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PostPosted: Sat Jun 27, 2020 8:58 am 
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Joined: Fri Mar 19, 2004 6:19 pm
Posts: 39151
Location: near Baulkham Hills, NSW
Maximum clamping force is achieved when the conical diaphragm spring is flat.
With new original parts this was so. However after 50 years of wear, flywheel refacing, and backplate refacing, this is seldom achieved. Unless you get a clutch shop familiar with Minis to set it up. Or do the following:

The 3 backplate lugs need refacing so that the spring is flat when assembled with the drive straps, backplate, and a new clutch driven plate.
To check this, after assembly on the bench I hold a 3mm drill against the spring. If spring is flat the drill will be parallel to the flywheel face.
If not, I remove 3 straps and assemble again and check spring.
Each strap is .035" thick. So I can guesstimate how much needs to be machined from the 3 lugs to make spring flat with 6 straps in.
Take all 6 straps out to check if needed.
I have seen 2 clutches that needed .070" off the lugs!!
I set the backplate flat on the mill and mill the lugs equally. I have a digital display on the spindle axis for height.
Do not set the spring beyond flat!! A little less is fine.

Engine builders with a hydraulic press (like GR) measure the amount to remove by using a dial gauge to measure how far the diaphragm is pressed down to get the spring flat.
I don't have a press!

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Peak ignition system fitted. :mrgreen:


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