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PostPosted: Wed Nov 14, 2018 1:18 pm 
Old School Grand Master
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kingoffootball wrote:
I wish I'd got details of the guy who bought my Gary Fisher Prometheus off me at Sheffield Cycle Jumble. He buys damaged titanium frames and repairs them. If anyone sees the Prometheus come up for sale it might be worth asking the seller about his repairs.



Interesting. You could also try F1 Industry forums/associated Businesses as people in that sector can do amazing work, fast and for reasonable money. I had one build me a custom Ti stem in the early 90s. He was a specialist welder of F1 car Ti exhaust systems etc.

OP by stuffed i assume you mean a cracked BB. If its not actually cracked you could try one of these Mavic BBs https://ebay.us/Ji2O7Q
Pretty bomb proof and easy to fit, just a bit of chamfering needed.


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PostPosted: Wed Nov 14, 2018 7:43 pm 
retrobike rider
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Quote:
just a bit of chamfering needed.
I have the MAVIC tool for chamfering if needed.
If you can't find the right MAVIC BB, YST make a version, and also Acor, First and Velo Orange etc.

Also, is the wayward sleeve a thread repair sleeve? These are used where the original BSA BB thread has failed.
The thread is bored out and re-tapped to the larger Italian standard, then threaded sleeves are screwed and bonded in.
These then have the correct BSA thread on the inside:

Attachment:
Screen Shot 2018-11-14 at 18.28.55.png
Screen Shot 2018-11-14 at 18.28.55.png [ 18.07 KiB | Viewed 517 times ]

If it's just these that have come adrift, a good clean up and some Loctite 638 Retainer should sort it.

All the best,


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 Post subject: Re:
PostPosted: Fri Nov 16, 2018 12:10 am 
retrobike rider
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Thanks for the info, that’s very helpful.

It does indeed have a steel repair sleeve. I had assumed it was line-bored and pressed in. I will take a look in more detail and see if there is a thread.

Any idea how to hold it to extract it? Is there a tool?

SP


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 Post subject: Re: Re:
PostPosted: Fri Nov 16, 2018 10:28 am 
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ishaw wrote:
I've investigated something similar fairly recently. My conclusion was:

Vernon will do an agricultural job which may or may not stand the test of time.

Enigma are equipped to do a proper repair.

In my case I have a possible crack in a drive side chain stay. Vernons approach to fixing it was a big was weld that in their words would not be pretty but should work. The enigma approach was to replace both stays and anything else as needed.

Of course there was a huge price difference, so much so that I could (and did) buy a second hand ti frame much cheaper than the enigma repair quote.

I may still get my frame repaired but I'd rather know it will be fixed than potentially fail again.

I did contact some local (to me) companies too, but none were interestwd enough to even reply.

If your frame is worth saving, enigma is probably the best place I've found to get a repair, but at a cost you may find uneconomical. To their credit they also offered me a discount on a selection of their own frames but I couldn't justify spending so much at the time.

I hope you find a solution. Good luck.


I concur with Vernon. I've had two repairs done by him. Both weren't pretty - and one required some fettling to get the seatpost back in the tube afterwards. The plus sides are that he's reasonably cheap, doesn't make promises he can't keep and turns them around quickly. Neither repair failed afterwards. Personally, I quite liked the battle damaged aesthetic too.

Enigma didn't even respond to my query.


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PostPosted: Fri Nov 16, 2018 7:06 pm 
retrobike rider
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How to get them out if they are adapters...

The Italian thread is RH thread both sides (bad idea, but there you go!).
Assuming the inserts are flush or proud of the BB shell face, it should just screw out of the BB shell if you fit a fixed cup and keep turning anti-clockwise.
The non-drive side should come out if you fit a cup with a lockring and turn anti-clockwise using the cup fittings (probably peg holes) rather than the lockring.

A little heat, such as a hot air gun should help if the sleeves are Loctited in. It will degrade at around 80 degrees.
Also the thermal expansion of Ti is slightly higher than that of steel so the BB shell will expand relatively.

If the inserts don't screw out easily, even after heat, Plus Gas etc, then they will need to be cut through and rolled up to remove.

If the sleeves get damaged in the process, I have new stainless ones for about £20/ set.

All the best,


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 Post subject: Re:
PostPosted: Sat Nov 17, 2018 9:55 am 
retrobike rider
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Thanks, that removal process makes a lot of sense! The drive-side is the one that has moved - about 3 mm is protruding. I just checked - there is no thread on there - I can actually see fine machining marks. :(


I guess I could screw in an old BB cup, heat the whole lot and drift it out. Then I'm left with the option of chamfering it or getting an Italian thread tapped into it - depending on the required bore diametre. The insert is 36.6 mm OD and the bottom bracket shell is OD ~40 mm

What do you reckon?


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PostPosted: Sat Nov 17, 2018 10:40 pm 
retrobike rider
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Well, unfortunately the Italian tap option is out as that thread is 36mm outside diameter, so too big a bore at 36.6mm.

If you can get the sleeve out cleanly, I'd suggest bonding it back in.
A good key on both surfaces, cleaned up and acetone. I'd use Loctite 638 retainer rather than epoxy.

Not sure that the 1.7mm BB wall is enough to support a taper fit system. I'll see if I can dig up the MAVIC spec.

All the best,


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 Post subject: Re:
PostPosted: Sun Nov 18, 2018 10:09 pm 
retrobike rider
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Thanks Dan.


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PostPosted: Sun Nov 18, 2018 10:30 pm 
retrobike rider
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I can't find any specific requirements for the MAVIC BB, but Schlumpf gearboxes have a fitting similar system.
These require a 2.5mm min BB wall on a steel frame, 3mm on alu. with an outer chamfer diameter of 39mm.
However, the Schlumpf has a lot more rotational torque since it's an epicyclic gearbox. A normal BB has much less force from the bearing precession.

I'll keep looking for the MAVIC instructions.

All the best,


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PostPosted: Sun Nov 18, 2018 10:40 pm 
retrobike rider
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OK, not such bad news...

MAVIC spec a 2 -2.5mm 45degree chamfer.
http://www.retrobike.co.uk/gallery2/v/M ... l.pdf.html
This would give an OD for the chamfer of 40 - 41mm on a standard BSA threaded BB shell.

I reckon that with a full chamfer across the BB face, your Ti BB would have 1.7 mm chamfer, so pretty close to the spec.

All the best,


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