MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Polybush - grease or no grease?

Hi Guys,

Suspension woes again. This one should be an easy one to answer.

I bought my polyurethane bushes ages ago (the orange type, from floflex I think) - but there are no fitting instructions and I remember when I did that rear suspension in the purple type, there was a white paste/grease that came with it. Nothing came with the orange ones - should there be grease or not? I'm thinking of just putting some bog standard white silicone grease on... any thoughts?

Cheers
C
Christian Carter

Ask the supplier, it's safer, that way, if there is a problem with the bushes, they can't blame you for "inappropriate" assembly!
Allan Reeling

I had the orange ones and greased them liberally with silicone, mainly for ease of assembly and water repellant purposes. No issues so far...cannot think there is any chance of a chemical reaction with the bush either.
Mark O

Yeah - or something like this white lithium grease - I use this white grease all over the car - its great for the window mechanism.




http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_categoryId_165705_productId_221665_langId_-1?istCompanyId=b8708c57-7a02-4cf6-b2c0-dc36b54a327e&istItemId=liltmr&istBid=tztx&_$$ja=cgid:5302137724tsid:35522cid:119462284lid:18283950120nw:searchcrid:21270118204dvc:cadp:1o1bku:1&gclid=CLnLqZ_fpbsCFSYHwwodpAwAcQ
Christian Carter

I rang floflex (the orange company) - they said they don't supply them with grease and that you only need it for assembly purposes if they are tight... the woman on the phone said "even washing up liquid will do"... she then consulted her friend Abi, who suggested copper slip.

Interestingly, competitor Powerflex suggest a "copper based grease" and even include some in their pack. See link below

http://www.powerflex.co.uk/road-series/fitting-guides


So at the moment, I'm inclined to use some copper slip, but I feel white lithium or silicone grease would be better.

Christian Carter


http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_219033_langId_-1_categoryId_165705
Christian Carter

I'd go with copper grease it's suitable for use with metal and can be applied as a thin film with a small brush whereas silicone grease is a lot more solid so will squash out and get everywhere and need cleaning up and white lithium comes as a spray and seems to leave a dried coating on non contact areas at least

I am biased as when I tried white lithium I didn't get along with it and gave the can away whereas I've had a can of Copper Ease for as long as I can remember - mind the tiniest spot of it where you don't want it can seem to spread over a very wide area
Nigel Atkins

more expensive but perhaps silicone oil applied with small brush or sponge

silicone - thin spray, much thicker oil, solid grease

note; silicone oil is good to use, about twice a year, on modern convertible roof seals to prevent leaking

Nigel Atkins

this edit got lost -

ETA: silicone spray is very thin WD-40 like, again a spray obviously

problem with slippy stuff is it can get everywhere making things difficult to grip and a spray gets air borne so can spread further to areas you don't want, perhaps you'd apply it with a small brush or bit of sponge
Nigel Atkins

A friend sent me this... basically saying the poly isn't going to degrade with any grease... so use what you like

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1920977

think I'm gonna use a bit of copper slip

Christian Carter

You must use a good silicon grease and lots of it. Rubber bushes work by allowing twist in the rubber martial. polybushes need to be able to slip.
Tim Dalton

Perhaps I will be using this

http://www.wickes.co.uk/silicone-lubricant-grease-500g-tub/invt/227226/
Christian Carter

fair enough but you wont need 500g, perhaps the 250g at that price (or a lot less would do)

apply it with a suitable brush and you'll have less wastage and cleaning up

the pot in my photo is 100g
Nigel Atkins

Silicone grease is supplied for easy assembly of push fit underground and above ground plastic waste pipes. GOT O YOUR LOCAL PLUMBERS MERCHANT.Cheap as chips!!
Allan Reeling

probably not as cheap as that Wickes 250g unfortunately
Nigel Atkins

I greased the superflex bushes " for live" with the silicone grease they delivered with the bushes. The superflex did fit without any fretting.
In my car it is seldom the bush that woes. In my car it is the spring.
Flip Brühl

The Wickes one is 500g
Ray Rowsell

OFFICIAL RESPONSE FROM FLOFLEX

"Hi, you would need to use a copper grease or lithium grease to help fit them

Kind regards

Rebecca"

Copper grease it is... that way I can sue their asses when the bushes melt into a blobby goo.

C
Christian Carter

There is a case for not using grease of any sort. Not because of reaction with the Poly, but because it will attract and hold road grit, which itself could grind into and damage the bushes.

I think that the principle of these Poly type bushes is that they clamp tightly into the joint, and then suspension movement is within the material itself flexing, rather than from rotation of the bush either around the inner shaft or within the outer bracket that they are supporting. This differs from a standard rubber bush where the pivoting movement is between the inner shaft and the bush, so some lubrication like copper ease is needed.

Guy Weller

Actually, it is the other way around.

Rubber bushes operate by flexing the rubber (the tightened joint grips the rubber, and, usually, the steel sleeve quickly seizes onto the bolt, and the suspension movement causes elastic distortion of the rubber material). This is the reason why the rear springs should only be torqued after the weight of the car is on it, so the rubber will be "caught" in a more or less "nominal" position.


On the other hand, Poly bushes often don't even come with a steel sleeve, and the ones that I've fitted, after torquing always allowed the pivot to rotate without twisting the poly at all. It is interesting to put the front suspension together and then flex it through its full travel without the spring to see what is going on.

The purpose for the grease, as I remember reading on one poly supplier's web site, is to prevent that movement from making noise if it slides while rotating.


Rubber will quickly degrade in the presence of oil/grease because its chemical bonds can be undone by being attacked by oils, so it ought to never be exposed to them (and this is why engine mounts fail). Poly, on the other hand, is fine with exposure to the stuff because the urethane resin is made by a catalytic reaction that can not be "undone" (almost like a thermoset resin, or, more like polyester resin).


Road grit, it is true, it will stick to the edges, but how much of it can get inside of the joint? If concerned about that, then definitely dry assembly can be tried, and, frankly might be fine, but if it makes noise you'll want to take it apart and use some kind of a dry lubricant (but not silicone, that, strangely enough, that tends to make sliding joints really noisy).



Norm
Norm Kerr

Roy,
on the linked Wickes page just below the 500g is also a 250g for £6.99
Nigel Atkins

Oh well, memory failure yet again! I did recall that there was a basic difference between the operation of rubber and Poly bushes. Just got my reasoning 180 degrees out! Thanks for re-setting my memory banks, Norm. I wonder how long that will last? ;-)

I think the bit about roadgrit was a random chunk of information that should properly be attached to a discussion on greasing of road springs (leaf)
Guy Weller

Christian,
again for applying copper grease use a very small paint brush, never the ones you get in with some tins of copper grease as they too big unless you're doing the Forth Bridge

I've still got half a tin of Copper Ease from many years ago (I wonder if it goes off?) from using a very small brush plus it stops the grease getting everywhere, a tiny spot of copper grease seems to transfer to loads of places you don't want it all at once and cover a great yardage
Nigel Atkins

I use copper ease on every nut and bolt as an aid to remove them when dissembling in the future... so i have tons of it...

doesn't go off
Christian Carter

I've managed to find the instructions for supapro bushes

Tim Dalton

thanks - good to know, to apply it to all poly on metal surfaces... which is what I had guessed
Christian Carter

Guys,

This is the set I got. I think I've got too many bushes. There appear to be twice as many as needed for the upper trunion? Am I imagining things?


http://www.ebay.co.uk/itm/MG-Midget-Front-Rear-Full-Bushes-kit-in-Polyurethane-/390378174756?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item5ae45a3924
Christian Carter

it does look like a lot of poly and metal inserts to what's usually shown but as I don't know I can only bump the thread
Nigel Atkins

(bump)

anyone

>>Christian Carter, Greater London, United Kingdom

Guys,

This is the set I got. I think I've got too many bushes. There appear to be twice as many as needed for the upper trunion? Am I imagining things?

http://www.ebay.co.uk/itm/MG-Midget-Front-Rear-Full-Bushes-kit-in-Polyurethane-/390378174756?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item5ae45a3924 <<
Nigel Atkins

I think the number number is correct. There are two for each top trunnion making 4. There are 4 each side for the 2 wishbones making 8. The others without a central sleeve are for the springs.
Bob Beaumont

No there 8 for the top trunnion? 4 too many?

Christian Carter

I only count 12 bushes in total unless the photo is misleading.
Bob Beaumont

the 4 at the back are pre assembled (ie stacked on top of each other)
Christian Carter

also, the ARB bushes are solid... presumably these need a saw cut to fit them - or are you supposed to heat them up in boiling water and stretch them over the ends?
Christian Carter

cut them with a sharp knife at what is the top when fitted - this is how they are usually are done by the manufacturer
Nigel Atkins

top when fitted... yes that is what I had intended. Thanks Nigel
Christian Carter

So - I have now fitted the inner fulcrums and thought I'd share my experience for those who have yet to undertake this - and confirm my understanding of what actually rotates and what doesnt - obviously most of you already will know how this works if you've rebuilt it, but for the benefit of those who haven't/the arcives here it is...

1. Grease or no grease and what grease? - it really doesn't matter that much, as you will see if you read to the end.

So - the polybushes are fitted to the wishbone - and then the "crush tubes" are fitted inside these. This is hard work as you are crompressing the poly up hard against the inside of the wishbone... this essentially FIXES the poly bush to the wishbone so there is no relative movement between the polybush and the wishbone... this means any grease at this point is pointless.

I found that inserting the crush tubes was hard work and required a clamp of somesort... and because of the slight taper on the bushes this made them pop out slightly - especially if I had greased them first! Mistake.

So, now its harder to fit them to the car. I found it was best to insert the poly bushes, then offer the wishbone to the car, then insert the crush tubes all from one end, using a clamp to pull them both in.

A quick one hand clamp helps with this until it gets tight and a G clamp is needed.

So, now you have the polybushes fitted and the wisbone is within its suspension mountings on the chassis. each mounting has a small hole on the inside and large on the outside - so as the suspension moves up and down the flat faces of the bushes ride against either the inside of the chassis mounts or the flat face of the tabbed washer... so these flat faces I greased with copper grease.

Now, the fulcrum pin goes through the crush tubes and its tabbed face locks into the suspension - so, the fucrum pin is fixed with no relative movement to chassis. This means the crush tubes rotate on the fulcrum pin...metal on metal contact... so I greased this area with copper grease.

Hope that helps someone in the future.


Christian Carter

"This means the crush tubes rotate on the fulcrum pin...metal on metal contact... so I greased this area with copper grease."

That's not how it's supposed to be Christian, poly or rubber bushed. The fulcrum nut is supposed to be tightened, so that it pulls the large washer surfaces tight against the shoulder of the fulcrum pin and the crush tubes. This will make all the metal bits effectively a single solid non moving part. If your crush tubes are rotating on the fulcrum pin, grease or no grease it's going to wear pretty quickly I reckon, because it's not meant to be a bearing surface.

With rubber bushes I use red rubber grease to install them, and the wishbone rotates around the bushes initially. Eventually the rubber "fixes" to the insides of the wishbones and just flexes.

I haven't used poly bushes here, but I'm pretty sure the same thing is supposed to happen, namely that the poly is supposed to flex.
Lawrence Slater

I reckon Lawrence is only partly correct. Yes the 'crush tube' should be solid with the fulcrum pins, but the bushes should not fix to either inner surfaces of the A-pans or the crush tube. If you think about the angular range of movement it's far too much for poly to flex, the polybushes must be free to rotate against their retaining surfaces. All IMO of course.
David Smith

Hi David, that's why I put fixes as "fixes". I agree they shouldn't, but I've found that after a few years or less, they have done. Mostly I think because moisture gets between the wishbones and the rubber, rust the bones and prevents the bushes slipping. That's why I use large amounts of red rubber grease to try and prevent it.
Lawrence Slater

It will with rubber bushes, agreed. The bit I disagree with is that it might with polybushes too; they are too hard to flex 30 degrees radially so the 'fixing' wont occur.
David Smith

Ah fair enough. I've never tried the polybushes there. I've got them in the top trunnion though. Have to say I don't find that much difference over the rubber. Wouldn't buy them again.
Lawrence Slater

This thread was discussed between 10/12/2013 and 15/12/2013

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now