Pulled barrel stud - any thoughts?

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DavidT

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Hello All,
Hoping for some opinions on the possibility of a repair to my barrels.

This is a '72 750 and sometime in the past, someone has replaced the the front right stud with an M8 screw, probably because the stud has pulled. Unfortunately the drill has broken right into the pushrod tunnel. Over the last few weeks I've been chasing a nasty oil leak from the cylinder head gasket - covers the front of the motor, blows back onto the primary and after about a 100 miles or so, everywhere else. It has been leaking for a while now, but usually only noticeable if I have been pushing on a bit.
I put on a new composite gasket but it still leaked even after tightening down at 50 then again at 100 miles. I tried tightening it down again this morning but that screw just didn't feel right. I lifted the head, and it looks like the little bit of the barrel that has been holding the stud has finally let go, undoubtedly caused by my tightening it. Not surprising it wouldn't seal though!

So, my question is, how to repair it? Do you think it would be plausible to braze or weld in an insert to take a standard stud?

Any advice welcome - other than that, these are good, useable barrels on standard bores after being re-sleeved a few years ago.

David

The pointer shows where the drilling has broken into the pushrod tunnel.
Pulled barrel stud - any thoughts?


Pulled stud hole and cracked material.
Pulled barrel stud - any thoughts?
 
DavidT said:
Hello All,
Hoping to for some opinions on the possibility of a repair to my barrels.

This is a '72 750 and sometime in the past, someone has replaced the the front right stud with an M8 screw, probably because the stud has pulled. Unfortunately the drill has broken right into the pushrod tunnel. Over the last few weeks I've been chasing a nasty oil leak from the cylinder head gasket - covers the front of the motor, blows back onto the primary and after about a 100 miles or so, everywhere else. It has been leaking for a while now, but usually only noticeable if I have been pushing on a bit.
I put on a new composite gasket but it still leaked even after tightening down at 50 then again at 100 miles. I tried tightening it down again this morning but that screw just didn't feel right. I lifted the head, and it looks like the little bit of the barrel that has been holding the stud has finally let go, undoubtedly caused by my tightening it. Not surprising it wouldn't seal though!

So, my question is, how to repair it? Do you think it would be plausible to braze or weld in an insert to take a standard stud?

Any advice welcome - other than that, these are good, useable barrels on standard bores after being re-sleeved a few years ago.

David

Any repair to that would be iffy at best. That plus sleeved 750 barrels are pretty iffy also. I would look for another set of barrels. Jim
Click to expand...
 
The only repair that I would trust would be to completely weld up that area and redrill/retap the hole.
 
I'm with Jim on this one. Anything can be repaired with enough effort, but this one wouldn't be simple. There doesn't look to be anywhere near enough support for any kind of standard thread insert, and by the time you find a welder who is qualified, and willing, to do a proper job of welding in a cast iron plug (preheat, Ni rod, etc.), and then a machinist to re-surface the face and drill and tap a new hole, not to mention grinding the weld in the pushrod tunnel for clearance, you could probably buy a replacement cylinder for the same cost. Of course if you've got the skills and equipment to do it yourself, you don't have anything to lose by trying. Good used 750 cylinders are pretty hard to come by around here, so if it was me, I'd probably give it a try just for the challenge, but I wouldn't be too optimistic about succeeding. I'm not too wild about sleeving 750 cylinders either. It just makes them more likely to crack at the base. In all fairness though, I've known people to do it on street bikes and never have a problem.

Ken
 
Add to the fact that a proper weld would require a preheat of around 1000 degrees and a postheat of red hot with a 24 hour cooling period and the bores would not longer be usable anyway.

And I have sleeved a few 750 barrels that lasted OK but I have also eaten enough of them that I will no longer sleeve a 750 barrel. Jim
 
Ken and Jim know what they are doing. I do not...

So I would consider making an oversized plug with coarse threads that I could tap for the stud and I would grind away the part of it that stuck out into the tunnel. It might only have threaded contact on 70% of the circumference or so but it might hold. Might. I'm not even sure what material I would use. Better ask the experts!

Russ
 
Somehow you have to get sound material to thread into. From the photo, I cannot tell which way the tunnel slopes - i.e. what is below the the stud hole. It looks as though there is a step lower down. It might be possible to just drill the hole much deeper, tap it and use a much longer stud ? I think that by welding the barrel, you must end up with a bodge job. The only other way might be to use a mill to move the hole centre away from the tunnel and insert a larger fine threaded plug as an insert and redrill the hole into the plug, possibly using a stronger stepped stud so you stay away from the tunnel . You would probably have to reface the gasket surface .
 
acotrel said:
From the photo, I cannot tell which way the tunnel slopes - i.e. what is below the the stud hole. It might be possible to just drill the hole much deeper, tap it and use a much longer stud ?
Click to expand...

Less and less material, it slopes under the stud.
 
Ream for 9 mm smooth stud and cross drill between the fins for a 5 mm steel pin ?
( nothin to loose ..)[/quote]

Best idea yet. :idea:
 
If the stud doesn't really need to come out, it might be easier to simply bronze weld it in, and use a hollow tool or a scraper to clean up around it ? I'm sure I've seen this type of thing done years ago on very old bikes, however I'd be talking to a welding supplies shop about what to use.
 
comnoz said:
Ream for 9 mm smooth stud and cross drill between the fins for a 5 mm steel pin ?
( nothin to loose ..)
Click to expand...

Best idea yet. :idea:[/quote]

Agreed. Wish I'd thought of it, or some variation of it. And as Ludwig pointed out, nothing to lose.

Ken
 
Gents,

Many thanks for your thoughts. Any repair is going to eat too much riding time, so I've ordered a set of the 850 pattern barrels from Andover and I can get someone to look at the broken ones at my leisure. It's a big chunk of money, but I see it as an upgrade!

Regards,
David
 
DavidT said:
Gents,

Many thanks for your thoughts. Any repair is going to eat too much riding time, so I've ordered a set of the 850 pattern barrels from Andover and I can get someone to look at the broken ones at my leisure. It's a big chunk of money, but I see it as an upgrade!

Regards,
David
Click to expand...

If it's from Andover it's not a pattern piece.
 
swooshdave said:
DavidT said:
Gents,

Many thanks for your thoughts. Any repair is going to eat too much riding time, so I've ordered a set of the 850 pattern barrels from Andover and I can get someone to look at the broken ones at my leisure. It's a big chunk of money, but I see it as an upgrade!

Regards,
David
Click to expand...

If it's from Andover it's not a pattern piece.
Click to expand...

I think David means he has ordered the Andover Norton through-bolt "850" type, 750 barrels.

http://www.andover-norton.co.uk/New%20Items%20In.htm
06-1705 Cylinder barrel, 750cc, in 850 barrel casting
Click to expand...
 
See David, the best experts and you still had to open the wallet! I know how much that hurts :D
How did Applecross go?
I'm sure Smokey Joe will soon loose the nickname after this latest financial injection!
Buffalo WY tomorrow to see how the Americans party!!
 
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