Poylbush hardnesses

[MikeNash]

Greetings Comrades!

Here's one of those "just for the record" thingies. A while ago I bought a cheap Chinese durometer i.e. a simple tool that measures the hardness in the Shore A scale of rubbers and other soft materials by pressing a shaped truncated cone into the target material and giving a reading of the depth of penetration. It looks like a micrometer clock gauge. I got it because I'd got some unexpected and unexplained vibration on fitting new engine and gearbox mounts, see here
http://www.mmoc.org.uk/viewtopic.php?f= ... ss#p576790

but then I got the bug and started prodding everthing I could find

So using the Shore A hardness scale we have for

1. Yellow rear damper links from ESM, 90
2. Black bushes from Minor Mania 95-100
3. Red ESM bushes 80-85
4. Green Bull Motif bushes 85-90
5. ESM rubber spring pad 72-73
6. ESM poly spring pad 89-93
7. NOS rear damper link bush 65-70
8. Michelin "sticky" slick tyre 60.

Now I'm not sure what this all means except that the hardnesses are all over the place and probably we need to be more knowledgeable in whatever we intend to fit. The above was just a play about with a few bushes that "Phil the Hill" had lying around and a more structured approach is, of course, required.

But I hope its got a few of you interested in the subject, MikeN.

[Declan_Burns]

Mike,
Well done-that is interesting.
Can you add the tie bar bushes to that list?
Regards
Declan

[MikeNash]

Declan,
At last got access to the front bush on the tie bar on my 1963 Trav and get a figure of 75 on the Shore A scale. How old the bush is I don't know, probably something over ten years since the tie rod bushes are showing surface cracks. I assume that in this role the rubber used shouldn't have much "give" so we might expect a high Shore hardness value. And do rubbers harden with age?

I apologise for the delay in answering you but the foot of my durometer is 18mm in diameter which prevented me getting it flush with the bush for a good reading. The retaining "penny" washer had to be moved but the securing stiff nut needed a couple of days of soaking in penetrating oil to allow it to be removed!

Regards, MikeN.

[Declan_Burns]

Thanks Mike,
I will do a few tests on tie bar bushes in the next couple of weeks as I have the mould.
These have been on my car since 2011 and are still perfect.
Regards
Declan[frame][/frame]
The mould

[frame][/frame]

Finished bush in Urethane 60 shore (if my memory serves me correctly)[frame][/frame]

[M25VAN]

How well do you find that the bushes seat Declan? Unlike yours, I have noticed that some tie rod bushes don't have any raised area to fit in the hole of the front mounting and rely on just sitting in the cupped washers. I had a tie bar wear quite a lot because this type of bush without the shoulder was able to move around. This is an image of a superflex bush to show the raised area and some shaping to match the dish of the locating washer.[frame][/frame]

[Declan_Burns]

Don,
Although they don't look professional, I'm quite happy with them and they seat quite well. I have ordered some polyurethane and will mould a few test pieces when it arrives. I will post pics of the results.

Regards
Declan

[philthehill]

Mike
I have found a NOS original MOWOG tie bar bush Pt No: ACA5264. The raised centre is 1.7mm in height.
I have also found several tie rod bushes enbosed with MOWOG Pt No: 135072. They are slightly thicker and do not have the raised part to insert into the tie bar chassis bracket either Pt No: AAA1530/31 but they do sit nicely in the cups of the chassis bracket.
If you want to shore A test them you are very welcome.
Phil

[M25VAN]

Don,
Although they don't look professional, I'm quite happy with them and they seat quite well. I have ordered some polyurethane and will mould a few test pieces when it arrives. I will post pics of the results.

Regards
Declan

They look pretty good to me Declan, just not as shiny as the Superflex ones.

Mike
I have found a NOS original MOWOG tie bar bush Pt No: ACA5264. The raised centre is 1.7mm in height.
I have also found several tie rod bushes enbosed with MOWOG Pt No: 135072. They are slightly thicker and do not have the raised part to insert into the tie bar chassis bracket either Pt No: AAA1530/31 but they do sit nicely in the cups of the chassis bracket.
If you want to shore A test them you are very welcome.
Phil

I think the cups on my chassis brackets don't have much dish left on them and if the front tie rod nut is not up tight they allow movement. Your adapted mini tie rod front mounting wouldn't have this problem.

[MikeNash]

Declan,
I see you've a castellated bolt on the tie bar which is secured with a split pin. Mine uses a stiff nut, see here[frame][/frame] (please ignore the rust!)

Your system (the original?) fixes the position of the nut whereas mine will allow the nut to be screwed down as far as you dare and thereby over compress the rubber bushes - as I fear it has been done. (You've also got a washer between the rear rubber bush and the chassis.) Having seen yours I've not done mine up as tight as it was, and indeed, had been for at least two decades. Just visible are the cracks in the rubbers which show less now that they're not over tightened.

I'd like your corporate comment, gentlemen, as to whether I'm right! Yours thanking in advance, MikeN.

PS Phil, I'll catch up with you on your NOS bushes shortly; family life is getting in the way!

[bmcecosse]

The more you tighten that - the better the castor angle - so TIGHT is good. But I'm surprised it doesn't bottom out on the end of the thread - however that washer in the wrong place is definitely not a good idea......

[philthehill]

Mike
The tie bar bracket comes fitted with concave cup washers spot welded in place either side of the main body of the bracket as standard. See attached link:-
http://morrisminorspares.co.uk/shop/pro ... c0e7e85436
Both yours and Declan's tie bar brackets are as they should be.
It does not matter if you have either a castellated or self locking nut the nut should be done up tight. There is no torque given for the tie bar front nut.
What I have found is that there have been at least two different tie bar bushes supplied - those with the raised centre to assist the bushes location in the bracket cup washer at 13.5mm (height) and those without the raised central at 21.3mm (height).
Those thicker bushes will have to be very compressed for the nut to be done up sufficiently.
Phil

[bmcecosse]

Yes - the 'cup' washers on the bracket - but that picture appears to show an EXTRA washer on the 'inside' which won't be helping the castor angle at all.

[philthehill]

I am certain that you will find that the extra washer is the smaller diameter of the cup washer.
The height of the cup washer from the main face of a genuine NOS BL bracket is 4.5mm.
Having the ability to lengthen or shorten the tie rod to get the caster angle correct or increase/de-crease is a bonus and can be easily achieved using a combination of Minor and classic mini tie rods.
Phil

[bmcecosse]

But also simply by varying (or even deleting) the little rectangular block where the rod yoke fixes to the lower suspension arm. But usually a decent application of negative camber produces enough castor angle anyway without doing anything else -for road use anyway!

[philthehill]

The problem with varying the thickness of the little block (Pt No: ACA5279) located between the tie bar bracket (Pt No: AAA2082) and the thin suspension arm is that even in its normal thickness of 6.2mm it bends when assembled, the resistance to bending is not helped by the lack of metal at the sides of the block which was done on purpose by BMC to enable the block to fit into the 'U' of the thin arm as part of the conversion from screw threaded top trunnion to rubber bushes.
Reducing the thickness of the block allows it to bend even easier and possibly break in half and fall out.
Deleting the block completely is not advised as it will put too much strain on the eye bolt bushes.
As advised above increasing the negative camber will produce enough caster angle for road use.
What ever way you try to increase caster angle you will need to get the steering angles (and tracked if spacing the eye bolts) checked out at your local steering geometry shop or you may well end up with a car that is not very steerable.
Phil

[bmcecosse]

Indeed I have had the 'fork' break - there's no doubt the later Mini arrangement is better - and probably why they didn't copy the Minor fork. But a slightly larger HT bolt is advised !

[Declan_Burns]

Here's a test bush in Shore 60. Not quite industrial quality but it seems to be the right grade.
Regards
Declan[frame][/frame]