Harley-Davidson Milwaukee-Eight (M8) Interactive Technical Teardown
The complete forensic engineering workshop guide for the Milwaukee-Eight 107ci, 114ci, and 117ci V-Twin powerplants powering the FLHX Street Glide, FLTRX Road Glide, and Ultra Limited. Complete architectural motorcycle blueprint, exploded component schematics, isolated 3-hole fluid dynamics, single-cam 4-valve pushrod mechanics, internal engine parts bill of materials, verified fastener torque specifications, and factory service kits.
Harley-Davidson Street Glide Architecture & Mechanical Dissection Map
Interactive elevation CAD drawing. Click any pulsing inspection beacon to isolate the mechanical subsystem and load workshop tolerances.
Milwaukee-Eight Multi-Stage Mechanical Disassembly
Drag the explosion slider or step through disassembly stages to peel outer covers, valvetrain, and crankcase.
S&S Cycle Multi-Layer Steel Head Gasket & 4V Valvetrain Seal Kit
Milwaukee-Eight 45° V-Twin Valvetrain & 4-Stroke Combustion Cadence
Visualizing the single 4-lobe camshaft, fixed pushrod actuation, 4 valves per cylinder, dual-spark ignition, and scavenge oil circuit.
Dual 40mm intake valves open. Piston travels downward, drawing stoichiometric 14.7:1 charge.
Dual DCPR7E spark plugs ignite simultaneously. 111+ ft-lb combustion wavefront drives piston down.
Milwaukee-Eight (M8) Engine Architecture & Parts Breakdown
Complete engineering analysis of the 45-degree V-Twin: 4-valve cylinder heads, single-cam reduction, forged knife-and-fork connecting rods, and TSB M1450 scavenge pump diagnostics.
| Engineering Parameter | M8 107ci (Standard) | M8 114ci (Special / ST) | M8 117ci (CVO / ST) |
|---|---|---|---|
| Displacement | 1,746 cc (106.6 cu in) | 1,868 cc (114.0 cu in) | 1,923 cc (117.3 cu in) |
| Bore × Stroke | 3.937" × 4.374" (100.0 × 111.1 mm) | 4.016" × 4.500" (102.0 × 114.3 mm) | 4.075" × 4.500" (103.5 × 114.3 mm) |
| Compression Ratio | 10.0 : 1 | 10.5 : 1 | 10.2 : 1 |
| Peak Factory Torque | 111 ft-lb @ 3,250 RPM | 122 ft-lb @ 3,000 RPM | 126 ft-lb @ 3,500 RPM |
| Valve Configuration | 4 Valves / Head (2 In / 2 Exh) | 4 Valves / Head (2 In / 2 Exh) | 4 Valves / Head (2 In / 2 Exh) |
4-Valve Pent-Roof Chamber & Dual-Spark
The Milwaukee-Eight utilizes two 40mm intake valves and two 32mm exhaust valves per cylinder head, delivering a 50% flow increase over the Twin Cam. Symmetric dual spark plugs are timed with microsecond offsets, ensuring uniform flame front propagation across the pent-roof chamber to prevent detonation and eliminate spark knock under heavy bagger acceleration.
Single-Cam 4-Lobe Chain Reduction
Replacing the Twin Cam’s dual camshafts and idler gear train, the M8 uses a single, chain-driven 4-lobe camshaft. This eliminates intermediate gear lash and cuts valvetrain frictional parasitic drag by 17%. Four hydraulic roller lifters ride induction-hardened lobes, actuating fixed chromoly pushrods and forked roller rocker arms that require zero valve lash adjustment for the lifetime of the engine.
Single Crankpin Knife-and-Fork Rods
Harley-Davidson preserves its iconic 45° cadence by mounting both fracture-split forged steel connecting rods to a single crankpin using the knife-and-fork big-end arrangement. Cylinders remain perfectly in line with zero lateral cylinder offset. An internal gear-driven primary counterbalancer cancels 75% of primary rocking vibration at idle while allowing 25% of the visceral V-Twin rumble through the chassis.
M8 Crankcase Sumping & 8-Tooth Pump Fix
Early 2017–2019 M8 engines featured a 10-tooth scavenge rotor lacking a backplate seal. Under sustained high RPM (> 3,500 RPM), crankcase blowby pressure resisted oil return, allowing up to 30 oz of oil to pool in the flywheel cavity. This drag caused sudden power loss and oil overheating. TSB M1450 decreeing factory 8-tooth scavenge pump #62400248 with elastomer seal increases scavenge displacement by 44% to cure sumping permanently.
Master OEM Reference Parts Directory
| Component Description | OEM Part # | Aftermarket / Cross-Ref | Subsystem | Service Interval | Engineering Specification |
|---|---|---|---|---|---|
| Engine Oil Filter (Black / Nut End) | 63731-99A | K&N KN-171B / WIX 57148 | Lubrication & Sump | 5,000 Miles (8,000 km) | 3/4"-16 UNF Thread, 17mm Nut End, 20-Micron Synthetic Blend Media |
| Laser Iridium Dual-Spark Plugs (4x) | 31600085 (6R12 Equivalent) | NGK LMAR7A-9P / DCPR7EIX | Ignition / Valvetrain | 20,000 Miles (32,000 km) | M12 × 1.25 Thread, 5/8" Hex, 0.031"-0.035" (0.8-0.9mm) Factory Gap |
| High-Flow Dry-Type Air Filter Element | 29400212 | K&N HD-1717 / Vance & Hines VO2 | Air Induction & EFI | 10,000 Miles (16,000 km) | Molded urethane body with wire screen reinforcement, 55mm bore fitment |
| Viton Oil Sump Drain Plug O-Rings (3x) | 11105 | James Gasket JGI-11105-V | 3-Hole Fluid Sump | Replace Every Fluid Change | High-Temp Viton elastomer resistant to 20W-50 and 80W-140 synthetic esters |
| Derby Cover 5-Hole Beaded Gasket | 25701080 | Cometic C9997-020 | Primary Chaincase | Replace Upon Derby Removal | Aluminum core with elastomer bead sealing; fits all 2016-2026 Narrow Primary covers |
| High-Capacity 8-Tooth Scavenge Oil Pump | 62400248 | Feuling 7016 / S&S 310-0998 | Crankcase Lubrication (TSB M1450) | Factory Update (2020+ Standard) | 8-tooth scavenge rotor with backplate oil seal; 44% more scavenge volume |
| Primary Chain Automatic Tensioner Shoe | 39968-06 | Twin Power 180-205 | Primary Chaincase | Inspect Every 10,000 Miles | Ratcheting nylon tensioner wedge; maximum allowable groove depth: 0.125" (3.2mm) |
| Front Brembo 4-Piston Sintered Brake Pads | 41300004 | EBC EPFA400HH / Brembo 07HO57SA | Chassis & Front Brakes | Inspect Every 5,000 Miles | High-friction copper alloy sintered compound for dual 300mm floating rotors |
| Rear Brembo Sintered Brake Pads | 41300053 | EBC FA409HH / Galfer FD304G1370 | Chassis & Rear Brakes | Inspect Every 5,000 Miles | Heavy-duty formulation with thermal backing shield; minimum pad thickness: 1.0mm |
| Carbon-Fiber Reinforced Final Drive Belt | 40024-09 | Gates Carbon Drive 140T-1.0 | Final Drive Belt | Inspect Every 5,000 Miles | 140 Tooth × 1.0" (25.4mm) width; 3/8"-1/2" cold deflection with 10 lbs gauge |
| Compensator Sprocket Center Flange Bolt | 10500031 | ARP 12-Point Heavy-Duty | Compensator & Crankshaft | Replace Upon Compensator Service | 9/16"-12 Grade 9 heat-treated bolt; torqued to 175 ft-lb (237 N·m) with Red Loctite |
| Clutch Hub Mainshaft Left-Hand Nut | 37495-91 | Colony Machine 8214-1 | Transmission Input & Clutch | Replace Upon Clutch Hub Removal | 1-3/16" Left-Hand Threaded Flange Nut; torqued counter-clockwise to 80 ft-lb |
Detailed Mechanical Subsystems
1. 3-Hole Fluid Sump & Oil Circuit
Three isolated fluid cavities, scavenge pump mechanics, and sumping diagnostics.
Milwaukee-Eight Diagnostic Forensics & Wear Tolerances
Real-world failure modes, root cause mechanics, factory wear thresholds, and certified remediation procedures.
1. Crankcase Oil Sumping & Scavenge Pump Defect
Fastener, Socket & Chemical Locking Matrix
Filter by subsystem or search by fastener name, socket size (e.g. 17mm, M14, 105 N·m, T27), or torque.
| Fastener Label | Thread Spec | Drive Tool Size | Torque Spec | Chemical / Sealant | Critical Warning |
|---|---|---|---|---|---|
| Engine Oil Sump Drain Plug | M14 × 1.5 | 5/8" Hex Socket | 15.0 ft-lb (21 N·m) | Clean / New Viton O-Ring (Part 11105) | Over-torquing strips aluminum sump threads. Never exceed 21 N·m; hand-spin first. |
| Transmission Case Drain Plug | M14 × 1.5 | 5/8" Hex Socket | 15.0 ft-lb (21 N·m) | Clean / New Viton O-Ring (Part 11105) | Located horizontally under transmission pan. Clean magnetic tip of steel filings. |
| Primary Chaincase Drain Plug | 1/2"-20 NPT | 3/16" Allen / Hex Key | 60 in-lb (5.0 ft-lb) (6.8 N·m) | Loctite 565 High Performance Thread Sealant | Tapered thread pipe plug. Over-tightening cracks the primary outer cover casting. |
| Engine Oil Filter (Spin-on) | 3/4"-16 UNF | 76mm 14-Flute Oil Filter Wrench | 11.0 ft-lb max (Hand-Tight + 1/2 Turn) | Pre-lube rubber gasket with fresh 20W-50 | Dry gaskets bind and leak onto the voltage regulator and front tire at highway speed. |
| Spark Plugs (4 Plugs Total) | M12 × 1.25 | 5/8" Thin-Wall Magnetic Socket | 13.5 ft-lb (162 in-lb) (18 N·m) | Clean Dry (or micro drop anti-seize) | Always torque into cold aluminum heads. Cross-threading requires head removal. |
| Cam Plate Mounting Bolts | 1/4"-20 Grade 8 | 3/16" Allen / Hex Key | 120 in-lb (10.0 ft-lb) (13.6 N·m) | Loctite 243 (Medium Blue) | Strict criss-cross torque sequence from center bolts outward to prevent plate distortion. |
| Clutch Derby Cover Screws (5-Hole) | 1/4"-20 T27 Torx | T27 Torx Bit (NEVER use T25) | 105 in-lb (8.8 ft-lb) (11.9 N·m) | Loctite 243 (Blue) on clean threads | Using a T25 bit strips the head instantly. Follow the 5-point star torque pattern. |
| Compensator Sprocket Bolt | 9/16"-12 Large Flange | 13/16" 6-Point Socket | 175 ft-lb (237 N·m) | Loctite 262 (High Strength Red) | Requires primary locking bar tool. Inadequate torque causes compensator knock. |
| Clutch Hub Mainshaft Nut | 1-3/16" Left-Hand Thread | 1-3/16" Deep Socket (LH) | 80.0 ft-lb (108 N·m) | Loctite 262 (Red) on cleaned threads | LEFT-HAND THREAD! Turn clockwise to loosen, counter-clockwise to tighten. |
| Voltage Regulator Mounting Bolts | 1/4"-20 Flange | 7/16" Socket | 90 in-lb (7.5 ft-lb) (10.2 N·m) | Clean threads for metal-to-chassis ground | Must maintain clean metal contact with front downtube for proper electrical grounding. |
| Front Brake Caliper Mounting Bolts | M10 × 1.25 Flange | 10mm 12-Point Socket | 35.0 ft-lb (47 N·m) | Loctite 243 (Medium Blue) | Critical safety fastener. Check caliper alignment prior to final torque stroke. |
| Rear Axle Nut | M24 × 1.5 Castle/Flange | 36mm Heavy-Duty Socket | 95.0 ft-lb (130 N·m) | Anti-seize on axle shaft; dry on threads | Verify drive belt deflection (3/8"-1/2" with 10 lbs gauge) before locking axle nut. |
1-Click Milwaukee-Eight Maintenance Bundles
Spectro M8 Complete 3-Hole Fluid Service Kit
Full Synthetic Engine Oil, Primary Lube, 75W-140 Gear Oil, Filter & O-Rings
- 4 Qts 20W-50 V-Twin Full Synthetic Engine Oil (JASO MA2)
- 1 Qt High-Shear Primary Chaincase Lubricant
- 1 Qt 75W-140 Synthetic Hypoid Transmission Gear Oil
- High-Flow Spin-on Oil Filter (Black / Nut End)
- 3x Genuine OEM Viton Drain Plug O-Rings (Part 11105)
NGK Laser Iridium DCPR7EIX Spark Plug
Authentic Laser Iridium Fine-Wire 0.6mm Center Electrode (DCPR7EIX)
- Laser Iridium Fine-Wire 0.6mm Center Electrode
- Pre-gapped to certified 0.85 mm (0.033 in) specification
- Trivalent metal plating provides anti-corrosion on aluminum heads
- Engineered for 4-Valve Dual-Spark Milwaukee-Eight cylinder heads
Metzeler Cruisetec Front Touring Tire (130/60B19 61H)
Performance Bagger Front Fitment for Harley-Davidson Touring FLHX/FLTRX
- Dual-compound layout delivering performance handling and extended mileage
- Optimized groove geometry for water dispersal and wet road confidence
- Load Index 61H reinforced carcass engineered for heavy touring rigs
- Qualified for $0.00 Free Domestic UPS Ground Delivery
Curated Touring Apparel for the Highway Slipstream
Ergonomically validated helmets, jackets, boots, and riding pants engineered for bagger floorboard postures and long-distance touring airflow.
AGV Tourmodular Carbon-Aramid Flip-Up Helmet - Grey/SV
P/J Dual Homologation with Drop-Down Internal Sun Shield
"Aerodynamically tuned in wind tunnel to cancel buffeting over the batwing windscreen; premium modular chin bar."
SENA Impulse Modular Smart Helmet with Mesh Intercom
Harman Kardon Premium Acoustics & Integrated Mesh 2.0
"Integrated speakers cut through dual exhaust rumble at 80 MPH with crystal clear Harman Kardon audio."
Highway 21 Gasser Full-Grain Leather Jacket
Top-Grain Heavy-Duty Cowhide with CE Level 2 Armor
"Classic American V-Twin cruiser styling tailored with shoulder expansion gussets for high-handlebar touring reach."
Highway 21 Radiant Heated Highway Touring Gloves
Lithium-Ion 3-Stage Heating with Waterproof Hipora Membrane
"Continuous thermal warmth for cross-country mountain passes; touchscreen-compatible leather index fingertip."
Highway 21 Tall Primary Engineer Leather Boots
100% Full-Grain Leather with Goodyear Welt Oil-Resistant Sole
"Solid tempered steel shank and reinforced ankle cup provide firm footing on wet floorboards and oily tarmac."
RST Kevlar Tech Pro CE Level 2 Armored Jeans
AAA CE-Certified Cordura Denim with Level 2 Knee & Hip Armor
"Relaxed urban bagger fit engineered for floorboard ergonomics with zero binding behind the knee on 500-mile runs."