head stays and chassis stiffness

[MXTex]

This is regarding a 2010 KTM 250SX that is ridden MX only. The rider went to Loretta Lynn's last year in the intermediate class. I share this to demonstrate how hard the bike is ridden.

As with many bikes, KTM uses the motor itself on this bike as a structural truss within the chassis. This is done via head stays which connect the cylinder head to the frames backbone. Recently, the head stays have been breaking on this bike with regularity. When we looked into things a little further we found the frames motor mount tabs and related case holes to be wolllered out. This allowed the motor to move around in the frame even when bolted up. So we drilled out the tabs and cases to accept larger, tighter fitting bolts and fabbed up two very beefy head stays. The motor is absolutely solid within the frame now and there have been no issues for two rides. But we are concerned. The OEM head stays are of very unique shape. So unique that we can't help but think that they are made this way to allow some flex. The head stays we have fabbed up and installed will allow no flex. Have we created a handling, or more importantly a safety issue by stiffening up the chassis like this? The rider noticed the difference initially but seems to have adjusted.

[harrperf]

Frame is probably stretched to some degree....without a new one and a frame jig to compare against - it would be tough to tell though.

There is no doubt you have altered the flex characteristics - but if the rider does not complain - I would no worry about it.

[mog]

The 125sx used to do the same , I doubled up on the head stays and it worked

[MXTex]

Thanks for the replys. Do you guys think that the strain-life of chromoly steel is an issue? In extreme cases, I wonder how many flex cycles these frames can take prior to failure.

[ktm kid]

Has the swingarm pivot or engine mounts been slack at any time? Used to happen quite a lot on the 125's, we made some solid ones, never happened agaiun.

Should be fine

[harrperf]

Steel can be designed to last basically forever...but whether that is the case here or not (if designed to last forever) would be only something ktm - or someone with a lot of time on there hands would know

Aluminum, on the other hand - will ultimately fail at some point.

That said - steel frames were always known to stretch terribly over time. I would probably see if you can find a new frame ultimately.

One of my super fast 85 riders on yamahas had to rotate frames every 2 months due to fatigue and ultimately failure. Thankfully ebay is abundant with jnew yz85 frames at a decent price.

I would doubt there are many ktm frames!