clutch and mainshaft

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Mick D
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Re: clutch and mainshaft

Postby Mick D » Mon Jul 15, 2019 1:59 pm

nevhunter wrote: The six small HARDENED bolts holding the clutch basket to the BIG sprocket are one of the most critical of all the fasteners on the bike --------- The 6 bolts need to be made of Bl**dy good stuff and tightened well.


Hi

These items on my FH look identical to those pictured by Alan earlier in this thread, do those 'who know' consider these to be original pattern? I ask because mine do not seem to be hardened or HT, (the slots on mine are distorted by use as Alan's look to be), they are also set bolts, as listed, which strikes me as strange, in a high torque / stress application I would expect them to be bolts and not slotted.
Could this be a case of an after market supplier not conforming to design specification or were the original items actually just bog standard set bolts with a slot cut into the head?

I had planned to fit stainless set bolts in this location but am now having second thoughts regarding sourcing a set of HT bolts.

Regards Mick

Edited to correct terminology - set screws - bolts
Last edited by Mick D on Mon Jul 15, 2019 6:37 pm, edited 1 time in total.

Simon.Gardiner
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Re: clutch and mainshaft

Postby Simon.Gardiner » Mon Jul 15, 2019 2:33 pm

The ones I've seen from unmolested bikes have all been set screws. As well as slots they might have a smaller hex size than a 'standard' bolt.
The slots have always tended to be a bit 'chewed'.
I once replaced a set with allen bolts (that are fairly high-tensile) - all carefully drilled, done up really tight and locked in pairs with proper locking wire. After a couple of thousand miles I found they'd all sheared at the top of the thread (just below the shank) - the remains were acting as pegs retained by the clutch centre so there was still drive although the clutch action had got pretty bad.
So I assume (as has been noted!) the material spec is quite important, and maybe they're not just bog-standard set screws.

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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alan.moore
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Re: clutch and mainshaft

Postby alan.moore » Mon Jul 15, 2019 3:15 pm

I believe the originals did have the slotted head, they are clearly shown as slotted in the WNG maintenance manual. The singles parts books shows them listed as 'Bolts' and mine do have a plain shank. They are not hardened ( a file marks them easily) but no idea whether they are HT.

Drags image of the bolts shows much less plain shank. The original plain shank is 1-2 threads short of the thread in the sprocket hub, with the locking washer in place, and the length is such that they are level with the rear of the sprocket when tightened.

They are 1/4" CEI thread with a 3/8" head

The plain section is a close fit in the clutch basket / hub which is important as it is this section of the bolt that provides the location of the basket/hub. The threaded section should not extend significantly into this area so a set screw is not appropriate (same idea as the rear wheel sprocket securing/locating bolts).

SDC12907.JPG

IMHO with decent clean bolts in good clean threads with threadlock and the locking tabs fitted normal tightening should suffice.

image a bit small but the WNG workshop manual shows the plain section of the bolt and the slotted heads
Clutch.jpg
Clutch.jpg (23.08 KiB) Viewed 379 times

Cheers
alan
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Clutch.jpg
Clutch.jpg (11.82 KiB) Viewed 379 times
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Re: clutch and mainshaft

Postby JohnnyBeckett » Mon Jul 15, 2019 6:03 pm

it is not the six bolts on clutch basket that was loose it was the gearbox chain sprocket nut i think it was not done up correct by owner before me

Mick D
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Re: clutch and mainshaft

Postby Mick D » Mon Jul 15, 2019 6:13 pm

Hi and Thanks

Plenty of food for thought there.
Simon: Did you fit Allen bolts or were they Allen screws, (threaded for the length of the fastener)? If sourced recently they would most likely have been 12.9, so very HT - shearing six heads is a little worrying.
Alan: Thanks for your images, I think I'll try to source a set of bolts - 8.8 if possible.

Regards Mick

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Re: clutch and mainshaft

Postby Simon.Gardiner » Mon Jul 15, 2019 11:05 pm

Mick
Allen bolts, mid-1980s.
They were working quite well as 'studs' - no bending or 'chewing'. I concluded that there might be more to material specs than just 'tensile' strength and went back to the originals with that painful tab-washer to lock them.
A friend made some spindles for some old Druid girders a year or two ago and the material spec for those got quite involved - maybe needing shock loading as well as tensile strength to be considered?

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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alan.moore
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Re: clutch and mainshaft

Postby alan.moore » Mon Jul 15, 2019 11:27 pm

I don't think tensile strength is the issue, they are only 1/4" thread so that really limits the torque you can put on them. They must be strong in shear, as that is where the load comes from. However, if they are too 'hard' maybe the issue is that they are more 'brittle'. Breakage where the thread joins the shank may be evidence of over tightening
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Re: clutch and mainshaft

Postby nevhunter » Mon Jul 15, 2019 11:49 pm

It is in sheer load but by having them definitely tight (not overtight as they are only 1/4 " I use a "relieved" 1/4" drive socket to get fully on the undersize head ) some of the sheer load is taken by the faces in contact. To get this effect the torque on the bolts must be such as to hold it quite firmly Once it starts to move the show is over. Hence I suggest a high tensile material. It's a bit of a crap set up if one is honest., I don't want to offend anyone BUT. Nothing's perfect. and it works if you give it a bit of extra attention Tight fit of the bolt threads in the chainwheel helps and the length of the plain section should be done right. Nev

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Re: clutch and mainshaft

Postby john.whiting » Tue Jul 16, 2019 5:59 am

Since Unbrako moved to a disused curry factory in Mumbai,there has not been a decent socket head screw on the market.......Unbrako s used to be DIN 11.9 or 12.8,soon as they moved to India ,they are all 8.8 ,this is equivalent to Gr 5 SAE..............incidentally,most of the Chinese fasteners on the market are simply hardened more to achieve SAE Gr 8 tensile.....the yield stress increases ,ultimate breaking stays the same,and the bolts are more brittle....You want to see 75% of the bolts broken in the slewing ring of a big cherry picker.

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Bob.Murphy
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Re: clutch and mainshaft

Postby Bob.Murphy » Tue Jul 16, 2019 10:39 am

john.whiting wrote: You want to see 75% of the bolts broken in the slewing ring of a big cherry picker.


:shock: :shock: I have a 'Cherry Picker', but its a 'Versalift NF36' made in Waco, Texas (mounted on a Ford Transit 190). Hopefully it doesn't have Chinese bolts . . . or should I be checking more frequently ???

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