Lotus Elan

Propshaft nut and bolt sizes

PostPost by: vernon.taylor » Mon Feb 16, 2015 8:20 am

Salut

What size are the propshaft nuts and bolts, please ? I assume same size both ends (Lotus 5-speed).

Should one use washers ? Nylocs ?

Thanks

Vernon
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PostPost by: dougal9887 » Mon Feb 16, 2015 4:41 pm

Gear box flange 1 1/4" ? 5/16" bolts.
Differential flange 7/8" ? 5/16" bolts.
Nyloc nuts. No washers.
The bolts have a 5/16" long grip.

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PostPost by: Chancer » Mon Feb 16, 2015 7:15 pm

They should really be close tolerance fitted bolts but I suspect that these days very few bother, in any case you must definitely not use setscrews (bolts threaded throughout the length) and the plain shank portion of the bolt should be a little less than the thickness of the two flanges.

I have seen some awfull disasters where people who really should have known better were ignorant of the above.
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PostPost by: vernon.taylor » Tue Feb 17, 2015 7:29 am

Merci les gars

Chancer - what are 'close tolerance fitted bolts' and where can I get some (internet site - nothing imperial here in France).

Merci

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PostPost by: CBUEB1771 » Tue Feb 17, 2015 2:36 pm

Chancer wrote:They should really be close tolerance fitted bolts but I suspect that these days very few bother,


Agreed, I have used airframe bolts (AN) in this application. The tolerance band on the diameter of the unthreaded shank of an AN bolt gives a larger average diameter than we have with garden variety fasteners. I find that AN bolts usually give the maximum diameter that can be used in a bolt circle unless the holes in the two flanges are reamed together as an assembly. I usually buy from Pegasus Racing:
https://www.pegasusautoracing.com/advca ... yID=ANBOLT
I imagine they will ship to France. You can almost always find an AN bolt of the correct length to assure than all shear loads go through the unthreaded shank.
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PostPost by: RichardHawkins » Tue Feb 17, 2015 4:03 pm

Vernon,

If I remember correctly a fitted bolt is one that is in a hole that has been reamed. This type of fit is described as "transitional" ie it is between a clearance and interference fit, sometimes called size for size, for example a 10mm bolt in a10mm hole. Usually in a transitional fit the bolt would have to be gently driven into the hole. I am not sure if this applies to prop shaft bolts, whereas this is definitely good practise, when applied to mass production, it would be difficult to achieve, so I expect the fit is small clearance with standard bolts. Bolts are important as opposed to hexagon headed set screws as mentioned above. Bolts in prop shafts are usually thought of as being subject to shear stress. In some applications bolts are referred to as friction grip, that is when the tensile load in the bolt is sufficient to create friction between the flanges sufficient to transmit the torque.

I buy my standard bolts from Namrick in Britain. ARP (Automotive Racing Products) in the USA may offer imperial bolts for prop shafts.

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PostPost by: CBUEB1771 » Tue Feb 17, 2015 4:35 pm

[quote="RichardHawkins"]ARP (Automotive Racing Products) in the USA may offer imperial bolts for prop shafts./quote]

ARP does not offer bolts specifically designed for prop shaft applications, I just checked their web site. Unfortunately ARP's bolts in the required lengths are fully threaded, meaning no length of unthreaded shank. Therefore I would look for another source. I don't understand why ARP makes the short bolts this way, it severely limits their applications in my view.
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PostPost by: prezoom » Tue Feb 17, 2015 4:44 pm

I'm with Russ on using AN style bolts when in a shear type of situation. No threads should ever be placed in shear. Coast Fabrication in Huntington Beach, California, http://www.coastfab.com, stocks what I believe to be the best selection of AN hardware. AN bolts come in various diameters and grip length, i.e., the unthreaded portion of the bolt. In the case of a prop shaft, I would choose a grip length that fills both the differential flange and the prop shaft flange. If the grip length is a little on the long side, AN washers come in two different thicknesses to fill any gaps. Another thought would be to use what are called Jet Nuts in place of standard loc nuts. Jet Nuts utilize a smaller hexagonal wrench size than would be standard, which makes it much easier to fit a wrench onto the head of nut. I have always used this type of bolt and nut combination when connecting a prop shaft to a differential.
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PostPost by: Chancer » Tue Feb 17, 2015 8:31 pm

Its all about the drive being taken evenly by all 4 fasteners, with proper design and production tol?rances, as in when the vehicles were produced, not necessarily true for aftermarket parts, the holes will have been produced to an H7 ISO tolerance, normally reamed and also critically to a corresponding positional tolerance.

If a corresponding h6 close tolerance bolt is used then the drive force will be equally shared by all 4 fasteners in shear.

If the bolt holes are oversize or standard h11 bolts are used there will be scope for some movement which may rapidly elongate the bolt holes, a correctly designed and manufactured propshaft joint does not need to be tightened to death to take the drive force and will not rattle loose even if they are only just nipped up.

Using setscrews (fully threaded fasteners) is a sure fire recipe for a pole vaulting vehicle.

Its years since I was behind the drawing board so I had to check some figures and I found that BS4500a that I used to work to seems to have been superceded by BS286.
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PostPost by: patrics » Tue Feb 17, 2015 8:54 pm

Hello Vernon,
I brought my prop shaft bolts washers and k nuts from:
Nasbolts.co.uk
Plenty of info to read through

Regards
Steve
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PostPost by: elanner » Tue Feb 17, 2015 9:28 pm

Ray at R.D. Enterprises sells AN bolts/washers/nuts for the diff pinion flange (http://www.rdent.com). ($1.85 x 4).

I had my diff pinion bolts out last year, but don't remember if they are setscrews. Sod's Law says that they are. :-(

Without this forum I would never have learned this. Thanks.

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