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Coil Spring Type Clutch Converting To Pre-Verto Diaphragm Type Clutch?

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Best Answer Spider , 15 September 2021 - 09:47 AM

Nice you have a result !

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#1 Tulloch

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Posted 13 September 2021 - 06:30 AM

Year: 1964
Location: Australia
Engine: originally 850 now 998
Parts listings: minispares

Hello everyone,

The engine is out of the car on an engine stand. I bought a 3 piece borg & beck diaphragm kit. I bought 6 new metal straps. Already replaced thrust/release bearing with a heavy duty one. (I didn't replace clutch plunger, it appeared to be fine)

Can the original pressure/back plate be used (2A3509)? Is there difference between the coil type and diaphragm type pressure/back plates?

I removed the short 9/16 bolts out of the original flywheel that were used for the metal straps (2A3658). I went to reuse the bolts on the new flywheel (C-AEG420) but it seems to require 5/16 short bolts (2A3659) the 9/16 fit too tight??
Will that mean I can use the 9/16 long bolts for the diaphragm to pressure plate or will I require long 5/16 bolts (2A3657) and a new pressure/back plate (22A598)?

TLDR; If I use the original pressure plate, can I use the original 9/16 bolts for the new diaphragm and then just buy new 5/16 short bolts for the flywheel metal straps?

I hope this made sense. Sorry, I'm a complete novice with anything mechanical. Any help/tips will be greatly appreciated, cheers.

#2 Spider

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Posted 13 September 2021 - 09:31 AM

Hi and welcome to the forum.

 

The Backing Plate should be fine to use here. There were quite a few different types used over the years, however dimensionally, they were similar, the thing to check when assembled with a new Clutch Plate is that the Diaphragm Spring is flat when all bolted up.

 

Typically, the standard short bolts are used with lightened flywheels, but they inevitably need spacers under them, and that sounds like the case here. They need to be in thickness to make up for the material that the lightened flywheel is thinner than a stock item, so say your new Flywheel is 1/2" thick and a stock one here these bolts go in is 3/4", then you'll need 1/4" spacers.

 

You would use the standard long bolts here to bolt up the Diaphragm to the Backing Plate.



#3 Tulloch

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Posted 13 September 2021 - 12:40 PM

Hello Spider, thanks happy to be here and thank you for your reply. Good to hear that the backplate should be fine. I'll make sure to get the diaphragm plate flat.

The spacers makes sense to me, I did notice when I tried putting the original 9/16 bolts in they would run too deep but my main concern is they seem too thick (very tight when I attempted to do up, I didn't want to force it as they easily fit the original flywheel) I think the new flywheels bolt holes are smaller?

If I bought the short 5/16 bolts (2A3659) these would be the correct bolts for this lightened flywheel thickness and length? (If not length then I'll just get/make some spacers). Tomorrow I'll try find a 5/16 bolt to fit into the flywheel for sizing.

As I said the need of spacers makes sense since losing thickness of the flywheel but the fact that the bolts seem too thick is what troubles me most now. My closest supplier is 750km away so I want to get my orders right haha. (Postage ain't cheap)

Thanks again

#4 Tulloch

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Posted 13 September 2021 - 12:50 PM

In regards to spacing the bolts to have the flywheel straps level so the diaphragm is flat. Is there any harm in spacing it out with multiple washers? Or should I find more robust spacers to suit? Cheers

#5 Spider

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Posted 14 September 2021 - 01:20 AM

Now worries Tulloch.

The correct Strap to Flywheel Bolts would be the 2A3659.

The correct Diaphragm to Strap to Backing Plate Bolts would be 2A3657.

I just looked up the C-AEG420 Flywheel and a heads up here that it appears it has a 217 tooth Ring Gear on it of the late Minis. The early Minis, like yours and all Australian Production had a 107 tooth flywheel. I'd suggest counting the teeth to be sure what you have and be sure to use the appropriate starter motor with it.

The only threads I've ever come across in any pre-verto Flywheel has been 5/16" UNF, but it would be wise to check in case it's M8, in which case, that will present an issue for bolts (in both the flywheel and backing plate) as you do need to use a shoulder bolt with the correct OD shoulder in order to align the straps. This is what centres the Backing Plate to the Flywheel.

You could use a series of flat washers as spacers here. I'd suggest though measuring each stack to get them within 0.020" of each other in fitted height and weighing them and get them in sets to a similar weight. If you can get flat ground washers, that would be better that ordinary stamped types.



#6 Tulloch

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Posted 14 September 2021 - 08:09 AM

Now worries Tulloch.

The correct Strap to Flywheel Bolts would be the 2A3659.

The correct Diaphragm to Strap to Backing Plate Bolts would be 2A3657.

I just looked up the C-AEG420 Flywheel and a heads up here that it appears it has a 217 tooth Ring Gear on it of the late Minis. The early Minis, like yours and all Australian Production had a 107 tooth flywheel. I'd suggest counting the teeth to be sure what you have and be sure to use the appropriate starter motor with it.

The only threads I've ever come across in any pre-verto Flywheel has been 5/16" UNF, but it would be wise to check in case it's M8, in which case, that will present an issue for bolts (in both the flywheel and backing plate) as you do need to use a shoulder bolt with the correct OD shoulder in order to align the straps. This is what centres the Backing Plate to the Flywheel.

You could use a series of flat washers as spacers here. I'd suggest though measuring each stack to get them within 0.020" of each other in fitted height and weighing them and get them in sets to a similar weight. If you can get flat ground washers, that would be better that ordinary stamped types.



Sorry Spider, I need to make a correction the new flywheel I have is the C-AEG421 (the packaging incorrectly labelled it as 420, I ordered it months ago), it has 129 teeth on the ring gear. You are correct my original flywheel has 107 teeth. This should suit my starter motor, as minispares list that it is for inertia starter. Sorry for feeding you the wrong info.

Yeah coming across the 9/16 bolts on the old flywheel is a bit of a curve ball. I'll order some new 5/16 shorts, as well as get a few flat ground washers and try get the stacks as close as possible as you said.

Diaphragm to Strap to Backing Plate Bolts I'm thinking the original 9/16 that were used may be viable as that's what went in the old backing plate but I'll order some long 5/16 bolts to be sure in case I've made an error.

Thanks heaps Spider, you're a legend! Really appreciate your help

#7 Spider

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Posted 14 September 2021 - 08:27 AM

Cheers Tullock,

 

One thing here I think I picked up on is I think there's a little confusion / misunderstanding, I'm sorry, I should have picked up on this sooner.

 

The Bolts. When you say ' 9/16" Bolts ' do you mean the spanner size ?  These Shouldered Bolts while having a 5/16" UNF Thread, do have a 9/16" AF Head on them, that's normally associated with 3/8" UNF Bolts.



#8 Tulloch

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Posted 14 September 2021 - 12:21 PM

Yeah I meant spanner sizing, so that explains that. Could it be possible the old bolts are UNC and the new flywheel requires UNF threads? Maybe that's why it seems a bit too tight to fit? Meaning the new bolts I buy should do the job and fix my issue?

Sorry I'm so new to work on cars, this is my first restore. I also have always primarily used metric measurement so this is all a real learning curve for me haha.

Thanks again Spider

#9 Spider

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Posted 14 September 2021 - 01:09 PM

Ah, OK, so that clears that up.

As far as I know, these bolts were all UNF, I'll have a look in one of the early parts books later to be sure, though, I just can't see them using UNC here.

I'd find it odd that they'd use anything other than 5/16" UNF in the flywheel too.

Can I suggest getting a hold of a 5/16" UNF Nut to test the Bolts on and a 5/16" UNC and M8 Bolt to test the threads in the Flywheel. It's possible the Bolts may have stretched on the threads, though usually they'll break before they get to that.

Did you buy the flywheel new ? If so, maybe contact the firm you bought it from and ask them what threads are in it.

You should easily be able to pick UNF from UNC.

If you take a Bolt from the Alternator (or Dynamo) Bracket, where it's bolted to the Block, that will be 5/16" UNF.

If you look at one of the Bolts from the (Alloy) Clutch Cover, that will be 5/16" UNC.



#10 Tulloch

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Posted 15 September 2021 - 08:15 AM

Hi Spider,

I'm resolved it. Yeah I bought the flywheel new, but one of the threads on it was no good and it just so happened to be the one I kept checking stuff on. I've got the thread fixed now, I bought some stainless steel washers as they were the only ones I could get that seemed adequate for the job to space out the bolts. I've assembled the clutch and flywheel now, with the help of a mate. Diaphragm is nice and flat, looks the part. Guess I'll find out what kind of job I've done once I get it up and running.


Hopefully I'll be able to show everyone some day my finished project. This brings it one step closer.

Thanks immensely Spider, legend!

#11 Spider

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Posted 15 September 2021 - 09:47 AM   Best Answer

Nice you have a result !







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