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WARNING Check your home made engine mounts!

tomgregory2000 - 6/9/09 at 11:15 AM

Further more to my fecking stuped car with the suspected broken engine rubber.

I have been removing my engine mounts and rubbers and look what i found
Can you see the problem yet?

Image deleted by owner

This pic should help you

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Image deleted by owner

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as you can see the they are not some light weight item, they were made to last and they have failed!!
Lucky i foud it when i did as it could have been rather bad if it failed completly

So check your mounts

speedyxjs - 6/9/09 at 11:17 AM

Howlor - 6/9/09 at 11:20 AM

What thickness plate did you use, looks a wee bit thin? It has obviously cracked along the weld. Maybe needed more meet past the weld ends.

Steve

MikeRJ - 6/9/09 at 11:30 AM

The plate looks way too thin to me, I'd be using 5mm as a minimum.

Volvorsport - 6/9/09 at 11:35 AM

thats because you havent followed the centre of mass for the engine and placed the rubbers in that plane . you get a roll couple and the inevitable stress/strain on the mounts rather than letting the engine rotate/vibrate around its mass where all the forces are taken through the 'joint' .

id be using 3mm minimum

Ben_Copeland - 6/9/09 at 12:02 PM

Good job the rubber went before the engine fell out

Volvosport: are you saying that the rubbers should be between the mounts and the engine.. rather than the mounts and the chassis?

mangogrooveworkshop - 6/9/09 at 12:45 PM

The caterham ones fail as well Its a zetec with 25mm square tube on to a plate as well.
Cracked on the tube plate was fine.
Its not just home emade ones that break

prawnabie - 6/9/09 at 02:00 PM

mine did exactly the same, claire reweld mine with 5mm plate and the difference was obvious.

Thats a point, I need to get the other one done too!

blakep82 - 6/9/09 at 02:31 PM

eek

yeah, to thin i'd say. the broken one looks like the exhaust side? the plate off mine is completely different

tomgregory2000 - 6/9/09 at 02:47 PM

quote:
Originally posted by blakep82
eek

yeah, to thin i'd say. the broken one looks like the exhaust side? the plate off mine is completely different

No its on the inlet side.
The other one on the exhaust side is fine, not even a bend in that one.

The plate is 3mm, and yes it turns out 3mm is to thin.

Going to complain to my fabricator(my dad) and get him to make me some new ones.

blakep82 - 6/9/09 at 02:55 PM

i'll get some pictures of mine if you want? made by SHP for their racing cars

tomgregory2000 - 6/9/09 at 03:29 PM

quote:
Originally posted by blakep82
i'll get some pictures of mine if you want? made by SHP for their racing cars

yes please

Davey D - 6/9/09 at 04:16 PM

is that failed mount form the opposite side of the engine that has had the rubber bush failure?

from the picture the mount looks stretched like what would happen from the weight of the engine excessively pulling on the mount due to the other side collapsing?

Volvorsport - 6/9/09 at 04:34 PM

quote:
Originally posted by Ben_Copeland
Good job the rubber went before the engine fell out

Volvosport: are you saying that the rubbers should be between the mounts and the engine.. rather than the mounts and the chassis?

yes and no , the rubber mounts should be placed on the plane of the centre of mass of engine and gearbox , otherwise youll introduce a force into the mount itself .

imagine a lever on the rubber mount - and apply your engine weight to the lever , thats the force the mount sees .

the flexible bit should not see that force if designed correctly .

its difficult to do with a FWD derived engine .

Ben_Copeland - 6/9/09 at 04:41 PM

Ah i see what you mean now... I'll keep that in mind !

tomgregory2000 - 6/9/09 at 04:45 PM

quote:
Originally posted by Davey D
is that failed mount form the opposite side of the engine that has had the rubber bush failure?

from the picture the mount looks stretched like what would happen from the weight of the engine excessively pulling on the mount due to the other side collapsing?

Sorry i should have cleared that up, the rubber mount was ok it was very streched but not broken.

I think what happened was that the mount on the o/s broke off at the top and caused the bottom of the plate to bend and the engine fall over to the o/s and instead of the engine weight pushing down on the mounts it was now pushing them apart which is why i thought the mount was fecked,

I also think that if my oil catch tank was not there it would have fallen over much further and smashed up my carbs so a couple Ł worth of catch tank has saved a few hundred Ł

blakep82 - 6/9/09 at 04:55 PM

ok, don't know if these will be useful, but heres what mine are like. i was given them free, they're very bent lol, think the car they're from must have been in some big crash lol

Description
exhaust side. don't know why they missed the bolt you used, but thats how they did it

Description
inlet side

Description

Description
6mm thick, and very bent rather than broke

those ones above are after i tried straightening them too! in the end i just bought some new ones

tomgregory2000 - 6/9/09 at 05:38 PM

fantastic, thanks for that.

I was thinking of something along those sort of lines, it just seems more secure if the rubber was to fail the bolt would hold everything together

blakep82 - 6/9/09 at 05:41 PM

yeah, it would mean more work to your chassis, but some brackets sticking up for the mounts (like mine to locate into) might give a stronger fixing for not much more weight.

but if you get the bits drawn up and water/laser cut it should be dead easy too.

if you want i can get a photo of the chassis? although you can really already work out what it looks like lol

jacko - 6/9/09 at 09:22 PM

This type of thing any good to you this is what i made for my car
More photos in my archive
Jacko
[img][/img]

cliftyhanger - 7/9/09 at 06:53 AM

I am convinced the actual rubber mount is important too. If too hard it is likely to transmit the vibrations/jolts and stress the actual steel mountings more. And the quality of some of the repro rubber monts is pants too...............seem many are now very hard and the rubber comes away from the metal plates very easily.

[Edited on 7/9/09 by cliftyhanger]

flak monkey - 7/9/09 at 06:58 AM

My original pinto ones broke, so I made some much stronger ones.

Seems the weld HAZ is the most common cause of breakage. A crack propogates from that area and eventually the mounts fail.

It would possibly help if the engine mounts were stress relieved after welding, but then most people havent got access to the equipment to do it (domestic ovens arent hot enough).