rear motor to cradle stud

First a big thanks to all of the forum members. I finally joined but owe you all a lot of thanks for the help you have given me over the last few years keeping my '71 750 on the road. I have been a major lurker and hope now that I will be able to contribute to the forum and not just use it as reference. Its a truly exceptional site.
My new problem is that my uppermost rear cradle to motor bolt vibrated loose, the nut disappeared and the threads got ground and abused as the bolt rattled around back and forth. Is there any way to replace this upper stud without pulling off the primary chain case? It is too long to slide clear without hitting the primary. I was hoping I could replace it with the appropriate grade 8 bolt but cant imagine a sneaky way to get the job done without removing the primary.
Thanks

I suspect that it can't be done without dismounting of the primary case. Cutting the bolts head and pulling from the other side
wouldn't work neither, because the timing case would be in the way.

Ralf

Pull the primary off time. The new bolt or stud should be kept very tight and checked periodically for secureness too. Observe the cradle holes to ascertain that they have not worn oval.

Bolts in the area are prone to breakage (ask me how I know). You you will need to pull the primary. I replaced all the mounting bolts with new ones.

Ok,
so the primary will come off. Is there any reason why I should not use a grade 8 bolt instead of a stud? Also what gaskets, etc. should I order since the whole thing has not been apart for some years. I already have a quality primary chain which I am going to install but I would like to do whatever I can to be proactive with the inner workings of the chain case while its apart. I have a clutch puller from Old Britts and I assume I can use an automotive style puller to yank the drive sprocket off the taper. I'd love to go belt drive but the budgets going to keep it stock for now. I have had some issues with oil working its way into the chain case when the motor wet sumps which is annoying. Thanks again in advance.
-RW

>>I have had some issues with oil working its way into the chain case when the motor wet sumps which is annoying.<<

Sounds like you should replace the crankshaft bearing seal on the drive side.
You can get at it once primary inside case off.

Yes, replacing the crankseal every time the primary is pulled is a matter of course. Never wait for it to fail. Try fitting the D.C. clutch pushrod seal while you're in there.

Dang it! I was just peeking in bored but found an new maintenance headache issue I was unaware of, ie: crank seal being so fragile. ugh. Might explain why this 3rd yr on renewed Combat the ATF in primary turns dark and thick and too full and I'm having to top off more oil than leaks or smokes can account for. Its certainly occurred to me but lazy denial is my style till forced to act. Being lazy I can't say how much sweat and swearing a good oil smoking heat saves for releasing pulley off its taper lock. New primary gasket is nice and I've not had to use anything for mine to seal good but some have to put silly con under it to get crush enough. I like to replace the three small bolts with studs. Crank seal is best sucked out by sheet metal screws driven in to pull on. Do not set chain tension too tight cold and just fill so lower chain just touches lube. Dextron ATF is good juice if not a 850 ES and helps to reveal source of leaks or contamination, ugh like in my Trixie case.

You might want to think about replacing all the engine bolts. You can get AN bolts from Aircraft Spruce with the right grip length so that they don't ride on the threads in the cradle plates. If the cradle or the bosses in the crankcase are shot you can go to oversize/reamed to fit replacements if you need to. Pick up a copy of Carroll Smith's Nuts Bolts and Fasteners for a primer on fasteners used in double shear and other interesting stuff. It's part of the Engineer to Win, Tune to Win series. This book is informally known as Screw to Win.

65tiger said:

... I assume I can use an automotive style puller to yank the drive sprocket off the taper...

Click to expand...

I would still recommend a special puller which is made for this job. The sprocket can be very stuck.

Ralf

Heat on the sprocket will usually pop it off with some tension on it.

Dave
69S

These studs are 3/8" and a good replacement for them are (OH the Horror !!!!) 10mm studs which are of course .019" larger and tighten things up noticeably.

DogT said:

Heat on the sprocket will usually pop it off with some tension on it.

Dave
69S

Click to expand...

Sure, but I doubt that a standard automotive puller would work at all.

So pulled off the primary today to get at the motor/cradle studs.

What a treasure trove of sloppy maintenance. First the three bolts that hold the footpeg and brake assembly were

top 12mm
center 1/2 inch
bottom 1/4 whitworth

Then when I got the outer cover off the real sin emerged. The primary chain was routed correctly over the engine sprocket but then only over the two outer sprockets on the clutch hub. So the outer chain links were filed flat on one side. Nice. I have only ever checked the tension and never had the outer cover off before today. I have gone miles on the highway and through two years of riding with the primary chain like this. Scary. Also the lower bolt holding the inner chain case to the motor was rattling around inside the chain case. The flow of oil from the sump to the primary was due to this unplugged hole. Thankfully the threads into the motor side are ok. The other two bolts were finger tight and it never looks like the fixing washers have ever been turned over the heads to lock them in place as intended. Instead of a nice new seal the po squeezed lots and lots of silicon between the chain case and the motor. New bolts in now, I did go with 10mm which really did tighten things up nicely and some torque nuts which were a new thing to me but worked great. I was going to install the new chain etc. but found out quickly that there were no clutch shimming washers on the bike at all. So I have a small collection of bolts and washers on order from Oldbritts. Thanks again for the guidance and advise. Hopefully if my 8 week old lets me I'll get it all together this week,
-RW

ugh

Primary school for all partys involved.

65tiger said:

Then when I got the outer cover off the real sin emerged. The primary chain was routed correctly over the engine sprocket but then only over the two outer sprockets on the clutch hub....

New bolts in now, I did go with 10mm which really did tighten things up nicely and some torque nuts which were a new thing to me but worked great.
-RW

Click to expand...

Your previous owner gets a slot in the DPO Hall of Fame. Is it possible that the chain was so loose at some time that it jumped over? BTW, what are torque nuts?

when I picked up the commando the chain was actually too tight and I've been on top of it keeping it close to spec since I've been riding it. I can only think that it stayed in place due to it being too tight when the po was riding it. I never would have thought it could stay on only two sprockets and I really could not tell what was up through the inspection hole. So the hardware guy shows me these nuts to fit the grade 8 bolts I got for the cradle and tells me that they were invented to deal with heat since nylock nuts have issues melting and getting brittle when they are exposed to heat. They are normal nuts with what I can only explain as lines cuts into the base. Apparently they stretch or something and grip the bolt threads. I know, sounds like BS !! They did the trick though and came in grade eight and were very tight on the threads as I ran them up. More like tight to thread on the whole way up the bolt instead of as you get toward the cradle if that makes sense. I would post a picture but I did not get a spare. Came from ACE anyhow, great hardware guy and he's just up the street. Very patient with weird bolt requests from greasy brit bike enthusiasts that wander in from the 95 degree sun.

Just looked it up,
officially known as "distorted thread locknut"
I like them so far, seems like they will handle the vibration better than anything else that I have seen.
-RW

Remember to properly shim the backside of the primary case to the center stud after first installing the inner cover just snug (not tight) with the three crankcase fixing bolts, then measuring the gap you need to fill as accurately as possible.

Bent tranny cradles (it happens) can affect proper primary chain alignment. Cracked/deformed primary inner cases can affect proper alignment also.