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Twinshock Clutch Plates Query...


cosmikdebriis
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Hi... I'm considering replacing the original clutch plates on my Alpina with more modern "friction material" as available from a certain well known Bultaco supplier (that I may not be supposed to mention by name but I'm sure it's pretty obvious). 

 

So... Is it worth the ninety odd quid it's going to cost me?

 

I should say, I'm in the middle of restoring the bike (1972 175 Alpina) and have not really tried the original clutch to see if there are any faults, just thought it easier to do now if it's worth it?

 

Thanks in advance... Dave

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Dave , replacing the steel clutch in your Alpina @ the mentioned price , for me would be a no go IMHO.

 

You only need 4 of the friction plates and these are usually available on internet @ far less.

 

The setup for the modern plates can be worrisome with the pin clutch setup I would gather you have. (no adjustment)

other than shimming.

You can achieve a 1 finger clutch buy the above method & 4 springs as the 175 shouldn't be as finicky as what a 325

is, so if you want a lighter clutch, give it a go.

Good luck

Larry

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  • 2 weeks later...

Hi all

 

I didn't change my clutch at resto time on my Frontera and it's heavy as a heavy thing, really pumps my forearms. I was also looking at more modern materials.

Larry, my Sherpa 325 has a lovely clutch - original clutch - You're suggesting replacing the current (don't know how many) with just four on the Frontera.

 

The 325 had the pin and cup arrangement - the Frontera has the nuts setup. (nuts and bolts... that is). Will the clutch really be up to it with just four plates?

 

Thanks for any info

Paul

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The reason why four plates, may be that they are thicker and only four will fit in the basket. That is the usual case with plates with friction material bonded on. If you make the metal part of the friction plate too thin, the tangs dig into the basket fingers, so it is unavoidable that plates with friction material added will be thicker than the standard steel plates

The reason why you can get away with replacing five steel plates with four plates with friction material on them, is that the friction generated per plate is greater with the friction material. If you can fit five of the new plates in there without the spring nuts hitting the clutch cover, or the stack being too deep for the basket, then use 5 plates and enjoy a lower lever pull force.

When setting the pressure plate spring preload, set the spring load only just high enough to stop it slipping at full power in top gear (top gear puts the greatest torque on the clutch). You can get pretty close to the ideal setting in the workshop by increasing the spring preload until the kickstart is just able to get the motor over compression.

As well as this basic setup, there lots of other things that can be done to reduce clutch lever pull force on a Bultaco. Here are a few:

Fit roller bearings to the clutch camshaft

Choose a leverage ratio that maximises the mechanical advantage between your hand and the clutch pushrod, yet still moves the pushrod far enough to completely disengage the clutch

Use a high quality cable

Use a high quality lever

Route the cable to minimise friction

Lube the cable

Service the camshaft

Set the cable and pushrod adjustments so that the clutch arm is at 90 degrees just as the full load of the pressure plate is achieved

Fit a hydraulic clutch with slave that bears directly onto the pushrod

 

The powerful versions of the 5 speed motor like a 370 Frontera will always have a heavier clutch pull than any of the 250c Trials and Alpina motors need to have. Even a completely standard clutch setup on a 250 Sherpa T can be made to be a one-finger operation, and the 325 trials motor can be made almost as light, but to cope with the power of a Pursang/Frontera going through the same design clutch, will require more force on the pressure plate, or more elaborate methods, to reduce lever pull down to single finger levels.

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Paul if you have a Bultaco with pin-type spring retainers, don't try and use anything but standard plates because it will be impossible to get the pressure plate load right otherwise. You should be able to buy a second-hand later model clutch with nut and stud spring retainers if you want to take advantage of the plates with friction material on them on your 325

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Paul, I have no experience with Frontera's!!

The reason I (and others) use 4 Barnett's is due to the thickness of the clutch pack, Sherpa T's clutch

basket & engagement of the pressure plate on clutch hub dictates how thick the pack can be.

We get by with 4 springs quite nicely, the main problem I have seen with a light clutch has been with

 slippage when kick starting , no slippage when going to 4th which is a big jump from 3rd in my experience.

As for levers the stock Amal's are very good other brands leverage not so good .

My preference only; Dexron ATF.

Be sure 1st plate in; earless. Pin type require shimming as you cant match the original pack thickness, had

good results on four Sherpa Ts using 4 Barnetts.

 

Larry

Edited by lbhbul
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Hi all

Back again.

Thanks for all your help and explanations.

Took the side cover off and sat looking at the clutch for an hour working out what pushes what etc.

Had a chat with the local Bultaco/Greeves/BSA engine builder and racer he suggested just winding the nuts off a couple of turns and see what happens. Yeah - why not!.

There are six plates on my clutch.

The actuating rod, lever, cable were all good and moved nicely.

Took off the clutch arm return spring - the clutch was 'closing' well enough without help from a strong spring as well.

Wound the nuts off a couple of turns - from about 6-7 mm threads showing, to about 3-4mm showing.

Spun it over with the kickstarter looking for runout (very difficult to see any - if any)

Started it with no cover and rode a few yards to see if I could make the clutch slip. Seemed fine. 

Wiped off the thrown oil! and back together, new ATF and away we went. 

Much better, nicer action - not light as the 325 but very much improved. I wasn't thinking how heavy the clutch was every time I used it or came to a stop.

Had a great time ripping across the stubble. did about 8 miles. No slipping. Great.

 

Ahem. One thing did surprise me. I put three litres in and drained two out.

That's 2 litres for 8 miles.

That's 1 litre for 4 miles

That's 4.5 litres (gallon) for 18 miles

 

mmm... 18MPG!

 

thanks again

Paul

 

Edited by sadlotus
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Paul, good thinking from your friend!!

We tend to get all wound up in helping and tend to not see the obvious!

You count 6 eared plates? You must then have maybe 7 others?

Question is   irrelevant as it is now satisfactory.

Fuel consumption is something , I have only experience with Sherpa T, but have seen a marked

improvement when changing the Bing for another brand.

Larry

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When i try my clutch out on setting it up i just replace the case and only use 2 bolts this stops the ATF oil flinging all over th engine once clutch is set i wipe edge of clutch case replace gasket top up with new oil. to get the pressure plat run true i tie wrap the clutch leaver in then turn kick start with my thumb on the edge off the pressure plate i check for run out and ajust each nut untill it runs true. Then put lock wire on the nuts.

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Hi all

Back again.

Thanks for all your help and explanations.

Took the side cover off and sat looking at the clutch for an hour working out what pushes what etc.

Had a chat with the local Bultaco/Greeves/BSA engine builder and racer he suggested just winding the nuts off a couple of turns and see what happens. Yeah - why not!.

There are six plates on my clutch.

The actuating rod, lever, cable were all good and moved nicely.

Took off the clutch arm return spring - the clutch was 'closing' well enough without help from a strong spring as well.

Wound the nuts off a couple of turns - from about 6-7 mm threads showing, to about 3-4mm showing.

Spun it over with the kickstarter looking for runout (very difficult to see any - if any)

Started it with no cover and rode a few yards to see if I could make the clutch slip. Seemed fine.

Wiped off the thrown oil! and back together, new ATF and away we went.

Much better, nicer action - not light as the 325 but very much improved. I wasn't thinking how heavy the clutch was every time I used it or came to a stop.

Had a great time ripping across the stubble. did about 8 miles. No slipping. Great.

Ahem. One thing did surprise me. I put three litres in and drained two out.

That's 2 litres for 8 miles.

That's 1 litre for 4 miles

That's 4.5 litres (gallon) for 18 miles

mmm... 18MPG!

thanks again

Paul

Drained out 2, means you used 1 ? = 36mpg

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The Frontera uses different plates from the Sherpa, they are thinner which is why there are more

 

Be careful how much you back the nuts off as they run very close to the inside of the casing and can catch when the motor is running, even if they appear to have clearance when setting up. I reduce the depth of the adjuster nuts on my bikes to about half their original depth so that there is no issue with clearance when backing them off

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