[Staowners] SCUTTLE SHAKE REVISITED

Mon May 12 09:19:32 EDT 2008

Hi All,

For what it's worth, I ran the following checks on mine some time back:

1) Drive the car on the road at above the affected speed, disengage  
the drive and coast into the affected speed zone.  The scuttle shake  
is evident when the engine is idling but the car rolling at speed.   
This is so whether the disengagement is from pushing the clutch in or  
from selecting neutral (i.e. the gearbox doesn't seem to affect it).

2) Drive it through the affected speed in different ratios (i.e.  
giving you a range of different engine speeds for any specific road  
speed).  Gear ratio selected seemed to make no discernible difference.

3) Place the car on a ramp, jack up the rear wheels and 'drive' the  
car such that the rear wheels are spinning at an equivalent 60 mph or  
so.  We couldn't reproduce any body/scuttle shake under these  
conditions.

Thinking in vibration terms, what's happening is that the scuttle is  
going into resonance.  Everything has a natural frequency - the  
frequency it will vibrate at if you whack it.  It's why musical  
instruments work and why soldiers break step to march over bridges.   
Things will go into resonance if they're being excited by something  
they're connected to that happens to be vibrating at or near their  
natural frequency.  It's kind of hard to measure, but my guesstimate  
was that the scuttle was shaking at a few cycles/ second (Hz).  If an  
engine is doing 2,500 rpm then its crank is spinning at around 40 Hz.   
At 60mph, its wheels are doing around 13 Hz, at 50 mph 11 Hz.   
Intuition says that the wheels are the heavier, tyres are made to  
lower tolerances than cranks, and the mass is rotating on a greater  
radius all of which point to wheels having more influence.

In the end we spent a lot of time setting up the camber, castor and  
toe-in accurately and the problem eased but it didn't go away entirely.

As to why sedans are different, my best guess would be that the closed  
box of the sedan will have a different natural frequency (higher,  
because the structure is stiffer), so the effect would begin at higher  
speeds and with the stiffer structure the amplitude of the vibration  
may be lower.

Hope this helps a bit,

Richard Atkinson

On 12 May 2008, at 13:49, terry poole wrote:

> Hi All,
>
> As I said many moons ago the only shake I've (my car, that is!)  
> experienced was due to an out of balance prop. shaft and easily  
> fixed with a new u/j.
>
> I have seen so-called scuttle shake mentioned in relation to road  
> speed but never to related engine rpm (different gears) which should  
> be relevant especially to some of the fancy high-tech engine faults  
> being debated?
>
> If it is only speed related is it more likely to be caused by severe  
> wheel wobble and nothing to do with the poor old much maligned engine.
>
> If it were an inherent design fault somewhere, we would all suffer.
>
> Long ago I also ran a saloon (sedan) with a broken head to scuttle  
> rubber for a while and never noticed the difference until I spotted  
> it visually.
>
> PIp-pip,
>
> Terry.  UK
> On 11 May 2008, at 15:16, Mal Clark wrote:
>
>> Hi Bob,I am almost convinced the front stabiliser mounts maybe the  
>> reason,as I said I can not see how the steering set up would cause  
>> the shake as when the shake occurs it transmits the sideways shake  
>> across the car and into the seats.you can see the dashboard etc  
>> shimmering, I also 'Lived" with this shake on the other Alpines,  
>> interesting,I would take someone to remove the mounts as you  
>> suggested to prove or disprove this, thanks Mal Clark.
>> ----- Original Message -----
>> From: Bob Hamilton
>> To: Mal Clark ; Staowners at sunbeamtalbot.info
>> Sent: Sunday, May 11, 2008 9:39 PM
>> Subject: Re: [Staowners] SCUTTLE SHAKE REVISITED
>>
>> Hi Mal,
>>
>> Interesting observations you have presented and confirm that I have  
>> absolutely no scuttle shake at this speed in the saloon. I have  
>> lived with this phenomenon in the '54 DHC for the past 46 years  
>> having had numerous wheel balancing performed on the latest  
>> balancing machines, on and off the car and have come to accept this  
>> shake as the "nature of the beast", likely a design fault.
>>
>> Perhaps the removal of the upper mounts corrects this problem and  
>> wondering if I should try the saloon rear mount on the DHC and  
>> Alpine and temporarily remove the rubber mounts on the upper front.
>>
>> Later,
>> Bob
>>
>>
>> At 07:49 AM 5/11/2008, Mal Clark wrote:
>>> Hi everyone.over many years there has been a debate on the Alpine  
>>> Scuttle shake at speeds,between 50 and 60 MPH,all my Alpines 3 of  
>>> them experianced the scuttle shake around 55 MPH, and as you know  
>>> this site in the past has had many owners suggesting why they  
>>> shake, wereas some owners haven't experianced the shake at all, My  
>>> latest Alpine fitted with power steering.air conditioning,disc  
>>> brakes and a 5 speed gearbox,does not shake at all in fact there  
>>> is no feedback through the steering wheel what so ever,and letting  
>>> the wheel go at these speeds it doesn't move of line,if fact it is  
>>> so good, brings me to think why,is it the power steering, (can not  
>>> see a great deal of difference over the original steering box),but  
>>> one thing that is different to the other Alpines I have  
>>> owned,because of all the extra's on the motor,(power steer pump.  
>>> air cond compressor),I can not fit the engine stabliser bars or  
>>> mounts.and could it be these bars and mounts creating the  
>>> shake,interested to know if sedan owners have the so called  
>>> scuttle shake,seeing sedans do not have these bars fitted, (I do  
>>> have the sedan rear mount on cylinder head) your comments welcome,  
>>> thanks Mal Clark.
>>> _______________________________________________
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Robert (Bob) A.C. Hamilton, Waverley, Nova Scotia, Canada
>> Sunbeam Talbots - Alpine, Drophead and Saloon, 1953-1954
>> Sunbeam Talbot Web Page: www.sunbeamtalbot.info (or .org)
>> E-Mail: hamilton at accesswave.ca or robertach at ns.sympatico.ca
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> _______________________________________________
>> Staowners mailing list
>> Staowners at sunbeamtalbot.info
>> http://sunbeamtalbot.info/mailman/listinfo/staowners_sunbeamtalbot.info
>
> _______________________________________________
> Staowners mailing list
> Staowners at sunbeamtalbot.info
> http://sunbeamtalbot.info/mailman/listinfo/ 
> staowners_sunbeamtalbot.info

This message has been scanned for viruses by TRENDMICRO,
an IESE technology affiliate company  and global leader in antivirus and content security software.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://sunbeamtalbot.info/pipermail/staowners_sunbeamtalbot.info/attachments/20080512/b97094ae/attachment-0001.html 