Frame dimensions for correcting Headstock angle.

Z

Zakredridge

Junior member
Location
United Kingdom
Hi
My frame has had a prang previously.
I'm sure I've seen on here a diagram of frame dimensions to check everything out.
I can't for the life of me find it on here.
Have I been seeing things?
I have a bent top tube!
How is this usually corrected, by replacement?
I remember an old Jota frame cracking on lower down tubes after straightening.
Thanks in anticipation!
 
Just as a comment, people have had frames straightened only to discover the frame comes standard with one not-straight tube. I forget the details, but someone will confirm, I bet. That's not to say you're wrong. Best to find the detailed dimensions and any other info before committing and then painting it. Time for some bracing to avoid cracking as well. There is always the old story about cutting the frame backbone in half as well. That's a fun tale.
 
Bent top tubes on triples seem to be pretty common. Some say they're ex factory.
Whatever, Phil Todd recounts racing a triple with a bent top tube that was a lot better on the track because the steering was quickened up.
Paul
 
Quick 'n dirty method of checking the extent of damage is measuring lower front engine mount bolt to front axle centre with forks fully extended, providing the stanchions are straight. You'll need to compare to a known, good similar model, different fork lengths and yokes can make a huge difference.

Top tube should be straight as an arrow. Downtube attachment at top tube is assymetrical, one downtube has a stupid-looking kink in it as standard to clear the header.

piet
 
The Sock said:
Hitting the centre pipe, with the mudguard hoop on Ceriani equipped Laverdas, can be an indication that the front forks need attention.
Click to expand...
Bent top tube is obvious, forks may have been repaired/replaced in the past. Seen it often enough...

piet
 
Hi Guy's
That's just the right information I require.
My frame is definitely bent as the mudguard hits the front pipe under braking.
What's the normal procedure, straightening and then repairing any fractured frame tubes?
Paradise have a frame for a grand, New!
 
Colin has thus far omitted to tell us which model triple he has...

2 types of Ceriani yokes for 1000 and 1200 with different leg lengths. There's also the rare chance of SFC750 yokes being fitted. Marzocchi has different yoke offset and trail specs, as well as longer legs. All have influence on wheelbase and measurements from frame fix points.

piet
 
My friendly engineer asked me to come round, to show me his progress.
Frame mounted on blocks flat and laser level through headstock centred with battery tube and front brace on front loop.
That 28° was a key indicator, the top tube slots internally into remaining top tube on both ends for rigidity.
He's taking 3-4 mm off tube to give the correct angle. Clamping it and welding it up.
Then off for powder coating.
Thanks guys unable to do it without you.
 

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That's certainly a bold approach!

Have him add some gusseting around the headstock, the downtubes will most probably be compromised in the area they always let go, a fracture waiting to happen.

Lots of gusset examples to be found here, been done to death.

piet
 
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