Pace RC200 F1 seat clamp repair

danson67

Retrobike Rider
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This stuff can be done...don't scrap your frame or hang it on the wall.

Here's the problem:
Someone fitted a 26.8mm seatpost instead of a 27.0. The post could then rock inside the seat tube, stressing the weld and cracking around the collar:

1635514191619.jpg

So, I hacksaw along the remaining weld, along the crack line down to the original tube surface, and lifted off the clamp piece:

1635514191616.jpg

Strip the anodising with a strong caustic soda solution and a non-organic paintbrush...the Pace stuff is very tough, it takes some time, light abrasion to cut the anodising and plenty of refreshes of the solution.
Here you can see the different reaction of the 7005 body material and the 5356 weld material to the caustic soda. The black is some of the non-aluminium alloying components which aren't dissolved being precipitated on the surface.

1635514191608.jpg

Quick dip into a nitric acid de-smut solution to clean the precipitate off.

1635514191604.jpg

Machine and file off any remnants of the original weld and put a chamfer on the joint to make sure that the penetration is better than the original:

1635514191597.jpg

Same chemical strip of the top section of the seat tube:

1635514191611.jpg

Wash, light going over with silicon carbide abrasive cloth (not aluminium oxide, which can contaminate the weld), and finally an acetone degreasing wipe over. Leave to dry, then line everything up with an expanding bronze heatsink inside to reduce any distortion and tack up:

1635514191590.jpg

Complete the weld, running from least to most stressed areas. Finished:

1635512573195_copy_1208x1015.jpg

The new weldment and surrounding original material will naturally age back close to 7005 T6 without an artificial ageing heat treatment cycle after around 30 days at room temperature.

Good for another 30 years.

All the best
 

hamster

Retro Wizard
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Wow, superb to look at, and fascinating to read a little on the craft, thinking and preparation. In awe.
 

27motorhead

Retro Guru
Love this Dan. Great attention to detail as always and so easy to digest/understand. Reminds me I need to get our cracked Raleigh Ti up to you for some TLC... Thanks for sharing!
 

madjh

98+ BoTM Winner
Yeti Fan
There is life after a crack

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velofrog

Gold Trader
MacRetro Rider
Yeti Fan
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Superb stuff Dan 😎

Must get my Alves posted to you, and now I have a Stooge bike box to send it in! 👍🏻
 
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