Minicomtesse and the Shake of Death

[steven mandell]

Historical review;
I first saw this Minicomtesse in the Sales and Auctions section approx. one and a half years ago.  Remember the silly picture of one doing a wheelie while supposedly towing a big car- yeah that was the one on EBay UK.
6 months later got it to L.A. to discover engine not working, and clutch exploded internally partially stripping crankshaft splines.
Now, approx. one year later I hope to have finally conquered clutch issues with parts rounded up from US sources, and much detective work re orientation and shimming of parts.  This was needed because I was not able to find enough good reference material, and both the parts that were shipped, and the clutch as it came were apparently assembled improperly.

My first attempted test ride brought heavy balking and stuttering and no forward propulsion.  The engine idled well, but I was hoping that perhaps the extra loading of engaging the wheels and attempting to propel the car and myself was showing a lack of engine tune rather than a still bad clutch, and that that was what was causing the commotion without motion.
After another day struggling to get at the points (engine cover held on by slot head screws recessed into tunnels too narrow for impact hammer, and likely tightened by a Gorilla 20 years ago), I got the ignition spot on.
The points were in good shape, but gapped 9 thousandths too large and opening 2 m.m. too soon.
This time I cleared out a path through the  microcar patch all the way to the road.  It took off surprisingly well, but upon the dreaded shift into second gear a resonance started that if allowed to continue, felt like it would rip the front wheel and engine right out of the car!  The equivalent phenomenal on 2 wheels is called a "tank slapper".  But why only upon the up shift to second gear?

I know that some sort of destructive, amplitude summating resonance must be getting initiated here, but I don't know exactly why these apparently unrelated parts are conspiring to self destruct.  Therefore, other than immediately backing off the accelerator pedal, which stops it immediately,  I also do not know what to do about it to stop it from becoming activated in the first place.  Sure I could and likely will put a steering damper on it to quell the chicanery, but why is it necessary for me to be dealing with this?
Anyone heard of this happening in other Comtesses  or other single front wheel cars.
The steering seems to have very little play- only about 1/4 inch either side of center at the steering wheel.
I have seen a diagram with French titling previously that appears to be showing how to set the chain tension on the steering gear that has the engine sitting atop it.  But with a total steering wheel play of at most 1/2 inch, could this really be what is at cause here?

[Peel replica, Steve Fisk]

Mate it sounds like it's behaving like a shopping trolley , if a bike had completely upright front forks it would tank slap , it needs to have abit of an angle to it like / , Maybe some shims are missing to make that angle

[Big Al]

Need it in front of me. The others I got going never did that. However any loose element or wonky drive could promote instability. I am slightly concerned when you state that the new clutch was assembled incorrectly.... And it happens when that is asked to operate, but is otherwise OK. What happened about the worn spline? Are we visiting the original problem that broke the car, that was never fixed? More sleepless nights I fear.

[steven mandell]

I understand that increasing  the rake of the forks would diminish this tendency.
However this is a non adjustable aspect of the car's design, so it couldn't be the deciding factor unless it was built wrong and did this from new.
Given the gravity of the shaking, that seems very unlikely.
So, assuming that I could redesign the front end fork angle, this could be a potential means of compensating for the thing that is wrong with mine that isn't wrong with the others.  But it would not be fixing the thing that is no longer doing its job the way it used to, as we still don't know what went wrong.

[steven mandell]

Al,
I was only able to get  a  lightly used almost complete clutch.
The condition that I received it in turned out to be assembled incorrectly.  But that was probably because who ever took it out couldn't remember how to put it back together.
In consideration of the fact that my original clutch was severely damaged, it seemed more wise to trust the undamaged lightly used clutch's assembly pattern. 
It wasn't until I took the clutch off for the second time, and just struggled through trying to figure out what its parts were trying to tell me about how it should be shimmed and assembled that I realized that neither clutch probably was likely to have been assembled correctly in the condition that I had received them.

I carefully, and lightly filed crank splines.  Only the last quarter inch or so that only engages the manual over ride to up shift into second gear is seriously compromised.  I used a metal filled epoxy on that last quarter inch to partially compensate for the loss, but do not plan on taxing the connection by pulling the rubber handled, dash mounted cable control that would cause  manually instigated 2nd gear engagement.  That is usually reserved for jump starts.
So I'll just make sure my battery is fully charged, or that someone has jumpers nearby.

That leaves me looking for something loose whilst the steering feels quite tight.
How would one check for vertical play in the steering head, and what amount of play would be considered to be normal?

[Rusty Chrome (Malcolm Parker)]

Other things that might cause tank slapping would be something running out of true or out of balance which increases in rotational speed when you shift to second or something that is flexing under load. Could something have been bent or forced out of alignment when the clutch was wrongly assembled by some ape trying to make it fit?

[steven mandell]

It seems to be triggerred by the transition into second gear, rather than the absolute speed of the rotating masses, as if I back off slightly during the upshift, the whole cascading calamity stops/ is avoided, and both engine and vehicle speed continue to rise smoothly.
The crankshaft does extend about 3 inches beyond bearing support to connect with the inner splined elements of the dual centrifical clutch mechanisms.  Wonder if that part could be bent, and how to check it without removing the 2 speed tranny/ clutch?
What could flex under load?

[Rusty Chrome (Malcolm Parker)]

What could flex under load?

A hairline crack or broken weld in the right place.

[steven mandell]

I like your reasoning, but we all seem to be missing the mark so far.
Schedule permitting, I will do a brief inspection and attempt to post a picture or two of the fork/ engine mounting next morn.
On a car as lightweight as the Minicomtesse this structure is shockingly overbuilt on a massive scale- so doesn't seem likely to have failed.
But something obviously has, and there aren't very many parts that could be involved with a car this simple.
So it makes sense to go over the few there are with a fine tooth comb.
I hope it gets tangled up in something that's easy to fix.

Any suggestions as to how to check out the single front wheel front end?

[steven mandell]

As the pics show, this is the only part of the vehicle that appears unlikely to fail.
My biggest open end wrench wasn't quite big enough to wrap around the big nut atop the steering axis.
But pushing the car in line with the front wheel axis demonstrated no percievable play between the side of the wheel rim, and the heavy bent plate that mounts the engine and front wheel spindle, and there is no shock or spring to complicate matters.
It is very simple, but I have no idea what it is.
Well at least it didn't disqualify it from entering the Concours de Lemons in Monterey in a couple of weeks.  As a matter of fact it just now earned the dubious distinction of being officially accepted into the program. 

[Peel replica, Steve Fisk]

Take the chain off and tow it , see what happens

[Rusty Chrome (Malcolm Parker)]

No idea whether it would make the slightest difference to the handling or not, but one thing that looks a bit different on your car compared to some other pictures on the net is the diameter and positioning of the plastic chain tensioner. Some appear about twice the diameter of yours and most have the tension point a lot closer to the outer edge of the front tyre than on your car.

[steven mandell]

Good observation.
That would put the other cars chain tensioner closer to mid span, which I would think should be more ideal.
Perhaps incorrect drive chain tension could be a factor in creating this resonance.
Anyone know exactly where to measure, and how much forced slack I should have?
I would like to be clear on  if the amount of slack is measured by pushing just one direction against The chain length, or if it is a total measure of the amount of slack created by pushing in opposite 90 degree tangents to the chain length, or about twice this amount.
That is something that I have been unclear about several times before.
This just in, I bought another Minicomtesse today.  However it is unlikely that I will see it for another few months.
So immediate utility for comparison purposes will not become available before I would like to have this one handled.

[steven mandell]

Still would like to know how to establish correct drive train tension.
  But that didn't stop me from taking my own advice to Bob re how to establish correct toe in with radials.  That is, I measured my current , as it came to me drive chain slack of 1/4" each side of rest / total of 1/2", and then loosened it up a bit to produce 3/8" each side of center for a total of 3/4".  It is just possibly starting to shudder at a slightly slower rate of oscillation.  I'll have to figure out some way of measuring the speed of shuddering before I can know if that statement is true.

But the magnitude of the "tank slapping" overall did not seem to be diminished.  I made an observation seemingly consistent with my prior observation that lifting off the go pedal momentarily during the transition to second gear engagement by its centrifical clutch, stops the whole cascade of horrors, and allows the car to continue to accelerate unimpeded.  The consistent observation is that, the shaking is worse when proceeding up a slight incline, and not as bad when on a slight decline.  So apparently the amount of load that the drive train is under affects the degree of shaking.

I no longer think that the chain tension is likely to be the primary at cause culprit here.  What a shame, as I had visions of an overly tight chain oscillating like a stretched, then twanged rubber band.  Although it still seems likely to be exerting some secondary effect- especially if chain tension does affect the rate of oscillation.

a possibly more fruitful image that has occurred to me via thought experiment, is that an oscillating drive train speed as the immediate inductor of steering shudder seems quite likely, as the drive sprocket for the single front wheel falls necessarily displaced from the wheel's  centerline.  The chain would have to run through the mid tread of the tire for this not to be the case.  So an oscillating speed of the chain should produce oscillating torque steer.  I now think that this is what is happening here.

It also occurred to me that my use of the correct amount of automatic transmission fluid in the clutch bath could be a factor.
I went with info I saw on the Fox Sundowner minibike forum on these shores for this recommendation.  I think that if it were the wrong fluid, and that was prime cause here, that some irregularity of first gear engagement would be noticed also- and it isn't.

But why just when second gear is engaging? Bent outer bell of clutch causing intermittent contact during transitional engagement?
Irregularity of anti centrifical force spring that resists expansion of the second gear clutch?- less likely, as it looked OK.

Feel free to chime in with your theory, or better yet an easy to do test that would generate inescapably significant  results that point to the true cause of origin of symptom.

Best case being someone with a 2 speed centrifical clutch car having had and conquered this problem before.

Jean Do?  French Minicomtesse club- are you out there?

[Stuart Cyphus]

 i can't say I ever noticed any sign of tank-slapping with mine. I always found my steering was totally and utterly neutral; it went where you pointed it and you pointed it where it goes. I can't remember if mine self-centered or not under drive but I know I had to shim out one of the small steering chain sprockets and also to tighten up the steering chain DEAD tight to stop the steering chain pulling off on full lock. The slightest precieveable slack in the steering chain and off it would fall at full lock.

 As regards shuddering when changing up into second, I never noticed mine doing such, but then mine would never change up automatically, only manually, so I was probably too busy holding steering wheel in one hand, pulling gear-change lever with other hand and blipping throttle with foot for just the right rev range for the gear to take in, to notice any peculiarities as the gear fed itself in, as all the above often had to be done three or four times in quick succession before it felt like taking second gear. 

 I can't recall ever having to touch the main drive chain for any reason. 

 Edit;  try changing up manually a few times & see if it still shakes that way?

 Of the battry/cubby boxes over the rear wheel arches, these were just simple open-topped fibreglass boxes sat on top of the arche & bonded to the inside of the car. I can't remember if they were a full four-sided box or a three-sided box using the side of the car as the fourth wall (like a Peel P50 petrol tank) but I seem to think the former sounds right. Two pics attached which are the best I have for showing these boxes.