22 replies to this topic

[colinu]

Folks,

 

Removed the flywheel today to fit a new clutch. Putting it all back together I'm now questioning if it was assembled correctly in the first place. Question really relates to drive straps and also the diaphragm plate/spring. Take a look at the first photo below...

 

 

That's taken with the backplate supported off my workbench, new friction plate sitting on top of it, then the flywheel resting on top of that. You'll see a gap between the backplate post and the drive strap (approx 0.8mm ... almost the thickness of a single drive strap). I understand that the gap should be zero, so do I:

a) add 0.8mm thick washer in the gap, or

b) do I machine down the 3/8" spacer that's bolting the other end of the drive strap to the flywheel... or

c) is either method OK?

 

Or shouldn't I be thinking about setting the above until I've looked at the assembly with the diaphragm spring/housing sitting on top of it (see 2nd photo)?

 

 

There's a gap of approx 2mm between the top of the drive strap and diaphragm housing. I'm guessing that's too small (even if I took into account the other .8mm under the strap that a total of <3mm ).

Now here's the bit I've never fully understood... am I correct in thinking that when this assembly is bolted together that diaphragm spring should be compressed so that it is no longer conical, instead flattened so that is is parallel with the flywheel face. Yes? If so then I guess that's why I've seen a video and a few posts with the assembly in a pillar press and using a DTI gauge to measure how much movement is needed to 'make things flat'.

Eyeballing my diaphragm spring it looks like it would take 4mm compression to flatten it. If that's the case then it won't be fully flat when I clamp this assembly together ('because there's <3mm gap in my assembly).

 

So... if the above is sound reasoning on my behalf, then should I machine down the backplate posts, or use only 2 drive straps per post (currently using 3 but going to 2 might make the gap big enough???), or should I be doing something else?

 

And if it's of any relevance it's a 9.5lb lightweight flywheel, AP Road/Rally clutch plate, standard back plate, orange diaphragm spring, 1380cc/90+bhp, 3.44cwp.

 

   Cheers,

   Colin.

 

P.S.

And why was I digging around in the clutch today... trying to see if it had anything to do with a "dry clatter" noise I'm hearing very occasionally for a second or two when bringing the clutch back up (i.e. re-engaging drive). I've only heard this happen when in reverse, or when going into 1st immediately after reverse. I say 'dry clatter' as it doesn't sound like the oil-damped sound I'd expect if it were inside the gearbox. However, when I stripped the clutch/flywheel down all looked pretty OK (except for the drive strap question above). So if it is not related to any of the above then I'm guessing it's most likely a problem with the idler gear/bearing 

Edited by colinu, 03 October 2016 - 07:30 AM.

[mini13]

as you saywith the assembly bolted up the spring should be flat or close to it, once yo  have that then the spacer at the other end of the drivs straps should be machined so the straps sit pretty much flat. I prefer to have the spaccer a little long so as the clutch plate wears they will end up flat, buit we are lonly talking about 1mm ish.

 

yeah the clatter is probably the idler,

[nicklouse]

Looks ok to me.

Using more or less straps will change nothing.

[tiger99]

Remember that the drive straps are intentionally flexible. 1mm is hardly important.

[colinu]

Tiger99: 1mm... probably not important to drive straps, but I still think I need to remove material from the post otherwise the diaphragm won't be compressed flat (i.e. won't have the full clamping pressure expected of the diaphragm spring... which kind of defeats the purpose of fitting an orange spring???).

 

Mini13: Yes I feared all along it's probably the idler causing the clatter... looking on the bright side it finally gives me an excuse to remove those straight cut drops and replace them with standard (quieter!) helical ones.

[nicklouse]

Makes no difference to the diaphragm. It will still clamp flat.

[tiger99]

I think that apart from your idler gear, which you are addressing, you probably don't have a problem. Diaphragms are not compressed to completely flat as a general rule. Bad things might happen if they are. They have two stable states....

Don't worry, more confidence will come from more experience, and you should always feel free to ask when in doubt. Your question was in no way daft. The topic is actually rather interesting, and it could well happen that there could be serious dimensional problems, with the state of parts supply these days.

[Spider]

Ideally, I'd shorten the spacers a little, but it really won't make that much difference as it is.

[colinu]

Thanks for all the advice As you say there's probably no real need to do any machining... after all this clutch has/is working perfectly well for me. I guess this post was more about answering the question of "if given a mix of standard and performance parts what machining etc is needed to make them work together 'perfectly' ". Of course 'perfect' changes as the clutch plate wears, so there's never really going to be a consistent holy grail!
Odds are I will mill down the spacers a little tonight, and if I can find a good way to clamp the backplate to the milll table I'll take drive-strap's width off the height of its posts (recommended if using 3 straps).

And then the joy of hauling out the engine and inspecting the idler...

[ACDodd]

Checks must be made with the assembly bolted together as the fiction disc compresses when clamped up. I am for flat diaphragm and straps when all bolted up. Adding extra drive straps changes the diaphragm position by a lot. getting this wrong results in wiped out crank washers and an unnecessarily heavy clutch.

 

I do not agree with most of the responses above.

 

I did a miniworld tech article on this a few years back.

 

http://www.minimania...FAQ__non_Verto_

 

 

 

 

AC

Edited by ACDodd, 03 October 2016 - 09:45 PM.

[nicklouse]

Agreed on extra drive straps and diaphragm position.

But will not change the perceived gap as shown.

Just rewatched the video.

Need to think and will have questions.

Edited by nicklouse, 03 October 2016 - 10:22 PM.

[colinu]

AC ... That's the very video that made me start thinking about about this! At the time I did't fully understand exactly what was being done - especially how the diaphragm could be set to flat in that press if the posts were still too tall. But looking at that video for the umpteenth time it looks like the flywheel is resting on the 'lips' of the press table and the backplate is free to move below it - correct???

 

So would my conclusions be correct?...

1. back plate post height determines how much the diaphragm is flattened (i.e. add/remove heigh so that it is flat when the fly/clutch/backplate/straps are all bolted together)
2. drive straps should be flat otherwise you run the risk of a hard-to-disengage dragging clutch (in my case I should remove material from the spacers)

Correct?

 

Oh and wiped out crank thrust washers... I don't want to go there again (that was the cause of this engine needing a rebuild shortly after I bought it).

[ACDodd]

Yes the back plate is free to move in the video.

1. Yes the backplate post height determines the flatness of the diaphragm

2. Not sure about hard to disengage or dragging clutch, bit can cause clutch slip in use. Flat is what to aim for

Look at the minimania link for a en excellent investigation piece performed many years ago which explains why the diaphragm needs to be flat

Just to add, every one I build is wrong and needs adjusting.

Ac

Edited by ACDodd, 04 October 2016 - 06:09 AM.

[colinu]

AC - Thanks for the reply. I measured my mine up this evening and looks like I need to remove 85thou from the post to get the diaphragm flat. Hoping to get it on a lathe at work before the end of this week.

[Spider]

 the diaphragm needs to be flat

Just to add, every one I build is wrong and needs adjusting.

Ac

 

I find the same.