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Blue or orange clutch diaphragm
Posted: Sun Jun 28, 2020 11:23 pm
by Minigman
At what point is a blue clutch diaphragm too weak?
1330 engine, stage 3 head, 276 cam, lightened flywheel currently fitted with an orange diaphragm.
The revs drop about 200 rpm when the clutch is depressed so I’ve had to set the idle at 1350rpm to ensure the car doesn’t stall, so I’m considering fitting a blue diaphragm to reduce the wear on the thrusts and make the car slightly better mannered.
I’ve got 92bhp and 88ftlb hence the initial decision to run with the orange, as the blue is supposedly only good up to 70ftlb.
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 7:40 am
by GraemeC
Without trying one and seeing if it slips, it’s hard to tell for definite if it would be too weak. Also depends on how well set up the flywheel and backplate are. That said, I would have thought an orange in that spec was sensible.
However, I’d be looking deeper as to why the revs drop, not just swapping the diaphragm out. If everything is right then you shouldn’t get a noticeable drop - I use a grey and have no change in tickover when the clutch is pressed.
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 7:59 am
by Blacktulip
Minispares say the blue standard plate is good for 70lb/ft if torque so you would need an orange one.
Strange why the revs drop so low. Have you got the correct sized thrust washers on the crank?
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 11:40 am
by Minigman
Yes, end float is bang on 4 thou.
It seems a very common issue when you google it.
Calver says blue is good for 110bhp but no mention of torque which is a more important consideration. I’d assume any 110bhp engine will be making a lot more than 70ftlb.
Might just give it a go and see what happens.
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 12:38 pm
by Minigman
GraemeC wrote: ↑Mon Jun 29, 2020 7:40 am
Without trying one and seeing if it slips, it’s hard to tell for definite if it would be too weak. Also depends on how well set up the flywheel and backplate are. That said, I would have thought an orange in that spec was sensible.
However, I’d be looking deeper as to why the revs drop, not just swapping the diaphragm out. If everything is right then you shouldn’t get a noticeable drop - I use a grey and have no change in tickover when the clutch is pressed.
I see your point. It’s been a problem for a while and was a problem before my idler gear bearing gave up the ghost after just 1200 miles. Everyone told me the thrusts would be knackered but when dismantling the engine to replace the destroyed box, transfer case and idler gear they were still good and had 4 thou end float. I replaced them anyway and rechecked the end float. And yes they are 100% the right way round.
Reading the turbo minis forum who tend to use heavier diaphragms this is a common problem and a few have split there engines only to find no obvious internal problems.
I’ve had the flywheel / clutch / primary gear out at least 4 times in the last couple of months, and gone on the replace all the hydraulics and all clutch components (arm, plunger, release bearing, clevis pins etc) and haven’t found anything obvious. Now I have this down to a tee I can swap the orange out quite quickly and fit the blue. Suck it and see approach I think.
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 3:43 pm
by CooperTune
I at one time ran a USA Solo 2 Cooper S in A S/P engine spec was 13330 S block ported big valve cyl head 13.3 to 1
compression ratio. Weber 45 DCOE9 Warnerford intake 3 into 1 straight pipe with megiphone. SC/CR, 4.35 CWP
Ultralite flywheel and back plate. I used std blue clutch kits. Tires Goodyear true gumball slicks on 6X10 Revs. I never
had any slippage issues and I shifted at 9200. I did find that a std clutch plate as supplied was not up to 9000 rpm
down shifts and once in awhile would turn to dust. I have been ask to remove orange p plates from street cars.
Over the years I have used green, blue, orange, gray and double gray. I had a orange in a race engine and it would
stall the engine when pedal was depressed. I pulled the flywheel assembly place the assembly in a Sunnen pin press.
This press has a pressure gauge, as assembled the clutch would not release at a reasonable pressure. I removed the
spring and greased the contact point between spring and flywheel. The clutch released at a very reasonable pressure
and did not stall engine any longer once back in car. That's my story and I'm sticking to it. Steve (CTR)
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 4:04 pm
by LuisM
A friend here had an issue with his race engine ( full race 1293 Grp2 specs ) using grey diaphragm, after flywheel change engine was stalling when clutch depressed, and 1st gear crunching , we figured out the diaphragm spring was not flat when assembled... machining ~1mm from the backplate horns did cured the problem.
Cheers
Luis
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 4:35 pm
by Minigman
CooperTune wrote: ↑Mon Jun 29, 2020 3:43 pm
I at one time ran a USA Solo 2 Cooper S in A S/P engine spec was 13330 S block ported big valve cyl head 13.3 to 1
compression ratio. Weber 45 DCOE9 Warnerford intake 3 into 1 straight pipe with megiphone. SC/CR, 4.35 CWP
Ultralite flywheel and back plate. I used std blue clutch kits. Tires Goodyear true gumball slicks on 6X10 Revs. I never
had any slippage issues and I shifted at 9200. I did find that a std clutch plate as supplied was not up to 9000 rpm
down shifts and once in awhile would turn to dust. I have been ask to remove orange p plates from street cars.
Over the years I have used green, blue, orange, gray and double gray. I had a orange in a race engine and it would
stall the engine when pedal was depressed. I pulled the flywheel assembly place the assembly in a Sunnen pin press.
This press has a pressure gauge, as assembled the clutch would not release at a reasonable pressure. I removed the
spring and greased the contact point between spring and flywheel. The clutch released at a very reasonable pressure
and did not stall engine any longer once back in car. That's my story and I'm sticking to it. Steve (CTR)
Brilliant info Steve - thanks. I’ve got a new blue diaphragm sat on the bench. I think it would be worth my while sticking that in and see how it goes.
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 5:55 pm
by Thorp
In one of my cars I run a 1330 with v similar spec (SW10 cam) and power and use a Cooper S clutch plate with Blue diaphragm; I’ve not encountered any issues with it over 5 years.
Certainly easier on the left leg too!
Re: Blue or orange clutch diaphragm
Posted: Mon Jun 29, 2020 7:43 pm
by Minigman
Thorp wrote: ↑Mon Jun 29, 2020 5:55 pm
In one of my cars I run a 1330 with v similar spec (SW10 cam) and power and use a Cooper S clutch plate with Blue diaphragm; I’ve not encountered any issues with it over 5 years.
Certainly easier on the left leg too!
Thanks for that confirmation. A blue will be going in this week. Fingers crossed my rev drop will improve.