mbell wrote:I have to admit to being a layman on the details of fasteners and fittings so not coming from this as an expert.
In the pursuit of increasing my knowledge what you are saying is that in the prop setup for the Anglia/elan flange bolts a significant portion of the power transmission and the friction between the flanges isn't sufficient to transmit the power. Therefore if bolts without the correct width and length of shank are used it is likely the two flanges would rotate with respect to each other damaging the flange bolt holes and possibly causing bolt failure.
Is this correct?
The drive is taken by the bolts in shear, if it were friction then the flange would need to be the same diameter as the clutch plate and made of friction material. Wheel bolts take the drive, its not the friction of the mating face, were that the case there would not be drive pegs on knock on wheels.
It is imperative that all the bolts share the drive force or the flange will come loose and/or the bolts fail just as if you only secured a road wheel with only one nut, this can only be achieved by the holes being centred precisely to a close positional tolerance, being drilled then reamed to a H7 tolerance and the bolts having close tolerance shanks, they used to be known as "fitted bolts" you can tell this by how tight they are when you push them in (a close clearance/transition fit) and often the 4th one will take a little persuasion.
Using the wrong bolts, and i am not talking about their tensile strength, will result in failure in exactly the same way that assembling a flywheel without the drive dowel or the correct fitted bolts if no dowel will shake loose.
I fitted a second hand steel flywheel to a forged steel crank on a highly tuned crossflow, I used the correct close tolerance cap head bolts, (I think there may have been 12) but had not realised that either someone before me hadn't and the holes had opened up or more likely like most of the Junk that is produced these days for our vehicles the manufacturer had no concept of tolerancing and the need for limits and fits. Testing at goodwood I was convinced that I had run all the main bearings or even broken the crankshaft, never heard a more horrible noise, I was suspicious though as I had not heard any big end Knock, just what I thought was main bearing rumble which at tickover (highest angular velocity changes) was at its loudest and sounded like a broken crank.
I suspected and found that the flywheel was rotating relative to the crank, the bolts were all still torqued up, I could not move it by hand but when I removed it I saw the oval holes and material from the flywheel had cold welded to the crankshaft.
I recovered the situation by reaming out 4 of the fixing holes in both the flwheel and to a short depth in the crank and using the hollow bellhousing dowels to take the drive, that way I could still use all the retaining bolts, had no problems after that but have heard and seen many other engines using aftermarket flywheels and steel cranks fail in exactly the same way.
I have also experienced nearly dropping the propshaft on a Caterham Blackbird where the wrong bolts were used in the Guido coupling from the gearbox to the front prop, in this case the drive was being taken by the threaded portion on one flange, that was bloody scary how long it drove without incident but how quickly it failed when it did with near catastrophic results.