Bottom Engine Mount - poly hardness

The lower mount is crap by design I think - and agree with CJJ on that. Far too much movement in my opinion.

You may have read here about my squeak noise under torque - I was sure it was that mount. It turned out to be a stainless screw on a hose clamp "just" touching the bodywork near to fuel tank. However the attention paid to that mount whilst trouble shooting has renewed my interest in improving it.

During the engine rebuild, I pondered upon how soggy this mount was, especially at the subframe end. I'd read about CJJ's poly replacement but was horrified by the price of a poly replacement set. For not much more money, I'd already replaced all the suspension rubbers with poly both front and rear. Yes I know genuine rear mounts are silly money but I sense the poly manufacturers are pricing to market demand and availability. I don't like being mugged and decided to make my own at a later date. Now is the time.

Got me a large bottle of poly and hardener at grade 60 and a used mount off Ebay to play with. Research tells me that poly graded at shore60 is more compliant than higher numbers. I believe (and stand to be corrected) that commonly available poly bushes for MGF's are shore70. This might explain why some folk report a harsh ride after fitting. I specified shore60 when ordering my poly set. Rubber bands are shore 20, car tyres are shore70. I reckon most of the rubber suspension bushes are akin to rubber bands - especially the larger of the two rear engine mounts! During the squeak tracing episode, the bulk of the movement is in that large lower mount. So I shall make up that mount first and see how that works as "some" movement is needed to absorb the torque shock and avoid bashing the car too much. If "some" movement remains too much then the smaller mount will be next to do.

Jeff

Will be watching this with interest. :broon:

hi,its best not to restrict the engine too much,as the front subframe bolts are weak.solving one problem can lead to another.the blue poly bushes act as if new rubber.the engine is designed to rock in a cradle it does not move much.but the car was never designed to have tight tolerances and by improving the car will make it worse.like a pair of shoes,replace bits with nice new rubber and they are better but more un comfortable.The sub frame isnt attached that well to be honest.
We have had a few cars in for suspension upgrade,really hard poly bush every thing tighten up like a race car.The car skid about like penguins on ice.You know your stuff and you are extremly knowledgable.But we have seen problems arise where things have been changed.

That's a good point. Race cars operate under different conditions than street cars and as appealing as it may seem to have RACE PROVEN parts on your street car they don't necessarily give the best results for everyday driving.
It will be interesting to see the results of your experiment Jeff. :yesnod:

Intersting - I thought poly bushes were akin to black magic.

I've got poly bushes on the MGF's suspension and they did improve the ride. I also did them on my TR and it now rattles your fillings loose. It seems every company with a lathe can make poly bushes and I'm sure that most of them don't do much if any R&D on specific cars so it's a matter of finding which bushings actually improve things and buying those.
I'm still not sold on poly engine mount bushings but fortunately I don't need any...yet.

I have now made a pair of bushes cast in shore60 grade polyurathene to suit the lower engine shackle/mount. So far so good.
I know Daz was wary about this and I've taken heed of what he said.

In a couple of days the castings will have attained max strength and I shall publish my experiences and opinions to the forum. As you Daz inferred, there's more to this shackle/mount than is immediately obvious.

Jeff

I too will be interested in this, Daz has made a very valid point about stiffening too much, an F that looks like Penguins on ice!!!! :bust:

Attached is a 7 page word document with text and embedded pictures.
I describe how the engine is mounted and shackled from movement, what I think is wrong with the original lower mount/shackle and what I did to make an improvement.
The improvement process is still work in progress and still under observation by me - I thought the techy members of the forum might be interested in an update.

Jeff

That is extremely interesting Jeff. How much does Pro Flex cost ?

IIRC £40 for both pots of material - see http://www.mouldlife.co.uk

I visited the supplier to collect (they are on Suffolk/Cambridge border not far from M11).
My two pots have loads left - I could probably make 15 mounts out of one set of materials!

Jeff

I originally poly mounted the engine to try and solve a few problems I was having. Not only did it solve these problems it actually improved the driveability of the car.

Yes, you do get a slight vibration through the bodywork at tickover and certain revs, but I was looking for it, and Anne says she would have never known unless I had pointed it out to her.

The engine needs to move to aborb shock loadings etc, but I don't thing it needs to move as much as it does. You lose a bit of torque on takeoff as the engine twists when you dump the clutch, it can cause a slight kangaroo effect and it can damage components if left to move around. I went through about 3 exhaust hangers snapping prior to fitting the new mounts and I have had no problems since.

I wonder if you can use this stuff to make shock absorber bushes, as I have yet to see any for sale. The rubber bush is a common failure leading to knocking, but on the TF you need to replace the whole shocker, whereas on the F you can buy replacement bushes.