I have a barnett lock up clutch in my Vortx's R1 engine and I'm just trying to get to the bottom of why the clutch is nearly unusable!

Basically you can pull away VERY slowly at idle but if you give it almost any revs it seems to lock up violently and stall, unless you give it so many revs it wheelspins off the line.

I guess the problem could be wear on the clutch basket so the plates get caught as they slide on the arms but I'm also wondering if there's something wrong with the lock up mechanism. At what sort of revs should it start increasing the clamping force significantly? I was thinking if it's over-weighted could it be clamping the clutch too tightly at low revs (like 3000 or so as you might use for gently pulling away)?

Anyone else using these clutches without an issue? From a thread from the previous owner it seems it may have especially strong springs in it too but as the pedal action is light enough to modulate easily I don't see that being the issue.

No personal experience, but a desire for one and minimum understanding.
I would go with your thoughts that its coming in too soon /too low revs.
Not sure what if any adjustment there is or whether youd need different weights fitting

I think you change the weight by adding and removing washers or nuts so I can try that easily enough.

Thinking about it again though, it still seems like it should be relatively progressive, as in, the faster it starts to spin, the harder it clamps rather than not clamping, not clamping, not clamping, then suddenly...DEATH GRIP. Maybe the issue is a mechanical fault that causes the locking mechanism to hang then suddenly release? Either wear or a mistake with the installation?

Anyway, I've ordered a new clutch cover gasket and lever rod oil seal to fix a leak so when that stuff comes I'll take the cover off and see what's what.

If it's like mine it has weights (nuts and bolts) that fly out to add additional pressure on the clutch pack as revs increase.

It sounds like you have to many weights, to start with you add nothing and see if the weight of the arms themselves are sufficient, if not add a small nut and bolt, try again if still slipping bigger nuts and bolts packs of washers.

high speed gear changes become stiff as revs increase so only have just what you need, no point in adding additional load.

My car has very little extra weight for nearly double the power as the springs alone were worth 30% more HP so topping up.

[Edited on 19/5/14 by mark chandler]

Does yours feel like a normal clutch at lower rpms? Is it Barnett or another make?

Mine has OEM plates and steels with Barnett springs, when they could no-longer hold the power it got the lockup clutch.

At low revs up to 3000 rpm it feels no different to standard, I have a long pedal so can easily balance.

High revs it goes harder, not by much but I just knock it up a cog without the clutch and aim to change down to the sweet spot that starts at 3000 rpm.

Take some weight out, I started heavy which was a mistake.

Thanks Mark, this is useful info.

So the locking action starts to make itself felt around 3k? When it was over-weighted, did it feel like how I described mine?

If all I need to do is take some weight off I'll be over the moon...the myriad problems this car had when I got it have so far all been easy and free to sort!

Engine revs have nothing to do with how a lockup clutch works - its mechanically connected to the clutch center , from there to the gearbox , and once in gear , to the back wheels .
So an increase in wheel speed is what makes them work - not engine revs .

On my Pro stock bike , tuning the clutch and lockup was the most important part of making i tall work - I ran a different primary drive ratio to slow the clutch down , then super soft springs to make the clutch slip - as soon as the bike moved , the lockup would then apply pressure to the plates and away you go........and all this was happening in the first second of the run.......

If engine revs alone affected the lockup , then putting it in gear and revving the engine would overcome the clutch release and lock up the clutch........

It felt heavy yes, worse with RPM and caused the pin that pulls from the cover to snap.

You do not notice really on a foot pedal as your legs are strong.

Maybe you had a different setup Claire, on mine you have levers that spin out, these pivot on a plate that pushes onto the standard top cover, the faster it spins the harder the weights try and move exerting more pressure on the clutch basket.

[Edited on 19/5/14 by mark chandler]

This is a picture of two lockup clutches, top view and back view, if you look at the bottom one you can see the little levers with holes drilled to take weight.

When the clutch is depressed the levers work at a different angle so the feeling is not so pronounced.

Tommy, if yours is the same make sure the fingers are not at 90 degrees to the original cover or they it will lock solidly in which case you either need to bring the clever bit closer to the clutch or install new plates to widen the pack.

If you have a spare steel you could drop in as a spacer to the pack to prove.

Regards Mark



[Edited on 19/5/14 by mark chandler]

It was exactly the same - bolted through the same bolts that hold the springs (which are in the clutch center , not the outer basket)
Trust me - thats how they work . To prove it , just put yours in gear , and without moving rev the engine.......absolutely nothing will happen . If it works as you think , you wont be able to keep still .

You'd feel it pull harder against your foot/hand but you'd still be able to easily hold it back wouldn't you?

Anyway, I'll have a look when my new gasket and seal arrive. Got some good ideas from this thread so hopefully should be able to fix it. Thanks for the replies.

quote:

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Originally posted by T0MMY
You'd feel it pull harder against your foot/hand but you'd still be able to easily hold it back wouldn't you?

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Clarie and myself are both right, see attached which hopefully explains



When the clutch is pulled in because it pushes in an arc and if the car/bike is not moving you are only fighting the springs as the lockup bit is not spinning.

Once the car/bike is moving the whole basket is spinning, the weights are thrown out and which forces the fingers onto the cover, the faster the engine is spinning the greater the force exerted.

From what you are descibing, if the pedal is really hard when you first push it then I suspect the levers are pushing near the end of the axis so effectively jamming it solid, right hand side of the sketch or maybe you have some ridges that have worn ito the top plate.

Try dropping in an extra steel plate to grow the clutch pack this will reduce the angle and stop the problem hopefully.

On mine if I change gears using the clutch at 10,000 rpm the pedal is heavier than at 6000rpm, the car is moving at this point.

Regards Mark

[Edited on 19/5/14 by mark chandler]

The pedal isn't actually hard...it's quite light and relatively smooth now I fiddled with the cable run. You can bring it up and feel it start to bite very lightly so the car just starts to move then there's nothing between that and fully locked. It basically means that this very slight friction is all you can use to get the car going so pulling away quickly is impossible...trying to engage the clutch further instantly locks it and stalls the engine. This is at idle revs...if you give it more throttle it's even worse and is just on/off.

[Edited on 19/5/14 by T0MMY]

Goes back to weights still, the moment the basket spins the weights are thrown and it starts to lock the clutch and fight you, try removing them and just rely upon the weight of the fingers, if you get clutch slip add a nut and bolt.

Or your clutch plates are just very grabby.

quote:

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Originally posted by T0MMY
The pedal isn't actually hard...it's quite light and relatively smooth now I fiddled with the cable run. You can bring it up and feel it start to bite very lightly so the car just starts to move then there's nothing between that and fully locked. It basically means that this very slight friction is all you can use to get the car going so pulling away quickly is impossible...trying to engage the clutch further instantly locks it and stalls the engine. This is at idle revs...if you give it more throttle it's even worse and is just on/off.

[Edited on 19/5/14 by T0MMY]

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The clutch shaft lever is already extended, about 8cm from memory. How far should the cable be from the pivot at the pedal end?

I have used lock-ups for drag racing and sprint engines, so I am very aware of their tuning capability. I assume that you are using the lock-up to make up for a high torque engine (turbo?), so you have to have it setup differently to the drag race setup. For drags the correct setup is to use very light spring pressure so that the clutch slips at low rpm (improve launch) and the weights move in at higher wheel speeds to drive down the track. The adaptor will be machined to reduce the spring seat pressures, as installed. For a track car you only want to supplement the normal springs to avoid slip at any time when the clutch is fully engaged.
1. Make up some spacers to restore the clutch springs to their normal installed height.
2. Remove all the additional weight from the levers on the adaptor. They will still provide additonal pressure as the speed increases. If you are coping with a lot of torque (boost), add an aluminium cap screw, and nut to each arm, and possibly a washer. Too much weight overloads the clutch basket and release mechanisms. I have seen drag racers push the rim off the inner clutch basket with too muuch weight on the fingers.

I read half the thread so I apologise if this has been said already.

I agree with Claire that it isn't engine speed, but the speed of the clutch inner that is important.
But, the clutch centre doesn't rotate at the same speed as the prop-shaft.
The reason for this is that the clutch is before the gearbox.

The answer is (as for most BEC questions) lose some weight.

You want it set up exactly as wombat has described.

I run mine exactly the same in my application. The lockup is not used for initial launch, it is used for when you have wheel speed in a high torque application where this can overcome the spring pressure on a std clutch.

Set the fingers up with the minimum amount of weight on them. You can get shim kits for the springs to make the pressure stronger if needs be. This will make the clutch as you want it. You do need some slip when pulling away to make a clean launch.

The lockup segment should not be working when initially pulling away. That sounds more like you have your clutch pedal setup so that it is too sensitive, or you have springs that are far too strong.

What engine is it fitted to?

It's on a bog standard R1 5PW engine so an excess of torque shouldn't be an issue...not really sure why it was ever installed.

As I mentioned, a thread from the previous owner mentions stronger springs than the standard barnett ones so that could be causing an issue but like I said, the pedal is light enough.

I would recommend either removing it and upgrading the standard clutch springs to HD Barnetts, or adding turbocharger

Lockups are not needed on stock engines unless you want to drag race it . . . rev to 9000 rpm and dump in clutch on a fully prepped drag strip . . . wait for bang from diff/axles/?

Lock up is useful if you have turbo, and in some cases on standard engines. But you only need to do one or the other, springs or lock up.

To support the torque in a turbo motor coupled with the added weight stress you need strong springs and lock up.

Springs that are too strong gives you a worse bite on the clutch, no slip at all which is bad for launch. Also the springs put increased stress on the housing and basket which can crack it.

The lock up allows you to use a softer spring and when set up will provide the added pressure to stop it slipping at speed where the soft springs can allow it to slip.

Well it seems I have both strong springs and a lock up clutch so we may have found the source of the problem!

I'd say so, get some standard springs back in it and see how it is.

You may need to change the pedal fulcrum though as the clutch will be lighter. Making the fulcrum smaller will increase the force needed to depress the clutch but will make a longer bite point.

Well first things first, I'll try taking the weights off as that won't cost me anything (I don't have the original springs to try). Of course I'm assuming it even has weights on it...still waiting on the new gasket and oil seal so I haven't had the cover off yet.

Weights do not affect you pulling away. There attached to the centre of the clutch that is attached to the gearbox. So they only start when the basket reaches a certain speed.

Check the lock up where it covers the springs isn't shimmed. Some kits come with shims to increase the spring pressure so you can fine tune the bite.

Well after finally getting the time to work on the car...it turns out that it does in fact not have a lock up clutch after all!

Just a normal barnett clutch by the looks of it, red anodised jobbie with 6 springs. It all looks to be in very good condition with no wear so I think the only thing to do is try lighter springs. That said, I only assume they're very strong ones as that's what the previous owner mentioned, but then he also thought it had a lock up clutch so who knows.

Here's an idea to test if lighter springs are the answer...could I remove some of the ones that are in there? If I took out 3 it would still be balanced but then I'd have halved the pressure and I doubt lighter springs are THAT much lighter so it would probably slip like crazy.

Any particular reason not to do this? It would be a temporary solution just to find out if lighter springs would help before I order some.

EDIT: Just stripped it down further and the splines on the clutch boss (inner hub thing) are quite worn. Not really sure how much is too much but this could definitely cause the problem I'm having! I could have a go at cleaning it up but it might just need to be replaced.

[Edited on 23/5/14 by T0MMY]

Its worth a try and might prove a pointy.
I can't help wondering if its a new clutch thats been put in and the steel plates roughed up?
Or, poor pedal action.
Or just how bad are the grooves in the basket?
Or you need more practice

Well now I've seen the splines on the clutch boss I've gone off the idea of it being overly strong springs. I'm pretty sure it's the wear as it fits better with the symptoms.

Hard to say how bad it is as I don't have much to compare it to. There are significant grooves though so I might try and file/emery them smooth.

I wish it was just practice but given the last two owners have both got threads on here about the issue it's not just me. I'm pretty used to bike clutches anyway...I have two track bikes and have been riding for 17 years!

[Edited on 23/5/14 by T0MMY]

How about a picture then
If your description of grooves, rather than light wear/burnishing is correct ten I suspect your right and you've found your problem

Here's some I prepared earlier





You can also see wear from the springs on the shaft thingys. They might make it a little jerky too I guess, but easy enough to sand down.

I'd sy it was quite bad. Interesting how the basket has worn less than the boss; I was wondering if it had been replaced at some point?

[Edited on 23/5/14 by T0MMY]

Technical term for that is... buggered!

I don't think rubbing it down will help and you'll need a new one. Start searching e-bay.

quote:

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Originally posted by adithorp
Technical term for that is... buggered!

I don't think rubbing it down will help and you'll need a new one. Start searching e-bay.

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one thing we do on race engines is rub the groves down if you cant get a new one but then on the old or new on the valley drill a small whole abour 3 mm in the middle then the next one drill 2 one half way from the edge and the middle whole then next vally drill 1 in the middle next 2 the same do this all the way around helps oil flow makes for a smooth clutch action and helps the hub last longer

Annoying that it's beyond help...not so much for the cash as they're not too expensive but I have the week off work and wanted to drive the bloody thing a bit, not sit and wait for parts

I might file it down anyway while I wait for a replacement boss as I don't see the harm. I guess the issue is the clutch will be even more rattly and it'll grind new grooves very rapidly?

Anyone have a spare clutch boss they're willing to sell me?

Thought I'd update this in case anyone searching on here for similar symptoms finds it.

I replaced the clutch boss today and it has completely tranformed the car...I'm astounded at the difference it's made as the old one didn't look horrendous really. The clutch action is Mondeo-esque in it's bland competency The car is now a joy where before I was always terrified of having to stop anywhere in traffic!

Another top tip too if you ever need one...in the UK Yamaha wanted over £400 for the clutch boss but from the US they're around £60-80, brand new, OEM part. I don't quite understand that one but anyway, with shipping and taxes it was about £100...just had to wait a while.