Changing the Sprag Clutch...

[HOCAdmin]

Right... I'm lucky enough that I've never had to do this, so what follows is "my best attempt" at a write up of this procedure.  I'm looking for assistance here, so please read on...

Changing the Sprag Clutch in the Starter Mechanism:

NOTE:  Read this through before you start, only start once you're sure you have the tools to finish the job

1.  To replace it, you'll first need to get one... It's a Borg-Warner part: BWX1310003 known as a "freewheel" or "one-way clutch" or "sprag clutch".  Hesketh Motorcycles will almost certainly have some stock.  (Failing that, a Mini (Austin) gearbox specialist may be able to help, as it started out originally fitted in some of the auto boxes fitted to that model).

2.   Drain the oil into a clean container, for re-use (unless you wanted to change it anyway).

3.  Whilst the oil is draining, MAKE CERTAIN THE BIKE IS IN GEAR and then take the  LHS footrest and mount off and release the gearchange pedal shaft from the gearchange shaft. (There should be a small metal key between pedal and shaft - don't lose it!).

3.  Disconnect the alternator wiring from the main harness (3 bullet connectors under the battery tray)

4.  Remove the M6 allen bolts securing the LHS engine casing and remove the casing (don't worry about the circular generator cover, or the oval clutch adjuster cover, they'll just come away with the engine casing).   You may find it useful to remove the oil filler and insert a "lever" between the clutch and the casing.  Whatever you use, gently does it and careful with those threads..!!

5.  Once the casing pops off, you'll see (from left to right), the starter pinion, the starter reduction gears, the starter chain and sprocket (behind the alternator rotor) and the clutch.

6.  There's a big nut holding the rotor on and it's a LEFT-HAND THREAD!! Get a handy mate/spouse to hold their foot hard on the back brake pedal and undo the nut. (This is why it had to be in gear).

7.  Now the alternator rotor may/may not come off... If it's reluctant, you'll need a puller.  Behind the rotor is a thrust washer, then the starter sprocket, which will lift away with the chain and last of the reduction gears...

8.  Behind this is the sprag, which is a push fit...

9.  When replacing the sprag, remember that it can be fitted either way around, but only one way is correct..!   The engine turns clockwise (when viewed from the clutch side) and the sprag outer must lock up when rotated clockwise (allowing the inner to freewheel when the crank picks up speed).

10.  Reassembly very much the reverse of disassembly.  The alternator rotor nut holds it all together and should be torqued to 50 lb/ft (same as T160 Triumph).

11.  The mating faces of the engine casings should be cleaned and sealed using clear RTV silicone (I use Dow-Corning, available from Screwfix - it's top notch stuff).  The casing screws should be "nipped up" all the way around, left for about 30 mins (to let the sealant start to set) and then torqued to 7 ft/lbs.  BTW:  It's easy to strip the threads in the crankcases, so keep an M6 thread repair kit handy...

Hope that helps.

There it is... PLEASE feel free to contribute if you think any part is wrong and/or missing detail... I'll correct/edit as applicable and (eventually) I'll delete this thread and pin up the verified procedure as a sticky (I'll delete the thread to prevent folk who really need the procedure from getting bogged down in this waffle when they really need help!!)

Ta!

HOCAdmin

[HOCAdmin]

Here's an update, courtesy of Les Roulstone:

Changing the Sprag Clutch in the Starter Mechanism:

NOTE:  Read this through before you start, only start once you're sure you have the tools to finish the job

1.  To replace it, you'll first need to get one... It's a Borg-Warner part: BWX1310003 known as a "freewheel" or "one-way clutch" or "sprag clutch".  Hesketh Motorcycles will almost certainly have some stock.  (Failing that, a Mini (Austin) gearbox specialist may be able to help, as it started out originally fitted in some of the auto boxes fitted to that model).

2.   Drain the oil into a clean container, for re-use (unless you wanted to change it anyway).

3.  Whilst the oil is draining, MAKE CERTAIN THE BIKE IS IN GEAR and then take the  LHS footrest and mount off and release the gearchange pedal shaft from the gearchange shaft. (There should be a small metal key between pedal and shaft - don't lose it!).

3.  Disconnect the alternator wiring from the main harness (3 bullet connectors under the battery tray)

4.  Remove the M6 allen bolts securing the LHS engine casing and remove the casing (don't worry about the circular generator cover, or the oval clutch adjuster cover, they'll just come away with the engine casing).   You may find it useful to remove the oil filler and insert a "lever" between the clutch and the casing.  Whatever you use, gently does it and careful with those threads..!!

5.  Once the casing pops off, you'll see (from left to right), the starter pinion, the starter reduction gears, the starter chain and sprocket (behind the alternator rotor) and the clutch.

6.  There's a big nut holding the rotor on and it's a LEFT-HAND THREAD!! Get a handy mate/spouse to hold their foot hard on the back brake pedal and undo the nut. (This is why it had to be in gear).

7.  Now the alternator rotor may/may not come off... If it's reluctant, you'll need a puller.  Behind the rotor is a thrust washer, then the starter sprocket, which will lift away with the chain and last of the reduction gears...

8.  Behind this is the sprag, which is a push fit...

9.  When replacing the sprag, remember that it can be fitted either way around, but only one way is correct..!   The engine turns clockwise (when viewed from the clutch side) and the sprag outer must lock up when rotated clockwise (allowing the inner to freewheel when the crank picks up speed).

10.  When fitted, there should be no gap between the sprag and the thrust-washer behind it.

11.  Reassembly very much the reverse of disassembly.  The alternator rotor nut holds it all together and should be torqued to 50 lbs/ft² (same as T160 Triumph).

12.  The mating faces of the engine casings should be cleaned and sealed using clear RTV silicone (I use Dow-Corning, available from Screwfix - it's top notch stuff).  The casing screws should be "nipped up" all the way around, left for about 30 mins (to let the sealant start to set) and then torqued to 7 lbs/ft².  BTW:  It's easy to strip the threads in the crankcases, so keep an M6 thread repair kit handy...

Hope that helps.

Thanks Les!  I've also added a cople of minor changes myself...

HOCAdmin

[REMF]

I went through an awful lot of sprag clutches over the years.
About 10 years ago I took the bike to a HOC meeting in the New Forest. I'd spragged it when leaving home, my missus jumped in the car and brought me a spare and I changed it on site.
It lasted 5-10 seconds. Maybe as long as that, it might have been less.
One of the club members, possibly Terry Spencer, pointed out that the sprockets wear as well.



He gave me a drawing showing the dimensions for the sprag so I could compare it to the sporocket; too much wear in the sprocket would make the dog teeth go up, stay up and there goes another sprag.
I sent the sprocket to Mick, he went through his stock and found a large variation in the sizes. I changed the sprocket for one with the tightest clearance and all my sprag problems went away,
According to Mick, the dog teeth 'drag' on the sprocket all the time the engine is running and in 30,000+ miles there was a small groove in my old one.
Sorry about the greasy fingerprints on the drawing

[Dave Snr]

Sound advice from Robin - I remember him changing the sprag in the New Forest- it was HOC 20th anniversary rally, fortunately Lord H's champagne helped to cheer Robin up.
Dimensions for sprag housing is 66.383 +/- 0.013 mm diameter and shaft 49.721 +0.008, - 0.005.
(Sorry haven't worked out how to include a drawing yet)
The sprag is engaged when not rotating i.e. engine stopped and disengages when the centrigugal force overcomes the spring pressure i.e engine revving.
So, as Mick says, it will certainly be dragging at tick over/low revs, but should disengage at higher revs.
My experience has been that the sprag teeth wear. After 30,000 miles the sprag teeth have flats on them.
I've done 67,000 miles on my Hesketh now and have changed the sprag for a new one at 30k and 60k.
Fortunately I've never had a sprag fail on me (tempting fate?).
No sign of wear on my housing or shaft, but as mentioned the housing dimensions do vary, so I must have been lucky with mine.
I suspect that regular use helps.
If an engine has been standing a long time then the sprag and housing will have drained of lube oil and may have some light corrosion, so when next started, significant wear can happen.

[Nigel A]

This is all very good advice on how to change the sprag clutch, i have been trying to obtain one from Dave Clarke of Hesketh motorcycles since August and have not been successful due to them being on back order.

Is there anywhere else these sprag clutches (Borg-Warner part: BWX1310003) can be obtained from or has anybody got any new one/s and are willing to sell one?

[Rob B]

You can but them from RINGSPAN (UK) Ltd, 3 Napier Road, Bedford, UK MK41 0QS.

I bought four from them against Order No. 09770 at 31.93 each plus VAT and postage

Their Part No. is 3677.049.602.000000 which is the BW P/N 1310003.

I have still got a couple left if you want one but at this price I would advise placing an order with RINGSPAN direct and sticking a couple on the shelf.

Best contact at RINGSPAN is Mark Luddington on 01234 342511

www.ringspann.com

Let me know if you run into problems

[Dave Snr]

Sprag part numbers are:-
Ringspann BWX 131003 (4C)
or
Formsprag - Steiber DC4972 (4C)
or
Renold REGP 4972 (4C)

Probably all made in the same factory!
My local bearing stockist was able to get them within a couple of days.
The (4C) is a reference to the 4 clips that hold it in the housing.

[Nigel A]

Thanks guys, i've managed to order a couple of sprag clutches from Ringspann so I should receive them next week hopefully which will give me enough time to finish polishing the crankcase cover whilst its been off.

Just for interest to you all them are now retailing at £47.90 + vat and postage.

[Rob B]

Good news! I last ordered in 2010 so they have gone up a bit.

If anyone is rewiring, updating or repairing wiring on their HESKETHS (or anything else) then I can highly recommend Kojaycat in Greenock. Great service, all the bits you will ever need to do the job properly and one of the best websites ever! My tip is to go for Marine grade wherever possible.


http://kojaycat.co.uk/

[NeilG]

My first foray into this forum.....

I have been attempting to change the sprag clutch on my recently acquired V1000.

All went well by following the excellent instructions on this thread until I came to step 6, where the alternator rotor nut is removed.

"6.  There's a big nut holding the rotor on and it's a LEFT-HAND THREAD!! Get a handy mate/spouse to hold their foot hard on the back brake pedal and undo the nut. (This is why it had to be in gear)."

Before I exert full force and humiliate myself, again, in the presence of my mate/spouse, I need a clarification.

On my bike there is a small outer nut, (about 13/14mm) and a bigger inner nut. (i'm guessing 32mm or so)  Are both to be removed? Both LH threads? Is this the normal configuration?

Or am I just missing something obvious??

[Miti]

Apologies for the HUGE photo, but this is what the generator nut on my V1000 looks like:



One BIG nut, deffo a left-hand thread (the crank rotation tends to tighten it rather than loosen it).

I hesitate to mention this, but some folk have had a situation where the end of the crank has snapped off (literally) and have been forced to effect a repair by drilling and tapping a new thread into the crank and re-securing the snapped end with another bolt.  It could be that you are looking at just such a repair..??  Any chance of a photo of yours..?  (If you're not sure how to host a photo, send it to HOCAdmin and ask for it to be hostedf via the HOC webspace)

HTH

Miti

[NeilG]

Many thanks for the prompt reply - I suspect that your explanation of a previous repair to the crank fits the facts.

I will take and post a picture asap. (added just now HOCAdmin)



Neil

[Miti]

Hmmm...??

That's a bit strange, eh..?  Neither the larger or smaller hex, nor the washer, look to be made from hardened steel...

The larger hex appears to be "half height".  Probably to allow clearance for the washer and smaller hex underneath the generator cover.

There also appears to be a square key secured under the washer, which suggests that the larger hex isn't screwed on and torqued up...

Do you have access to the bike's previous owner(s)..?  It may be worth asking some questions before breaking out any big spanners..?  I would definitely be taking all that aparft though, just to find out what's underneath, if for no other reason at all...

Hope this helps

Jeff

[Dave Snr]

Hi Neil,

Just caught up with your post.

Jeff's photo shows the original fixing nut with LH stamped on it for left hand.

As Jeff correctly says, your photo definitely shows a fix.
A previous owner has sheared the end of the crank.
Quite common - I know of several Heskeths that have been "fixed" by drilling and tapping the crank to put a stud in.
Checked my records -  previous owner was of course Harvey, like you in Canada. Before that the bike was in Wales and before that in St Helier, Jersey. I don't know the previous owners apart from Harvey.

Only thing to do is to undo the small bolt and take it apart.
99% certain it will be a normal right hand thread - I can't imagine any one going to the trouble of buying left hand taps.

As Jeff says, the big nut with keyway is interesting!

Let us know what you find.

Dave H