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Cracked Crankcases !
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sparkplug



Joined: 10 Jan 2006
Posts: 124
Location: SPAIN

PostPosted: Tue Jul 08, 2008 3:45 am    Post subject: Reply with quote

Hi, Keith!

That engine looks nasty...!

Thanks for your help. The cases are 850 74' same as the rest of the bike.
They look pretty good (I guess...)

I've locked the conrods with a bar through the holes and against the cases (well protected), then tried to unlock the nuts, but... I'll try with a longer bar or impact tool as you point.

When you talk about the sharp edge on the crank as a start of potential crack, do you mean a crankshaft crack?

The contact breaker wires (the copper) is still there, but all the plastic parts of the cables were destroyed, but not the plastic on the wires going up to the coils, which seemed ok. Shocked

Thanks a bunch for the reply!
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Keith1069



Joined: 10 Jan 2005
Posts: 231
Location: Hampshire UK

PostPosted: Tue Jul 08, 2008 4:59 am    Post subject: Reply with quote

It was nasty! It had suffered a minor blowup with the previous owner an dthe cases were not good but it seemed a new rod bolt let go. Dunstall tuning notes recommend removing machining marks from the narrow diameter and mine did appear to break there.
If those wires are only overheated locally then it looks like they were touching the cases, so a short circuit is probable cause.
I cannot find the reference to the crank sharp edge. It was on the Britbike site and a search does not reveal the messages. The forum member was talking about a sharp edge (excessively small radius) inside the drive side crank web. This aligned with the left side of the rod journal and could lead to a fracture. I think he was referring to 750 cranks, it may not be on the 850 although I'd guess they are the same parts if not Mk3 which had the longer shaft. Sorry, hope I haven't worried you more!
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Keith1069



Joined: 10 Jan 2005
Posts: 231
Location: Hampshire UK

PostPosted: Tue Jul 08, 2008 5:12 am    Post subject: Reply with quote

I found the reference, seems it was on a '99' not a Commando. Apologies.
Keith
To all/ anyone thinking of having their Norton cranks hardened or anyone about to strip them..
Have the D.s. half crack tested paying particular atention to the big ends outer 90 thou radius area. You could well find cracking taking place.....thanks to Norton introducing a stress increasing raiser into the crank half roughly directly beneath the outer 90 thou stress reducing radius when they cleaned it out with a drill or something that left a sharp corner/strss raiser.
I had a 99 crank fail, at this point in the very distant past..
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sparkplug



Joined: 10 Jan 2006
Posts: 124
Location: SPAIN

PostPosted: Tue Jul 08, 2008 7:11 am    Post subject: Reply with quote

Thanks for your help and patience!
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The Unapproachable Norton Commando

At the end of 1967 the Norton Commando was announced.

The Norton Commando was greeted with a certain amount of scepticism because on first sight the commando appeared to comprise of the old Norton Dominator twin cylinder engine mounted at an inclined angle in a set of new cylinder parts.

It was not realized that the new Norton Commando Isolastic method of engine suspension damped out all engine vibration and produced a machine which had uncanny smoothness for a vertical twin. In due course the critics were silenced and the Norton Commando had the distinction of being regarded as the first of todays so called superbikes. There can be little doubt that the original design concept of the Norton Commando has proved correct, since comparatively few modifications of any real consequence have been made since production commenced during 1968.

Now nearly 40 years later Norton Commando riders like us are a breed of our own, and as far as we are concerned its still more fun to go for a blat on the old Norton Commando, and fast. As a Norton Commando owner and enthusiast, my goal here is to promote and give credit to those who keep the Norton name going.

It is more deserving to give credit to the Commando itself, for after all these years it continues to be respected. The original Commando designers like John Favill are those who deserve the credit for developing this incredible motorcycle.

The Norton Commando Roadster and Interstate of the late seventies, never died. Although the Norton Villiers factory dispersed the tradition lived on. Today Kenny Dreer in the USA is developing the new 952 CC Norton. What a great looking bike this is, and its engineering is still based on the original layout. It will be interesting to see how the new 952CC Norton does in todays tough motorcycle market. One thing is for sure, I would own one if I could afford it.