Thursday, March 24, 2011

How to fix gears on Yamaha FJ1100?

Fixing 2nd gear of Yamaha FJ1100.

Tools: 36mm socket, 30mm socket, Torx #30 bit, snap-ring pliers, metric hex keys (allen wrenches), metric wrenches and sockets, clutch holding tool, torque wrench, and Yamaha FJ1100 Service Manual.

Medium strength (non-permanent) Loctite, and Threebond #1211.

All "left/right front/back" orientation is relative to how the engine normally sits in the bike. If you're doing this in a winter climate, and your engine will be open for a few weeks, take as many pieces as you can indoors where it's warm, to save them from corrosion. Everywhere possible I put bolts back in their bolt holes after disassembly, so I wouldn't lose them and so the bolt holes and threads wouldn't collect dirt or get damaged.

- go for a last ride to heat and stir the oil

- remove chin scoop

- drain oil and remove oil filter housing

- remove complete exhaust system

- remove fairing air scoops, and fairing

- remove seat, battery, side panels, and fuel tank

- loosen the four air intake hose clamps from carb intakes

- remove 3 air cleaner box bolts (2 sides 1 top)

- slide airbox back

- remove boost control hose and choke cable from carbs. Make careful note of how these hoses are routed, as you may not remember at all by the time you're putting the bike back together again.

- loosen four hose clamps on the front of the carbs

- lift the carbs out; the group of 4 hoses feeding down and back on the right side of the carbs may be tough to pull up and out, and again take note of how they're routed so you can do it when you put them back together again.

- remove throttle cables from carbs

- undo crankcase vent hose from the crankcase below the airbox

- undo the electrical connectors to the left and behind the battery, and remove the battery ground cable from the motor

- remove the sidestand cutoff switch assembly and cable

- lift the flexible heat shield and remove the starter cable from the starter

- remove oil cooler from front of engine

- remove clutch release assembly from left side

- remove gear shift pedal arm from the splined gear shift shaft on left side

- remove left crankcase cover (covers the chain drive sprocket), dowel pins, and clutch pushrod

- pull the chain drive sprocket off the drive shaft (36mm socket, and you may have to loosen the drive chain)

- remove the down tube frames (the bottom front sections of the square frame tubes), stays and collar

- block up the engine

- remove the final two long transverse bolts from back of engine. The top one is behind the shiny chrome plastic caps, and has a different hex key size on each end.

- the engine can now be removed from the frame. I used motorcycle tie down straps wrapped around the engine, hooked to the end of a long 2x4 (wooden beam). The 2x4 was pivoting on a sturdy camera tripod (on the right hand side of the bike), and my wife operated the other end of the 2x4. As she lowered the engine, I turned the engine 90 degrees clockwise (front of the engine facing right side of bike), and pulled the bottom of the engine out the left side of the bike until we could lay the front of the engine down flat on the floor. I could then unstrap the engine, and manhandle it out from under the bike frame.

- remove right side clutch/crankcase cover and dowel pins

- remove the clutch spring and plates. Careful of the pushrod and the little ball behind it.

- remove the clutch boss nut (30mm nut, and a good time to have a clutch holding tool), and the clutch boss.

- put two bolts into the clutch collar, and hold the clutch housing while pulling the collar out (see the manual!)

- remove oil pump drive gear (the collar behind this gear was tight, and tough to remove)

- I didn't remove the oil baffle plate, but it's easier if you do

- remove oil pump driven gear (snap-ring pliers, and make sure to cover as much of the open crankcase you can with a cloth, so that if you drop the snap-ring it doesn't fall down the crankcase), and oil pump assembly. Careful of the 3 O-rings, collar and dowel behind it. The pump has to come off because it hides one crankcase bolt.

- remove the starter motor and generator, as they each hide one crankcase bolt

- remove left side crankcase end cover

- remove the pickup coil base assembly (careful of the small loose dowel pin). This bolt was exceedingly tight on my machine.

- flip the engine upside down

- I didn't remove the oil sensor from the oil belly pan, but unclamped its cable from the engine

- remove the oil pan

- remove oil strainer cover (this was tough, and has to be "pried" off without bending everything), then the housing under it

- pull the relief valve out

- remove main bearing retainer (from behind the clutch assembly) with Torx #30

- remove crankcase bolts in reverse numbered order from 37 down to 1. The higher numbers are on "top" of the crankcase, so the engine is flipped upright for them again, then flipped upside down for the remainder.

- lift the lower crankcase off the engine (careful of the loose crankcase dowels, and the half-clips on the bearings, and the little orange O-ring in the middle)

- note the position of the "dowel pin" embedded in the bearings, and how they align with positioning slots in the two crankcase covers.

- (pedantry warning of excessive detail!) The "drive" shaft is the one closest to the "back" of the engine, and the usual suspect 2nd/5th gear pair is the pair of gears on its left end (the left end of the drive shaft is where the small sprocket goes that drives the front of the chain to the rear wheel). The other shaft is the "main" shaft. The gear teeth are the obvious teeth on the outside edge (perimeter) of the gears, that mesh with the teeth of the gears on the other shaft. The power transfer done by the teeth is front to back between the two shafts. The dogs and windows are the parts of the gears that mate sideways between two gears on the same shaft, so power transfer is sideways between them. The leftmost gear on the drive shaft is the "2nd wheel" gear, and has 6 "windows" in it. This gear is free spinning on the drive shaft (i.e. there is never any direct power transfer between this gear and the drive shaft), and cannot move sideways along the drive shaft. The next gear to its right on the drive shaft is the "5th wheel" gear, which has 3 "dogs" on its side pointing towards the windows of the 2nd wheel gear. This gear is splined to the drive shaft, so it always turns or is turned by the drive shaft's rotation, and it is free to slide sideways on the drive shaft. The 2nd wheel gear is the larger of the two, and its teeth mate to a gear on the other shaft. The 5th wheel gear does not mesh with any gear on the other shaft. The Number 1 (leftmost) shift fork mates directly to a collar on the 5th wheel gear. When not in second gear, these two gears do not touch each other, and rotate at different rates. When you shift your transmission to 2nd gear, the Number 1 shift fork slides the 5th wheel gear left, so that the 3 dogs mate with 3 of the windows in the 2nd wheel gear, thus creating a power transfer between the two shafts (engine power through the main shaft, into 2nd wheel gear, into 5th wheel gear, into the drive shaft, and out to the chain sprocket, the chain, and rear tire). Other than the friction between the dogs and windows, the Number 1 shift fork is the only thing holding the 2nd/5th wheel gears together during all that power transfer.

- inspect all the gear dogs on both shafts (you can spin and move all the gears). The dogs on my 5th wheel gear were obviously rounded off on the outside leading edges. The dogs on all the other gears appeared fine. Also inspect the shift forks and drum, but this is where damage is less obvious to my untrained eye. If the 5th wheel gear is separating from the 2nd wheel gear under power, it is taking the Number 1 shift fork with it. That means the shift fork is almost certainly bent, and the forces against the grooves in the shift drum may have damaged the groove walls also. Interestingly enough, when I look at the dogs on all the other gears, I see perceptible undercutting (the width of the dog from front to back is less where it meets the gear than the width at the very outside tip of the dog). On the 5th wheel gear, however, the dogs appear to be perfectly "flat" (the same width everywhere).

- back to the lower crankcase cover now; slide out the shift fork guide bar, and remove the shift forks

- remove the gear change shaft

- remove the shift cam stop lever and spring

- remove shift cam bearing retainer

- slide out the shift cam

- back to the engine; lift out the drive shaft assembly (the shaft closest to the "back" of the engine)

- on my model, the leftmost bearing is pressed onto the drive shaft. Therefore, remove all gears via the right hand end of the shaft (need snap ring pliers)

- I bought a new 2nd/5th wheel pair (CDN$80/$104), a new Number 1 fork ($38), a few O-rings and circlips, medium strength (non-permanent) Loctite, and Threebond #1211 (CDN$27!!)(instead of Yamaha Bond #1215).

- undercutting: After talking to Larry at Niagara Race Crafters (near Niagara Falls, Canada), I shipped him my full drive shaft assembly with the old gears, the shift cam, the shift forks, and the 2 new gears I bought. I should have done this before I bought the new gears, as he said they can sometimes fully recover the existing gears depending on the extent of the wear. He adds 6 (or was that 7?) degrees of undercutting to the 3 dogs and all 6 windows (CDN$85 for doing the pair).

2003 update: apparently Niagara Race Crafters no longer does undercutting. However Fast By Gast in New York does.

Finally got the gear assembly back again. The shift drum and forks 2 and 3 were undamaged, in their assessment. Put the gear shift drum and forks back together, and put the drive shaft back in the upper crankcase. I then experimented with putting the lower crankcase back on top of the upper crankcase without any Threebond applied (a "dry" run), to make sure I could get the shift forks aligned with the gears properly with a minimum of fuss. Then apply the Threebond and do it for real. Make sure you check the gear shifting pattern through all 5 gears and neutral before you start bolting the crankcases together again. If you put your engine back in the bike without the gears shifting correctly, you may experience undue emotional stress.

Tighten the crankcase bolts in order from 1 to 37 with a torque wrench. Make sure you get the correct clamps back on the bolts.

Put the 3 Torx screw main bearing retainer back on (use Loctite where appropriate as indicated in the manual). Then the oil pan pressure relief valve, and the strainer housing. Before you put the oil strainer back on, clean out the screen. Mine had a surprising amount of debris in it. Put the oilpan back on.

Continue to reverse the disassembly steps, nothing fancy. When you're putting the engine back in the frame, make sure you route all cables and hoses correctly as you're doing it. It's a good idea to get the drive chain looped around in front of the drive shaft before you bolt the engine back into the frame (if you can), as it is tough to do it afterwards. Getting the carbs back in is the toughest part for me, since the airbox doesn't really slide back out of the way at all.

I reused the old oil filter at this time, and filled the engine with new oil. I started up the bike, and it runs and shifts correctly! Then I had to wait for a couple weeks for a day nice enough to take if for a short ride. Second gear is solid as a rock, which is wonderful. I even noticed that it takes a little more effort to get it out of 2nd and into 3rd.

I figure one ride is enough to circulate the oil and pick up some junk from all the work on the engine, so I immediately drain the oil again, change to a new filter and refill with new oil. Now I wait for the riding season to begin...

I installed the "newer" pair of gears in the bike, and I still have my original pair which are now undercut. The undercutting was indeed enough to recover them.

Thanks are due the FJ Mailing List members who helped me out with their advice and experience and previous posts doing this. Thanks everyone!