Wednesday, June 27, 2012

Royal Enfield sprag clutch starter problems diagnosed

sprag clutch was used in early electric-start Bullets.
I ride a Royal Enfield Bullet motorcycle, but I am no mechanic. So, when readers ask technical questions I often urge them to post their problems on the Royal Enfield Yahoo discussion group or the Royal Enfield USA Community Forum. The Yahoo group was founded in 1998. By now, members have heard it all — and some have the expertise to recommend how to fix it.

A reader named Tom recently asked this:

"David, I have a 2005 Military Bullet. When I try to kick start the decompressor does not work, but cable seems OK. Electric start will not work either. The kickstart is always hard to push and seems engaged with turning over. Any ideas?"

I pointed him toward the Yahoo Group, where he soon got this very complete answer from member Rick F:

"Most likely the sprag clutch in your starter drive has disintegrated and jammed, forcing the crankshaft to turn the starter gears. Been there, done that. Is your engine now very difficult (virtually impossible) to turn over? If so, you may need to replace the sprag. It's a simple mechanism designed to allow rotation in one direction but not the other. Looks sort of like a large diameter ball bearing found in the starter gear train.

"To get at it you must remove the primary drive including clutch, then remove the inner primary case to get access to the compartment that houses it. Nothing terribly complicated but it is a tedious disassembly/reassembly; not a 15 minute job.Hitchcocks Motorcycles has a good exploded diagram in the parts section of their website.

"If you've heard a loud 'clang' when the engine kicked back on starting or stopping, that's it trying to turn your sprag backward. Doesn't take too many of these kickbacks before the sprag is broken."

Tom replied:

"Thanks Rick! Sounds like you have really hit the nail on the head. I have heard the 'clang' on a number of starts, when I switch from kick starting to using the electric start. Sounds like time to order some parts and dive in."

There is more information about the sprag to be found on the Royal Enfield USA Community Forum, where one of the members is president Kevin Mahoney. He told his readers there that, at some point in production, Royal Enfield began equipping AVL (Lean-Burn) Bullets with an updated ignition control box that protects the sprag from kickback. He urged his readers with Lean-Burn powered Bullets to make sure that the Transistor Controlled Ignition (TCI) box on their motorcycles is green in color.

"I want to remind all of you Lean-Burn owners to check the TCI (ignition) box underneath your seat. It should be green, which is the newest model. If yours is black either call us with your VIN number at 800-201-7472 or go to your dealer and get a free replacement. The new one may help save you from a sprag clutch repair somewhere down the road."

These concerns don't apply to the new Unit Constructed Engine models (C5, G5 and B5 as they're called in the U.S.). They use a different design.

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