Engine mount failure again GRRRR

[Rubce]

Hi All

Whilst tinkering with the GT6 this afternoon I happened to take a look at the engine mounts and much to my disgust found that the offside mount was on the verge of failing >:(. Hey ho you might say, rubber components don't last forever.

However, to put this engine mount failure into perspective you need to realise that it has only been on the car for 460 miles after the previous mount failed last October as I was driving the car >:(. The previous one failed by de-bonding away from the metalwork.

This one has simply torn itself to bits. At least this time I spotted the problem before it actual broke in two. Fortunately I had a spare in the garage and fitting the replacement only took 45 minutes as I have become quite a dab hand at doing them given all my recent practice! Having my Goliath crane also helps in these situations.

Regards

Bruce

[junkuser]

I wonder how long before fitting it was manufactured.

[rotoflex]

I consider the design of the GT6 mounts & try to think of a solution, like modern car enthusiasts come up with, but the mount design thwarts me.

Homefix upgraders often fill modern factory mounts with silicone or polyurethane or something, but those mounts all seem to be designed like donuts.  A sleeve carries the bolt or weight, it's in a donut of goo, & the good donut is in a larger sleeve (like an archery target).  Downward force just sandwiches the goo tighter.  But the GT6 mount has shear applied to the goo body, which is most of the problem.  A redesign of the mount would seem the solution, but I can't see how.

Something must be done!
http://www.youtube.com/watch?v=JN99jshaQbY

[JohnD]

I fear that this is not a design fault, else Triumph engines would have been falling on the floor years ago.
No, when made to the old standards, they last for years, even when coated with the Patented Triumph AntiCorrosion System (AKA Oil leaks).   The real cause is crap rubber material in modern repro parts.

I've had exactly the same problem with rear gearbox mounts , overdrive type, which have a similar construction (not the bobbin type).  The rubber just breaks up after a few hunderd miles.   After having that, and even though there is some minor cracking on my main engine mounts, I'd not dream of changing them for new.  
JOhn

[junkuser]

Agree Bill that the design ain't good Bill and I have modified Zephyr mounts on the Spit, but that was to stop engine movement at idle which was causing rising fuel levels in the bowls.
That was with the SUs, bowls rubber mounted and very responsive to resonance.
The further the fuel rose, the more the shake, the more the shake, the more the fuel rose and on and on to stall unless the throttle was opened to clear the carburetors.

Asked the only Spitfire guru I knew at that time and he said they all do it, so decided to go for the stiffer mounts.

The mounts were originals off a 1959 Zephyr. Fitted in about 1977 and still OK.

P.S. Sorry, I did not mean to disagree with you John, you posted whilst I was slowly keying.
Mal.

[Tim Bancroft]

Maybe change the mount to the system used on the prototype Le Mans GT6 that never got raced, utilise the front plate off a saloon engine. Bit of a pain though?

[Clive]

I had new mounts fail very rapidly. The solution was to refit the original ones, even though they had a slight sag. However, they were still on the car about 15 years later. I tend to keep original mounts now, though my stock has just about dried up.
On my Toledo, I adapted jag e type mounts, original ones were (are?) still available. However the shape doesn't really adapt easily to spit/gt6, though it has been done. However, there are bound to be something out there that works.

[Sheepy]

If they are failing so quick, take them back to the place you bought them for replacement!

When I built my lotus seven style kit car, I went to my local motor factors and said "I need an engine mount, can I rummage?"
They let me look through all their engine and box  mounts to see if I could find a suitable one! (I did) but its amazing the style and shapes they have.

Worth a shot, then you will know what ones to go and get from a scrapyard (as they should be original type rubber) or go to the main dealer for that mount (whatever model it fits)  ;)

[Nick Jones]

Repro parts not fit for purpose.  Simple as that.  I don't know who makes all these "rubber" parts but they need a rocket up 'em.

Nick

[Velocita Rosso]

Not always the case of poor rubber though
What about vibration?
If the gearbox mounting is shot and there is vibration from the prop shaft ,this can also contribute to the deterioration of the mounts, as the vibration transmits through the engine.
Never ever had problems with the mounts on mine or the GT before, however after the 10CR and the gear box problems,I found that the mounts had parted the rubber from the metal.
So as the transmission is only `suspended` by the two front mounts and box tail mounts everything should be well balanced or the weakest point(rubber) will give way

[MikeTeesside]

This is a bit disconcerting.. as I've just changed my cracked-to-heck old ones for brand new ones. :o

Mind you I did get them from Canleys so the quality should be okay. That and the fact the old ones were mounted incorrectly and spaced with suspension shims. The heck was the PO thinking??? ??)

[JohnD]

Mal (junkuser) ,
No offence!   But we do need to talk about apples and not oranges.   You were writng of a Spitfire. The OP and I have Six cylinder cars.

VR,
Rubber has its own enormous science, and what leads to failure of a rubber component is a large part of that.   This review paper has 150 references!  http://archimedes.ing.unibs.it/andrea/Bibliografia/Gomma/Fatica/Prima%20ricerca/Mars-IntJournalFatigue24.pdf   Vibration is only one factor, and I would suggest that these modern rubber components sue an inaapropraite type of rubber, if so many fail so quickly.
THis paper might allow us to identify whatis happening: http://www.imechanica.org/files/Manuscript%20LE%20CAM.pdf
   And as the four and six cylinder engines differ so in mass, their natural harmonics will also differ widely.   They will vibrate at different frequencies, yet the two engines mounts seem to suffer failure equally.  THat points to the material, not the vibration.

Mike,
Ahem!  My failed rear O/d gerabox mounts came from - Canley's

As it seemed impossible to find a good one, I modified a modern one by drilling through the outer and inner metal parts, and the intervening rubber, and putting two bolts through.  These retain the metal parts and limit movement, while letteing the rubber cushion vibration.  Not really possible with an engine mount, or advisable
John

[drofgum]

Hi,
The poor quality of the rubber isn't just a matter of cost savings on the part of the manufacturers. The environmental regulations governing their waste and air emissions have forced changes to the rubber. Bluntly, "green" processes seem to make less suitable rubber.
                                                                                      All the best,
                                                                                      Paul

[thescrapman]

8778 wrote:

and spaced with suspension shims. The heck was the PO thinking??? ??)

Fitting suspension shims under teh mounts was done at the factory.

Notsure why though.

To get engine level I guess..

Cheers

Colin

[Velocita Rosso]

JohnD wrote:

Mal (junkuser) ,
No offence!   But we do need to talk about apples and not oranges.   You were writng of a Spitfire. The OP and I have Six cylinder cars.

VR,

   And as the four and six cylinder engines differ so in mass, their natural harmonics will also differ widely.   They will vibrate at different frequencies, yet the two engines mounts seem to suffer failure equally.  THat points to the material, not the vibration.

Mike,

Not necessarily so
I`v been fitting such things to Triumphs ,especially Spits, since the early seventies
Also as an industrial buyer ,had to purchase such items for the agricultural industry and got involved with the manufacture to various shore hardness.
Vibration played a big part in such failures, so its not worthy of dismissing
......especially with personal experiences and not having any contamination issues to consider assisting in any deterioration      

[MikeTeesside]

thescrapman wrote:

Fitting suspension shims under teh mounts was done at the factory.

Notsure why though.

To get engine level I guess..

Cheers

Colin

I stand corrected. Very odd though as it would only change the level by a few millimetres. Surely can't make that much difference can it? :-/

Old mounts were also being slowly bent sideways due to the aforementioned incorrect fitting.

[Rubce]

I haven't noticed any adverse vibration in the car. The gearbox mount was renewed as part of the resto 480 miles ago. I will pop down into the pit and have a look at that mount later this week. There is no oil contamination involved as the engine bay is clean which is not surprising considering the resto was only completed last September.

Seems odd to me that both times the engine mount has failed it has been on the offside. The nearside mount has done 4,000 miles plus with no signs of deterioration.

Bruce

[junkuser]

My reference to the reason for changing my mounts was to point out that it was not due to failure of the mounts as was the case with the O.P.

I realise a 6 would be less likely to move about at idle than a 4 but, from the picture, the design of the 6 mount seems similar to the 4 ones, so was simply suggesting that there may be other mounts that could be adapted for the job and how well the rubber in old mounts lasted.

I'm good at confusing people by the way I express myself!

The area of rubber to metal bonding on the Zephyr mounts is probably twice that of the Spitfire ones and the loading is less in shear. so a design like this should be suitable for a 6 I feel.

[Velocita Rosso]

2806 wrote:

Seems odd to me that both times the engine mount has failed it has been on the offside. The nearside mount has done 4,000 miles plus with no signs of deterioration.

Bruce

...Heat from the manifold?

[esxefi]

^^that's the problem,torque reaction.

I made some movement limiters which bolt up through the hole in the inner steel part so when I do my 'drag race' starts they lock up solid but in normal use they work as intended.

they are the original mounts and still fine :)

[Martin M]

Hi,
try the uprated engine mount UKC 8330 from Moss.
Martin

[Rubce]

2822 wrote:

Hi,
try the uprated engine mount UKC 8330 from Moss.
Martin

Hi Martin

Thanks for the tip :) I have just spoken to Moss and ordered a pair. Apparently they are a harder rubber and not hollow, originally designed for a TR8. Only time will tell how they perform on our GT6.

Regards

Bruce