EVO: Suspension

Rigid Mount Engine Mounts

Rubber Mount Engine Mounts

Notes gathered from the XLFORUM:

  • Having to replace bushings and bearings related to motorcycle suspension has been a normal maintenance routine since the beginning of time. Keep in mind the rubber mount design also has 3 stabilizer links that connect the engine to frame and allow vertical movement from engine vibration, but also maintain side to side alignment of the engine and frame. Make sure they are tight. In addition, there is a pivot shaft that supports the swing arm bearings/bolts on the outside, and goes through the rear mounting lug on the tranny case. If the pivot shaft is loose in the rear mount lug, it will need to be replaced also. Lube and properly tightening steering head bearings are also important part of the process. 1)
  • Symptoms of swingarm problems:
    • Excessive play in the rear wheel, difficulty keeping in a straight line in slow moving traffic. 2)
    • Spherical Bearings having play in them 3)
    • Rear rubber mounts well out of shape. 4)
    • Torx bolt head shearing off. 5)
  • All of the rubber mounts are open to this problem… Because of the fact that the swing arm is mounted to the mount… An it's rubber-mounted with a spherical bearing… It's got some “flex” stock most don't notice it… Till its really bad! 6)

Replacing the mounts:

  • You can use a couple small automotive scissor jacks, one towards the front and one towards the rear, to support the weight of the motor and give some flexibility in moving it around to line things up. 7)
  • The front right is a pain to pull out, you need to pry the motor an inch to the left… right up to the frame, remove the front pipe and a couple case bolts underneath. Even with the engine right up tight to the frame it is a pain to pry the old mount out. Once out, the new one slipps right in. 8)
  • Use a 6“ C-clamp to pull the front of the motor right up tight against the frame. You cut the puck off the end of the threaded rod part of the clamp, and now it has a round ball on the end of that clamp. You use that round end to keep the C-clamp from sliding off the frame as you tighten it and pull the front of the engine over towards the left side of the bike (the ball on the clamp is inserted into the hole for one of the support plate's bolts). So when you get it pulled all the way over to where it contacts the frame as you mentioned, you just keep turning the clamp and somehow it pulls the rear of the engine over just enough to where the mount will fall out on it's own if it's sitting at the right angle. 9) Don't lift the front too high else it will hit the frame before it is over far enough. 10)
  • Remove the rear mounts and then change the fronts. Getting the right front out is easier when the tube is removed from the old mount. You can get loads of hassle getting the drag specs fronts in and having the extra movement by not having the rears in place will make it easier. Disconnect all the stabilizer links and put a jack under the front of the engine while someone sits on the bike to hold it upright and used pry bars to get the thing to move enough. 11)
  • It's best if you RUN the motor with the mount bolts loose for a few revvs then torque them to factory spec to let the engine settle in the mount. 12)
  • Front mount- There is a “shaft” on the RIGHT mount if it (there is actually 2 “shafts”) but removing the SHAFT from the Right mount will make things easier. If you have forward controls, remove them and the above is correct remove the “dog bone” mounts it will help you “move” the motor to 1 side. If your mount is really bad out of shape it will be HARD to remove the “LEFT” mount and the right will be almost impossible… REMOVE THE SHAFT with a LONG punch then remove the rubber bushing… now you should have enough room to install the front RIGHT mount. Align it and install the left mount… reinstall the dog bones. 13)
  • REAR: Remove the rear brake line it will help… and on the rear mounts they will come out ALOT easier than the front… even with removing the swing arm… ect. i found it to be ALOT easier than the front mounts. Take your time with the rear. The REAR shaft that goes through the engine that holds the RIGHT mount in place… and replace those TORX with some grade 8 hardware and tighten them down… TIGHT!!!!! they tend to brake if they come loose…14)
  • The LEFT mount will not come out easy if it is OUT OF ROUND. Turn it like 180deg and out at a angle.. it helps to REMOVE THE LOWER dogbone and rock the rear of the engine around… the NEW “round” mount will go in much easier… the RIGHT mount should not be a problem it will slide out once the AXLE shaft (the one with the 3 screws that break) is knocked out…. it doesnt matter the “shape” of the old mount it will come out pretty easy… but the primary and the frame will create some issues getting the RIGHT mount out IF it is droopy. 15)
  • Replace the swing arm bearing when you have it apart… and above all else… follow the TSB for reinstalling the rear brake don't cross thread the pivot bolt. 16)
  • When you have the swingarm out, use a few sockets and some all thread (a bolt could work as well) in a vise to press the bearings out. 17) There might be some surface rust in there, just soak it with some rust solvent for a couple of hours before you press it. 18)

Replacement Options:

  • OEM Mounts:
  • If you don't want more vibration, use the H-D mounts, but plan on replacing much more often. 19)
  • Drag Specialty Mounts (Poly):
  • The DS mounts seems to be slightly stiffer than the HD mounts… The HD mounts seem seem to soft and don't seem to last long I bet there are alot of sportsters with softened mounts or saggy that needed replacement. 20)
  • The reason for using solid motor mounts is to increase chassis rigidity to facilitate improved high speed stability and handling, however, the use of solid motor mounts will contribute to accelerated wear of the motorcycle chassis components, which may in turn lead to the breakage of the chassis or powertrain components. 21)
  • If it was questionable to use the nylon motor mounts and if they could cause frame failure, since the rubber-mount frame is heavier gauge steel to begin with then I don't see it. 22)
  • I notice the extra vibes at idle with the DS mounts, but I don't feel any difference above 2k. The bike just seems happier, and although I can't quantify it…it is smoother and seems to vibrate less at speed. 23)

Broken Pivot Bolts:

  • I think the design issue is that the pivot shaft is too small for the hole it goes through in the engine. It should be a tighter fit like an axle through a bearing. The purpose of the lock plate is to keep the pivot shaft from spinning so you can tighten the swingarm bolts. I think it does that job just fine. But, because the pivot shaft is too small, when you install the lock plate, the lock plate centers the pivot shaft in its hole. So the engine transmits its forces not directly into the pivot shaft, but rather into the lock plate bolts, then into the lock plate, then finally into the pivot shaft. Those little lock plate bolts cant handle that kind of stress so one or two of them break. I think a better fix would be a larger pivot shaft, or a shim or bushing of some sort to take up the space between the pivot shaft and its bore. 24)
  • I agree that a tighter pivot shift fit would help but the plate also holds against lateral shift of the shaft to the left under hard cornering loads. The combination of that force plus wiggling of the shaft in the motor opening definitely contributes to the problem 25)

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