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MG MGF Technical - Scuttle shake and mass dampers

During these winter months, and feeling withdrawal symptoms, I've been thinking about what further improvements I could make. Apart from the obvious add-ons I had the thought that it would be nice if it were possible to reduce the amount of scuttle shake. It's not especially bad, but it does rattle the hood (at least on mine). I've done some doodling and added a page to my website http://www.lejambonfute.f2s.com/page32.html where I've tried to show how I think it could be done using mass (or harmonic) dampers.
Not that I can actually do anything about it, but perhaps some brave type might have a go!
Just a thought...meanwhile spring's not too far away.
M Cunningham 1

This is an interesting idea which I haven't seen discussed here before but it worked wonders for the London's wobbly bridge

I guess the effectiveness of your system will depend on having chosen the right spring rate and the resonance frequency.

The obvious place to dampen scuttle shake would be to by mounting a damper directly on the scuttle, but it would be difficult to hide without resorting to exotic materials. An alternative would be to place the dampers on the subframes, but there may not be room. Where-ever you decide to located the dampers you might have to consider the less than perfect rigidity of the car body causing only partial damping.

My concerns are (a)that the F is already relatively heavy and really cannot afford to carry even more weight, unless it makes a significant different to performance, (b) you could induce cracking if the mounting points are not well chosen.

Chris
Chris

Hi M ( for Mike?), I was not aware of excess scuttle shake on the MGF - non of our club members (West Lancashire MG Owners Club - www.westlancsmg.co.uk)have mentioned it - rather than use a mechanical damping system ( your drawings & formulae brought back memories to a retired physics teacher)is there any mileage in using adhesive sound proofing material on the bulkhead to damp any vibration there? I like the French version of our surname - I got fed up of the English version which I was sometimes confered on me - sly bacon!! Cheers Cam
Cam Cunningham

Chris, the location I thought for the front damper was under the front bonnet, between the spare wheel and the heater cover. It could be attached to the panels over the front springs, and the central bar would also add to the structural stiffness. On M2DYK where I've replaced the Hydragas with TF subframes, I've got two nice reinforced holes where the front dampers used to fit! As for the weight increase, there would have to be some experimentation by trial and error to find the best trade-off between weight and effect.
Cam - I quite agree it's not a big problem, but it's certainly there. Have you listened to my Knockhill lap on the website? You can hear the hood rattle as I ride the kerbs ;-), which is where I estimated the frequency. The stick-on stuff only works for audible frequencies, whereas the harmonic dampers deal with significant stuctural vibrations. I too was sly bacon - aren't people original!
M Cunningham 1

Interesting this, I am just in the process of chopping a TF body we have scrapped for Donor parts. Looking at the shell there are some interesting features, firstly the weight and thickness of the windscreen surround very substancial. I think it would be hard to stop that amount of mass flexing the area where its attached.
The tube that runs accross under the dash is very large but is only triangulated into the centre tunnel on a small frame. To us it looked like the centre of the car could do with more bracing as there is no real trianglulation to resist twisting from front to rear, the sill sections do not look that substantial, this coupled with a lot of the shell strength front and rear in the upper parts of the shell.
I appreciate the subframes stiffen the front and rear but the bushes would allow quite a bit of movement.
My point being rather than tune out the vibration why not have a go at fixing the cause.

Ultmate souluting would obviously be a roll cage, but looking at a more subtle mod a brace bar that attached to the square metal support behind the top of the drivers seat down to the nearside door pillar area where the dash cross tube meets. Bracket it up and make it detachable for track days etc.

Joe T

What about the kit put out by www.vehiclehandlingsolutions.com their underdash improved brace is ment to resolve scuttle shake.
Andrew W Regens

This thread was discussed between 19/01/2007 and 20/01/2007

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