Clutch center bewilderment

I am having one of Hobot's Norton induced "deer in the headlights stare moments", and hope the community here can help me out. I am rebuilding my '73 850 after years of it sitting waiting for me to get moving. I stated to put the primary side together last night, using an eBayed hardened (I hope) clutch center bought years ago. I put it together with a nice new bearing, and installed it, and the primary gear and chain, tightened up the mainshaft nut over the soft steel locking tab washer. To my utter surprise, after applying 50 ft-lbs torque, I noticed the washer was twisted up and had pulled out of the locking hole.

On closer inspection, the cause seems to be that I have a clutch center with a bevelled/countersunk/relieved hole where it fits on the mainshaft end. This bevel is missing from the original center, and another used one I have. Has anyone else seen one like this, and what washers are used to back up the nut? The hardened washer I took off is so small in outside diameter that I fear it will disappear into the bevel if I tighten it up. Clearly the locking tab washer is not going to work alone, given the ability of the bevel to eat it up.

Here is a photo of the beveled one in the clutch basket, and the old one for contrast. Any help appreciated.

1. No time for blank staring before deer knock downs, just blank starring with some jaw slackness at some new unexpected non understood show stopper at home or away.

2. The soft lock tag washer is a known hazard to crush down to give up nuts clamp force. About any harden wide washer works for me the better experts say use a cupped spring washer or the star edged kind and nip up enough to hold fast but not enough to over come the thin circlip.

3. If the width of these clutch centers about the same then I don't think the bevel version is an issue if doing number 2.

yep, the tab washers are not good, they are soft and eventually compress and the clutch nut loosens, had that happen on my bike. I learned here that a Belleville spring washer and blue Loctite on the nut is a better solution. I had to order a dozen to get one so if you can't find one locally I can mail you one for cost + postage, $4.00. Also IIRC the manual spec for clutch nut torque torque is way too high and can break the circlip on the gearbox shaft, 45 ft-lbs or so is enough

airedale said:

an eBayed hardened (I hope) clutch center bought years ago.

On closer inspection, the cause seems to be that I have a clutch center with a bevelled/countersunk/relieved hole where it fits on the mainshaft end. This bevel is missing from the original center, and another used one I have. Has anyone else seen one like this, and what washers are used to back up the nut? The hardened washer I took off is so small in outside diameter that I fear it will disappear into the bevel if I tighten it up.

Click to expand...

The original clutch washer used up to 1972 (with the unhardened centre) was part: 040374 which, according to the Stainlessbits fastener list is: 1-1/8" O/D.

The washer used '73-on (so used with the hardened centre and tab washer) is part: 063447, according to the list, that washer is only 7/8" O/D, so I think perhaps what you have there is an unhardened centre.

http://stainlessbits.com/link12a.html

The hardened centres should ring like a bell when held by the central boss and struck with a metal object, and I believe the unhardened items do not.
[Edit: Apparently this information can now be regarded as something of a myth]
I also have an old hardened centre, and it does not have bevelled/countersunk splines.

I agree with the advice given above - make sure you have the correct washer to go between the tab washer and the nut - 06-3447 - and only torque to around 40 ft-lbs. If you go to the 70 ft-lb value in the manual, you risk shearing the circlip (06-0752). Regardless of the torque, its a good idea to change this clip each time you remove the clutch basket, as this little piece if steel has the task of locating the entire clutch assembly in the output shaft, and typically sell for less than $2.


I have a copy of this technical article from OldBritts in my shop binder - it's a handy reference, as all the torque settings are in one place.
http://www.oldbritts.com/n_torq.html

I have heard that 06-8072 is a heavier replacement for the clip and will work.

Dave
69S

BillT said:

make sure you have the correct washer to go between the tab washer and the nut - 06-3447

Click to expand...

Yes, but the point is, the 063447 washer (which airedale appears to have) is the wrong item to use with that centre because 063447 is only 7/8" O/D.

L.A.B. said:

BillT said:

make sure you have the correct washer to go between the tab washer and the nut - 06-3447

Click to expand...

Yes, but the point is, the 063447 washer (which airedale appears to have) is the wrong item to use with that centre because 063447 is only 7/8" O/D.

Click to expand...

I see your point. I was just looking at the correct part for the year, rather than the part for that center. With the beveled face at the spline, the 06- washer would be too small. The 04-0374 is another 1/4" larger, 1-1/8 v 7/8, and is listed in the fastener reference as a beveled spring washer. That should put plenty of meat on the flat of the center.

i got one last month, and the heat pattern is easily distinguishable. I can't see a heat pattern on yours

Thanks all for the information. I gave all three of the used centers I have lying around a whack, and the two that are chewed up by the clutch plate tabs rang like a bell. The third one, the beveled hole one installed in the clutch basket rang but less clearly, possibly due to the rest of the mass of metal surrounding it. I will take a file to each of them and see if any are hardened. I did not notice any heat treatment surface patterns, so who knows.

I will let you know what I learn with the file, and also see about getting a Belleville washer. And I will replace the circlip, happily I have a couple new ones waiting to be abused.

here's the one from rgm

I can't see a reputable dealer nowadays selling you a soft early style clutch center as a lot o' water has gone under the bridge since the problem was heat treatment/hardened/ fixed. Using 828 style sintered plates will eventually eat into center causing notching regardless. Should ring like a bell with spanner strike , enough to make you wake up and want to go to church.

I ran a triangular file's edge across each of the three centers I have. The non-bevelled one that came out of the bike was deeply notched by the clutch plates, rang like a bell and was very hard according to the file test. The center that I unearthed from my old parts collection was non-bevelled, very slightly notched, rang like a bell and was as hard as the first one. The used one I put in the clutch basket is the bevelled one, was unnotched, but didn't ring as well, and was clearly softer than the other two by the file test.

So I will replace the bevelled soft center with the only slightly notched one and run it for a while as I don't want to spring for a new one right now.

Should I still get a Belleville washer for this one? I clearly won't use the soft locking tab washer, and will torque to 40-45 ft-lbs only. And replace the circlip by the way...

Thanks for all the help,

Its a bit tricky no matter what washer used > to not destroy the locator circlip nor nut come loose on the fly as I've had happen more than once during initial run in rides. Also rarely mentioned is loosing the clamp force of nut on the opposite end of main shaft too but had happen twice so far for loss of clutch stack adjustment and engagement. Nothing quite like a Commando to test your mettle as a handy man, which has both improved and beat my own self opinion to snot.

Here's an update. Switched out the bevelled clutch center for the square-edged hole, hard to file, rang like a bell center. Gave the bevelled one, now free of the clutch basket's grip, a whack with a screwdriver, and it rang as clearly as the other two, despite being softer as per the file test.

I've some Bellevilles coming to me courtesy of Bluto, thank you, and will use one of them to back up the nut.

Will install a new circlip - if I can get this one off - then the spacers, and make sure the engine gear wheel and the clutch basket are in line. I have installed a second P-chain adjuster on the drive side of the engine cradle.

Then the clutch center nut will be Belleville washered, blue loctited and torqued to 40 ft-lb. I am hoping I will have enough thread left on the end of the mainshaft for the Comeau clutch rod seal I have.

Thanks for all the advice and suggestions.

I had to remove any washers under the clutch nut to make my clutch rod seal seat properly. I just used blue locktite.

Dave
69S