Following on from this:

http://locostbuilders.co.uk/viewthread.php?tid=128747

I am still in 2 minds as to what to do with the engine mounts and whether or not to beef them up now, or see how it goes and if one breaks fix it.

My gut feel is that the chassis end of the mount is around 12" from the crank centre line and expecting around 220lbft of torque means the most load each mount will see is 100kg + what the engine weighs, so around 150kg per mount. Tension one side and compression the other.

However if I was to strengthen them up then I would be thinking of something along the lines of this:







So...what would you do?

Beef them up, you can forget about them then!

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Originally posted by prawnabie
Beef them up, you can forget about them then!

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I'm sure your weight calculation is probably correct but , just to look at wonders me if they will stand up to the twisting/movement as well?

make stupidly strong then forget

last thing you want is the engine mount failing

Probably a lot less work to beef them up now than to wait until one fails and sort it, and any other damage, out then

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Originally posted by speedyxjs

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Originally posted by prawnabie
Beef them up, you can forget about them then!

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X2

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On the sound engineering principle that if it looks wrong then it probably is wrong - I would certainly beef those up - they just look wrong somehow

So on that basis, what are the thoughts on my beefing up proposal?

Any other ideas?

Just do it as per your pictures. A man of your knowledge/experience/skill know sit makes sense or else you would not have needed to ask.
Been there on several occasions myself. It's just that you don't want to damage the paintwork etc and your hoping that someone will tell you it'll be fine.
YOU KNOW WHAT TO DO bite the bullet and do it

If you are worrying about it now, better to do it and stop worrying

Looks like I will be speding a day doing some more welding/fabrication next weekend then!

I'll cut the existing tube through perpendicular to the plate on the engine as well so there is a proper joint between the tubes.

Now I just need a couple of offcuts of 2mm steel plate to weld to the chassis. Sure I can raid some from somewhere....

If it was me doing it i would move the rubber mounts so that they were square with the enginge mountings then use a single piece of an appropriate sized channel cut and then welded to the mounting plates, that way the bottom bolt could be easily acessed and would give you a we bit more space.
This way any load would be placed square on the mounts,
Just my thoughts if it helps.

Mike

As i said last night, triangulation is your friend....

Beef it up and forget about it, dont want it breaking and causing damage or an accident !

Chassis tube is much more likely to fail ----- see mods below stiffners can be bolt on.
Rescued attachment 212.jpg

Not sure I follow what you mean BT with regards the bolt on stiffeners.

It looks like it will be easy enough to add another plate to the chassis to add in some triangulation to the mounts anyway.

Can you do it like in your first photo but have the second mount rubber at 45% it would stop the engine moving side ways a bit like this

engine mounting

[Edited on 7/2/10 by jacko]

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Originally posted by flak monkey

My gut feel is that the chassis end of the mount is around 12" from the crank centre line and expecting around 220lbft of torque means the most load each mount will see is 100kg + what the engine weighs, so around 150kg per mount. Tension one side and compression the other.

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quote:

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Originally posted by MikeRJ

quote:

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Originally posted by flak monkey

My gut feel is that the chassis end of the mount is around 12" from the crank centre line and expecting around 220lbft of torque means the most load each mount will see is 100kg + what the engine weighs, so around 150kg per mount. Tension one side and compression the other.

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The side in tension will obviously be under much less stress since the torque reaction will be removing the engine weight from that side, and transferring it to the other side....

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quote:

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Originally posted by miikae
If it was me doing it i would move the rubber mounts so that they were square with the enginge mountings then use a single piece of an appropriate sized channel cut and then welded to the mounting plates, that way the bottom bolt could be easily acessed and would give you a we bit more space.
This way any load would be placed square on the mounts,
Just my thoughts if it helps.

Mike

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The penetration of the welds is good, there may be some room to add triangluation to the mount as it is.

I could just make the mounts straight, do we think that if they were just straight and placed the load directly along the mounts that they would be strong enough? Would need to cut the existing plate off the chassis and remake both mounts for the best result. That said the plate is only held on with 4 short welds along the top I think...

I would probably still use the 1.5" tube for the mount though? I dont much like the caterham style mounts which sit at 90 deg to the engine and therefore put massive amounts of stress through the welds....

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Originally posted by sebastiaan

quote:

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Originally posted by miikae
If it was me doing it i would move the rubber mounts so that they were square with the enginge mountings then use a single piece of an appropriate sized channel cut and then welded to the mounting plates, that way the bottom bolt could be easily acessed and would give you a we bit more space.
This way any load would be placed square on the mounts,
Just my thoughts if it helps.

Mike

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This indeed would be, I believe, the best and certainly neatest solution.

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presumably the mounts have to react the gearbox output torque with the primary reduction of the gearbox rather than purely crank torque. what's the ratio of first gear?

a hard launch in first would probably light the tyres up limiting the torque, but you're not just dealing with the crank torque.

i'd be happy to chance the mounts as they are, but belt and braces never hurt anyone.

what about bracing the back of the head onto the bulkhead? you've got doubleish the lever arm between your current mounts and the crank then.
tom

So this is what I have ended up with.

What do we think now? Certainly feel more substantial...


Finished engine mounts 1


Finished engine mounts 3


Finished engine mounts 4