EVO: Engine Mechanicals

Timing Inspection Hole


Motor Mounts

Click here for Engine Mounts in the Evo Suspension section of the Sportsterpedia.

Cylinder Mounting Studs

Weakest cylinder mounting stud holes in the case. 1)

Cam / Gearcase Cover

Sub Documents

#2 Cam - Cover Seal (86-03)

Seal number (11124):
This surrounds and seals #2 cam when the cover is installed.
See also Removal / Installation of the #2 cam cover seal in the Sportsterpedia.

This side faces out. 2) This side faces #2 cam shaft. 3)

Primary Cover


Shifter shaft Seal

This is a shifter shaft seal on a 1998 1200S primary cover.

Engine Case / Sump Drain Plugs

Sump drain on 04 model 4)

Crank Assembly


The same flywheel set was used in all Sportsters 95-99.
Sold as a unit: part number (23905-89A) consists of the flywheels, shafts and rods.
Each flywheel casting number (23931-88A)
Connecting rod set: part number (24275-86A)
Left connecting rod casting number (24320-83)
Right connecting rod casting number (24321-83)
Rod bearing set (24354-87A)
Rod bearing race - front (2)-(24341-52A)
Rod bearing race - rear (2)-(24352-52A)
Piston pin bushing std (2)-(24331-36), .01“ O.S. (24332-36
Crankpin std (23960-80A), .001” O.S. (23948-87), .002“ O.S. (23949-87)
Crankpin boss washer (2)-(6508)


Flywheel assembly 23905-00 5)
Flywheel assembly 23905-00A 6)


91-99 (all) Flywheels.
Flywheel set part number (23905-89A).
Each flywheel casting number (23931-88A).

91-99 Flywheels 7)
Crank pin boss washer (5608) 8)

From '91 to '03 the Crankshaft/Flywheel was balanced according to the engine size, either for 883 pistons or 1200 pistons. From 2004-later, the flywheels are balanced to be between the weight of the 883 & 1200 pistons. 9) This is one reason why riders would use Wiseco pistons in early (pre-2004) 883 to 1200 conversions - the Wiseco 1200 piston & pin was closer to the weight of the 883 combination rather than the 1200 piston & pin from HD.

Crank Pin

Crank pin (23960-80a) used from L81-03.

L87-03 crank pin 10)

The sprocket shaft nut torque for 2004 & later Sportsters and 2003 & later Buell XB models has been changed. 11)
The torque has been increased from 190-210 ft-lbs. to 240-260ft-lbs.
Remember to clean the threads and generously apply LOCTITE Threadlocker 262 (red) onto the threads of engine sprocket shaft and use a sprocket locking tool.
Some examples of sprocket locking tools are here in the tools section of the Sportsterpedia.

Connecting Rods

Pinion Shaft

Removing / installing the pinion shaft nut

To remove or install the pinion gear nut,
You'll need to lock the pinion gear from moving while turning it.
It's very important to hold the crank on the pinion side with an appropriate pinion locking tool whenever you take the pinion nut off or put it on.
If you hold the crank still from the primary side (or by putting the bike in gear and holding the brake),
The twisting torque applied to the pinion nut gets transmitted through the crank, from one side to the other.
The crank pin is not designed to resist much twisting force.
You'll risk scissoring the crankshaft (knocking the crank out of true), which requires a full tear-down to fix. 12)
So this is one of those situations where it's best to use the proper tool. 13) The pinion nut takes a 15/16” wrench size.

90 and Prior Models (4 Speed)

Homemade Pinion Gear / Removal / Installation Tools 14) Homemade pinion gear press 15) Pinion Gear Puller 16)
Large fender washer cut into a “C” shape and a gear puller
Homemade Pinion Gear Puller 17)
3/8“ stainless steel plate with 20° spokes (for 18 teeth),
sawed initial groove to depth and widened it with files
Homemade pinion gear locking tool for '89 models 18)

91 and Up Models (5 Speed)

See also in the Sportsterpedia:
Oil Pump Drive Gear
Origin of the Grindlock Tool

  • You can use a 15/16” wrench or deep well socket to remove / install the pinion gear nut.
  • The Grindlock Pinion Shaft Locking Tool engages for the full depth of the pinion gear for max. strength.

19) 20)

  • Due to a change in the pinion gear in 2000, there are 2 different versions of this tool:
    (L) - (91-99) year models & (R) - (2000 to present) year models 21) 22)

23) 24) 25)

  • Once the pinion shaft nut is removed, the pinion gear may or may not slide off by itself.
    You can use a gear puller to remove it if it is stuck on.
  • It's very important to hold the crank still from the cam side (not the primary side) when torquing the pinion nut. 26)
    If you for example put the bike in gear and hold the rear brake and torque on the nut, you run the very real risk of knocking the crank out of true.
    It's not designed to transmit torque from one side to the other and it tries to twist the crankpin connection.
  • In respect to the key shearing, it's a very common issue particularly when heavy valve springs are used.
    However, it shouldn't be the one thing that keeps the gear from spinning. The clamp load should do that.
    The caption in the second pic below describes the fix:
    Loctite red and 70ft-lbs instead of the factory specified 50ft-lbs. You won't have this issue again.

27) 28)

Pinion Shaft Runout

Attach a scrap piece of metal to the outside of the gearcase and position a gauge holder on it so it won't move while turning over the engine. 29)
Install a dial gauge on the holder with the pointer on
the pinion shaft. Find the lowest spot while turning
the engine over and 'zero' the indicator. 30)
This setup is made with a piece of angle iron for the magnetic base to stand on 31)
This gauge post is threaded into a cover mount hole. 32)

Crankshaft Seal

Here is a trick to hold the spring in place to stop it popping off while you are fitting the seal. 33)
Before fitting it, pack some grease around the spring in the seal groove. You only need a small amount.

1) , 2) , 3) , 19) , 23)
photo by Hippysmack
7) , 8) , 10)
photos by Hippysmack
HD Tech Tip #211 dated September 16,2005
Grindlock 91-99 & Grindlock 2000, designed by XLFORUM member, “~Grind~” and Built by Hammer Performance ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1618841
photos by anachris of the XLFORUM
photo by Grind of the XLFORUM
photos by dezzertrat of the XLFORUM http://xlforum.net/forums/showthread.php?t=1860581
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