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Wolf in sheep's clothing.

Submitted by bob_scholes on Sat, 17/11/2018
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Commando

i have a 72 registered 750 commando which is proving to be somewhat odd. Registered 72 and distributed to Gus Kuhn in jan 72. This has matching numbers in the 200,000 series. However, clutch issues prompted removal of the primary chain case to reveal a 5 plate sintered bronze clutch, I believe this was only fitted to the 850. Barrels are 850 models and carbs are 32mm with Amal 220 jet. Question is, is this a set of 850 barrels on a 750 crankcase, I believe these are non-interchangeable so is the crankcase an 850 case? I have not taken the heads off to measure the bores - looking for ideas or detailed, dimensioned engine drawings to help solve the mistery. Bike had an extensive rebuild back in 93, by John Massey classic racing and restorations, many small items but no majors such as engine overhaul etc.... all previous receipts that I have are all minor odds and sods. Last detailed receipts are from 1996 f d motorcycles, again all smaller items. Any thoughts or suggestions here are most welcome. Bike has been in dry storage from mid 90âs until early this year when it moved north to my collection. It has been suggested that this was a dry run of the 850 prior to its formal release - again, any suggestions are most welcome.

Submitted by richard_payne on Sat, 17/11/2018

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I have an idea that 850 barrels will fit straight on the 1973 750 Mk5 cases and onto the earlier castings with a little easing. Does it have an 850 head ?

If the number is a 235000 series then it could be 750 short stroke or 850...but I don't believe they were as early as January 1972.

Do the cases have a steel cover plate behind the timing chest or is it one casting ? A photo would help.

Submitted by boo_cock on Sat, 17/11/2018

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Many years ago I had a Gus khun 850 short stroke Commando. According to the engine numbers it was a 750. If you look in the NOC trade notes book at the engine numbers all will be revealed. For mine it said, last of the 750's, unless you know better. Mine was an unless you know better jobbie. It had a short stroke crank, 850 top end, Omega 9.5/1 pistons and a Piper 3S cam. Went like snott off a stick. Does anyone know what happened to YOD58L?

Submitted by boo_cock on Sat, 17/11/2018

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Previously john_holmes wrote:

Do the cases have a large sump plug, 72's do not have one.

As far as I remember yes it did.

Submitted by bob_scholes on Sat, 17/11/2018

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Previously boo_cock wrote:

Many years ago I had a Gus khun 850 short stroke Commando. According to the engine numbers it was a 750. If you look in the NOC trade notes book at the engine numbers all will be revealed. For mine it said, last of the 750's, unless you know better. Mine was an unless you know better jobbie. It had a short stroke crank, 850 top end, Omega 9.5/1 pistons and a Piper 3S cam. Went like snott off a stick. Does anyone know what happened to YOD58L?

Submitted by bob_scholes on Sun, 18/11/2018

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Thanks all, certainly got me scratching my head. Did not realise there are so many variants. To answe a couple of the questions, yes it has a big old sump plug, and no, timing case is a one piece casting. For the short stroke barrels is there a flange to face dimension? Also, did not find the trade notes section referred above, link here would be most welcome.

Submitted by john_holmes on Sun, 18/11/2018

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So the crankcases are not 72, if they are stamped 235xxx then they are not 72 as the 235xxx were later. My 72 has an early number e.g. approx Mar/Apr 72 but a later build date of Sept 72 in the despatch records and first registered in 74 so the factory was in a mess.

Submitted by bob_scholes on Mon, 19/11/2018

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Previously john_holmes wrote:

So the crankcases are not 72, if they are stamped 235xxx then they are not 72 as the 235xxx were later. My 72 has an early number e.g. approx Mar/Apr 72 but a later build date of Sept 72 in the despatch records and first registered in 74 so the factory was in a mess.

Thanks John, engine number is 202668. Stamping looks to be on the original cast surface, would anyone please post pictures of engine numbers so as to compare font and style etc.... ?

Submitted by john_holmes on Mon, 19/11/2018

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That's very early in the 72 MK4 range, 2075XX is Apr 1972 so it suggests you have a replacement engine which has had the original numbers transferred over onto them.

Submitted by bob_scholes on Thu, 22/11/2018

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Previously john_holmes wrote:

That's very early in the 72 MK4 range, 2075XX is Apr 1972 so it suggests you have a replacement engine which has had the original numbers transferred over onto them.

Here is a link to a photo that includes an engine stamp.

https://postimg.cc/H8xfBvxy

Many thanks John, font and style appears the same - so there is a blessing and supports the replacement engine theory.

 


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