so, you wanna fix yr largeframe’s cruciform without dropping the motor? here’s how:
first off, decide if you’ll ‘drop’ the engine. dropping the ass end of the engine lets you remove the barrel without fooling around with the cylinder studs and gives you great access to the clutch (just in case you need it now or later). the downside is that it might take longer, and you need a bucket or crate to rest the body on.
if you are interested, click here now.

if not, stick around.
in either case, these instructions should be helpful. however, some of the instructions on this page are unnecessary if you have dropped the motor.

1. remove all the extraneous stuff that’d prevent you from cracking the engine apart. this means things like

the cylinder shroud
the fan cover
the selector box
removing the sel. box is easy if you first remove the nuts, unclip the cables from the little bracket that may or may not be hanging from a case stud, then turn the gearchange past the 4th gear position. the box will then push itself off the studs, more or less. wiggle it off the selector rod and y’r all set. (note: it will leak a little oil ). drain the oil now, because you’ll have to one way or another later.

2. disconnect the electrics @ the junction box, so that you can pull the case halves apart without ripping all the wires outta yr stator!!. on a pseries the junction box is on top of the engine next to the airbox and a little behind it.

3. remove the flywheel . on a p this means using yr flywheel puller. on an older bike, just backing the flywheel nut off will pull the flywheel, provided the little circlip that allows for this to happen is still in place.

4. remove the stator (optional). mark the position of the stator relative to the case to ensure good timing on reinstallation. tape the wires together at the top before you pull them thru the tunnel in the cases. this will make threading them back thru much easier, and it will protect the connectors from being yanked off.
you can just let the stator ‘dangle’ in the shallow case half. you will have to move it to get to the inner ‘ring’ of case nuts. don’t forget about these nuts later, or you will wonder why the case won’t split!

5. remove the exhaust (optional) the problem here is that there’s a little locating dowel in the bottom of the jug that seats in the shallow case half (the one y’r removing). the exhaust will prevent the barrel from sliding up its studs if it’s still bolted on, preventing the dowel from clearing the case and preventing the case from cracking open. if you have a helper, and only after you’ve removed the head and the cylinder studs (see step 7) and removed all of the case nuts, she can kind of yank the barrel towards the front of the bike as you try to wiggle the cases apart. the exhaust will flex enough that, as she pulls, you’ll see the dowel and you can see when it clears the case.
if you don’t have a helper, you’ll have to remove the exhaust by loosening the clamp on the barrel stub and completely removing the bolt thru the swingarm on the battery side of the bike. this will require removing or deflating the rear tire. it’s often necessary to give the pipe a few taps once it’s unbolted, cause it kind of resists sliding down the stub sometimes.

6. remove the cylinder head nuts and head by loosening the nuts evenly and slowly, working in a crosswise pattern. otherwise, you may warp the head. one will contain a taller spacer nut that the screw for the cylinder shroud threads into… remember that you’ll need to loosen this, then the nut under it to really loosen the head evenly. once y’r done, remove the head. be careful to catch all the hardware that has a tendency to fall all over the place.

7. remove the cylinder studs (optional) in the right-hand/shallow case half. (note — if you drop the motor, ignore this step.) if you thread one nut onto the stud, then thread another nut on after it, you can effectively use the two nuts against one another to remove the stud. hold the lower nut with a wrench and tighten the top nut against it with another wrench or socket. then use yr wrench on the lower nut only to remove the cylinder stud. voila – now you can remove the case half without having to remove the jug!

8. remove the case nuts in a counter clockwise pattern, working from the bolts nearest to the crank first, then working yr way around the outside of the case and loosening the nuts evenly and progressively. remember the stud under the selector box area, which faces backwards, and the studs right next to the mouth of the crankcase. make sure you catch all the hardware.

9. split the cases. a good way to start is by pressing the kickstart lightly (use yr hand)… often this will cause the cases to lever themselves a little bit of the way apart. then you can wiggle them gently til they come free. remember that exhaust thing, if you didn’t remove it. do not insert a screwdriver or anything else in between the gasket faces and try to pry them apart. one thing that may be helpful is to tap around the gasket face with a rubber mallet. also, depending on the bike, there’ll be a little lip on the shallow case half near the “backwards” stud that will let you tap on the case half without damaging anything.

as the cases come apart, be sure to watch out for the kickstart gear spring and the kickstart gear, which may try to fall onto the ground @ this point. catch em and put em someplace safe (where you’ll remember them, unless you like bumpstarting yr bike every time). clean the old gaskets off the gasket faces, but don’t use a screwdriver to scrape em… you can use a razor blade, but be very careful.

10. remove the circlip on the output shaft. this is the lower of the two gear-carrying shafts, the one that carries loose gears, and the one out of which the selector rod is sticking.

11. remove the gearbox end float/shim and the loose gears, making sure that you keep them facing in the right direction. if you get confused, don’t worry. the outside of first gear is usually marked with engine-marking paint. if not, remember that the gears have a raised inner lip on one side, and that that side faces out towards first gear. first gear’s lip faces in, making an extra-big space between first and second where neutral is.

once you’ve got ’em out, take a look at their teeth and the faces where they engage the cruciform (on the inside of the gears). any rounded edges on either parts mean it’s probably time for new ones (but you can get by without it if y’r out of money…. but you’ll only wind up going thru cruciforms like they’re candy. do yrself a favor and get new gears.)

12. loosen the selector rod and remove the cruciform. remember that the selector rod is a reverse thread, so clockwise=loose in this case. once the rod is free from the cruciform (don’t lose that washer on the end of the rod), turn the cruciform flat, so it slips out of the output shaft. remember its orientation – its raised center should be closer to the shallow case half than its edges.

13. install yr new (piaggio only, please) cruciform. reinstall gears and check clearances! remember that the thread on the selector rod is reverse, so anti-clockwise=tight. a drop of loctite on the threads wouldn’t hurt.

use two feeler gauges to check the clearance between the end shim and the end of the shaft…. failure to shim the box tight will kill a gearbox faster than you think. check the haynes manual for specs for yr box. if in doubt, go for tightness. shim oversizes (if you need them) are in the haynes manual. do the math to figure out which one you need.

14. reassemble motor. first clean out any dirt yr grubby little hands have gotten in crevices, using a lint-free rag. run a thin bead of rtv gasket maker around the gasket surface of both case halves — a good rule of thumb for keeping a nice thin coat of rtv is that if you can just barely see the color of the rtv on the gasket face, y’r doing ok. if not, you’ve got too much on. remember to wipe away the excess, especially around the crankcase area. put the gasket on the deep side case half (the one still in the bike). it will probably be a bit too long near where the cylinder meets the case. cut this excess off with a razor or knife so that you still get good cyl/case sealing
then flood relevant bearings with oil:

-bearing for sel rod
-‘rest’ for end of layshaft/input shaft in inside of shallow case half
-flywheel-side main bearing
-and grease the lip of the flywheel-side seal to keep it from rolling
now place the kickstart gear back on the input shaft. use a dab of grease to hold the kickstart gear spring into its recess in the shallow-side case half.

now mate the two case halves with each other. if you used the exhaust-yanking trick, you will have to do it again, just to get the cases to mate. the cases should be very close together if not touching — if you have big gaps, you fucked up somewhere. again, depressing the kickstart can aid in sticking the motor back together. don’t forget any of the case bolts when buttoning things back up!

reverse the earlier steps to finish reassembly. remember to torque everything to spec!!!