XRAY - Model racing cars

I am 99% certain that you are all having a problem with one or more items being assembled under some kind of pressure.

The servo could be the cause as described earlier. More likely is that the front and/or bulkheads were mounted onto the chassis while they were under some kind of lateral load. Even more likely is that the top deck was mounted while the chassis was not on a flat surface.

Sooo, what to do I hear you ask. First, take of the top deck. Second, loosen the screws holding the servo onto the servo mounts (don't take them all the way out! Next slightly loosen both the front and rear bulkheads (all 12 screws) and at the rear also untighten the left hand screw for the bulkhead brace behind the layshaft if you are using it. Next put the chassis on a flat surface (and I DO mean perfectly flat: e.g. a Hudy setup board) and check whether the chassis seems tweaked. If it does (this is very unlikely) remove everything and check again. Also check the top deck on the same flat surface, it should not be tweaked either.

Ok, assuming the chassis and top deck are not tweaked you should be able to assemble the car tweak free. First, let the chassis sit on the flat surface and tighten the left to screw on the servo until it just touches (don't tighten it all the way). Next do the opposite screw the same way, i.e. the right bottom screw. Then the right top followed by left bottom. Now following the same sequence tighten each screw a little bit further and keep repeating the sequence until you think the screws are tight enough. Let's call this approach to tightening the screws "cross-tightening" for want of a better word. During this whole exercise make sure you keep the chassis flat against the flat surface.

Next hold the car upside down with one hand and using only the screws on the four corners of the bulkheads use the cross-tightening methodology to install both the front and rear bulkheads. Once the corner screws are tight enough (DO NOT overtighten these) do the remaining four screws as well. Once done check the tweak on your flat surface. If there is now a tweak you need to investigate whether it is caused by the front or rear bulkheads. If the chassis does seem tweaked you may have a bent bulkhead (again VERY unlikely) or may have introduced a tweak while tightening. When you are confident all is ok, don't forget to retighten the screw for the rear bulkhead brace.

Ok, nearly done. The stuff you did until now is usually something you only need to after a major rebuild or if you had a very serious crash. Normally you only need to loosen the top deck (the only thing not installed at the moment).

TIP: During a race you can redo the top deck without even taking the wheels off if you have a flat surface (setup board) and the blocks that come with you (Hudy?) droop gauge. All you need do is untighten the top deck screws and put the chassis on top of the droop blocks on top of the setup board. Make sure the droop blocks are not underneath any of the screws. E.g. between middle and rear bulkhead screws front and rear. Also make sure the tyres are not touching the board (if they are you have to take the tyres off, sorry ). You can check tweak simply by feeling the outer edges on each block. If you can move an edge easily you know there is a tweak.

Ok sofar so flat. Next put the top deck back on without the screws. Make sure the top deck is flush with the top of the bulkheads and can be moved without any binding. If it cannot use some sanding paper to sand the edges of the top deck until it can (will normally not be necessary). Next use the cross-tightening methodology to reinstall the top deck. Once again check that the chassis is still not tweaked.

Done...

Hi Rob, just to make sure I understood you correctly: you checked the chassis after having removed everything (i.e. nothing mounted on the chassis) and then the chassis is higher where the servo would normally be?

If so then the chassis is tweaked and you can run it that way (if it is a minor tweak) or replace it. But if sofar you only checked with things still mounted (even if the bulkhead screws were loosened) I am not convinced the problem is in the chassis itself as opposed to an assembly problem.

after reading this thread id thought id check my car out...and it appears to be worse than your cars.

at the rear its 5.5mm, at the front in between the wishbone and bumper its 5mm (at both sides) on the esc/reciever side its 5mm and slowly goes upto 5.5..

on the servo side it goes from 5mm to 6.5 (yes thats right..6.5mm!!!!!!!!!!) then back down to 5.5

i followed the things that Tonyv said and it was the same..no change, i also put the servo posts on the chassis and put my servo on after but that didn't help.

i need a new chassis anyway because mine is broken (only at the front where the bumper goes on, still works but could do with replacing )

so not only do i have problems with shocks, now i have problems with the chassis..what next?

there must be a solution to this wonky chassis business..any ideas guys?

Guys, just a thought here, but could you have a look at the outer edges of your chassis and see whether the right hand side has worn more then the left hand side? If you usually run on tracks counter-clockwise then this would be quite normal. If you then measure the ride height anywhere on the outer edges of the chassis your measurement will be off (higher then you'd expect) because the chassis is worn on the outer edges during cornering...

well in the UK we run clockwise so it would be our left hand side that is worn more...so this makes it even worse

Tonyv yes i've checked the chassis with everything loosened and just the bare chassis, Like i said in my original post its not just the chassis thats on the car (xrc) its every chassis i've had from xray.

I understand what you are saying about chassis's being worn but i virtually never race outdoors (work forces me to not race on sundays in the summer ) and the xrc thats on the car is about a month old without a mark on it.

To be honest the car goes very well even with a tweaked chassis but its just annoying me now.

Ok Rob, I'll have to think about this a bit. I'm not sure what could cause this problem having not seen it before.