Leftside Engine Mount Failure

PostPost by: type26owner » Fri Feb 11, 2005 5:14 pm

Why is it the the leftside is always the one that breaks first? It's the one which is UNLOADED when the engine is at WOT afterall and should last longer than it's counterpart. Occurred to me to look for another reason other then it gets really hot. Just look around that area and the answer is quite apparent if you know what to look for. Upstream in the airflow is a generous and constant source of OZONE coming from the generator or the alternator. Ozone is a killer of rubber normally but hot rubber really makes this a particularly bad situation. Lotus obviously caught on because the later cars had a hole cut through the fender to let in fresh air to dilute the badness.

I've not cut the hole in my S2 though. Instead I've installed a heat shield which is one of those aluminumized fiberglass shield to heat shield a starter. Velroed that on top of the alternator and the mount. Added a scoop which hangs down below the chassis by an inch just behind the vacuum box to divert fresh air up to cool the alternator and bath the mount with fresh air. So far, so good , testing in progress.
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PostPost by: lotusanglia1965 » Fri Feb 11, 2005 9:41 pm

;) This would be the same problem with tyres.How many people change them after five years,regardless of treadwear? ozone and ultraviolet light is what kills rubber,not just heavy size tens! We are constantly amazed at customers at work who happily spend thousands on an engine upgrade,but leave their ropy old tyres on as they still have tread! Too much emphasis on legal tread depth maybe? I too have noticed the poor quality of bonded rubber replacement parts these days,take care, cheers,
Martin
"He's not the messiah, he's a very naughty boy"
Monty Python's The Life Of Brian,best film ever.
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PostPost by: lotuselanman » Sun Feb 13, 2005 9:57 am

;)
Gidday,
Failure on the left side engine mount is quite normal on all North South drive cars. If you took the bonnet off and went for a drive you would observe the engine lifting on the LH side under acceleration as a normal torque reaction, no rocket sience required.
Yes the Lotus item may be of poor quality but then consider the original cost, that's ACBC was interested in. If up-market units are not available then make one.
Have a look at the World Cup X-member and Engine Mounts on the MK2 Escorts.
Good luck, Les.
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PostPost by: type26owner » Sun Feb 13, 2005 4:23 pm

Hi Les,
Isn't it easier to apply a fix to the real problem and use the mounts we already have? Bet they will work great if the plume of ozone is diverted away. Any mount put in it's place will get chemically attacked in the exact same way. There's no mount available that is protected with a layer of getter material that I'm aware of.

Had this design problem to resolve on the 216 hydraulic mirror positioning actuators rubber belloframs on the Keck Telescopes which are on Mauna Kea. On those we incorporated sintered housing air vents which were made of a getter material to react with the ozone and keep it away from two rubber diaphrams inside. Those $2 vents were suppose to be replaced every year to get new fresh getter material there as a barrier. They have stopped doing the yearly maintenance I've been informed. Hope can I retire before they all leak out the mineral oil at the same time. Some 'expert' probably an astronomer is calling the shots there now.

Left-hand side mounts when at rest have the weight of the engine resting on them. When the torque is applied that side of the engine is lifted cancelling the gravity and the forces upon it approach zero thereabouts. The mount on the right-hand side does exactly the opposite. Both the gravity and the torque add together to load the crap out of that side but it's not the one which normally fails first. Therein lies the clue it's due to some other effect. Strongly suspect it's due to the ozone.

That's not so bad. Understand on some air-cooled Porches they had a problem with the ozone streaming out the dizzy and attacking the fanbelt or the timing belt, I don't recall which. If either variety breaks though it's bad news. They added an air vent from the dizzy over to the stoplight lense housing so it could breath via the water drain hole. Another kludge.
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PostPost by: Frank Howard » Sun Feb 13, 2005 6:06 pm

Your thoughts brought a thought to my mind. Not being a mechanical engineer, it just seems to make sense that if you have a piece of rubber (RH mount) and there is a certain amount of compression on it (weight of the engine) and then that weight is increased when the engine twists, there will be a certain amount of wear imposed on the rubber. But if you have a piece of rubber (LH mount) and there is the same amount of compression on it (weight of the engine) and then that weight is released and the rubber is actually stretched when the engine twists, there will be more wear imposed on that piece of rubber than the other one.

Can I have my honorary engineering degree now?

Frank Howard
'71 S4 SE
Minnesota
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Minnesota
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PostPost by: steveww » Mon Feb 14, 2005 10:44 am

It was on the Porsche 964 which has 2 spark plugs per cylinder provided by 2 distributors (dizzy). The primary dizzy is driven off the cam and the second is driven by a rubber belt off the primary. Indeed your are correct in that a vent pipe was fitted from the dizzy housing to the engine cooling fan housing to vent off the ozone.
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PostPost by: pereirac » Sat Feb 19, 2005 6:24 pm

I thought the left hand mount failed first because it got 'fried' by heat from the exhaust manifold, or is that too 'simple'.. ;)
Carl

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PostPost by: type26owner » Sat Feb 19, 2005 7:48 pm

Both of the metal pieces are heat sinked quite well to the chassis and the engine block. The airflow which bathes the mount when the car is in motion is from the radiator exhaust. The hottest heatload is off the exhaust manifold and that only happens when the engine is at wide open throttle but normally the car is always in motion when that is true. The exhausting blast of air from the radiator controls any manifold convection heatload one would assume and is swept downstream away from the mount. That leaves the radiated load. Emmissivity of the mount is high and a fairly good receiver of infared since the mount is painted black. Black is actually the worst color to paint the mount possible BTW. A reflective silver color paint would be best. Even better is to drape a reflective heat shield over the mount to thermally block the infared heatload from reaching the mount and bath it in room temperature air instead. Redirecting the flow of ozone away and reducing the operating temperature is the best cure. I think.

I'm waiting for my exhaust system to cool down at this moment so I can 'play' somemore. Going to add the plumbing for the crankcase evacuation check valve. Have to make my own Lotus-sized venturi fitting to weld into the downpipe it turns out.

Oh hey, now that I'm ripping apart my SILVER painted exhaust manifold I remembered it's best to also paint it a color that makes it poor emitter of thermal radiation too. It's a significant blackbody thermal emitter.
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