Where do you get s new 850 mk11 crankshaft these days

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johnm

johnm

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So today I learnt my 1974 850 crank is cracked at the drive side main.

So far I have found none of the usual suppliers have them and the lead time on a new crank made down here in NZ is 6 months.

A search finds a few second hand ones advertised by a certain UK dealer but I’m not happy to go there.

Happy to pay for new. Actually maybe not happy but prepared to pay for new

Any ideas short of six months ?
 
IMHO I wouldn’t use those pistons anyway, looks like they’ve been welded up and re machined for the valve pockets?

It’s a 91mm stroke, so the piston is gonna go down 1mm more and up 1mm more than stock.

That’s easy to cope with with a plate under the block if necessary.

You could use any diameter pistons you wanted, you just have a bit more capacity with the stroked crank.

Main point is, it’s a billet NRE crank which are basically as strong as they come. And no longer available.

Arrows rods are up there with Carrillo’s too as far as I’m aware.

So, use the pistons as paperweights / ash trays, but the rest is good stuff and a bargain at the listed price.

Not suitable for those looking for a lightweight crank tho...
 
Couple of questions for the seller before you click buy it now,

Distance between centres big end to small end

Size of small end hole for gudgeon pin
 
My local Norton dealer Murray from Cyclecraft Engineering in Perth offered me one recently as a replacement for mine. The main bearing ring was loose on the primary side but I decided to repair mine so if you are lucky he still has it. Bid ends reground, ready to go. Murray said it would fit my 850 MkII.
 
Hey John,

I'm pretty sure I've got a crank or two on the shelf, they came in a large collection of parts I bought years ago. Shipping from Canada to NZ would be quite expensive. I'll dig them out and see what I've got. Are there any obvious adifferences to identify an 850 from a 750 crank?
 
johnm said:
So today I learnt my 1974 850 crank is cracked at the drive side main.
Click to expand...

If you're going to use a stock crank - Its just going to crack again unless you put a radius on the beginning of the stub shaft.
 
johnm said:
So today I learnt my 1974 850 crank is cracked at the drive side main.

So far I have found none of the usual suppliers have them and the lead time on a new crank made down here in NZ is 6 months.

A search finds a few second hand ones advertised by a certain UK dealer but I’m not happy to go there.

Happy to pay for new. Actually maybe not happy but prepared to pay for new

Any ideas short of six months ?
Click to expand...
A certain UK dealer also lists new cranks. Are they not in stock?

Ed
 
jseng1 said:
If you're going to use a stock crank - Its just going to crack again unless you put a radius on the beginning of the stub shaft.
Click to expand...
Yes.

The cranks made here have that radius. It’s just they have six month lead times.
 
APRRSV said:
A certain UK dealer also lists new cranks. Are they not in stock?

Ed
Click to expand...
Andover have none in stock and none expected.

They told me that basically can’t get suppliers to do the job properly.

Quote

I even have the original Norton drawings for one piece cranks. Some of the suppliers are reluctant or are not able to carry out a process step that stops them breaking, which is not helping.

If you mean Mr Emery then my previous dealings with him don't encourage me to go there thanks.
 
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Interbak said:
Hey John,

I'm pretty sure I've got a crank or two on the shelf, they came in a large collection of parts I bought years ago. Shipping from Canada to NZ would be quite expensive. I'll dig them out and see what I've got. Are there any obvious adifferences to identify an 850 from a 750 crank?
Click to expand...

Thanks. I’m not sure and will follow up and get back thanks

Regards John
 
johnm said:
So today I learnt my 1974 850 crank is cracked at the drive side main.

So far I have found none of the usual suppliers have them and the lead time on a new crank made down here in NZ is 6 months.

A search finds a few second hand ones advertised by a certain UK dealer but I’m not happy to go there.

Happy to pay for new. Actually maybe not happy but prepared to pay for new

Any ideas short of six
johnm said:
So today I learnt my 1974 850 crank is cracked at the drive side main.

So far I have found none of the usual suppliers have them and the lead time on a new crank made down here in NZ is 6 months.

A search finds a few second hand ones advertised by a certain UK dealer but I’m not happy to go there.

Happy to pay for new. Actually maybe not happy but prepared to pay for new

Any ideas short of six months ?
Click to expand...

I have just bought a lot of Commando cranks , mostly dissembled. Haven’t checked them yet.Some will be 750...are these a possibility? You would need to let me know dimensions. Jan, UK.
Click to expand...
 
What are the differences between a crank for a 750 and one for an 850cc ?
Could a crank for a 750cc be modified for use in an 850cc?
 
Staytite said:
What are the differences between a crank for a 750 and one for an 850cc ?
Could a crank for a 750cc be modified for use in an 850cc?
Click to expand...

As I said above I'm following up on the 750 and 850 differences. The Mk 11 850 and the Mk111 are also different.

I will also follow up on the overseas second hand ones advertised but would probably want to crack test them before paying to send them around the world. I'm guessing many vendors would not be interested in that.

Broken cranks are not so uncommon it seems.
 
750 and 850 crank halves are the same (excluding Mk3s). It’s the flywheel balance that’s different. I have used complete 850 crank in 750 with no problems.
 
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