What am I doing and why.....

What am I doing and why?? any ideas? Its at a Mallory Park practice day in August......

It´s just as I thought -- even in practice you experience rushes of blood to the head...

Nice picture Mike! Lovely looking bike -- you oughtn´t to be allowed to break it!

It reminds of a pleasant Saturday at Thruxton -- I think in 1968 when I had a chap name of French up my exhaust pipe all the time and on the last chicane -- about 50 yards from the finish I lost control completely and did the same as in your pic but managed to stay on hence cutting out the chicane and holding onto 4th position. Both rims were well dented and I said to M.French that he should put in an objection but he said the scrambling action was worth the 4th place...
Good old days -- Naked Bantams-- no fairings.

One of the questions I wanted to ask: what changes hae you made to the NORMAL layout of the Bantam gearbox? If you wish to maintain secrecy then send me an e-Mail...
Cheers!

Looking desparate for the gents I recon....
Chris

I'm not practising crashing, well not deliberately!

There is a reason why I had to bail out....

Ned should know the reason

Hi mike
looks like the throttle got stuck???

or your brake pads fell out ???

mjpowell wrote:

I'm not practising crashing, well not deliberately!

There is a reason why I had to bail out....

Ned should know the reason

Could it be that the clipon has broken off. Or has the brake lever gone back to the bar ?

Stop on! My clip-on had become a clip-off and i couldn't get the pressure needed on the lever.

So jumped off and threw bike down before hitting tyre wall.

Fatigue Failure --

I Foff esq....!

I´m right!
I diagnose Road Rage!
M. Powell trying to wind on more throttle has exceeded the Ultimate Tensile Stress of the weld??
Weld? the other part was brazed -- can´t see any braze on the broken bit...hmmm

I M Foff.

Had another look -- there is a tiny smear of yellow at the top of the broken tube -- but that brazing on the other bit looks like yellow bubble-gum.

`Scuse me for being so critical.

Mike,
Great pictures ,on the latest evidence i have decided to have my bars crack tested as opposed to my layshaft !

Nick!
You must take care of your Lay Shaft ...

John ,
thanks for your concern, my layshaft is new old stock so what do you think of a part that has sat on the shelf for years ?
by the way like your posts and agree with most off your opinions.enjoy all your funny stuff keep em coming!
I do worry on some of the techno stuff that it stops people posting an opinion but ha ho thats life. For me the old school racers / tuners posts are magic.

Cheers Nick.

A few kind words at last -- thanks Nick.

Your old layshaft -- crack detect it and you´ll feel better. Fatigue cracking is an unfounded scientific phenomonen which in plain English means its very doubtful that your laying shaft-- sorry I mean layshaft -- is in any way Unserviceable. The Bantam one is less than 4 inches long and by vitue of that fact be very durabkle.

Re Mike´s Layshaft failure.
Note the number of undercuts on the layshaft -- 7 -- and where Mike´s L/S broke was at the middle (1.9ins from end) undercut and root of splines -- that is, according to the gearboxdrawings Alan has put on the front page here.
The bending & torsion stress act at the stress concentration of an undercut even if it has the tiny radius -- as shown in the drawings...
Just for the heck of it I calculated the torsion stress as being 5,866lbs/in² torque then doubled it for MRR*** shock loading as 11,733lb/in² which is 6.5% of UTS of 80ton/in² steel. Should never break by torsional loading!
So I conclude that torsion stress alone could never have been the cause even if the steel was only 60ton/in² would still be only 8.7% of UTS and doubling for MRR would only be 17.4% of UTS....

The bending stress is a complete unknown. I suggest it is there and in combination with torsional loading contributes to the fatigue cracking... after several million rotations of the layshaft...

If you want to see the calculations for the torsional stress I shall show them.

*** this is a new phenomonen in the science of Layshaft Failure fault finding -- Known as Mike´s Road Rage gear changing....
I wonder if it is the only case, or is there a Robbie one too??

Cheers!

PS.. torsional stress was based on a max torque of 12lbsft.

Was that torque too small?

John,
watching mike drive past me out off the old hairpin at Pembrey in the wet race leads me to believe that his motor has more torque than that !(think i was in front of him for all of 3 seconds)he then disappeared into the distance along with Ian & Tom never to be seen again.
On the Robbie gearbox failure i think his layshaft survived.(did it Rob)
Perhaps his problem was one of a combination of unfavourable circumstances,possibly ;A very powerfull motor (again one that disappears in the distance) B over enthusiatic gear changes. C big heavy flywheels (didnt break Rossis box at the moto gp) D excess bearing clearance. What do you we all think?

regards Nick.

Have to answer you Nick before you let the doom & gloom get at you because those three made you feel bad by passing you at Pembrey... Makes one feel like kicking the cat -- do you own a cat?

Taking your comments in order -- A. They had Very powerful motors -- All three obviously DO have very well-tuned motors -- and it takes only a couple of horsepower more, or getting the extra bit of torque in earlier -- that makes it look as if you are standing still -- I know the feeling when riding a `slow´ Bantam. Borrowing a quick 250 improved my self confidence and made me more aware....

B. Getting back to layshaft failure & the `overenthusiatic gear changing´ (I mentioned as "RR"). I did see some very snappy gear-changing by two of the three (above) when at Lydden in 2005 but that, as cause of layshaft breaking, is still only a remote possibility based on shock-loading well above that which I calculated and needs looking into relative the factors involved from flywheel to rear wheel but, as I said, so far, even the shock-loading seems far too low to cause the shaft to fail.
C. I´d say Rossi´s gearbox failure was more likely to be a bit poor preparation of his Ducati -- if you have read John Koschinksy´s comment on Italian mechanics and heard my son Slick´s opinion you might agree. I must say Rossi seems very wild....
Slick saved Fogarty´s engine from total destruction at one WSB meeting when a mechanic, who was changing the oil (and had already drained the old oil out) took it into his head to start the engine before putting the fresh oil in.

This heavy-flywheel versus light-flywheel argument I thought was brought in as a factor of handling in that power coming-in, in a rush can upset -- unseat -- a rider not used to the tendency.
In terms of adding to the stress to break a layshaft it would mean that bit of extra stored-energy would have to be applied with the back-wheel locked as it were -- and that doesn´t happen, frequently, in road racing -- does it?

Of course the failed shaft could have had an inclusion, or have been wrongly heat-treated -- as Derek suggested-- and the 12,000lbs/in² shock-loading stress been enough to break it.

I shall think a bit more about Light/heavy flywheels and what the difference means -- saves me thinking about things -- I oughtn´t to think about.

Nick!
how long have you been racing a Bantam?

I ask because except for a DNF you are well up in points.

Your note D. was it? about clearances?
What B... clearances?

If you meant between parallel gear shafts & mating gears I´d say, Yes! that could have a bad effect on geabox reliability because the teeth of gears (involute form) are meant to ROLL on each other -- not slide or skid. I am a little out of my depth here and no doubt someone will put me right. I think when the teeth of gears mesh too deep that can cause lots of trouble with a Big T but when at greater than design depth (too much clearance) they still roll together in correct manner -- the only thing then is backlash which might have a bad effect on the surface hardnes and develope into an eventual tooth failure....

Very important check to make is on teeth condition.

Just an afterthought -- I wonder what a `rocking´ layshaft might do?

Cheers!

hi john - glad to see you admitting this faliure was due to some form of unknown failure in the manufacturing or metal structure.

I have to remind you I have been saying this allalong, and did say this on the very first day i posted a reply to this post.

Regds Derek

Hi Derek!
You are back!

No! No, I didn´t ADMIT anything...

Re the broken layshaft -- I only said IT COULD HAVE BEEN a failure, as per Derek´s suggestion attributable to inclusion, material or heat-treatment defect -- which might not be exactly as you said it but was the same meaning....

I would not claim to know what happened until I have all the FACTS. So far the only postive fact is that this layshaft is an old type and that Mike has given it a hard time for 300 hours -- or so -- because it was originally in an engine meant only to transmit a max of 5 horsepower ....

I also stated earlier that I might be wrong in assuming a Fatigue Failure BASED on the one pic shown ...

Mike doesn´t seem all that bothered -- pic next week he said and it is now Thursday and no pics of the other part of the shaft. I would like to see the first picture showing more detail of the failure face...

Fact is a fatigue crack failure shows it is so by having parrallel lines across the face of the broken surface which indicates -- that like the ageing of a tree, by its rings -- you can see, with a broken shaft, that there was an initial crack a long time back, then another crack a big bit later then another crack in a lesser bit of time, and following in order, parallel lines showing cracks occurring in lessening time periods -- and so on until -- the bit of shaft left taking the turning force fails because the torsion stress (plus bending stress if any) exceeds the material´s UTS (Ultimate tensile Strength).

What I find as a positive distinction is that the layshaft failed at the middle undercut. I looked up the gearbox drawings Alan has put on the front page and the layshaft drawing show the total length as 3&13/16s" with that middle undercut at 1.9" from one end. Roughly the middle!!!

It could be coincidental that an inclusion could be exactly there -- or it could be
that the inclusion ran the whole length of the shaft.
Heat treatment defect similarly....

Another aspect which brings me back to the Wölher theory of fatigue failure is that the layshaft drawing shows radii at the undercuts as 0.006", which is far too small (in relation to the effectiv dia) by modern engineering standards.
Norm or Standard now for down steps of dia in a shaft are r/d as a minimum of 0.1 of d, which means that with a shaft of d = 0.5" the minimum radius should be 0.05".
Maybe, on the drawing, I read the number wrong and need new specs....

To show how important the quality of a machined or ground radius relative a change of diameter is, shot-peening and rolling of radii was introduced in the late 60´s.

To conclude -- no ill-feeling re the above -- argument withOUT a bit mouth-frothing is hardly real debate.
Cheers!

JayBee.