Carbon mtb frame repair

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#1

Hi guys,

I have bought cracked frame ghost lector, got it really cheap, the guy said that he rode bike with crack for few months and crack didnt spread.
Im hoping to repair it and ride it when I get other parts to compleat it.

Here are some pics of the crack, it is inside the tube too, my question is what would be the best option to repair it ?
During process seat tube would be inserted so the inner diameter dont change.

My thoughts are going on hand layup:
1)UD put it vertically on crack and +3 layers each rotated for 45deg
2) twill or plain 3-4 layers
3) twill or plain with rotated layers
4) cut the cracked area 0,5-1cm around and new layup with cloth

I would try to avoid 4. option but if it is the best ill give it a try.

Material I can get my hand on and price :
Plain 200g 1m^2 ~42€
Carbon twill 200g 1m^2 ~ 30€
twill 2/2 3k 200g 1,2mX1m ~ 44€
Uni 12K 300g 1,2X1m ~60€
uni 200g 1X1m~35€
±45 12k 1,2x1m~45€

epoxy for hand layup 1kg- 30€

I have some experience with fiberglass, of tool I have only electrical tape and cutting tools so nothing for vacuum bagging and baking only electrical tape.

Maybe some guess what would be the cause of the crack, would it be of the seat clamp too tight ?

Thanks guys :slight_smile:

#2

My guess for the crack would be seat clamp too tight. I believe the normal torque for the seat clamp bolt is only about 4 or 5 ft/lb.

If it was me personally, I would just use UD tape in different directions (like you said) and I think I would try 90, +/-45, 90, +/-45, 90 and see how well that worked (I will probably be corrected by someone in the know).

#3

Another option could be to cut off the damaged section and insert/bond a new carbon tube into the frame and either turn down the seat post to fit the new smaller internal dia or source a suitable seat post.
Chris
Carbon fibre works LTD

#4

Can you layup on the inside? Seems like it’s close to the edge.

If you could clean it up from the outside and then bond prep the inside, then you could layup plies from behind and in front which would be better than just one side. When you repair you can make the area stronger at a cost of adding weight. In this case it would obviously not add much but you could also beef up the area where the clamp goes to decrease the risk of this happening again.

#5

Fixed ID for seatpost.

#6

Ive repaired quite a few frames and usually use an internal doubler plate to bag onto, but with the fixed ID, Id say the best bet is to just relay -the seat post around the outside, build it up from the top tube, and add a few additional plies for sacrificial sanding afterwards prior to painting.
Use heat shrink wrap or a bag for compaction.
Layers wise - use what you have access to or can afford, that’s normally the defining factor!!
Include UD axially along the tube if you can, and twill as these are likely the handiest for you. Its not going to be production standard so I wouldn’t worry too much about it.