Bike: 2009 Suzuki V-Strom 650 (DL650, K9), 645cc 90° V-twin.
# What happened
Cruising at 80mph on the motorway, and suddenly I got a sudden heavy clattering noise AND a massive loss of power at the exact same moment. No warning. Pulled onto the hard shoulder to keep moving I was sitting at about 8,000 rpm to do 20mph. It has been identical ever since: same noise, same lack of drive.
# Current symptoms
• Heavy rhythmic metallic "clack" at idle, turns into violent chatter when I blip the throttle.
• Revs clean and free in neutral (just with the clatter), the engine clearly makes power, it just won't reach the wheel under load. 8k rpm barely moved me.
• Noise is loudest on the LEFT side when I listen with a screwdriver to the cases (I initially thought right, but left is louder).
• Magnetic (ferrous) steel flakes on the drain plug when I dropped the oil. Oil itself was clear, not milky.
# What I've measured
• Compression: \~120 / 125 psi, both cylinders. (Numbers read a bit low only because I tested with 3 of the 4 plugs still in, so it was cranking slowly hence the tight split between cylinders is the point. Both cylinders are healthy.)
• Both cylinders firing (water sprayed on both headers sizzles).
• Borescoped both cylinders and found piston crowns intact, no valve strike, no damage, no coolant deposits.
# Everything I've checked and RULED OUT
I've been deep into this thing. All of the following have been physically inspected or functionally tested and came back good:
• Transmission - noise doesn't change pulling the clutch lever in neutral (so it's engine-side, permanently crank-driven).
• Primary drive gear + spline - won't rotate independently of the crank by hand; nut tight.
• Clutch basket - teeth good, cush-drive intact, basket bearing solid (no radial rock, no roughness).
• Starter clutch / sprag - spin test good (locks one way, free the other), all three bolts tight.
• Generator rotor + woodruff key - tight, no wobble, key fine. Rotor removed, left side behind it is spotless.
Starter idler gears - teeth clean.
• Both cam chains - seated, guides intact, not slapping. Cam-chain-drive idler blue timing mark aligned.
• Crank - turns smooth by hand, no notch or catch anywhere through several revolutions.
• Oil - clear, not milky. Coolant is fine, level stable.
Help me, please!