My 131 abarth (never ending) story - 2017 season updates

[miro-1980]

Drive train inspection.

The shaft we have is used but rebuilt when installed mid October last year. The spiders were standard - not heavy duty. During inspection we noticed as follows:

a/ The small free play between splines on the sleeve yoke and the shaft. ( The shaft yoke will be replaced . maybe the short shaft as well)

b/ Bearing of the shaft support , the bearing flexible carrier and bearing carrier outer tube worn, All will be replaced

c/ Shaft spiders worn ( will be replaced )

d/ signs of movement between shaft flange and and diff flange. ( We will now use 12 grade bolts and nuts to get it tighter. We also will put between them a micro thin diamond friction sheet to prevent any movement when bolted together.

e/ we still need to check the state of the gearbox flange and the state of the gearbox shaft splines.

Re: Clutch

FRICTION PLATE WEAR .jpg (80.07 KiB) Viewed 11360 times

The wear brought the friction plate to minimum thickness. I measured it : the total thickness (side to side) now is between 7.25 (close to the outer edge) and and 7.56 (close to inner edge). The friction material thickness is 1.5 mm. The distance between the rivets and the face of the (worn) friction plates is about 0.5 mm

PRESSURE PLATE 2.jpg (113.47 KiB) Viewed 11360 times

The pressure plate is discolored and just slightly showing signs of mechanical wear. It was apparently caused by the powdered friction material. Minimal scratches on the rivets I holding friction plates in position. Again this was caused by the powdered friction material , and not by direct contact of the rivets with the pressure plate.

The plate was still usable when we took it off , but the pedal felt higher than when it was originally installed.

Re causes: As I am not in habit of ridding the clutch pedal and the cable was not too tight the cause must be one : my driving style , or what you call "outrageous standing starts" . When you compete on “stop and go” events with relatively large number of standing starts , some of this is to be expected. Especially with the short diff. With the metallic clutch traffic, traffic driving (pulling up few meters several times before you can get pass the green light) is also a contributing factor.

So clutch wear must be expected, buy after just five events seems bit too often.
I must do something about or face expenses of changing a clutch after every season. Will start by drastically altering standing start strategy: start at 5 K RMP and accelerate when the clutch is fully released, further limit traffic driving to necessary level only. Making sure that cable is properly adjusted ,etc.

Note that this is something I faced before. Before , when I was using standard clutch an original (NON-GCRE) engine a standard Sachs heavy duty clutch would last me one season only and standard non -heavy duty - clutch would last me one event only So new task in front of me : think clutch use !

Miro

[TomLouwrier]

Hi Miro,

d/ signs of movement between shaft flange and and diff flange. ( We will now use 12 grade bolts and nuts to get it tighter. We also will put between them a micro thin diamond friction sheet to prevent any movement when bolted together.

If your bolts want to loosen up, just tightening them harder (and fitting 12 grade ones) may not be the best solution.
A bolt is is really nothing more than a spring holding things together. The longer the bolt, the more flexible it is while giving the same pulling force at a certain point.
Short bolts are stiff and will lose pretension quickly when their length alters (from settling gaskets or from washers or flange surface giving in a bit).

Short or standard bolt has steep relation between clamping force and length

flange with bolt and nut.png (19.48 KiB) Viewed 11355 times

Longer bolts will hold their pretension under those circumstances and thus also the friction that keeps the bolt/nut from undoing. Also, and this is a bonus for your shaft: longer bolts have a longer life under vibration.

Longer bolt is less affected by changes in clamping force due to differences in length

flange with spacer long bolt and nut.png (18.48 KiB) Viewed 11355 times

I'm not sure how much space you have around those flanges, but you may be able to fit a bush (as in 'a very thick washer') between the flange and the bolt head. I'm thinking something around the flange's or bolt's thickness, so anywhere between 10-20mm.

regards
Tom

[miro-1980]

Tom,

Most interesting and informative !

The situation is this.

The bolts we used so far were ca 40 mm long. The space between flanges is minimal. The friction is caused by the fact that the flanges are not one piece mechanical element but a two piece element. When shaft flange starts applying turning force the diff flange the diff flange resists with opposite force and before it diff flange is forced to move along with the shaft minimal movement occurs. The shaft flange starts mowing between the diff flange does, so you can look at at as a slight delay caused by the connection not being stiff enough. This is minimal, but potentially threatening the bolts being cut off.

FLANGE FRICTION .jpg (38.77 KiB) Viewed 11350 times

Its is not that the bolts loosen up, it is that due to their grade we cannot tighten them any more.The pulling force of the bolts is not large enough to resist giving in to the turning force applied by the shaft.

So my solution is two fold :

1/ increase strength with which these flanges are held together (going from 10 grade bolt to 12 grade )
2/increasing friction between the flanges so the movement is limited and hopefully eliminated.

I see no possibility of fitting them any tighter in the respective flange holes.

There is sufficient space on either side of the flanges and thick washers can be applied. Do you think installing them would help limiting this minimal movement.

Miro

Note : when you add up all the minimal delays caused by wear from where the shaft starts and where it ends this is at least a 1mm. When you do a standing start suddenly these series of minimal looseness' accumulate and at the diff side becomes a sock which may damage the diff gears. We will try to eliminate the signs of wear so the total accumulation of "free play" will be reduced to absolute minimum

[Guy Croft]

Can't say I fully understand the failure mode on this shaft thing.

Any chance of an annotated photo showing what is wrong?

G

[miro-1980]

Guy,

The Shaft is at a shop being fixed , but when I pick up I will take pictures to show what was wrong.

Essentially , the problem was the wear of all connections of the shafts which accumulated to cause a "free play" which I want to eliminate.

Thanks

Miro

[TomLouwrier]

If these bolts do not give enough preload on the flange to withstand the torque then you should consider putting dowels in there like Guy does on flywheels. Bolts are not meant to resist shear loads, it's the friction between the flange faces as result of the clamping force that transmits the torque.

You may be able to fit two hollow ones around two of the bolts, using the existing holes as location. Drill both flanges in one go (bolts in the other holes to fixate the pieces).

regards
Tom

[WhizzMan]

I've seen bolts loosen up on drive shafts on a few occasions. So far, those were all cured with some thread lock (BMW actually wants you to use that on the E28) and/or nylock nuts (Alfa fwd cars). Both have 10.9 grade bolts. I've yet to see those fail when they did not come loose first. Tom's suggestion of doweling may be a very good solution to prevent play as well.

[Guy Croft]

"Bolts are not meant to resist shear loads, it's the friction between the flange faces as result of the clamping force that transmits the torque"

not entirely correct. It actually depends on the application and in many cases of rotating joints the bolt will accept some of the torsional shear load. You see this with non-dowelled flywheels - they 'walk' until the FW is in hard contact (in direction of rotation) and you cn (depending on the bolt design) get embedding of the threads in the bore of the FW hole. I use the word 'bolt' loosely - more strictly speaking it is a 'screw'. A bolt joins to a nut and a screw goes in a threaded hole in the adjoined part but - it matters not frankly. Ideally the bolt will have a shank so the shear load is taken on the full diameter but if the bolts are strong enough - it doesn't matter. Fiat used to use shanks on early TC FWs but dumped the idea later on. This torsional shear/shank rule is also applicable to racing clutches eg 7 1/4" types.

The integrity of any joint depends on the applied loads and joint (overall) stiffness. (Something, Tom, you're clearly familiar with). Apart from torsion we can expect tensile loading and vibration effects so joint security is worth dwelling on in some detail.

Insofar as this propshaft joint is concerned with a bolt array of only 4 bolts (I assume) and given that the flanges are probably ordinary carbon steel one can assume a degree of embedding of the bolt heads in service and fractional loosening so it is inevitable the flanges will exhibit a degree of relative rotation and that's OK provided the bolts don't actually shear.

As for dowels etc, more later,

G

[TomLouwrier]

hi Guy,

Agreed of course.
I accept that flywheels and such shift under load until they settle on the bolt. However as structural factor in designing the joint I would mostly consider that a bad practice. It would be quite difficult to predict and control the total combination of tension, shear and bending (plus the residual torsion in the bolt from torquing up).
Shank bolts are indeed a nice integration of both a bolt and a dowel into one. They do need their own specific holes, with the shank extending into the threaded part, so that it bridges the joint.

regards
Tom

[Guy Croft]

yes Tom, agreed.

When fitting FW in fact I always turn the item contra direction of rotation prior to bolting-up, thus ensuring that it is already bearing on the bolt.

This kindof makes good sense..


G

[miro-1980]

Thanks Gents,

This is most informative and will indeed help me understand the physics of the shaft/diff flange connection.
It ain't as simple as it looks, especially when performance loads are involved.

Thanks again,

Miro

PS: Nowhere else but exclusively on this exclusive forum one can count on such educated and informative exchanges. How could I live without it ? Thanks you Guy for keeping this forum so professional and thank you all members for your invaluable contributions.

M

[miro-1980]

It looks like our car is gathering a lot of interest of rally fans in Poland.

Major internet rally services announced out participation in "St.Barbara Rally- the race of the champions"

I am surprised ... but quite happy ...

Miro

[Guy Croft]

yes well just make sure you get a 'finish'.

GC

[miro-1980]

Guy,

I always follow the rule coined by Sobiesław Zasada, winner of European Championship ( before it was called WRC). He said : "The winners are at the finish line". So the first goal is to make it to he finish line intact , the rest is only a position among the winners...

This really be an exhibition event on my part. So, I do not anticipate any push for time at all. Anyway, I will be among the true champions of this sport in Poland in 2011 including three times Polish Rally Champions and winners of 2011 Rally Monte Carlo : Bryan Bouffier i Xavier Panseri. as well as Legendary Polish rally drivers of 70's and 80's so even contemplating to compete with them on equal footing would be arrogant and absurd. I just want to show this car in rally action and do a decent exhibition drive.

Miro

[WhizzMan]

You're not fooling me, you are going to try your best to put a decent time on the boards there, regardless of the competition. No matter who else is racing in an event, you'll always be racing yourself. You may not be up on the podium, but you'll want to go home and be proud of your achievement, no matter what position.

Good luck, and make sure we get to see some video of you and your car in action!