atlanticgreen.

Thanks for that, David. I'll get on it tomorrow morning.

I looked at some of your other photos on photobucket. The rear loop looks wide and the inner frame gussets at the top shock months look original. My opinion is you do have an 850 frame with 750 yokes. Now the question is why did a previous owner change the triple clamps, maybe a front end accident. That would make me want to check the frame for bent tubes.

might explain this issue

what-with-crooked-norton-t21958.html#p286949

Rear wheel not centered can be caused by the inner bearing spacer (p/n 06-2069) assembled backward. The short reduced end goes toward the brake drum. Look at the exploded view in the parts book, item 29.
I bought an 850 frame for $20.00 that had front end damage. The backbone is bent, the headstock twisted and right side smaller tubes bent. The lower triple clamp is twisted, but the upper seems to be straight. Just some idea of where to look.

Based upon Dave Comeau's comprehensive chart on frames (thanks for the link to atlanticgreen.com), the hoop width of mine is correct for March '74 (it's indeed 'wide). The serial plate on the front is canted to the right when viewed from in front of the bike (which means to the left if seated like a rider and viewing down on it). Comeau says it should be to the right. I'm going to write to him for clarification.

I put a straightedge on the frame tubes, and everything seems to be fine.

I'll check on that rear wheel spacer. I did spend a good deal of time measuring the wheel alignment and altered it a little since that photo was taken. I also shifted the fender to centre it better. The result is that the rear wheel appears to be properly centred now.

Nielsen said:

illf8ed said:

850 frame for '73-early '74 will have the fame part number 06-4140 stamped on the left front gas tank bracket looking from the front.

Click to expand...

there are no numbers on that bracket unless they are underneath the bracket in the area covered by the bracket for the coils which is bolted to the gas tank bracket. I haven't taken that coil bracket off. Should I? I thought I understood that the numbers were on the leading edge of the gas tank bracket--and there's nothing there.

Click to expand...

The 850 frame part number is normally found in the area shown below, although it's often faintly stamped in small digits so is easily missed:



The extended inner shock plates makes it the later 850 frame so the part number, if found, is likely to be 065404 and I would expect it to have the *850*F1xxxxx* frame number stamped alongside the certification plate?
Example:

WZ507 said:

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I wish I had visible numbers like that...... nothing on the rear shock tower brackets, and as you can hopefully see from the photos, nothing on either the gas tank bracket or beside the serial plate. Is it worth drilling out the serial plate to see if there's a number stamped underneath it? I could also sand down the area beside the serial plate, but there's absolutely no sign of anything, so I find it hard to imagine that there's a number hidden under the paint.

Nielsen said:

........ Is it worth drilling out the serial plate to see if there's a number stamped underneath it? ]

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I would vote "no" to drilling out the rivets to remove your I.D. plate. But having said that, I have not seen them riveted on like that before. From what I remember, they use the small pressed in "screw pin" not sure what they're actually called but they have a button head and the teeth on their shank bite into the frame tube when pressed in. Maybe your bike was in an accident and then repaired/reassembled onto another frame, but then again maybe not :shock:

Nielsen said:

Is it worth drilling out the serial plate to see if there's a number stamped underneath it?

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That's up to you, I doubt it will be under the plate although you may find a five-digit (00xxx) number in that area?

I notice the plate has been pop-riveted on, which does suggest that the plate has been removed and re-fitted or switched to a replacement frame at some point as the plate would have been fixed with "hammer drive" rivets originally.

The hammer drive rivets are called PK screws

That frame plate has been off the bike at least once as the fixings are not the correct rivets but pop rivets which were not used by the factory, it also looks like it was chiseled off at one point on at least one corner. For the pre MK3 the NOC dating officer told me the number directly stamped on the frame was to be placed so the plate hid it, well it was not hidden on mine and was used for its first registration. Maybe you have a spares frame but it should still have a part number stamped on it somewhere.

Ignore my PK screws bit. Looks like they are hammer drive rivets. My mistake.