AF Clutches Shearing Rivets

[NorthernJordan]

Since the euro Lambretta I have had two af clutches shear its rivets in the spider. Same bike, same engine set up, same problem. The first clutch had been in the engine for 3-4 years with annual new plates and corks, so just assumed it was old age and a hard life. Second time was an entirely new clutch but the same af road cassette clutch.

Any ideas why this would be the case? Anyone else had the same issue?

Cheers

[Warkton Tornado No.1]

Unfortunately the standard two piece design of the clutch inner is limited in the torque able to be transmitted by the rivets used to hold it together.

An easy fix would appear to be replacement of the rivets with something like M5 high tensile screws, tapping into the splined part that goes onto the gear cluster. I’ve yet to find one that is soft enough to allow any modification to the holes, as they are really hard.

That’s the reason most resort to welding or brazing the assembly together prior to the rivets shearing.

If you do decide to fix things in that manner, make sure that the assembly is concentric. Chances are, it was unlikely to have been in the first place, so you have the opportunity to put more than one thing right!

[MickYork]

What is the engine spec' and do you know what torque/HP you're producing ?

I'm also wondering if the front cush-drive spring is working ok ? that should be taking the initial surge and grab making life easier on the clutch

[NorthernJordan]

Workton, are you saying that this is a particular problem with all Lambretta Cluthes, or the AF cassette clutch?

My engine is a moderate power engine, 19-20hp so would have thought this wouldn't kill clutches quickly?
Its an RT230, 60/110 crank, 19t front sprocket, IWIS Chain, AF Cassette Clutch, Cyclone 5 Speed.

Would chain alignment cause issues in this way? Some form of sideways strain putting extra pressure on the rivets?

Jordan

[NorthernJordan]

Would think the bush would wear first if its an alignment issue?

[Warkton Tornado No.1]

Workton, are you saying that this is a particular problem with all Lambretta Cluthes, or the AF cassette clutch?

My engine is a moderate power engine, 19-20hp so would have thought this wouldn't kill clutches quickly?
Its an RT230, 60/110 crank, 19t front sprocket, IWIS Chain, AF Cassette Clutch, Cyclone 5 Speed.

Would chain alignment cause issues in this way? Some form of sideways strain putting extra pressure on the rivets?

Jordan

In the first place, it was late last night when I responded to your Post & in my haste to help, I missed the fact that you are using an AF Cassette clutch. Schoolboy Error!

Secondly, I apologise for the confusion I have caused as my comments were relevant to the OEM design.

[a-teamlambretta]

a tack weld near where each rivet goes ?

[NorthernJordan]

It could just be coincidence that they have both failed. New spider is faulty and the original was just old and worn out?
However, obviously want to get to any root cause if there is a fault with my engine.

Jordan

[Psychedelicropcircle]

I've yet to open my cassette clutch but it's a little dissapointing to read it has rivets! On the standard clutches its best to weld the spider maybe this is the road to go..... Que my paranoia on the way to brid

[NorthernJordan]

http://afrayspeed.co.uk/index.php?page= ... buteID=CLU

You can clearly see them in the photo here.

I can only think of two scenarios:

1. Coincidence, don't really believe in this too much but it is a Lambretta. Like I say second one is a diff one, poorly made and it was just a matter of time. The original went because of old age and it was as simple as that.

2. There is something genuinely wrong with my engine internals. Something is a training someone where and it is being taken out on the rivets. If the chain was that out of alignment, I would have thought weaker components would have failed first such as chain or bronze bush. Need to have a thorough inspection of the front a project but nothing jumps out as an issue.

This has really baffled me as it had been so trouble free previously. I've not heard of any issues of this nature with an AF clutch. I've heard if standard clutch rivets going, but surely 19-20hp shouldn't kill rivets so quickly?

[holty]

a tack weld near where each rivet goes ?

this is the solution to your problem, a nice bit of weld will fix it together and job done.

[NorthernJordan]

Yeah, I could get that done at work and obviously a well known trick.

Other than the rivets being quite loose there isn't any damage so could i just have it welded as it is?

Just one I'm struggling to get my head around!

[Warkton Tornado No.1]

http://afrayspeed.co.uk/index.php?page=catalogue_details&catID=1339&listing=catalogue&attributeID=CLU

You can clearly see them in the photo here.

I can only think of two scenarios:

1. Coincidence, don't really believe in this too much but it is a Lambretta. Like I say second one is a diff one, poorly made and it was just a matter of time. The original went because of old age and it was as simple as that.

2. There is something genuinely wrong with my engine internals. Something is a training someone where and it is being taken out on the rivets. If the chain was that out of alignment, I would have thought weaker components would have failed first such as chain or bronze bush. Need to have a thorough inspection of the front a project but nothing jumps out as an issue.

This has really baffled me as it had been so trouble free previously. I've not heard of any issues of this nature with an AF clutch. I've heard if standard clutch rivets going, but surely 19-20hp shouldn't kill rivets so quickly?

Until now, I was unaware that the cassette clutch uses the same two piece assembly process as the OEM Lambretta.

I am amazed that the shearing of the wrought (softish) rivets has not been a widely publicised issue!

There's the problem, right there.

It might seem little consolation to you right now, but @ least you should relax that there is nothing ominous about the rest of your engine & that it produces enough torque to shear the rivets.

My earlier remarks about concentricity should still be borne in mind when re-assembling. It would also be great if the splined centre was able to be tapped to M5 to allow the use of high tensile fasteners to replace the rivets as they would cope & avoid welding too.

[NorthernJordan]

There is many a higher powered engine using these clutches than mine, so would have thought it would be a known issue if it was just that it needed a little weld to beef up the fixing.

That is looking like my best option, but can I repair my current one with loose rivets like that?


Jordan

[Sticky]

Any chance you can put some photos up Jordan so we can see the issue?

[NorthernJordan]

I'll try tonight...

It's just one of them that's quite hard to capture.

Just noticed it when I had side casing off and thought I'd check everything was tight.
This was rocking quite noticeably, so I tightened everything down again, still the same.
Pulled the clutch apart and noticed the rivets were loose and the clutch had been rocking on itself. This rocking had worn down the tabs on the clutch corks as they've been hitting the crown wheel.