Clutch drive straps - MiniSpares parts

[Benny]

Ianh1968,

What you don't seem to be realizing is that my picture above includes 0.170" spacers ON TOP OF THE HORNS in an attempt to get the drive straps flat. When I remove them, I will get additional compression/flattening on the diaphragm spring, and would only then need to shorten the spacers to keep the straps flat.

We are really saying the same thing, but my 'horns' are nowhere near as far out as you currently think they are.

[ricardo]

Benny, ian is correct, but maybe we didn't understand one thing. Forget for a moment the drive straps levels, washers and spacers size and concentrate only on the diaphragm spring.

When you assemble it like mine below (clutch plate - friction disc - flywheel - drive straps bolted ONLY between horns and diaphragm - diaphram - bolts at 16lbft), does it make the diaphragm spring go beyond the flat level - that is, spring turning gently towards the diaphragm release bearing side?

If that's the case, then I understand the need of 'increasing the height of the horns' to bring back the spring flat, but I think the common solution is to machine the friction disc surface of the clutch plate. That would release the extra compression without the need of washers.

http://s1212.photobucket.com/user/rsn-mk1/media/MR-56-35/MR-56-35_0700_zps53298c5d.jpg.html

I have the exact same parts you have in the garage, bought a month ago from Minispares. I'll do a mockup tomorrow to see how it turns. I'll post some pictures.

[Benny]

Ok, here is an updated picture that support my argument. With the 0.170" washers removed from the horns, the diaphragm spring flattens out considerably. For testing purposes, I also removed one of the straps, which gave me an additional 0.031" of compression, and the diaphragm was DEAD-FLAT....possibly slightly beyond flat.

So, perhaps my set-up could be optimized by taking 0.025" off the clutch plate horns, but at the moment, I'm having a hard time buying the idea that 0.025" is going to be a game-changer on a road going Mini. At the very least, my set-up is much closer to optimized than I believe Ian previously thought.

[ianh1968]

Deleted

[Benny]

Benny, we are trying to help you here, but YOU are not understanding the concept of which
part is the ACTUAL spring which needs to be flat

Believe me, after about my second post, I fully understand what is meant by 'getting the diaphragm flat'. Look at my second pictures vs my first....the diaphragm spring is compressed an additional 0.170" in the second pic, and is SIGNIFICANTLY flatter. As I said in my last post, with an additional 0.030" of compression, it may even be going beyond flat.

I'm a mechanical engineer....I'm under no illusion that the straps are providing the clamping force. I appreciate the help, but I don't think you are reading my posts carefully before bashing on your keyboard.

We are virtually in total agreement, you just don't realize it.

[ricardo]

Ok, good we all understand and agree.

As promised, some pictures of my parts, similar to yours, bought last month from Minispares (flywheel made 15-07-2013 as stated in the box).



Each case is a case of course, but when I rebuild this clutch, the horns will be machined.

Another thing, I was wrong when I said the short bolts were for the horns, it is the other way around. So, not as just I pictured above. Just figgured it out while doing the mockup, the horns even have the recesses for the bolts spacer. This is just a side note to correct my previous coment about the bolts.

[Benny]

Another thing, I was wrong when I said the short bolts were for the horns, it is the other way around. So, not as just I pictured above. Just figgured it out while doing the mockup, the horns even have the recesses for the bolts spacer. This is just a side note to correct my previous coment about the bolts.

Yes, I caught that, but forgot to comment. With my short bolts going into the flywheel, they pass all the way through, so there would be no benefit to the longer bolts in that position. With the spacers shortened, that situation will even be exacerbated.

[ianh1968]

Benny, I have deleted the text of my previous post so as not to cause offence...

Sorry if this was the case

I have left the photo as this will help demonstrate to others among us about
what is meant by "flat". This spring is not yet flat, the amount of "not flat" being
the difference in height between the middle and lower blobs...

If you want to test the 0.030" removal theory, why not do what I did with my dummy washers...
As an engineer, you should have access to plenty of shim - just stick in a few pieces to
make your friction disk "thicker" effectively pulling the spring down onto the flywheel by the
same amount. If the spring is then flat, then 0.030" is the figure to go for... If it still isn't,
try thicker shim until it is...

It's a bit difficult to see, I know, and a bit of engine builder's judgement is required, but mine
ended up requiring 0.050" removing with all brand new parts being used.

You already worked out that only putting in one layer of straps effectively causes the spring
to clamp up more. I have seen tuning articles in the past which suggest using three layers
instead of the standard two. None of these articles mentions machining the horns by the same
amount as the thickness of one strap layer. Well, if only using one layer increases the clamping
with no other changes, adding a layer with no other changes will decrease the clamping.

I fell into this trap once - I was not aware of "getting the spring flat" at the time so my backplate
was "as bought" - I then added an extra layer of straps because that's what the tuners suggest.

It was only after not many miles when my clutch started slipping that I realised that the few
thou thickness of that extra strap layer was causing a noticable pressure reduction in the spring.

The thickness of one strap is about 0.030", so yes, 0.025" could make a difference, a lot of
difference, if the clutch is assembled with the spring nowhere near to being flat.

Mostly, I have always used the solid type disks, but on one engine I managed to put in a
standard type one without realising. The result of using this is shown in the photo...

Apart from a lot of dust, there was very little trace of the rest of the disk. It appeared to
have literally disappeared in a puff of smoke.



... and I still drove the car home like it...

Standard type disk:
http://www.minispares.com/product/classic/C-AHT595.aspx

Uprated type disk:
http://www.minispares.com/Product.aspx?pid=35698

The moral of this story is to always use a decent disk...

[Spider]

So, perhaps my set-up could be optimized by taking 0.025" off the clutch plate horns, but at the moment, I'm having a hard time buying the idea that 0.025" is going to be a game-changer on a road going Mini.

From my own experience, as much as that certainly did make a difference for me.

ianh1968, last time I saw a plate like that, it was from shagged primary gear bushes. Nice effort

[Benny]

Ian,

No offense taken, and again, I really appreciate your efforts to help.

I'm swinging by my retired tool-maker friend's house tomorrow after work. He's got some proper measuring equipment, a mill, and a lathe in his home garage, so we'll get this properly sorted between us.

[1071 S]

http://www.minimania.com/imagesbig/fig8.gif

Go here - this is the raw data that describes the relation ship between clamping pressure and backplate displacement.

Thanks to an enterprising Canadian...

Suffice to say that the difference between a diaphragm as pictured - and one set up flat - is amazing. As is the effect on the life of the current release bearings..

Cheers, Ian