The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: nigeldtr on 15.09. 2009 06:48

Title: Slipping clutch ? foreign bodies
Post by: nigeldtr on 15.09. 2009 06:48
I have a slipping clutch on a GF plunger 1951 and have not started to look into the problem yet, all adjustments seem ok. Would be pleased with some tips on what to look for.

I have followed the thread ?what goes in this hole then? and have been amassed and a little shocked (ok and bit of over dramatisation) to see so many far East conversions ? are the BSA clutches really so bad ???? how can anyone do this to a British bike  *eek*

PS Fully respect the conversions and the super engineering work and please nothing personal.

Nigel
Title: Re: Slipping clutch ? foreign bodies
Post by: beezalex on 15.09. 2009 15:25
Nigel,

Has the bike wetsumped?  If the engine oil in the crankcase gets high enough, it will seep into the chaincase which, when it gets to a certain level at the clutch hub will allow the clutch to fill with oil.  Once inside, it will never come out.  Take the cover off the clutch and if it's filled with oil, degrease the clutch plates, make sure they're still flat and then re-assemble.  That's typically all that's needed.
Title: Re: Slipping clutch ? foreign bodies
Post by: a10gf on 15.09. 2009 15:42
Hi, I've got the 6 spring original clutch, and it's one of the few devices that have been working flawlessly for the 10 years I've owned the bike. Excluding any problems with the lift mechanism, just needs parts in reasonable good shape, and use whatever time necessary adjusting to get adequate spring pressure (basically just make the clutch lever comfortable enought to use) + finetune for even lift, should give years of use without further attention. Tolerates some oil in there. But I suppose a filled up primary would be a problem.
Title: Re: Slipping clutch ? foreign bodies
Post by: RichardL on 15.09. 2009 16:03
I'm confused (what's new?). Is the plunger clutch supposed to be dry? As far as I know, the swing-arm is a classic wet clutch as described below. 

From Wikipedia (...a possible source of bad information, I know, but this seems right.):

Wet and dry
A 'wet clutch' is immersed in a cooling lubricating fluid, which also keeps the surfaces clean and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. A 'dry clutch', as the name implies, is not bathed in fluid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in transmission oil), stacking multiple clutch disks can compensate for the lower coefficient of friction and so eliminate slippage when fully engaged.


So why the concern for the clutch over excess oil in the primary. There are other reasons, but it seems, coated or submerged the clutch would have about the same performance. I really don't know this from experience, so I need to be educated.

Richard L.
Title: Re: Slipping clutch ? foreign bodies
Post by: a10gf on 15.09. 2009 16:10
The plunger clutch is closed, supposedly dry, with a dome cover + gasket, but I'd never expect it to be completely free from oil traces. I'd guess old, hardened and worn (cork?) friction plates, maybe + weak springs, combined with a little oil would give slipping, and newer modern materials in friction plates would tolerate much more oil presence.
Title: Re: Slipping clutch ? foreign bodies
Post by: RichardL on 15.09. 2009 16:14
I also read where the friction material for dry was different than for wet, but maybe that's for single-disk automotive clutches, et cetera.

Richard L.
Title: Re: Slipping clutch ? foreign bodies
Post by: A10Boy on 15.09. 2009 16:28
I run BSA clutches in ATF instead of oil and when properly set up dont have any problems. Those Yamasukiwaki clutches do look nice though.  *smiley4*
Title: Re: Slipping clutch ? foreign bodies
Post by: beezalex on 15.09. 2009 16:29
Richard, even the later clutches aren't really wet clutches.  While they tolerate some oil, if you overfill your primary, they'll slip and drag.  Centrifugal force gets most of the oil off the clutch with the correct oil level.  Most "wet clutch" friction materials have a much higher friction coefficient when used dry.  On the rigid/plunger clutch, the enclosure for the clutch is a blessing and a curse.  The totally dry clutch works very well but once oil gets in there, it doesn't get out and even partial immersion renders the clutch useless.
Title: Re: Slipping clutch ? foreign bodies
Post by: Rusty nuts on 15.09. 2009 16:31
Hi, I've got the 6 spring original clutch, and it's one of the few devices that have been working flawlessly for the 10 years I've owned the bike. Excluding any problems with the lift mechanism, just needs parts in reasonable good shape, and use whatever time necessary adjusting to get adequate spring pressure (basically just make the clutch lever comfortable enought to use) + finetune for even lift, should give years of use without further attention. Tolerates some oil in there. But I suppose a filled up primary would be a problem.

Agree, also have six spring & very robust will tolerate quite a bit of oil.
In fact an engine I bought had no domed cover fitted, yet the guy I bought it from swears it worked just fine for the ten years he used it!
Washed oil off friction plates & works just fine, with a cover fitted I hasten to add!
Title: Re: Slipping clutch ? foreign bodies
Post by: RichardL on 15.09. 2009 16:46
Thanks to all.

That clears up a lot. I am also using ATF in my clutch at the strong recommendation of some members here. Works very nicely. Mine is six-sping and no complaints, so far.

Richard L.
Title: Re: Slipping clutch ? foreign bodies
Post by: Rusty nuts on 15.09. 2009 17:47
One last comment *ex*
I have original cork plates, am told later Surflex plates are much less tolerant of oil.
Cheers
Title: Re: Slipping clutch ? foreign bodies
Post by: LJ. on 15.09. 2009 17:50
Apart from plates and oil... I'm betting here that the push rod may not have been hardened properly and has worn down. The remedy apart from fitting a new one, is to cut in half and put in a ball bearing. But do make sure the ends of rod are well hardened.
Title: Re: Slipping clutch ? foreign bodies
Post by: mike667 on 15.09. 2009 17:52
Thanks to all.

That clears up a lot. I am also using ATF in my clutch at the strong recommendation of some members here. Works very nicely. Mine is six-sping and no complaints, so far.

Richard L.

ATF is great to discern where an oil leak is coming from since its distinct color let you know it is the primary drive or else where - i use it in my 4 spring and it works nice!
Title: Re: Slipping clutch ? foreign bodies
Post by: nigeldtr on 15.09. 2009 22:05
Thanks to all for the replies. I suspect there is a bit of oil on the plates and will take a closer look at the weekend. When I fired up after rebuilding the top end, it took a long time for the oil return to start so the sump probably had about 1/4 of the oil tank in it! As the return picked up, I did notice a fair bit of oil coming from the LHS of the bike and could have been from around the gearbox sprocket?

Nigel
Title: Re: Slipping clutch ? foreign bodies
Post by: Brian on 15.09. 2009 23:31
Lets try and make some sense out of all this.

Being a 51' model it doesnt have a crankcase oil seal so if the bike has sat for some time and wet sumped it may well have excessive oil in the primary case. If so even with the cover on the clutch some oil may have worked its way into the clutch. These clutches will run wet but not if the cover is still in place as this traps the oil in.

These clutches are, in my opinion, the best clutch BSA ever made and work very well and rarely give trouble. I only use Surflex plates and I use them in both wet and dry applications and have found them to be the best available.

Nigel you need to dismantle and inspect the clutch and take it from there, replacing whatever is necessary. Once you get it sorted it will work perfectly and you should not need to look at it again for a very long time.

The oil you have seen coming out on the left side after you started the engine was most likely from the engine breather which exits the crankcase in front of the gearbox sprocket.

Just on the subject of oil in the primary I know a lot use ATF and while I think that is fine I have always used engine oil. The only thing to be wary of if you use engine oil is to make sure it is a motorcycle specific oil that is suitable for wet clutches. A lot of car oils have friction modifiers in them and can cause clutch slip.

My two bobs worth.
Title: Re: Slipping clutch ? foreign bodies
Post by: nigeldtr on 16.09. 2009 05:50
Brian,

Thanks for this and seems highly likely as to what has happened. I was wondering where the breather exits the casing!

I have been using single grade "straight" oil made for classic cars/bikes. The oil topic is probably worth a new thread as this is a really interesting topic.

Nigel