EVO: Transmission & Final Drive

1986-1990 4-Speed Constant Mesh Wet Clutch Transmission w/Trapdoor

  • The rear compartment of the left and right engine case halves form the transmission housing or case. An access cover, or trapdoor, is mounted on the left side of the case (inside) behind the primary cover. The main components of the transmission are mounted to this trapdoor to allow you to detach the one cover (together with all the transmission components) for easy removal and servicing without having to split the engine cases in half which otherwise would be a full engine re-build.
1990 4 Speed Transmission 1)
1990 4 Speed Transmission 2) 1988 4 Speed by WI_duker))

Specifications

Clutch

1986-1990 Wet Clutch Information 3)
Clutch plate thickness–Friction (drive) plate (fiber)0.0150 in. (± 0.0031 in.) / 3.810 mm (± 0.079 mm)
–Steel plate (driven) plate0.0629 in. (± 0.0020 in.) / 1.598 mm (± 0.51 mm)
Minimum Thickness (wear limit)–Friction (fiber) plate 0.130 in. min. / (3.302 mm)
–Steel plate 0.060 in. min. / (0.0254 mm)
Maximum allowable warp-age–Friction (fiber) plate 0.0010 in. max. / (0.0254 mm)
–Steel plate 0.0010 in. max./ (0.0254 mm)
Capacity174 ft-lbs
Spring ForceEngaged: 304 lbsDisengaged: 260 lbs
Clutch shell bearing on clutch gear (loose)0.0000 in-0.0010 in. / (0.0254 mm)

Primary Drive (engine to transmission)

YearDomestic Model(s)Engine SprocketClutch SprocketRatio
1986-1990All Models4)34 Teeth59 Teeth1.676:1

Primary / Transmission Oil Capacities

The MoCo publishes for 1986-1990 5)1.5 pints (24 oz), (710 ml)

* This quantity is for a dry application. When changing oil, use your own judgement not to overfill as you won't need a full 1.5 pints to re-fill the oil.

Transmission

  • Internal Gear Ratios are the number of clutch gear revolutions to drive the mainshaft sprocket one revolution.
  • Overall Gear Ratios are the number of engine revolutions to drive rear wheel one revolution.
Year (all models) Internal Gear Ratios
1st2nd3rd4th
19862.521.821.381.00
1987-19902.291.661.251.00
Year (all models)Overall Gear Ratios
1st2nd3rd4th
198610.007.255.483.97
1987-19909.126.594.983.97

Final Drive (Trans to Wheel)

Final Drive Sprocket Torque (on Chain Drive Models)
Nut DescriptionNut SizeTightening TorqueNotes
1986-90 1-1/8“ Nut - Right-hand Threads 35-64 ft-lbs Max 90ft-lbs
(use only 2 or 3 drops of RED threadlocker on this nut)
YearDomestic Model(s)Transmission SprocketRear Wheel SprocketRatio
1986-1990All Models6)21 Teeth48 Teeth2.29:1

Fastener Torque Specs

Mainshaft nut locking screw50 - 60 in-lbs.
Mainshaft nut35 - 65 ft-lbs.
Engine sprocket nut150 - 165 ft-lbs.
Drain plug14 - 21 ft-lbs.
Front chaincase / primary cover screws80 - 110 in-lbs.
Access \ Trapdoor cover bolts14-19 ft-lbs.
Stator Torx nuts30 - 40 in-lbs.
Footrest nut24-36 ft-lbs.
Shift lever pinch-bolt90 - 110 in-lbs.
Neutral indicator switch3 - 5 ft-lbs.
Chain tensioner stud nut8 - 12 ft lbs
Clutch release mechanism22 - 30 in. lbs

Mainshaft Group

  • Clutch gear ball bearing in access cover: .001 - .00012 in. loose
    • Wear limit: .0035 in.
  • Ball bearing on clutch gear: .0009 in. max. tight
    • Wear limit: .001 in. loose
  • Clutch gear needle bearing journal diameter: .7495 - .7500 in.
    • Wear limit: .7485 in.
  • Mainshaft right side retained roller bearing: .0004 - .0015 in. loose
    • Wear limit: .0035 in. loose
  • Mainshaft end play:
    • Minimum: .006 in. / Maximum .020 in.
  • Mainshaft third gear on shaft: .0027 - .0038 in. loose
    • Wear limit: .004 loose
    • End play: .006 - .020 in.
  • Clearance between clutch faces:
    • Mainshaft fourth gear and second gear: .040 min. - .080 in. max.
    • Mainshaft third gear and second gear: .040 min. - .080 in. max.

Countershaft Group

  • Countershaft end bearings: Retained needle roller bearings
  • Countershaft needle bearing journal diameter:
    • Access door side or end: .7500 - .7495 in.
      • Wear limit: .7490 in.
    • Right crankcase side or end: .6875 - .6870 in.
      • Wear limit: .6865 in.
  • Bearing fit in case: Press fit
  • Second gear on shaft:.001 - .0025 in. loose
  • Low gear needle bearing journal diameter: .6875 - .6870 in.
    • Wear limit: .6865 in.
  • Clearance between faces:
    • Countershaft low and third gear: .040 - .080 in. max.
    • Countershaft second gear and third gear: .040 - .080 in. max.
  • Countershaft end play: .004 - .015 in. max.

Countershaft Low Gear Changes

Countershaft Low Gear -17TChange YearModel(s)Notes
35760-84A
Late 1984-1990 7) 8)
Late 1984

Discussion

1986-90 Evo Sportsters: What every owner should know but were afraid to ask
An __XLForum Thread__ By Four Speed



3)
1986-1990 HD HLX FSM pg 6-1
4) , 6)
1986-1990 HD Sportster FSM pg 6-1
5)
1986-1990 HD Sportster FSM pg 2-1
7)
1979-1985 HD Sportster Parts Catalog pg 51
8)
1986-1990 HD Sportster Parts Catalog pg 37
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