Upper Fulcrum Shaft Bushes C8672 - Sloppy Bores ?

[rfs1957]

I haven't got to the bottom of this yet, but thought it worth flagging up in case anyone else is rebuilding this area on the car.

I've got both my front upper wishbones off, and am fitting the adjustable camber spindles C15369ADJ from SNGB.

(More on these later, elsewhere, but it should be grasped that the "movement" quoted as 6.90mm is very misleading ; in fact the max available is only 6.40mm, and this is split either side of a neutral zero - so whatever you had with standard spindles, you can actually only move 3.20mm either way. As we're all trying to dial in negative camber (for radials), in practice this is less than 1°..........)

But I digress.

The new C8672 bonded-bushes that I have (from a usual) are such a sloppy fit on the fulcrum shafts that I got the vernier and the mike out.

Their bores are in the 16.10 - 16.20mm range (including quite appalling machining in the bores) wheras the shafts that run in them are around 15.86mm.

That shaft diameter is confirmed by other / older shafts I've measured.

Granted the "spacers" that form the cores of these are meant to be tightened up HARD, but there is no reason for that much slop, save sloppy machining.

The previous ones that I removed (imprinted METALASTIK, age unknown) have bores that are a satisfactorily close-fit, around 15.90mm.

Watch this space.

[mgcjag]

Rory..are the C8672 you purchased genuine OEM or aftermarket C8672*...Steve

[Gfhug]

One would hope after market ones would still fit properly, especially if being sold by the same company that is selling the OEM parts!

Geoff

[mgcjag]

You can hope Geoff...but we all know that after market parts typically are not correct.....as an example the SNG website actually give the dimension of their after market upper bush....I have discussed this with suppliers and they give buyers the cheaper or more expensive options.....in the long run though they are cheaper for a reason.....Steve

[Gfhug]

I notice Polybush sell a set of C8672 for £46.10 + vat. SNGB sell individual ones at £17.80 (but that does include vat ). Frustrating I know but is it worth asking Polybush for sizes?
Also SNGB seem to only sell C8672* aftermarket ones (or the Polys).

Geoff

[rfs1957]

Not sure what version of those bushes I was fitting, and I may even have had them in stock for a few years before I fitted them .........

SNGB through their QC guy are adamant that they sorted all the issues around these bushes years ago, so it would appear that we can now order either Poly C8672U or standard C8672* (actually invoiced as C8672A) with a clear conscience.

The C8672* are said to have an ID of around 16.01mm, hence not the (mad) 16.23mm shown on their web-site, which is quoted for both the Std and the Poly.

I ordered that version as, correctly produced, I can't see where the upgrade in four-times the price might lie.

PS - I bet that on a Porsche you wouldn't be buying bushes at 16.01mm, never mind 16.23mm, running on shafts at 15.86mm ........... but maybe the bushes would be £50 each After all, it does cost a LOT more to make a smaller hole .............

[rfs1957]

You have to hand it to SNGB, sometimes .......... I ordered their standard bushes on Thursday morning and had them fitted by Friday lunchtime, UPS delivery direct from their depot in Holland.

They look well-made, and the bores - cleanly machined - are a snug fit on the shafts.



Anyone short of ideas for their X-mas present should leave a picture of one of these lying around, brilliant piece of kit.



Plus, when things need a jerk, a copper hammer on the crown does the trick.

[Philippe-J.]

Hi Rory,

this shot of a bush fitted in a block had me interested as it illustrates the concern I am facing at the moment.
As with mines the rubber got over the inner bore when it was squeezed into the block, by +/- 2 mm.
Can you then achieve that the washers be in contact with the inner metallic bore of the bushes when you tight the slotted nut on the shaft (according to workshop manual page J.10)?
I explained my problem in another thread by I jump to yours as you are at this very stage yourself.
Thanks for your explanations.

[rfs1957]

Salut Philippe,

The rubber is deliberately longer than it's interior sleeve, so that tightening the nut crushes the excess, increasing its diameter, so that you effectively end up with a stepped or H shaped rubber, whose shoulders act to keep the bush centered in the block.

Tightening up the nuts is therefore not difficult, and the crushing effect is normal.

Good luck.

Rory

[mgcjag]

Hi Philippe note that you fo not fully tighten the bushes untill you ride is correct and the car then sitting on the ground....Steve

[Philippe-J.]

"Tightening up the nuts is therefore not difficult"
--> you must be very strong! I have the feeling that the excess rubber is too thick to allow the nut tightening to push the washer into contact with the inner sleeve. Or even to just clear the hole in the shaft for the split pin...
I measured a lower sleeve length of ~ 46.9 mm when the length of the rubber in the block is 52.3 mm. So I have to crush 5.4 mm of rubber, which I find quite big.
Or should a certain shoulder of rubber remain also between the washer and the sleeve, contrary to the figure in the workshop manual?



Steve: I am aware that I should tight all the suspension only under full weigh of the car, which is far away in my future

[mgcjag]

Hi Phillipe....what bushes are you useing and where did you get them...part number please..and a photo might help...Steve

[Philippe-J.]

Steve,

these are lower wishbone bushes (C8673) and, in a lesser way, upper wishbone bushes (C8672). I had them from SNG, in the standard option.
Here is a shot of one of them in situation:



You can see that the rubber bead is quite thick

Regards.

[mgcjag]

Looks normal to me......Steve

[Phil P]

Hi Philippe-J,
The objective of the bush is to isolate suspension from the frame and provide compliance during movement of the suspension arms. There has to be an amount of rubber between the washers and the fulcrum block/frame mount otherwise there would be no isolation.
The section Fig. 6 is not contrary to what you have in the picture but describes it exactly.
Yours,
Phil

[Gfhug]

And a reminder nuts on some suspension parts should not be tightened up and split-pinned until full weight on the wheels and if possible driven a short distance to fully settle everything.

Geoff

[Philippe-J.]

Thank you all for your responses.
Just to make it clear, you confirm that the following situation:



must be avoided?
That's the situation I dread when I see how thick my rubber beads are and reluctant to being crushed under slotted nut tightening

[mgcjag]

Hi Phillipe....can we be sure no rubber gets trapped...no..unless you then undo and check....however most will fully tighten the nut to lock the washer against the sleeve...if a tiny film of rubber is trapped between washer and sleeve I don't see it causing a problem...Steve

[Philippe-J.]

Thank you Steve, that's sort of a relief!
I'll try and tighten as full as I can with the suspensions out of the car. It will be easier to assess the residual rubber film trapped. If tiny (I'll see that in a few days ) , then I'll just have to untighten, install the suspensions on the frames, and wait for the car to be completed, and driven a short distance, before fully tighten and split-pin the slotted nuts.

[rfs1957]

The ones I’ve just bought are bog-standard ones, of recent fabrication, via SNGB.

There was relatively little excess width of rubber beyond the centre sleeve, and there was no tendency for any rubber to get trapped - and in any case, the centre sleeve is of such a thin section that it will go like a knife through butter through any rubber that gets in its way.

You should be able to tighten those end-nuts up good and hard, the whole point of this chain of components is that the shaft and the sleeves become one continuous block.

The nuts are easy enough to get at on the left, and on the front right, whereas the rear right one, under the carbs, requires - I found - a careful choice of socket (3/4” AF) and extension in order to be able to get a second hand on the head of the ratchet and apply a proper torque.

Like Steve says, you wait until the car is sitting under its own weight before the final tightening, the point is that the shear in the rubbers is then shared between upward and downward movements of the suspension, whereas if to lock them when the suspension is on full droop then the rubbers get over-stressed, and eventually torn, because the angular rotation imposed on them is all one-way, and exceeds their elastic capacity.

Bon courage.