is it a combat (2015)
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Dyno Dave's web site "crankcase evolution" explains the reasoning on the transformation mid stream in the model year. Some of the mounting boss were failing due to machining these area too deep. Around 208000 they made the changes and were reinforce in many areas with beefier radii. This is one reason I felt quite lucky to get my hands on a 210xxx set for my rebuild.bill said:
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I bought this 1972 sight unseen, it was done up as a cheesy 1960's "chopper". Turned out to be a legit Combat. Had Dave Katz and Jack Manning of CBE go through it and transform it into a respectable rider. VIN #204539.
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For some reason I had sent DynoDave pre-peel March/72 cases & he found microscopic evidence of fracture in one of the sharp cut radius so I ground them all out, took to welder who freaked me out how deep he began melting into each area to point out more microscopic fractures at their source below surface, then kept on melting deeper and deeper till the thin dark squiggle disapeared and fill back in layer upon layer - repeated on all case flats. Real work began afterwards but held up well in Peels pounding. Btw thin 750 cases tend to leak on the long unbolted seam behind barrels to was able to add 11th clamp bolt there too.
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Just received McGrath’s Norton The Complete Story as a Christmas gift. Page 129 “In 1970 the Roadster was introduced.” later..”The same year a higher-performance engine, the Combat motor, was offered as an option.” Page 130 mentions 1972 intro of the Interstate and an even more powerful version of the Combat motor. Bacon’s Norton Twins Restoration page 220 states June 1970 Combat engine available. However page 216 200976 is the first combat engine which contradicts the statement on p220. Looks like some confusion was introduced and subsequent publications propagated an error without vetting the information. Bacon’s book first published 1987 while McGrath is first published 1991. Would be interesting to know the outcome of this “myth”...I’m saying that as I’ve not seen anything in NVT advertising offering a combat option until the 1972 brochures.
For the authors I’m sure they’ve taken some heat over this and not trying to persecute them.
For the authors I’m sure they’ve taken some heat over this and not trying to persecute them.
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I think that should be taken as first production model Combat (200976) as up to that time the Combat engine was optional.
The Interstate was the first to have the Combat engine and disc brake as part of the standard specification. The Combat spec. engine and disc brake were "optional" for other models, however, once the Combat specification was freely available as a 'production' option I have no doubt the likes of Berliner would have demanded the US Roadster (and Fastback?) should also be to Combat spec.
MCN, 5 January 1972
"....the new Interstate, Norton's most powerful road bike."
"When the Commando Roadster is fitted with the Combat engine and the front disc brake as optional extras,......"
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Hi L.A.B.
Wow, quite a confusing response. So the Interstate only came with combat engine in 1972 from what you say which made standard equipment the same meaning as production....OK.
From all I have read over several decades the combat engine advertised as 65 HP. If the Interstate combat was even higher output than previous combat spec, what was the earlier combat difference to this higher output? Has anyone an example of a pre ‘72 machine with factory option combat?
Wow, quite a confusing response. So the Interstate only came with combat engine in 1972 from what you say which made standard equipment the same meaning as production....OK.
From all I have read over several decades the combat engine advertised as 65 HP. If the Interstate combat was even higher output than previous combat spec, what was the earlier combat difference to this higher output? Has anyone an example of a pre ‘72 machine with factory option combat?
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The Interstate was the only model that initially had the Combat engine as standard. Nothing confusing about it as far as I can tell.
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In Roys Norton Twins book printed 1981 he repeats much the same info about the combat being a mid year 70 introduction of the option, in the price lists for 70 model year he has the Combat option listed as costing £56 14s and 10p, no separate price in the 71 model year price list for the Combat option, its not listed in the 72 price list either but the Interstate costs approx £49 more than the other models which is in the right ballpark as it was fitted to all Interstates.
Never seen any Combats other than 72's so even if the option was listed in 70/71 were any made and sold or was it a limited kit so a Combat tuned engine was allowed into Production classes for racing eg 200 for Homologation purposes.
Never seen any Combats other than 72's so even if the option was listed in 70/71 were any made and sold or was it a limited kit so a Combat tuned engine was allowed into Production classes for racing eg 200 for Homologation purposes.
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According to Magrath's book, page 131, the original ('70) Combat engine compression ratio was "increased by machining the cylinder head by 0.5mm..." approximately half the amount machined off the '72 Combat cylinder head (1.0mm/0.040").
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My friends 72 interstate was combat engine and disc brake, vin was 200205*. No evidence on any hardware that it was anything but original from factory...
*Edited by the moderator as dynodave subsequently discovered the number to be 202005.
*Edited by the moderator as dynodave subsequently discovered the number to be 202005.
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Hi Dave
Does your friend know the original build form of 200205 was an Interstate? I have a copy of the factory build records for that number. It shows this number was a fastback shipped to Cohen & Hughes N4 on 2/20/72. I got these copies from the NOC records project almost 20 years ago.
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Hi L.A.B.
Confusing is probably my concept of “production” which is any machine produced and sold to the general market. Options are part of production if the whole machine was produced and sold in that form. Just trying to understand machines produced with combat engine prior to the MkIV 750. I have not ever seen one.
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I agree, as Magrath ssays: "...the Combat motor gave 65 BHP and soon gained a reputation for being unreliable." so was possibly considered more of a racing option rather than for road models?
Coburn & Hughes is still going (now in Luton). Edit: Or perhaps not! Apparently closed now but the company is still listed as active.
http://www.motorcyclesupermarket.com/dealerDetail/?DealerID=10500&Bike=Coburn-&-Hughes
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Yes, you've posted a couple of those pages here before.
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