Endplate fixing studs

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johnny650
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Well my engine gearbox rebuild has stalled once again. Its 1 step forward and 2 steps back at every turn . This time its the endplate fixings that are holding up progress.

The studs contained in the 2x Endplate Stud packs that I have been supplied by 2x different top Lambretta parts supliers are apparently the correct length but are completely useless .

The studs supplied are M7 x 26.5mm x 1mm pitch and when correctly fitted to the case they barely show above the level of the endplate. There is not even sufficient space to fit a thin 1mm washer let alone a flate washer, spring washer and nut !.........

The stud that is required to secure the endplate satisfactorily needs to be at least 32mm long preferably 35mm .(This goes for a M7 bolt if one should decide to use a bolt instead of a stud although great care will be needed if using a bolt so that the bolt does not bottom out before reaching full fixing torque.)

The crankcase endplate fixing holes are tapped to a depth of 12mm with a further 4-5mm insertion depth below that.. so a minimum thread insertion depth of 10mm and a maxmimum of 14mm would seem appropriate provided the case threads are cleaned and the holes cleared out.
To this we can add 9mm for the thickness of the endplate 0.5mm flat washer 1.5mm spring washer and 4.5mm for the special thin M7 end plate nuts . That gives a total of 25.5mm - 26.5mm .

The supplied studs are 26.5mm in length which would theoretically be just long enough with nothing to spare however there is a problem.

The threaded portion of the studs are approx 10mm but like all studs ,have a 2mm tapered lead in. This tapered portion of the thread contributes nothing to the strength of a fixing nut .We are therefore left with barely 8mm of thread to insert into the case which is clearly insufficient to secure the endplate when you bear in mind the magnitude of forces applied by the layshaft. In addition to this the fixing nut is likely to only have 2.5mm of effective thread to be secured to as the last 2mm of thread is tapered both ends

I suspect that the majority of endplate and hub failures are due to the endplate fixings failing due to insufficient stud thread insertion in the casing where builders , in order to leave sufficient stud projection to fit the endplate washers and fixing nut, unthread the studs too much leaving insufficient threads in the case. This is probably compounded by worn case threads and no application of threadlock .

So what is the answer ? ...., before someone says ‘fit bolts instead mate’ ....clearly if we wish to stick with studs we should consider fitting longer studs so that we can reliably and consistantly achieve a 10mm minimum thread insertion of the studs, in the case (preferably 12mm ) and still leave sufficient stud length to fit the plate , flat washer, spring washer and nut with say 3-4mm thread spare.

I would suggest that the ideal stud length would be between 32mm and 35mm the latter of which co-incidentally matches the Vespa cylinder head studs. M7 x 35mm 0.1mm pitch.
Happy days


[fbvid=]Imageendplate studs by John, on Flickr[/fbvid]
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Monty
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Sounds like you are winding the studs in till they bottom out. Most studs even chaincase ones need to be set to leave the correct amount above the face edge. Obviously the hole will be deeper but you don't have to go in all the way. I won't go down the dangers of punching out the back, hydraulic cracking. Use some locktight and set the leangh leave to set move on. Ore get your veasp ones
johnny650
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Monty wrote: Wed Oct 04, 2017 6:47 pm Sounds like you are winding the studs in till they bottom out.

how did you come to that conclusion ? :) I know my post was rather long but I thought that I had made it clear that the maximum insertion was 8mm ? ;)

To 'bottom out' the stud would be impossible as the threaded part of the studs is only 10mm and the hole depth is 16mm+ ;)
Boreham
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I had a similar dilema, the MB bolts are threaded 25mm so plenty of 'meat' in the casing, i prefer the studs into alloy so looked about and Citreon 2CV exhaust bolts are a good alternative, total 40mm with 20/13mm threaded with a 7mm central section, also hardened !
johnny650
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Boreham wrote: Wed Oct 04, 2017 8:08 pm I had a similar dilema, the MB bolts are threaded 25mm so plenty of 'meat' in the casing, i prefer the studs into alloy so looked about and Citreon 2CV exhaust bolts are a good alternative, total 40mm with 20/13mm threaded with a 7mm central section, also hardened !
excellent ! thanks for posting thats very helpful. I have been searching the net all afternoon with no result other than very expensive vespa cylinder head studs at £6.+ each :o
I'll check out your lead thanks
GeorgeS
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Is buying a length of M7 threaded rod and cutting your own an option? Plenty on eBay.


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johnny650
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GeorgeS wrote: Wed Oct 04, 2017 8:24 pm Is buying a length of M7 threaded rod and cutting your own an option? Plenty on eBay.


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good idea George but probably not really a good idea for this application unfortunately. Its probably best to use a fastener that has a 7mm plain shank to fit and support the endplate fixing hole. A threaded shank would be too thin and might allow the end plate to move about under stress.
if it was somewhere easily accessible I might have tried it but I'd hate to have to strip the gearbox to sort a problem later :(

I've got 2x options to contact tomorrow. A Citroen dealer and a DeLorean dealer believe it or not the DELorean used a similar M7 manifold stud .
Reckon my Special 200cc will be a time machine soon :D
GeorgeS
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Yes, good point. I guess you could make some collars up and press them in to the endplate but now we're making things more complicated than they need be!

Those 2CV studs look like a great option.



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HxPaul
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Endplate studs are supposed to be 28mm in length with a 10mm thread on each end,by the way you dont need to fit a flat washer,just a spring washer.
johnny650
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HxPaul wrote: Wed Oct 04, 2017 9:56 pm Endplate studs are supposed to be 28mm in length with a 10mm thread on each end,by the way you dont need to fit a flat washer,just a spring washer.
thats all very well but as i said 2x top sellers sold me studs that measured just 26mm and a 10mm thread has only 8mm useable thread at best.
Try running a nut onto the first 2mm of a stud and see what sort of secure fix you can achieve .
A flat washer is the original fitting and spreads the torque better . it also protects the softer aluminium from damage by the spring washer
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