Birth of a kit

[Strummer10]

^... having had a layshaft fail on me, I'm wondering what benefit the new design may actually have? I say this as the failure point that I experienced, which matches all other failures that I know of, which is where the shaft fails at the thread cut for rear hub nut. As we appreciate from cracks forming at square cut piston windows, sharp corners of bodywork, square cut steps in crank pins, etc. so I am concerned that redesigning the spline section of the body may not in any way address the failure point, which seems to be the threaded end of the layshaft. Unless this section is made thicker (bigger diameter) for a larger nut size, we may not end up with a product that is any better than the current layshaft.

Do we know if this threaded length and nut size are being increased?

Adam

Adam i'd be inclined to agree with your point also, unless a mechanical / materials engineer can conclusively prove there's no requirement to increase sectional size via engineering calculations......... including I guess the usual factors of safety (or however they do these things lol, .....don't ask me its way outside my knowledge).

AND Also is there a secondary device that can be designed to capture the fact if a layshaft does shear as Adam has noted, how the hub could be retained onto the engine case some way to keep the scooter safe .......only a thought again.................

[Sticky]

^... having had a layshaft fail on me, I'm wondering what benefit the new design may actually have? I say this as the failure point that I experienced, which matches all other failures that I know of, which is where the shaft fails at the thread cut for rear hub nut. As we appreciate from cracks forming at square cut piston windows, sharp corners of bodywork, square cut steps in crank pins, etc. so I am concerned that redesigning the spline section of the body may not in any way address the failure point, which seems to be the threaded end of the layshaft. Unless this section is made thicker (bigger diameter) for a larger nut size, we may not end up with a product that is any better than the current layshaft.

Do we know if this threaded length and nut size are being increased?

Adam

Breathe slowly Adam. The original design of the fully splined hub/shaft was with the normal size thread, but I explained to Vittorio that threaded section snapping off was the biggest problem and that has now been increased in diameter from 16mm to 18mm thread size with a special nut to suit.

Fingers crossed (subject to testing) that should be two weak links (hub and layshaft) resolved.

For me the remaining one is a gearbox that is significantly stronger than standard. There are now quite a few different people working on gearboxes in UK and Italy so we'll have to await the results of their labours.

We'll put more about this on SLUK as news comes out.

[Adam_Winstone]

Hi Sticky,

Cool, that's the response that I was hoping for. I'm glad that you offered that input as it is often the case of others being able to offer a good alternative view that stops fairly simple features (but very beneficial!) being overlooked.

Having had to address another case of snapped standard chain guides recently for a club member, I took him through the whole thought process of working out/avoiding known weak links to reduce the chances of something nasty happening and to increase the chances of making it from point A to point B reliably and safely on these old shopping bikes of ours. Layshaft is becoming increasingly more and more the weak link for those spending money on improved component upgrades so I'm glad to see that some thought is being put into it.

With an increase in diameter of threaded section, this may prove to be a worthwhile upgrade... providing the metallurgy, specification and manufacture is up to the job (thankfully in capable hands).

Nice work.

Adam

[Strummer10]

As well as Casa, I understand Tino is also developing a new engine case and components, and perhaps other designers..........is it worth them 'pooling their knowledge base' to collectively resolve some of these 'weak-links'....without the commercial aspect getting in the way......which ultimately would benefit safety overall.

[Knowledge]

^ Betamax Vs VHS

[Strummer10]

Wasn't the Betamax better, but the VHS stole the march.........lol

A bit like apple and IBM...........

[Sticky]

There's lots of new cases being developed. I've seen pictures of a new Tino one with external studs on Facebook but he has ignored our requests for more info so I can't comment any more.

Cases is a weak link that should be sorted by now with the parts available. Hopefully layshafts and hubs are resolved too, but only time will tell. There are plenty of good chainguides. cranks and clutches on the market now.

Gearboxes and engine mounts still need a bit of work IMHO, and the perfect ignition system (Japanese grade reliable, advance retard and good lights) still seems elusive. IMHO

[Knowledge]

Wasn't the Betamax better, but the VHS stole the march.........lol

A bit like apple and IBM...........

VHS stole the march because there was more porn available on VHS than on Betamax.

I'll stop now before I go off message.

I will add to Sticky's list of parts that are not yet available a decent headlight for a GP.

[Warkton Tornado No.1]

The subject of layshaft failures has been touched upon before, & whilst I can hardly argue that it is not a worry, I really find it frustrating that the issue has not been quantified precisely by those that talk about the subject as if the design is flawed.

Mind you, just because I’ve never witnessed, or heard of a failure during all of my road & racing experience doesn’t mean it doesn’t occur, but I think it reasonable to presume that racing would place the greatest stress on the layshaft. Yet despite this being discussed again, as far as I am aware, no racers, either past or present, have confirmed breakage to be an issue. However, I stand to be corrected....
Until this current thread on the subject, I’m also unaware of the reason for failure being pinpointed.

Despite the generalisation of it being ‘the thread’ I would place a lot of credence with Adam’s assertion that it is the undercut to the thread where failure occurs.
As he says, sharp corners are a stress raiser.

Nonetheless, greater stress leading to the likelihood of failure is far more likely due to inappropriate torquing of the M16 x 1.5 nut itself. Too tight or too loose @ any time within the life of a layshaft is likely to lead to failure.

Human error is far more likely to contribute to the failure of the Innocenti designed layshaft, yet, yet again, there is the pre-occupation in blaming the component!

Currently, I do not have access to a competent 3D modelling package, but I would bet somebody reading this does.....In which case, FMEA is likely to be available to them.

I’d be amazed if it could be proved that there is nothing less than a large safety factor within the design of the layshaft, despite there being the possibility of far greater loads with the transmission of the torque available in tuned engines. Of course, the braking load is not insignificant either.

As for the issue of hubs ‘failing safe’ as I have pointed out previously, the Innocenti designed rear hubs are designed to do precisely that by fracturing ‘inwards’

I can vouch for the fact that they do precisely that having been riding full chat @ Pembrey when one failed. There is no doubt that the Serveta hubs (early Innocenti design derivative) are stronger than the later Innocenti.

[Knowledge]

Well done WT1. You have expressed my own opinion on the layshaft failure very well.

I fear that the high torque figure for the rear hub nut is such that many people feel obliged to put all their strength into tightening the hub nut. This must lead to over tightening and stretching if the thread below the nut. The other factor is that this practise may have been on-going for decades before a layshaft that otherwise appears sound comes into the hands of a more attentive owner. Too late, the damage has been done.

So the issue may not be the design, but the age of the components.

[Sticky]

The design is not necessarily flawed, and agree that over or under-tightening can be a factor.

However, two things are certain:

1. at least one death can be attributed to a broken layshaft, and several crashes I know of (DSC Scotty among others)
2. the layshafts are now being stressed way beyond any design specifications both by the power of modern motors and pie and pint consumption of modern scooterists

[Warkton Tornado No.1]

Post by Sticky » Wed Nov 02, 2016 10:49 pm

The design is not necessarily flawed, and agree that over or under-tightening can be a factor.

However, two things are certain:

1. at least one death can be attributed to a broken layshaft, and several crashes I know of (DSC Scotty among others)
2. the layshafts are now being stressed way beyond any design specifications both by the power of modern motors and pie and pint consumption of modern scooterists

If the reason that anybody died due to a layshaft failure, then surely there must have been a full analysis as to why.

Whether the failure was due to inherent bad design, metal fatigue or any other reason, thorough tests would show the reason.

If I was in the remotest way connected with a person that died in such circumstances, I would want to know why.

Sticky, I don’t doubt what you say about the failure of a layshaft.

However, I doubt the reasons you suggest might be the total cause of the failure.

Before you cast such doubts upon the integrity of the design, & I’m sorry to repeat the phrase, you really ought to quantify, & qualify, the total facts.

I really am surprised @ the assumptions you’ve made & it’s not for the first time you’ve mentioned the fatality, tragic as it is.

That gives neither you, or I, the right to dismiss what can be proven to be an inherently sound component (having served well in tens of thousands of instances) just because it may be the case that another 'sexed-up' design awaits in the wings....

[dscscotty]

(DSC Scotty among others)

Yep I've had one snap on route to Belgium Euro, two up @ about 65mph, not a good feeling, mine was a series 2 Italian type, giving good service for nigh on 20yrs to me, and its former owners whoever they may have been. A pal travelling with me who has worked in the metal inspection industry for many years pointed out to me some flaws within the surface of the snapped shaft, he called it marbling ( i think?). basically you could see , tiny lines within the metal, which was fatigue, when I asked what may have caused that his reply was age! 6 months later my clubmate-Daz Ts1- Westgarth had one snap on way home from the coast to coast, same thing, also Italian. I know of another 3-4 locally in recent years, In my opinion no design flaw just fatigue / age and a part operating outside its design limits.
I now only use new more modern type layshafts, if nothing else they're not 50 years old.

[Adam_Winstone]

^.. the more people raise this issue, the more people then come forward with other known examples, as though this is more common than people are aware of.

I agree that fatigue over time may be an issue, as may incorrect loading on the thread (working outside given torque parameters), and I also think that loads imposed by riders may be a factor. I know that my layshaft had always been torqued correctly in the time that I had it, however, I also know that the combined weight of rider (rider and pillion in years gone by), tent, luggage, spares and oil must contribute to the stress that goes through the rear wheel/hub/layshaft assembly, all of which I believe may have been contributing factors in my case. However, these scooters are designed to carry 2 plus luggage so I guess that we then get into the questions of 'for how long' and 'for how many miles'?

How many years of hitting potholes can a layshaft take? Certainly, I've noted on Euro rallies that rear hub failures in Ireland (in the years when Irish roads had a lot more potholes) increased % dramatically. So, are we seeing failures because of application as much as, if not more than, failures because of assembly? I've yet to see a race track covered in potholes or 2 great lumps (2-up) with luggage or a race motor stay together for 30 years and 100,000 miles, which may well mean that racing is not the right application to highlight layshaft failures.

Good that people are discussing this issue though as failures do seem to be becoming more of an issue, which in itself might suggest that the age of these components and prolonged stress is a serious factor here. That said, I know of 2 failures of new layshafts, one Indian (thought to be SIL) and the other from a respected aftermarket source.

Adam

[Warkton Tornado No.1]

I reason that there are two issues @ the centre of this debate:

• Layshafts have failed for reasons as yet not fully determined
• As a consequence, the presumption that failure may be imminent & that a new non OEM design may remove that risk


Everything in life has a point @ which it needs replacement.

With a systematic approach, which may include many factors, such as ‘conditions’, ‘age’, ‘history’ & ‘design remit’ there is every opportunity to limit any dire circumstances that may come about as the result of failure & actually replace components before it can occur.

The race car industry is a typical example of where ‘lifing’ is applied to all of the components that are involved in any vehicle, from pistons through to suspension wishbones.

Why should Lambretta layshafts be any different? I would welcome that particular initiative to be taken on safety critical items were some respected body to take up the responsibility. Don’t hold your breath....

However, just because there is no such system in place, does not give anybody the right to cast doubts on the design of the component that has been the subject of this debate.

I have no vested interest in Innocenti or in ensuring that the designs should be considered to be beyond reproach or that they cannot be bettered.

However, unfortunately, there are factors involved in advocating the replacement of some components that have undeniable financial consequences.

What I take exception to is the presumption that failure of any part is said to be due to certain factors without there being something approaching absolute proof.

We may not all be privy to the full manufacturing processes involved when Innocenti were churning these things out, but, no doubt, there is an Italian with a high profile currently associated with Lambrettas that does have a precise record. I wonder if he’d be willing to share that knowledge.

The last time this subject raised its head, I believe that I suggested that it shouldn’t be difficult for any manufacturer of replacement layshafts to prove their worth with a full list of the material & processes involved in the manufacture.

In other words, if there is any claim that a superior product to the original is being produced, they really ought to be able to prove it....

[bsso78]

Phil Bevis had two layshafts let go on his Group 4 in quick succession and I had one snap while torquing it up on my Group 6.

[NorthernJordan]

(DSC Scotty among others)

Yep I've had one snap on route to Belgium Euro, two up @ about 65mph, not a good feeling, mine was a series 2 Italian type, giving good service for nigh on 20yrs to me, and its former owners whoever they may have been. A pal travelling with me who has worked in the metal inspection industry for many years pointed out to me some flaws within the surface of the snapped shaft, he called it marbling ( i think?). basically you could see , tiny lines within the metal, which was fatigue, when I asked what may have caused that his reply was age! 6 months later my clubmate-Daz Ts1- Westgarth had one snap on way home from the coast to coast, same thing, also Italian. I know of another 3-4 locally in recent years, In my opinion no design flaw just fatigue / age and a part operating outside its design limits.
I now only use new more modern type layshafts, if nothing else they're not 50 years old.

Didn't you have one go en-route to Cleethorpes about 3 years ago? When you were bringing me that end can?

Jordan

[Dazts1]

Another reason I thought about was suspension setup! Or lack off.
Before I started racing I was convinced I needed my suspension set hard. This was to stop the wallowing into corners of our performance enhanced scooters.
I myself have run R1 shockers with minimal travel at the rear of the scooter, convinced I was doing the right thing. Add pillion and weight from camping tools and spares. The rear shock will be compressed, not only R1shocks but other performance upgrades to. How many people actually try to set up a rear shock, or just bolt it on , Possibly set to hard. Them potholes bumps etc have got to be absorbed somewhere. The rear wheel is exactly where this will be absorbed. Put a performance motor to hard set suspension and a fatigued rear layshaft all into the equation. Something's going to give !

I'm not saying this is the reason behind the failure's. But since I've started racing I've realised you do need suspension that works. Them tracks may look smooth but very few actually are. To hard a setup results in the bike skipping all over. It's got to be absorbed somewhere. If not through the shocks then through the wheels.

Daz

[Warkton Tornado No.1]

This debate can run & run but as far as I’m concerned, the gauntlet has been thrown down.

Post by Warkton Tornado No.1 » Thu Nov 03, 2016 2:17 am

I reason that there are two issues @ the centre of this debate:

• Layshafts have failed for reasons as yet not fully determined
• As a consequence, the presumption that failure may be imminent & that a new non OEM design may remove that risk

Verifiable proof (as to why layshafts fail) is what it all boils down to.

It’s the first I’ve heard of layshafts failing in racing, but, with respect to Phil & you, Barrie, were the layshafts brand new or of absolutely known providence? I doubt it.

As for road conditions, yes, with the exception of the ‘Twisted Sisters’ a race track is usually much smoother than our roads, but what about Indian roads?

Again, if anybody knows of wholesale failure there, bring it on! Are the Indians any more likely to have stuck religiously to any advised torque figures than any pre-owned Lambrettas sourced from the UK or any part of Europe?

What else?

Tyre pressures? Aftermarket suspension?

Both are issues discussed in some detail for other reasons, but both do their part in absorbing shock.

Hopefully, somebody is busy squirrelling away somewhere to bring some unquestionable proof to this debate, rather than allow the wholesale dismissal of an OEM component.

I have no doubt that the Lambretta layshaft can fail, but I have far greater doubts about the human beings & circumstances involved in any failure & feel they may have contributed more than any other factor.

In all probability, there will be a way by which existing layshafts could be tested by a non-destructive means.

If I had the resources combined with the long term concern for the safety of Lambretta owners, I'd be investing in such a means of proof, rather than concentrating on the replacement of a component that has failed for reasons , as yet undetermined but widely speculated....

[Nudger]

I'm reading this thread with interest as it's particularly poignant for me.
I was rushing back from the 2015 Euro Lambretta after receiving the news that my Dad had been killed in an accident.
I was on the German autobahn when my rear brake felt like it was beginning to bind a little. Just at that moment I was able to come off at a service station.
This is what had happened & I think God had decided that for my family, two accidents was enough.

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