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MG MGB Technical - Polyurethane engine mount

Does anyone make polyurethane engine and or transmission mounts? If not how come?
Bob

I haven't seen any but if you were to put them in it would be just about like bolting the engine in solid with no mounts. The noise and vibration would drive you out of the car.
John H

John, the hot rodders and street rodders have been using these for some time without any complaints as far as I've heard. Here's an example of the common type engine mounting from Speedway Motors http://www.speedwaymotors.com/pl/122,7631_LS1andLS6-Chevy-Weld-In-Motor-Mounts.html
Looks to be the same type bushing as used in the front A frames etc.
I think the main problem for MG applications is that urethane doesn't bond well to steel like rubber does, so a urethane mount really needs to be a "confined" (that is encased in steel) mount and not a sandwich type where the steel mounting plates top and bottom are bonded to the center isolator.
Bill Young

I can understand poly cross-member pads and other suspension bushes as they give sharper response at the expense of more noise, but I can't see why anyone would want to mount the engine/gearbox in a similar fashion for road use.
Paul Hunt 2

Paul, I can think of a couple of reasons. First, as you know there are various varieties of urethane bushings, some harder than others. I would think that the urethane selected for motor mounts would be of the softer type. Second, on a lot of modified cars such as street rods clearance between the engine and chassis or body, so restricting any unnecessary movement may be a plus. I used rubber bushings for a street rod I built many years ago, but they were pretty hard and thin. I didn't seem to have any unusual harshness from engine vibration. Most engines run pretty smoothly if well tuned and balanced.
As far as increased harshness and noise from the suspension, I think you'd be surprised how many cars had urethane bushings in the suspensions in some locations from the factory. Mostly used in sway bar mounts and end links, but some others as well.
Bill Young

The main reason I would like polyurethane is durability especially the oiled soaked trans mounts.
RPB Brownlow

Just an idea: Why not just put some silicone over the rubber to protect it from the evil grease/oil etc.? I tend to think rubber is better in most cases for motor and tranny mounts. But I agree it would be nice if they didn't turn to mush. Worth a try to coat the rubber with black silicone, in my opinion.
Tom

Bob,
As Bill Young mentioned urethane is a product which is available in different grades from the rock hard used for skate board wheels down to a very soft urethane softer than engine mount rubber.

Urethane is rate by an index called a "Shore rating" and the rating about 80 is equal to engine mount rubber.
The higher the number the harder the material and many makers colour code the material to give a visual reference.

Urethane has a much longer life than rubber especially in the areas where high levels of heat are involved and it is virtually impervious to most chemicals used in cars.

Pete.
Peter Thomas

Tom,
I have done exactly that in all the cars I have owned.

I use a grease called "rubber grease" which has silicon as a base and is black so it doesn't show although there are many products on the market doing a similar job.
Try the 3M website and search there.

The way I have done it is to remove the rubber item and ) wearing a pair of disposable gloves )apply a very small amount to the item and rub it in until it vanishes.
Repeat as necessary until the grease no longer vanishes. This normally is about three coats.
The rubber should have a low sheen gloss.

With new rubber items wash them in warm soapy water until the water no longer "beads" then continue as above.
This removes the chemical residue left from the molding process.

Never use this stuff on drive belts and fluid hoses for obvious reasons.

I first used this on a set of bellows / gaiters on the steering of a DS Citroen ; a vehicle know for high under hood temperatures.
One side was treated and the other not.
The not treated side split after three years and the treated side was still fine when the car was sold six years later.
Yes we replaced the split bellows before the car was sold.

Cheers , Pete.
Peter Thomas

This thread was discussed between 09/01/2008 and 11/01/2008

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