FRAME SERIAL NUMBERS

As per Dave Comeau's artical 02/25/2007on the INOA website, concerning frame numbers. I would like to add some information from my machine.

VIN MFG Frame Batch Sequence Seat Letter Dash / VIN Plate Coil
Date Number Number Loop Size on No Dash Reference Bracket
Width VIN Frame Centre Hole Shape

303 … May 73 unknown unknown Wide Small None Left of Centre Round

I would like to find out what model this machine left the Factory as ... I suspect it may have been an Interstate from the wide seat loop but the original owner passed on in 1991 and I never asked when I purchased the machine in 1975. It was set up as per Paul Dunstall Cafe racer at that time.

You might just find a clue in the instrumentation as according to the 1973 750 brochure only the Interstate had a trip function (which meant Veglia clocks as the green spot Smiths of the period had no trip facility). Non scientific observation over the years suggests that this rule probably applied to 850s up until the Mk111 as well.

However, an easy thing to change and what left the factory may not have been what left the dealer.

Brit303 said:

I would like to find out what model this machine left the Factory as ... I suspect it may have been an Interstate from the wide seat loop

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I don't think the body style can be identified from the width of the frame loop? Apparently it was a change made during production, and there was only ever one frame part number for any one production year, so all body styles in a particular year would have used the same frame type, as far as I know?

Thanks 79x100. Easy to check and just quirky enough to be English. L.A.B. - I was assuming the Fastback used the narrow seat loop and the Interstate used the wide loop ...

Brit303 said:

I was assuming the Fastback used the narrow seat loop and the Interstate used the wide loop ...

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Your Commando frame appears to be the 850 version (303??? serial), and there were no 850 Fastbacks built as standard. The 750 Fasback model was discontinued at the end of 1972 (or maybe early 1973?) and the Dyno Dave website info which only deals with the 850 model frames doesn't list a "narrow loop" version frame before July '74.

Also, what I said about there being "only ever one frame part number for any one production year," isn't strictly correct for 1973, as of course the 750 and 850 models had slightly different frames with 1 degree difference in their headstock angles.

LAB,

Do you happen to know if there was much difference in neck angle from the featherbed?

Cookie said:

LAB,

Do you happen to know if there was much difference in neck angle from the featherbed?

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I have not, as yet, been able to find that information for the Featherbed frames.

Since so many are still made I imagine specs could be found, the reason I ask is the discussion Grandpaul had in his restoration thread when he mentioned he had a G15 frame that had been chopped. He was thinking of setting the neck angle to that of a Commando. It makes me wonder if they used the featherbed neck angle on Commandos since they already knew it worked well. I don't want to tear the bikes down to measure but as close as I can tell holding up a protractor and plumb bob the ones in my garage look within a degree or two.

hi cookie,acording to roy bacons restoration book the frame head angles taken between steering head and lower frame tubes,in degrees are manx and wideline =26 slimline=24 750 commando=27 850 commando=28 ,theres no mention of the hybrids

Thanks Chris, it helps my curiosity. My hybrid G15CSR did not handle as well as a Commando, adequate but not the best I've ridden. I know the G15 frame was used for a lot of applications, sidecar, tourer, and off road bikes. What I was wondering was that if you were to set the hard points the same as a featherbed, if you could approach featherbed handling.
A lot of builders did just that to develop handling bikes but many of them cribbed pretty blatantly as far as mounting points went.