Workshop disasters: Sprag hell!
Mechanic Simon Harris reckons this owner could’ve avoided a giant bill
Glorious weather and lockdown-softening tempted one Tiger 1050 owner to drag his bike out and go for a short shakedown. But the moment he thumbed the starter, his 2007 Triumph went into a lockdown of its own with an ominous graunching. Simon Harris, of GP Motorcycles in Pontypridd, told us: “I was pretty sure what the issue was before it even arrived in the back of a van.” ‘The backlash was enough to shear teeth off the gears’ To get big triples to spin up fast enough to fire into life you need a decent kick from the battery so the starter motor’s gear meshes into an idler which engages with the sprag clutch on the crank. Unfortunately for this guy, he’d simply parked his bike up at the end of last season and thrown a blanket over it. Because it didn’t have an immobiliser/alarm fitted, he assumed the battery would hold enough charge to get it turning over. Big mistake.
Instead of the battery pushing them over the peak of top dead centre where their momentum would help the process, those big pistons, conrods and the weighty crank didn’t make it to TDC cleanly and bit back hard, setting up a backlash through the gears and bearings which was sufficient to shear the teeth off the starter motor gear.
“If the starter motor isn’t involved, it’s pretty easy to fix behind the right-hand engine cover. You’ve just got to drain the engine oil, remove the clutch and it’s all on show. But you can’t just replace the starter motor gear in situ as it’s a sealed unit. That means the tank, airbox and fuel injection system all have to come off, which is 4-5 hours of labour,” explained Simon. “Then there’s the parts. The starter motor is £601. If he’d invested in a trickle charger for £30£50, he’d be out riding now.”