The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: limeyrob on 11.01. 2025 13:29
-
Paul has been servicing a customers RR that has done very little mileage since a rebuild by someone else. It's becoming clear that the rebuild, while looking shiny, has been done very poorly from a safety angle. A number of us (me included) saw the 8" TLS and suggested he check that very carefully given how poor the other work was. I don't think anyone was prepared for how bad it is. A real lesson in how not to fit an 8" TLS to an A10. Had the owner not brought it in to Paul for a once over this bike would be getting ridden!
https://www.youtube.com/watch?v=hU8DKhlL5c0
-
The strength of that torque anchor block and its weld need to be tested.
-
The video shoes the front wheel spindle sticking out of the LHS. On mine the spindle has a groove that has to be in the right position so the bolts can go through.
I know Triumphs have 6 1/2” and 6 3/4” spindles that can but should never be mixed up, and I think BSAs are the same.
Could this be a longer spindle with the shorter yolks?
John
-
I think it could be the wrong spindle and I've suggested he check that, so much is wrong that it could be anything.
-
Hi Rob,
With all due respects to "Paul" iI do not think he is over familiar with A10's and their "fobies"
I have had a look through the videos he has posted and do not envy him if he has to sort out everything on that bike *eek*
Things I could see at a first look.
The breather sleeve is too loose
There seem to be a "nut" used as a spacer on the lower rear mounting of the primary case?
No wonder the final drive split link is hitting something.
As to the front brake,
If my memory serves correct, there was a cranked stay used to clear the tls levers on later BSA/ Trihards? It looks that there is a cranked stay bolted at the front where it is attached to the mudguard??,
I don't know much about those tls brakes but the linkage thats bent is working as a pusher rather than pull? It dont look right to me *????*
As he found the cush drive nut loose odds are that it has shat a shim into the crankcase
Does he know that the cush nut needs to be torqued to 65ft/lbs or fully FT
John
-
I must admit that this is news to me. I have always tightened it up as tight as I could. Another job for winter - check the Cush drive torque.
Now what else don’t I know?
John
-
Does he know that the cush nut needs to be torqued to 65ft/lbs or fully FT
John
He does now, I felt I should tell him after I pointed out the end float was way out of spec and the possibility of shims being torn up and lying in the sump. This bike reminds me of my one. The more you look at it the worse it gets! I'm starting to wonder whether RM has had a hand in it?! *sad2*
-
Can somebody help me out here? What's the connection between a loose cush drive nut and shim-sh*tting? Surely the attachment of the cush drive to the crankshaft has nothing to do with the endfloat of the crank within the cases?
-
Oh good I am not the only ignorant one. From the SRM website in support for selling their Cush drive nut.
“The nut is critical for holding the drive side bearing tight, so torque setting is 65 ft lbs & use a small anount of thread lock.“
It was news to me last night.
I am always worried about what I don’t know. Unknown unknowns.
Something along Donald Rumsfeld
“There are known knowns, things we know that we know; and there are known unknowns, things that we know we don't know. But there are also unknown unknowns, things we do not know we don't know.”
John
-
Sure the cush nut has to be tight, but this is one answer to the question "Why"
The inner race of the main bearing is a tight fit on the crank, that is why shimming the bearing between the race and the crank cheek is such a pain, pulling your new bearing off the crank without damage, trying shims, tightening down, off again, you know the score.
The cush nut tightens down onto the drive sleeve, which in turn pushes the inner race and shims hard against the crank.
Now unless these parts are nicely clamped together and despite the inner race being tight when cold, there is evidence that in use the inner race can move, rotating on the crank and gradually wearing away the shims, bits of which end up in the sump, the crank then develops the sideways movement that spells a strip down.
So to answer Mik's conundrum, the big nut must do the two job's of tightening the drive sleeve against the bearing, shims, crank, plus act as a retainer for the cush spring.
BSA Service Sheet 208 (Engine Re-Assembly recommends a C Spanner, and to tighten the nut "as securely as possible"
In practice folks tightened the nut with a hammer and drift just enough to get the split pin to fit. By which time the original nut was looking somewhat sad. This is in any event not tight enough, as certainly the nut is bearing on the spring, but not entirely on the drive sleeve enough to lock the bearing inner race in place by friction against the sleeve, shims and crank cheek.
That was how it was done by the average backyard maestro, me included. In these more enlightened times make a peg spanner or buy a Peugeot ball joint tool and give that nut some real oomph.
All these cush foibles are well covered in previous Forum Posts along with the possible incorrect cush drive sleeves some fool has fitted in a previous top class rebuild.
If buying a used crank, wear to the shim position is an additional awkward repair, and easily overlooked, more so if displayed with a bearing in place.
Swarfy.
-
Hi All,
Explanation for those who are new to this *ex*
The cush drive nut clamps the cush drive sleeve, crank spacer main bearing inner race and end float shims against the crankshaft web.
If the nut is loose then movement occurs between the crank and above components
The shims being the weakest link get hammered from vibration and break up .
End result is excess end float and shat shims in the sump *eek*
John
PS, I like the expression " shims shitting" *smile*
Crossed with Swarfys detailed post
-
i had shim shitting years ago then i punched the nut up with daddies heavy drift and a 7lb hammer [ joke ] until i heard that lovely thump of that buggers up tight
-
Back to my original topic - the TLS brake:
What concerns me is that this is a nice looking bike that's been rebuilt and then bought in good faith, but by good fortune the owner has taken it to a reputable workshop. The person who built that bike ground 1/3 through the brake lever, left the fork clamp nuts loose, had the stay hit the brake lever and worse. We often get questions about fitting the 8" TLS in and A10 (mine has this conversion) and the implication is that its simple because you see a lot but this video shows its not simple and can be very dangerous if done by someone who doesn't know what they are doing. Like others here I was so concerned I messaged Paul.
Re shims: Mine came like that, the TS main had spun and worn a depression in the TS crank flange and there was about 020 play and no shims. I had do make an 010 shim with the OD and ID to drop into the groove then sit the correct shim on that. Loctite plus SRM nut plus 70lb ft and its still holding well.
-
Quick note on shims - Thanks for the explanation - All is clear now!
-
The other result of the cush nut coming undone. For me always loctite and the SRM nut.
-
I went double indemnity on mine. Fitted a new standard nut at 67ft/lbs plus loctite then turned my old nut down to make a lock nut that is done up with a pin spanner and a hammer with more loctite! Me paranoid? Never! *pull hair out* Oh and the split pin went in the bin!
-
Paul has just posted an update on the brake and its even worse, large amounts of the spindle ground away to make it fit. He's justifiably furious with whoever did the work.
-
Paul has just posted an update
Where?
-
OK OK... *computer*
https://www.youtube.com/watch?v=nuKkOo6w1Jw