Norton 650 SS

Hi John,

I too live in Northampton and have a 650 too.

If you want a 2nd pair of eyes to look over your issue  then I would be more than happy to have a look with you. 

If you wish me to, Pm me.

Regards, 

George 

PS: Northants and Leics section meetings are not far away to meet up with other owners.

Both impressively ruined. How did that happen? Replacements required urgently. I would suggest that a normal replacement pair will solve the meshing problem. The big question is why did one gear stop and the other keep going? Something fundamental amiss there. 

Four suggestions to inspect.

Was the hexagon nut loose on the crankshaft? (The lower, smaller, gear).

Or was the bush inside the upper (larger) gear worn so badly that it wobbled on its shaft? 

The upper gear has a hardened washer behind it.  Its shaft is intended to be tight in the crankcase but it often spins.  Has it actually worn the case to an over size hole?

If the shaft is loose, it can easily come out when the timing case is removed.  Then the washer behind the upper gear can fall down behind the lower gear.  It that went unnoticed, it might well jam something.  The shaft can be Loctited back in.  There is a correct top and bottom.  Its been discussed before here (which way round it goes).

My hardened washer goes against the case behind the big gear.  So it goes onto the shaft before the big gear goes on.

The smaller gear has teeth stripped as if it was stuck on one place.  But that's very odd since that is keyed to the crankshaft end, so that's the gear that should be turning, and the other one stripped.  Unless the small one is simply not hardened enough...

The  big one has one visible broken tooth.  Is there damage elsewhere?  If so, perhaps the broken tooth was where it was jammed by a foreign object, and the other damage location was where it ripped the teeth off the small gear when it suddenly stopped spinning.

Note that the inner sprocket is missing most of the tops of the teeth.  This is the chain that drives the magneto. The damage looks fresh and is possibly the reason for the crankshaft pinion  carnage. This kind of damage occurs when a timing  chain is set far too tight.

I am afraid that to sort this mess out is going to require a complete engine strip and clean.

Notice in the pix above, the twin chain outer sprocket teeth are at a needle point and the chain  roller cavity seems exceptionally wide as if the cam chain ran incredibly loose.

The pix below is for a almost "as new" sprocket. Note square tips.

added

A very loose cam chain would cause a cyclic chain snatch when the valve goes over the top of a lobe, since the 22 lb flywheel is relatively immoveable. The sprocket and gear would suffer under the severe pounding by the valve spring in an unrestrained fall.

I was fairly sure the points on mine are quite sharp.  A quick Google images search for images of 'Norton timing gears' confirms that sharp points are common on new ones.  That alone wouldn't worry me.

But whatever the exact cause, it does look like an assembly problem unless the crankcases were wrongly machined.  Washer in the wrong place and/or chains too slack and/or chains too tight and/or a mixture with one tight and one slack...

And as Phil says - unfortunately there might be bits of broken steel almost anywhere, including scavenged up into the oil pump.  Although the gauze filter in the sump plug should stop the bigger bits going into the pump.

hello

is everything accounted for ,

. woodruff keys,

. thick triangle washer and thin shield washer behind crank pinion.

. thrust washer behind double cogs

. circlip , bolts ect.

strange its happened before .with the gap in teeth on the cogs. could the crank shaft that side be bent . causing a gap then closeing up as it rotates ,putting strain on the teeth meshing. what about valve timing and pistons condition. what with the damage. how far has it gone.

Barry

Found several more sprocket samples. It seems depending on the era of the engine the teeth shapes vary.

3 had the squared off teeth and 2 were pointy. Have 3 more twin chain engines but I was not going to pull the covers off.

9451X Manxman is pointy