Morris Minor Owners Club

Hahahaha

Whilst not up to lab standards you can check the relative hardness of 'Poly Bushes' (or rubber bushes) by using a drill press, a blunt centre punch, a pair of 'V' blocks, a dial gauge and a spring balance.
For example the relative hardness of the eye bolt poly bushes can be determined by the following process:-
Place blunt centre punch in drill press chuck.
Place poly bush on eye bolt pin and place ends of pin in 'V' blocks and position under drill press chuck/blunt centre punch.
Place dial gauge on top of drill press chuck.
Place spring balance on drill press handle.
Pull down drill press handle until the end of the blunt centre punch just touches surface of bush but does not indent the bush surface. Note dial gauge reading.
Pull down drill press handle by using the spring balance a further predetermined amount and note spring balance reading. That first spring balance reading will give you your datum point. Make sure that the spring balance is retained in the same place on the drill press handle when applying the load to the different bushes otherwise the readings will not be accurate. Also the same predetermined amount of downward movement of the drill press chuck must be used on all comparison tests.
Replace bush with one from another supplier (different colour) and repeat test.
Repeat tests until all bushes have been compared.
You should now be able to see from the readings that you have noted which bushes are the harder and which are the softer.
So long as you repeat the tests using the same process and in the same manner you will have a comparison chart that is more than adequate for the needs of fitting poly bushes to a Minor or any other vehicle.
Carrying out the above process you have completed a simplified Shore durometer test!

Declan, do you need to coat the molds w/any type of release agent?

Richard, that really is a most helpful chart. It's a shame that some of the parts suppliers don't publish useful information by default! Would it be possible to include the hardness rating of standard rubber bushes in the chart for ease of comparison? That info might be somewhere earlier in this thread, but if it is, then I apologise for missing it. Thanks again for excellent work.

The problem with modern rubber bushes isn't about the hardness though, it's about durability.
You can feel the difference in your hand, I just found some tie bar bushes while looking for other stuff in my garage, flipping firm, but not rock hard like the nylon ones I have. I think I got them because they are Black.

katy wrote:Declan, do you need to coat the molds w/any type of release agent?

Katy,
Yes, you need a release agent. I have used both wax and film type release agents-both work well.
Regards
Declan

Anyone wanting to know more about poly bushes should contact Jono at JLH - he has a wealth of inside information on these bushes and is happy to share ! http://www.jlhmorrisminors.co.uk/

Latest update on the supplier replies:
[frame][/frame]
Not very impressive really. Makes you wonder how much they understand about what they are claiming and selling?

Polybush gets my vote the next time I need any replacement bushes.

If the Shore hardness reading/spec is so important and some suppliers are not able to give a hardness spec use the procedure I described above to determine the hardness of those bushes without a Shore hardness specification.
You can use the Poly Bush BLUE at 65 Shore and Poly Bush RED at 85 Shore as the upper and lower datum points.
When you have determined a hardness/reading of the Blue and Red Poly Bushes using the process described above use the same procedure on those bushes provided by other suppliers without a Shore Hardness number. When all bushes have been tested it should be easy to transpose/relate the readings you have obtained on the other bushes to readings obtained for the Poly Bush RED and BLUE bushes and where they sit on the Shore hardness scale. The other bushes have to be below the BLUE or between the BLUE and RED or above the RED or even may be the same. It is all a matter of relationship to the datum points!
If you use a fine digital readout spring balance as say used by fishermen and use an adjustable turnbuckle between the spring balance and a fixed point you should be able to get a very accurate reading.
I agree with MarkyB hardness does not mean durability as more than just hardness effects a Poly Bushes (used in a generic term) resistance to wear i.e. environment, how they are fitted etc. Durability is the key!
Please note:- I am not volunteering to do any testing as I have more than enough to do on my Minor

One thing that puzzles me in say the eyebolt application - as the lower suspension arm moves up and down - is the movement supposed to be taken within the urethane material - or is there intended to be relative movement between the bush and the pin and/or the suspension arm?

One problem I am finding with Poly Bushes and related to the front suspension eye bolt is that when fitted the Poly Bushes do not deform like the old rubber bushes (because they are so hard) to allow the front (pressed plate) suspension arm to come up easily against the front shoulder of the eye bolt fulcrum pin. The suspension arm when bolted up should fit against the shoulder. This could lead to problems with the durability of the Poly Bush and could lead to the loss of the securing nut if the nut had been considered to be done up tight but has not pressed the front arm against the pin shoulder.

Islip Minor.

Birmingham MMC do supply poly bushes. Theirs all seem to be green from my experience (the last lot I bought there anyway!).

when fitted the Poly Bushes do not deform like the old rubber bushes (because they are so hard) to allow the front (pressed plate) suspension arm to come up easily against the front shoulder of the eye bolt fulcrum pin

If there is no perceptible give in them you may be able to file some off, I wouldn't be happy doing this though as I'm fairly sure the compressed rubber is supposed to twist rather than act as a bearing surface.
If you can still get them J2 van rear spring Metalastic bushes work great and seem to last for ever.

MarkyB
What I have done to get over the problem on my modified minor (I thought I would try Poly Bushes as a change from the hard nylon one piece bushes previously fitted) was to manufacture some new slightly longer (between the shoulders) eye bolt trunion pins so that the front plate suspension arm is retained hard against the front shoulder of the longer pin whilst still keeping lateral pressure on the Poly Bushes. This modification was made possible by my revision of the antiroll bar mountings/links where connected to the lower suspension arms.

And do the two parts of the lower arm still butt up tight together?

Yes - but with spacers between the rear and front arms where they are bolted through and between the front arm and the outer trunnion pin front thrust washer of a thickness corresponding to the increase in length of the eye bolt trunnion pin so the arms are kept parallel. The spacer between the tie rod mounting bracket and front arm has been removed (but could be reduced in thickness) which is no problem as I have adjustable tie rods so can still obtain the correct caster angle. That spacer was not fitted previous to the fitting of rubber top bushes so its removal is acceptable. The rear cast suspension arm is relieved between the inner clamping bolt and the tie rod mounting bracket so a continuous spacer is not required nor would it be of any benefit. The rear arm is set in its original position and used as the datum point with only the front arm moved slightly forward so keeping the original steering geometry.

You could just use washers rather than longer special pin.........but frankly - would seem much easier to simply shorten the poly bush slightly.....

The spacers and Poly Bushes are only part of the story as this mod is part of my revised anti-roll bar link fittings and attachment to the lower suspension arm(s) so just fitting washers or shortening the bush would not be appropriate in this case.

MarkyB wrote:Some of the poly bushes I've got feel like they have been machined out of nylon, no give at all, too far from what was fitted originally for my taste.
Comfort grade sounds fine given the quality of rubber parts these days.

Someone did make nylon bushes at one point - very uncomfortable.

One of the manufacturers I've spoken to said their polybushes would never need greasing. My own experience is that the bushes need copper grease. I had horrendous noises coming from the suspension but of a type that didn't sound like it was suspension or bushes. It sounded more like the floor of the car was being over-strained. If you've ever had disc brakes that squealed it gives some idea of the level and annoyance ungreased bushes can produce.

Dismantling and re-greasing silenced this.