Manufacturing marks or wear?

[mk1-mark]

IF it is wear there will be corresponding marks on the other part of the assembly. Are there?

[Ruairidh Dunford]

Are the marks in line with the teeth or the valley between? Could the clutch plate come back far enough to chatter against the gearbox primary splines?

This was my first thought but (to answer the above question from Mk1) I don’t have the gearbox to compare...

[Ian Williams]

To my mind these look like manufacturing marks, if they were wear from hitting the primary splines they would be more rounded and polished in appearance, probably with a slightly raised edge rather than having such obvious machining lines in the marks.

[Colin Morgan]

Does the likely diameter of the spline cutting tool used match the curvature seen in the scrapes?  Is there a feasible size of circular cutter that would produce these marks in that place at the end of its travel?  

Colin

[Colin Morgan]

Had a look at this - a cutter about size of a pound coin could have made the marks...?

Colin

[Ruairidh Dunford]

Several people have now contacted me to say they have seen similar wear when the flywheel is sitting too far back, I will investigate this.

Also received the following:

“I’m more inclined to think that the witness marks are due to wear and chatter and not any sort of manufacturing mark. First off, they look too fresh and bright to be the remnants of the original manufacturing process. Secondly, I don’t think the splines would have been ground as suggested. The tolerance build up indexing from one spline to the next would, I believe, cause a problem and maintaining the accurate shape and size on the grind wheels difficult. Given the large numbers produced I’d expect that the splines would have been finished to size by broaching, possibly using a matched set in a sequence similar to first, second and plug taps. Broaching would be far quicker than grinding each individual spline allowing high production rates and would give good consistent accuracy. This may also explain the mystery of the master spline – it’s included to ensure that each broach (in my imagined matched set sequence) is placed on the shaft in the same angular position as the previous broach in the set.

Ready to be shot down in flames but I’m not sure that you can hob splines on a shaft and leave a master spline?

So if it is wear, what’s causing it? There’s not much of gap once the gearbox is fitted so if the flywheel is sitting slightly too far back the plate could be chattering on the gearbox input shaft female splines. Possible causes, I don’t know, how about the front bearing flange having been repaired positioning the crank slightly too far back, new crankshaft fitted and flywheel ending up slightly backwards, badly worn gearbox bearings, problems with the rear roller main.”

[Colin Morgan]

Interesting that every mark looks identical - same shaped scratches to same depth.

Colin

[Andy Bennett]

From an engineering rather than Austin 7 perspective, aren't the marks too broad to be wear marks? For the mating part to be able to make so many clearly visible individual grooves it would need to either have this profile on every rubbing part to wear a replica profile or be able to move side to side by 3-4 mm and so be an incredible loose mating fit to chatter around so much? Is that even possible with the size of spline without the mating splines being about 1mm thick to give the lateral movement required?
Also if chatter is the cause and the splines can move around enough to produce multiple grooves then why are there no slightly lateral scratches, why is every mark perfectly radial?
And is the diameter of the wear marks no much larger than that of the mating splines, or is that an optical illusion?
It just doesn't look possible for a mating part to wear such an identical and yet severe chatter against every spline. If you look at the marks on the picture then every one is truly identical, they are like finger prints, right down to a rounded profile to the top right and small square missing from the 'cuts' on the bottom right of the profile as viewed in the picture, along with the location of a deeper groove at the top.

There is no way that wear from different points of contact could produce such identical marks. In my opinion it has to be tooling of some type, where it was set up with identical passes and thus caused identical marks.

Andy B

[Chris KC]

I just took a look in the shed at a couple of old clutch plates and one has strikingly similar marks, albeit less clear through a layer of rust (they certainly don't look fresh, and as mentioned above they are to one side only).

The marks are outside the diameter of the gearbox input shaft, yet within the diameter of the aluminium casting which houses it and which forms the ID for the clutch release bearing assy. (n.b. on a 4-speed box).

My marks also align with each spline (male).

Even if a crankshaft let go or gearbox fell to bits I can't imagine how this could occur through contact with other parts, as there aren't any in this area - in my humble opinion it's got to be part of the manufacturing process (or possibly subsequent clutch 'rework').

[Paul N-M]

From an engineering rather than Austin 7 perspective, aren't the marks too broad to be wear marks? For the mating part to be able to make so many clearly visible individual grooves it would need to either have this profile on every rubbing part to wear a replica profile or be able to move  side to side by 3-4 mm and so be an incredible loose mating fit to chatter around so much? Is that even possible with the size of spline without the mating splines being about 1mm thick to give the lateral movement required?
Also if chatter is the cause and the splines can move around enough to produce multiple grooves then why are there no slightly lateral scratches, why is every mark perfectly radial?
And is the diameter of the wear marks no much larger than that of the mating splines, or is that an optical illusion?
It just doesn't look possible for a mating part to wear such an identical and yet severe chatter against every spline. If you look at the marks on the picture then every one is truly identical, they are like finger prints, right down to a rounded profile to the top right and small square missing from the 'cuts' on the bottom right of the profile as viewed in the picture, along with the location of a deeper groove at the top.

There is no way that wear from different points of contact could produce such identical marks. In my opinion it has to be tooling of some type, where it was set up with identical passes and thus caused identical marks.

Andy B

I've just offered up a plate to a gear box to see if any contact from the female box splines could be made to the 'dome' of the male spline plate even when its pushed fully into the casing. Answer is no. Marks are caused by something else.

Paul N-M