650 Crank sprocket valve-bolt issue

Information relating to the Matchless G12 or AJS Model 31 650cc twin
lostinsdf
Posts: 37
Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

650 Crank sprocket valve-bolt issue

Post by lostinsdf »

What is the torque spec for the crank sprocket bolt on my 1960 650 CSR? Also, I cannot find a nut to hold on the magneto gear. Spares does not have one nor does other places I have looked, including EBay. , AMC Classic etc. The nut on there now is from a connecting rod. Anyone know where I can find the correct one? Does it matter?

Thank you.
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magnetonut.JPG
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Last edited by lostinsdf on Thu Sep 08, 2016 10:45 pm, edited 1 time in total.
TrevorCSR
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Location: HERTFORDSHIRE UK

Re: 650 Crank sprocket and an annoying magneto issue

Post by TrevorCSR »

I don't think British manufacturers issued torque figures for everything like the Japanese do. Basically it needs to be tight. Lock the motor and use a good strong arm (Breaker bar) of at least 2 foot and push firmly down on it. My preference is to use Locktite here, so make sure you de-grease both inner and outer threads. I use Locktite on most stress nuts and bolts in the engine, better to be safe than sorry.
Looking again at your picture, I think you may have the wrong bolt in the crankshaft end. It should be a hollow bolt with a breather disc at the end. Unless of course the engine has been modified with a crankshaft end seal and has some other form of crankcase breathing.
I'm pretty sure the magneto nut is 3/8" BSF (20 TPI). (Google confirms that) Head size (Across Flats) 0.600". AMC conrod nuts are 5/16" BSCy (26 TPI) so they will not fit. If you've fitted a nut from a US engine conrod it's sure to be 3/8" UNF, which is 24 TPI. Head size (Across Flats) 9/16, 0.5625". Quickest way to check between British, American and Metric threads is try your spanner. Doesn't work on 5/16 UNF/C and M8 as 1/2" is virtually the same as 13 mm.
Again, tighten firmly with approx 1 foot long arm spanner or socket ratchet.
lostinsdf
Posts: 37
Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

Re: 650 Crank sprocket and an annoying magneto issue

Post by lostinsdf »

Thank TrevorCSR for the reply. I will get the correct nut for the Magneto. And I understand the torque and thread lock for the bolt on the crank. But the bolt itself? It is the one that came with the bike when I took it apart. There is no crank seal; just the bearing, spacer then the sprocket. Do you have a part number for that? Picture? :-)

Thanks again.
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Stuoyb
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Location: BEDFORDSHIRE UK

Re: 650 Crank sprocket and an annoying magneto issue

Post by Stuoyb »

The sprocket bolt/relief valve assembly is :-

025526 RELIEF VALVE ASSEMBLY
http://www.amoc-parts.com/store/comersu ... duct=21613

You also need :-

023268 LOCK WASHER CRANKSHAFT TWIN
http://www.amoc-parts.com/store/comersu ... duct=21536
lostinsdf
Posts: 37
Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

Re: 650 Crank sprocket and an annoying magneto issue

Post by lostinsdf »

I will get those ordered. Thank you Stuoyb!
lostinsdf
Posts: 37
Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

Re: 650 Crank sprocket and an annoying magneto issue

Post by lostinsdf »

Hi Stuoyb and everyone else checking this post. I fear the worst and I hope someone has a solution for me.

I got the valve 025526 and tried to install it in the crank. However, it would not fit. The threads are different. It is an RBW bolt which, after a quick search on the web, is a bolt from an American car. What to do? The crank does not look molested in anyway and the RBW bolt screws into the crank end smoothly with no hint of binding etc. Is there any way around this? I fear the worst answer is no and that its the wrong crank etc. and the engine has to come apart.

Thank you for all the help.
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lostinsdf
Posts: 37
Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

Re: 650 Crank sprocket and an annoying magneto issue

Post by lostinsdf »

Just reading through this again and I noticed what Trevor CSR has said. The crank may have been modified. But how do I know there is another type of crankcase breather if this bolt is what I am stuck with? Can I modify the crankcase for a breather (without taking the engine apart? My instincts say no).

Thanks again
alanengineer
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Location: KENT UK

Re: 650 Crank sprocket and an annoying magneto issue

Post by alanengineer »

whats the difference in the thread dia and thread pitch . Why does it not fit?
lostinsdf
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Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

Re: 650 Crank sprocket valve-bolt issue

Post by lostinsdf »

The dia.s are the same for both. The issue is the thread pitch. The bolt that was in the crank is 18.
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The Valve that is supposed to go in there is 20.
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I used a U.S. thread gauge. I don't know if there is a difference with British threads. However, U.S. or not, there is a pitch difference.

My first question is why did someone put this Bolt in there? Is the crank different from what I thought it was? This bike has become a jumble of different parts, something I am learning the hard way after things are assembled.

Second question is the more important; what do I do now? Do I use the RBW bolt and vent the crankcase another way? If so, how should accomplish that?

Thank you for your suggestions.
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lostinsdf
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Joined: Fri Nov 29, 2013 4:52 am
Location: Washington State, USA

Re: 650 Crank sprocket valve-bolt issue

Post by lostinsdf »

I renamed the post in the hopes it may generate more specific interest, replies and searches for anyone else facing similar issues.
Locked