Cracks in frame vs cracks in should i be worried?

[nihontobiker]

bit of an unusual one this really.
I recently went and collected a frame i bought on ebay.
And upon further inspection i noticed that on a weld there is what apperaed to be a cracks in the paint very thin.
So after removing the paint there was nothing under it not cracks not damage.
Not my question is could this be cracks were the frame has actually flexed or been under stress at some point or could there be hidden damage?
I know there is a place in UK that can repair cracks but heat treating is my main issues.
The damage to the paint was a small line and then lots of little lines off that line like spidering.
But like i say nothing under it.
Should i leave as it is and paint it and ride it or should i be worried?
Frame in question is a diamonback sabbath.

 

[captainchrisstc]

If the crack was just in the paint i wouldn't worry about it, as the paint can be less plastic then frame. and some lacquer is quite brittle. If there's a crack in an ali frame it's pretty much game over,a s you said heat treating is an issue. Usauly when a fram cracks it's in the tube not in the weld. and when it'as at a weld. it's almost against the weld, not on/through the weld. Unless it's a really bad weld.

Though from what you said, i'd repaint it and carry on as normal.

(on a side note the only frame i ever had that had a guarantee on the paint was on an 2000 orange patriot LT. I broke the frame, as it had a bit of design flaw, but he paint was very flexible, and diffferent from most bike frames)

 

[nihontobiker]

If the crack was just in the paint i wouldn't worry about it, as the paint can be less plastic then frame. and some lacquer is quite brittle. If there's a crack in an ali frame it's pretty much game over,a s you said heat treating is an issue. Usauly when a fram cracks it's in the tube not in the weld. and when it'as at a weld. it's almost against the weld, not on/through the weld. Unless it's a really bad weld.

Though from what you said, i'd repaint it and carry on as normal.

(on a side note the only frame i ever had that had a guarantee on the paint was on an 2000 orange patriot LT. I broke the frame, as it had a bit of design flaw, but he paint was very flexible, and diffferent from most bike frames)

Thanks buddy , well here is a picture of the frame , i removed the paint using wet n dry 500grit and there is nothing under it.
So good news i hope

 

[nihontobiker]

Right strange question here , i have removed the paint and nothing is visible at all now is there such thing as a crack that cant really be seen and anyway to test this out , also is there such a place were you can send a frame were they scructuraly test is for cracks and weakness

 

[kvs766]

Re:

do a search on web for Dye Penetrant Crack Testing
i think this is what you are looking for

 

[jimo746]

Re:

what frame is that?

 

[nihontobiker]

Re:

It is a diamond back sabbath gearbox bike

 

[Grease Monkey]

Looks pretty much like the paint stress fractures you would see on a carbon frame. The deal with ageing paint is that it gets more brittle and fragile over time. This can take 3-5 years depending on the quality of the paint - the metal /carbon underneath doesn't age as badly (carbon almost not at all, it has a tensile strength rating of 100 years plus) so the frame will move with normal use, but the paint is now brittle so fractures appear.

You did exactly the right thing sanding back - the advice with carbon is, if you don't find any damage or cracks underneath carry on as usual. Cracks, especially ones that will be mechanically dangerous normally follow the joint or the line of the weld. That's not a hard and fast rule but it's one you see on carbon frames with regularity. Paint fractures are usually random in orientation.

 

[Grease Monkey]

I just had a look at the close up magnified in Photoshop, it doesn't look bad but to be on the safe side I would sand back all the way along the crack and check the aluminum weld underneath, it's likely a paint fracture but if this is carbon I would definitely be sanding back to inspect the joint. It's an easy place to repaint and you can mask it off simply enough to rattle can the inspection site.

 

[nihontobiker]

Re:

Yes it is an alloy frame grease monkey well I have
Removed the paint and no damage underneath
I will upload another pic for you to inspect would it
Be wise to use watered down acrylic paint and see
If it settles into any cracks as that rattle can stuff
Is 35 quid