Jugs breaking

J

john robert bould

Joined

Sep 26, 2009

Messages

2,210

• Nov 4, 2014

• #1

Is it common for 750 barrels [jugs] to fracture above the lower flange?
What would cause this, Compression?
Did Norton change to through bolts on the 850 because of this?

 

comnoz

Joined

Dec 10, 2008

Messages

7,253

• Nov 4, 2014

• #2

john robert bould said:

Is it common for 750 barrels [jugs] to fracture above the lower flange?
What would cause this, Compression?
Did Norton change to through bolts on the 850 because of this?

Click to expand...

Yes, They are very thin. Almost a guarantee of a crack if they have been sleeved.

Boring to an 850 would have made them even thinner so through bolts were an absolute necessity.

 

J

john robert bould

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Sep 26, 2009

Messages

2,210

• Nov 4, 2014

• #3

OK . but what caused the break?

 

comnoz

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Dec 10, 2008

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7,253

• Nov 4, 2014

• #4

john robert bould said:

OK . but what caused the break?

Click to expand...

Just stress. How far oversize is it?

 

Hobot

Joined

Oct 19, 2005

Messages

18,978

• Nov 4, 2014

• #5

Besides the boring out surrounding metal the reason may be this cylinder survived a broke rod event that slammed a stress riser internally to finally wash up on shore. Maybe just over heated past grabbed piston in bores to seize? Cast iron is known for its brittleness. There is a video of bored Commando piston being seen moving in cut away fin valleys but barrel not yet moving with pistons.

 

J

john robert bould

Joined

Sep 26, 2009

Messages

2,210

• Nov 4, 2014

• #6

So is this cylinder breakage common?

 

SteveA

Joined

Dec 20, 2011

Messages

3,475

• Nov 4, 2014

• #7

john robert bould said:

So is this cylinder breakage common?

Click to expand...

It is a 'known problem', it is well known! ..... and Norton went to a lot of trouble with through bolting the 850....

Last 750 I rode had 850 style barrels sleeved to 73mm bores...Andover Norton supply through bolted barrels new as 73mm...

Lots of reasons to think it is not 'rare' ... does that mean it is 'common' ... I guess not because there are still a lot of 750s out there that are not through bolted!

 

comnoz

Joined

Dec 10, 2008

Messages

7,253

• Nov 4, 2014

• #8

john robert bould said:

So is this cylinder breakage common?

Click to expand...

It's common if the cylinders have been bored more than .040 or if they have been sleeved.

It's common if the bike is being raced.

It happens occasionally just because. Jim

 

auldblue

Joined

Nov 20, 2012

Messages

1,200

• Nov 4, 2014

• #9

750 barrels condemned .