just about to order some sprockets, and not sure whether to make the drive hubs 8 bolt or 6 bolt.

Sprockets are 40 tooth 630 chain (3/4" pitch) bolted on a 133mm PCD, and transmitting 160hp ish at 2.5:1 ratio (16t to 40 t)

Will 6 M10's do the trick or would 8 be better? Just saves some indexing and extra drilling and tapping for me when I make the hubs!

I have 10 on my siera lsd, but that is standard on the diff.
I think 6 will be chancing it especially if you have a split sprocket like mine.
Contact Douglas at west garage here


52 tooth sprocket



[Edited on 6/3/2007 by nitram38]

Congratulations!!! You have posed a question to which I have no idea which to recommend.

I know M10 8.8 bolt is bloody strong but they will be in shear but still ....

We now await a mechanical engineer to do the maths.

Or find somehtingin similar stresss - anyone know about bolt size and number holding Range Rover crown wheel?

Sierra propshaft only has four bolts and that's probably transmitting a broadly similar torque at about the same PCD. Use 12.9 grade bolts if you want an extra margin of safety.

The Quaife ATB I have, has 8 M10's, the bolts are 12.9 graded, these bolts came from Powertec in the fixings kit so should be more than strong enough

Cheers
David

I use 12x 5/16 unf to hold my sprocket on, transmitting 200bhp+ through 9inch slicks.
Never sheared any bolts, but they do come loose regularly.
ATB
Phil

8 bolts at 5/16 or 8mm will do it easy, 8 bolts of 6mm or 1/4 would do it if the pcd is around 6"

if you really want to know nat, let me know how much torque your engine is making and I will work it out.

As a first approximation, I reckon 4 M10 12.9 bolts is enough.

David

OK,

A 12.9 grade M10 bolt will take 3,518kg in single shear.

Assuming your engine produces 200Nm of torque thats 500Nm at the diff (2.5:1 ratio, i.e. 200x2.5=500Nm).

The force at the bolts is:
500Nm/0.0665m = 7,518N (0.0665m is the effective radius at which the torque is acting (i.e. 133/2 = 66.5mm = 0.0665m)

So 1 bolt is actually easily enough in this case...but I need to know what the 1st gear ratio is in the box as well, as this will also multiply the torque up as well.

Assuming its a similar ratio to a T9 box: 3.6:1 1st gear

Then the torque at the diff is 1800Nm

Which gives a force of 2,759kg (27,067N) at the bolts. Which still means one bolt is enough...

So 6 is fine if thats what the diff/sprockets are avilable in.

David


[Edited on 6/3/07 by flak monkey]

as FM says, 1 bolt is all you need

re: the ^^^^ calcs; this is assumes maximum torque which would occur in 1st gear; chances are you would never actually be able to plant that as the wheels would lose grip.

Also the bolts will be done up tight so the friction between the sprocket and whatever doofer it is bolted to will take a lot, dunno how much, of the shear off the bolts - just check they don't come loose.

I agree with Nick, don't have any sums to back it up tho, only old age and experience to go on

Al.

The load should all be taken by the friction between the sprocket and what it mates too.

Therefore to work it out you need to know the max torque that will be transmitted, the clamping load of the different bolts you are looking at and the coefficient of friction between the 2 materials - oh and pick an appropriate factor of safety.

Chris

Fine, a bolt when torqued up to its recommended force creates a clamping force equal to approximately 75% of its tensile yeild strength.

So a single 12.9 M10 bolt produces 4,397kg of clamping force.

The slip coefficient of an untreated steel-steel bolted joint is 0.15-0.2

Need a lot more data to do those calcs though.

David

[Edited on 6/3/07 by flak monkey]

It's got 8 now!

Cheers folks,

As was said, if it was a driveshaft then 6 would be fine, but my concern is that being a sprocket it has to take the side load as well, which is obviously also fluctuating and therefore will try to loosen the bolts as well.

Incidentally in the centre of the same hub will be a 94mm 6 bolt pcd to take a 108mm lobro joint, but that takes no seperating force (or whatever you call it with chains rather than gears! )

i hope you make the chain adjustment simple as i have to do mine after a few miles and thats running one v-twin i tested an rsv yesterday and had a quick blast and have to say its a good package for a bec with the sump etc. didnt have the bottom end of the tl but did pull better further up the rev range

Hi Froggy!!!

Just in the process of milling 16mm by 2" slots in some 50x8mm flat, to weld to box sections which will mount my 50mm bore self-lube bearing blocks that hold the twin sprocket shaft with the CV's each end. I plan on welding on threaded bosses with a longish push bolt each side to push the bearings along the slots once they are loosened slightly, to tension the chains, then nip em back up again.

I'm also using twin 630 chains, good for 300hp each so they should be ok..... (hopefully! )

Just ordered the sprockets from JB Gears in Leeds this afternoon, very helpful place!

PS hope to do something about the bottom end, I will be running a pair of DTA S60 pro ecu's, so everything will be mapped to suit the installation, and there will be none of the emmissions guff of the bike, plus I will be making some much longer ally ram stacks for the throttle bodies with airboxes to suit, plus going up a touch on the primary exhaust lengths.

trust me a pair of twins you wont be dissapointed ive got half the power and its plentyi hope you paint it a pretty colour,ive got some lovely primrose yellow for the cbr three wheeler

quote:

---

Originally posted by NS Dev
but my concern is that being a sprocket it has to take the side load as well, which is obviously also fluctuating and therefore will try to loosen the bolts as well.

---

With 1 12.9 M10 Bolt with nyloc nut.
Its bolted thru the axle (sow it needs to cut the bolt twice).

Tks

quote:

---

Originally posted by 02GF74

quote:

---

Originally posted by NS Dev
but my concern is that being a sprocket it has to take the side load as well, which is obviously also fluctuating and therefore will try to loosen the bolts as well.

---

nylocs won't be strong enough?

can you fit catellated nuts and drill the bolts or wire the nutes on?

---

I'd be tempted to wire the nuts as at least it would buy a bit of time if they all decided to come undone.

Unfortunately the load across the chainwheel to hub interface is going to have a large vibrational content additive to the theoretical torque from the power, it can be this that is trying to undo the fasteners if there is even a small amount of play between the chainwheel and hub.

The vibration comes from the engine / load, snatch in the chain from load / overrun and from cyclic variation from the polygonal effect that chainwheels with a low number of teeth have.

Minimising the bore clearance and dowelling the chainwheel to the hub can help prevent it slackening off the fasteners.

Colin

Cheers Colin, you've put my concern much more succinctly than I did, hit the nail on the head!

The problem with alloy sprockets is obviously they are of lower strength than the bolts holding them on, therefore as far as I can see you can't torque the bolt properly as the ally will just compress.

On balance I don't think it will be a major problem, I've certainly got bigger concerns, but its always good to air issues on here!

Putting thick spreader washers should help on the ally compression front.