Broken Cush Spring

[chaterlea25]

Hi All,
If I was going to use Richard's method
I would be tempted to take the threads down to the root diameter at the inner end???
When I was working on the electric starter I was clamping a straight edge to the crankcase using the threaded holes, I inadvertently locked the crank and for a minute wondered why ? But it seemed to be very solid.
If someone could work out the pressure on the bolt when 65ft/lbs are applied to the crank nut it might help to decide one way or the other.
Regarding stuffing the cylinder with rope unless the pressure is evenly spread over the piston crown it could "bend" the piston skirt 

John

[RichardL]

John,

By my calculation, it looks like about 285 lb exerted on the bolt, given the distance from crank centerline to bolt center being right around 2.75". My calculation being this:  (12/2.75) X 65 ~= 285. I'm pretty certain that is not enough force to bend the bolt (given the short moment arm), or crush the thread (though, I like the idea of grinding off the thread). As for the crankcase, I, personally, think that is also not enough force to distort the casting, but would not want anyone taking my opinion if they, themselves,  were not 100% comfortable.

Richard L.

[RDfella]

What this really needs is a plate, say 10mm thick, bolted to bottom of the crankcase (replacing plate and gauze) and with a bolt, say M12, located in centre of said plate via a nut welded to the upper side (thus shortening distance to flywheel). End of bolt reduced to fit into an appropriate balance hole drilling. Working on a larger radius that the primary case bolts would reduce strain / torque on locking bolt. As the 'sump' bolts are fairly small, clearly such a plate would need to be sturdy so the load is evenly spread over all four bolts / studs.

[Greybeard]

What this really needs is a plate, say 10mm thick, bolted to bottom of the crankcase (replacing plate and gauze) and with a bolt, say M12, located in centre of said plate via a nut welded to the upper side (thus shortening distance to flywheel). End of bolt reduced to fit into an appropriate balance hole drilling. Working on a larger radius that the primary case bolts would reduce strain / torque on locking bolt. As the 'sump' bolts are fairly small, clearly such a plate would need to be sturdy so the load is evenly spread over all four bolts / studs.

How about adding raised edges that fit inside the sump aperture to take the strain off the sump studs.

[RichardL]

Don't even need to weld. 1/4" (min.) plate with a threaded hole would probably do it. Here's a downside: not so easy when you are in this state of the build and want to button things up. I suppose tightening could wait until it was on wheels.

Richard L.

[Swarfcut]

 What a good idea. Alas the pick up pipe position may pose a further difficulty, and repairing damage here turns a 10 minute job into a major headache. Belt strap around the flywheel?

  With the spring and cush removed, the nut could be tightened to the required torque, holding the drive sleeve in a way to avoid damage. Marking the nut and crank would enable assembly, tightening 'til the marks line up plus maybe a bit extra for luck, assuming that the drive sleeve and nut can be viewed through the compressed spring and we are not a whole turn too slack.

 All fine and dandy, but the problem still remains of holding the crank with the cush assembled. Time  served hooligan method was bike in gear, rear brake on and smacking the wrench, peg spanner, C spanner, drift or whatever 'til it felt right. Bearing in mind my earlier comment that some of the torque has to overcome the spring, this alternative method stands a good chance of really loading the sleeve and producing a good clamping force on the  bearing against  the crank. All a bit long winded for something so simple.

 Take your choice, certainly easier to assemble  the cush with barrels off,  holding the crank still with a wooden block against the crankcase. Rattle gun has my vote.....

 Swarfy.

[JulianS]

I use these tools to hold the crank when 4 spring clutch fitted.. First photo.

Second photo shows the top tool being used to hold the clutch centre for tightening the centre nut. Put the bar over the crank to undo it.

To lock crankshaft leave the primary chain on and use the bottom tool to lock the clutch parts together and with the top tool in place, bar under the crank, the nut can be tightened. Bar over crank and the nut can be undone.

I always use thread locker on the thread and a very long ring spanner on the nut.

Yes the bar has bent after being used a number of times.

[RDfella]

With respect, Julian, that does not address the conundrum of how much the shock-absorber cam is influencing the torque applied to the crankshaft nut - the whole point of my argument.

[RogerSB]

I'll probably get shot down in flames, but this is how I've tightened mine twice.
Unusual for me as I didn't take a photo (normally I photograph everything for future reference) and so this photo is a mock up using the best photo I have to show it. I used a piece of stainless steel rod left over from push rod material. Also in 1st gear, brake applied and rear wheel strapped down to my work platform with ratchet tie down.
Rog.

[muskrat]

G'day Fellas.
The nut on a HD is done up to 150Lb  . The method with them is to use a wedge between the sprocket and chain as any percussion is to be avoided due to the pressed up crank.
I had forgotten I did my plunger this way last time years ago.
Cheers

[Greybeard]

G'day Fellas.
The nut on a HD is done up to 150Lb  . The method with them is to use a wedge between the sprocket and chain as any percussion is to be avoided due to the pressed up crank.
I had forgotten I did my plunger this way last time years ago.
Cheers

Got to admit that I have used a bit of wood on the primary chain to wedge the drive sprocket. This was before I got an air rattle-gun. That idea might not be ok on a swing-arm setup.

[BagONails]

Locking the crankshaft or the crankshaft drive sprocket will take the cam lobe ramp angles out of the mix in terms of torque reaction and lost effort.
Friction in the thread and between the nut and the spring will still be present however to reduce the 65ft/lb figure down a little, but that is common to nearly all nut tightening scenarios. I have used Loctite red, "studlocker' on mine after degreasing the thread. You can also use an activator if you want to go the whole nine yards but not really necessary. Studlock is incredibly strong and you MUST heat the nut gently to cook the Loctite before attempting to undo the nut in the future.  A plumber's blow lamp used gently on the nut will suffice you don't need to make it glow!

Colsbeezer and I both came up with the same excellent sprocket locking tool, basically I used an 18" length of 5mm x 25mm steel strip with a short length of old primary chain attached to one side and wrapped around the sprocket. This grips the sprocket on multiple teeth and will do no damage. The end of the strip reacts against the floor or the frame where the side stand attaches depending on your preference. This does an excellent job of reacting against the nut tightening forces and keeps all forces within the confines of the sprocket/crankshaft/ splines system with no stress on the clutch etc. in fact the primary chain is not even in place at this stage.

Col put up a picture of his set up in my primary escapade thread here, mine is a bit more ghetto but the same principle.
(Us non IC powered cyclists use the same tool albeit a somewhat lighter version to prevent cycle freewheels turning when undoing the retaining nut)

https://www.a7a10.net/forum/index.php?action=dlattach;topic=16279.0;attach=56825

[Peter in Aus]

Peter,

Very interesting. May I ask, did you let the crank web come fast and hard against the bolt or nudge it up slowly? I have doubts about the web causing a slow crush of the threads on the stop-bolt, but can easily picture it when there is considerable inertia. I just looked again at the bolt I used and see no apparent thread crushing. Granted, I only tightened to 65 (or so) ft-lb, not the three or four hundred hinted at earlier. I DO believe this is a worthwhile topic for continued discussion because, if the method is harmless, it can be an easy and effective method for getting the bastard tight.

Richard L.

Richard,
I didn't let the crank bang against the bolt, but it damaged the thread just a bit so as when I removed the bolt it damaged the thread in the housing, not that much just had to run a tap through it and it was ok,
grinding the thread off the end of the bolt would stop that but I think it puts to much strain on the housing.
 I now use a chain raped around the sprocket method and a rattle gun, don't know what the torque is but it is well over the 65 ft-lb, no problems so far.

[bikerbob]

I have been following this thread and my own personal opinion is I fail to see where that SRM nut is an improvement on the original BSA set up that has worked for  me on 2 bikes for at least 25 years. Yes I did have a cush spring failure once but I think that was just spring fatigue nothing to do with the cush drive nut coming loose.  I tighten the cush nut up with a homemade C spanner then give it a couple of hits with a hammer and that is it. The only extra addition I have made is I made a washer that fits snugly between the nut and the split pin, in fact I have tap the split pin into place you cannot just push it in. There is no way that the cush nut can come loose with this original set up.

[RDfella]

Locking the crankshaft or the crankshaft drive sprocket will take the cam lobe ramp angles out of the mix in terms of torque reaction and lost effort.

 In the case of locking the sprocket, one is tightening a nut whilst a cam is pushing back. I have no idea how much tightness is lost through compressing the spring and fighting against the cam, but it certainly won't be insignificant. An indication would be to see how much torque is required to get the nut to just before it touches the sleeve - remembering that the more one tightens after that, the more the cam effect works against you.