KTM 790 Duke Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
97 Posts
Discussion Starter · #1 ·
After my crash a few weeks ago I'm moving forward with the fixes on the 790.

Unfortunately I found out that I don't have a bent handlebar but a twisted frontend.
I.e. the wheel is turned some 3-5 degrees to the left when the top triple tee is perfecty perpendicular to the frame.

The forks don't look bent and I was able to drive back from the track 110km as long as I kept the handlebars slightly turned to the right.
There is a way/process/sequence to try to get the wheel aligned again?

TIA
 

·
Registered
Joined
·
100 Posts
First thing I would try is loosen lower triple clamps on fork legs, bounce front end vigorously, tighten lower triple clamps, then repeat this with the upper triple clamp. See if it improves. If not you will need to remove the forks and examine everything carefully for distortions
 

·
Registered
Joined
·
97 Posts
Discussion Starter · #3 ·
Didn't improve and no real time to work on it further... duke in the hands of the dealer's mechanic.
Fingers crossed
 

·
Registered
Joined
·
9 Posts
Didn't improve and no real time to work on it further... duke in the hands of the dealer's mechanic.
Fingers crossed
Hi Mullasci,

Did you ever resolve this issue? I've had a similar sequence of events and have narrowed the issue down to a bent lower triple clamp. With the OEM clamps being a relatively soft cast material, I assume this would be the component most likely to twist under a crash load before things like the steering stem or forks.

Would you mind shedding any light on what you found?

Just for reference, I performed the following checks before concluding the triple clamps are the cause of the turned front wheel orientation.​
  • Removed and reinstalled the front wheel and triple clamps per repair manual instructions. Result: Wheel returned to identical twisted position.
  • Removed forks and performed a very non-scientific runout of the outer aluminum fork tubes. (Rolling the outer tube portion of the forks on a known flat surface and detecting lift at either end during the roll.) Result: No perceivable bend.
  • Removed forks and performed measurements from the bottom of the inner tube's clamp piece to the top of the outer tube at several different rotated angles to reasonably ensure the inner tube was unbent. Result: all measurements returned the same and was almost identical between both forks. Inner tube most likely unbent.
  • Most conclusive test: Removed the triple clamp assembly from the bike and placed the machined bottom face of the lower triple clamp on various known flat surfaces. I then gently vibrated the top tube of the lower triple clamp to detect wobble or non-uniform contact with flat surface. Result: There was a noticeable wobble on the machined face, and a raised portion of the machined face on the left side of the triple clamp. Raised portion measured roughly a 0.0625 inches [1.5mm]. To reinforce this result, I assembled the upper and lower triple clamp independent from the bike and placed the fork tubes in the triple clamp assembly. Not only was it difficult to fit both forks through the assembled triple clamp assembly, but the bottom of the forks did not lay down identically when laid and tilted on a known flat surface.
I concluded that the twisted triple clamp was pointing the triple clamps askew, resulting in a front tire position perpendicular to the askew axle mounting axis. 1.5mm at the triple clamp can express itself as significantly more at the axle mounting plane.

Curious to see if your misalignment was caused by a similar issue.

Best,
-Blake
 

·
Registered
Joined
·
439 Posts
Hi Mullasci,

Did you ever resolve this issue? I've had a similar sequence of events and have narrowed the issue down to a bent lower triple clamp. With the OEM clamps being a relatively soft cast material, I assume this would be the component most likely to twist under a crash load before things like the steering stem or forks.

Would you mind shedding any light on what you found?

Just for reference, I performed the following checks before concluding the triple clamps are the cause of the turned front wheel orientation.​

  • Removed and reinstalled the front wheel and triple clamps per repair manual instructions. Result: Wheel returned to identical twisted position.
  • Removed forks and performed a very non-scientific runout of the outer aluminum fork tubes. (Rolling the outer tube portion of the forks on a known flat surface and detecting lift at either end during the roll.) Result: No perceivable bend.
  • Removed forks and performed measurements from the bottom of the inner tube's clamp piece to the top of the outer tube at several different rotated angles to reasonably ensure the inner tube was unbent. Result: all measurements returned the same and was almost identical between both forks. Inner tube most likely unbent.
  • Most conclusive test: Removed the triple clamp assembly from the bike and placed the machined bottom face of the lower triple clamp on various known flat surfaces. I then gently vibrated the top tube of the lower triple clamp to detect wobble or non-uniform contact with flat surface. Result: There was a noticeable wobble on the machined face, and a raised portion of the machined face on the left side of the triple clamp. Raised portion measured roughly a 0.0625 inches [1.5mm]. To reinforce this result, I assembled the upper and lower triple clamp independent from the bike and placed the fork tubes in the triple clamp assembly. Not only was it difficult to fit both forks through the assembled triple clamp assembly, but the bottom of the forks did not lay down identically when laid and tilted on a known flat surface.
I concluded that the twisted triple clamp was pointing the triple clamps askew, resulting in a front tire position perpendicular to the askew axle mounting axis. 1.5mm at the triple clamp can express itself as significantly more at the axle mounting plane.

Curious to see if your misalignment was caused by a similar issue.

Best,
-Blake
Did your replacing the triple clamp fix the problem?
 

·
Super Moderator
Joined
·
1,286 Posts
I concluded that the twisted triple clamp was pointing the triple clamps askew, resulting in a front tire position perpendicular to the askew axle mounting axis. 1.5mm at the triple clamp can express itself as significantly more at the axle mounting plane.
That's a strange story. Although I do not doubt any of what you described, it is very hard to believe how this failed to be discovered during QA, on a new bike. If after a crash, it is very unlikely that the triple clamp will bend while both fork legs will show not warping or other damage.
 

·
Super Moderator
Joined
·
1,286 Posts
After my crash a few weeks ago I'm moving forward with the fixes on the 790.

Unfortunately I found out that I don't have a bent handlebar but a twisted frontend.
I.e. the wheel is turned some 3-5 degrees to the left when the top triple tee is perfecty perpendicular to the frame.

The forks don't look bent and I was able to drive back from the track 110km as long as I kept the handlebars slightly turned to the right.
There is a way/process/sequence to try to get the wheel aligned again?

TIA
Twisted front end is VERY likely after a crash. There is a procedure to check and realign the front but if you are not familiar with it, it is highly recommended that you have the bike inspected by a good shop. They will, hopefully, fix this and make sure nothing else is wrong with the bike.

Ride safely.
 
1 - 7 of 7 Posts
Top