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.

10 comments:

  1. Now and again I get horrible noises when I try and start my C5, electric start only, I am far from impressed with only 8000 miles on the clock. piece of shite no wonder India ia and always will be a 3rd world country.

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  2. I agree with you. the parts from this bike sucks

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  3. I just bought an '08 bullet with only 6000 miles on it a month ago. The sprag clutch has already failed me twice. I've tried starting it several different ways, but cant seem to avoid the terrible "clang" sound when it turns over. I'm thinking to just letting the e-start go and using my kickstart only. Do I need a working sprag clutch to kick start my bike?

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    1. The reply I received from experts I asked: "It needs to be removed. It is always engaged at all times with the front primary gear. As it disintegrates, it will drop metal parts down into the primary, and they can end up jamming into the chain and sprockets."

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    2. And this: "One doesn't need a working sprag clutch to kick start an e-start bike -- but if one has a jammed sprag, it can lock the electric starter gear train and motor to the crankshaft so that the whole plot turns with the crank. This could make kick starting and running virtually impossible. Mine failed this way once. The replacement, installed a couple of years ago, has never given trouble since I began using the compression release for starting and stopping the engine, taking care to avoid kickbacks. So the answer to the question I think is being asked, is, it depends on how the sprag fails. If it fails in a manner that leaves everything free, no problem kick starting. If it jams and cannot be freed, the sprag must be removed or repaired to enable starting, kick or otherwise."

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    3. And this: "With the possible exception of the likes of Gina Lollobrigida, foreign bodies and motorcycles are not compatible. Take out the bits before they cause more trouble. Not a difficult job, and the resulting peace of mind is well worth the time and effort.
      I got about 30K kilometers on my original sprang and the replacement is doing OK using the decompresser for starting and stopping although I did experience a sort of clattering sound the other day."

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  4. David, your advice has been invaluable. I cannot seem to kickstart the bike, so im assuming its jammed. im replacing the sprag next week. is there a specific technique used for decompressing while starting and stopping. Thanks for your time!

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    1. The advice concerning the decompressor is simple. The motor can not run without compression. When starting with the electric start activate the decompressor briefly to allow the motor to get spinning past the point where it could ever kick back and then let it go to create ignition. When stopping, don't use the kill switch or turn off the ignition: activate the decompressor and let the motor happily spin its way to silence with, again, no possibility of kick back.

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  5. One sprag clutch desintegrated and damaged, can damage the starter motor? Please I need help! Thanks, David

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  6. I must say the sprag clutch is basically junk, the little flat cage that holds it together is a poor design. It really cannot hurt the starter motor itself, The good news is just pull out the sprag unit and just go with a kicker. However it is wise to get the proper pullers for magnito, clutch, and primary gear, about 100 bucks on ebay, total time to fix about 3 hours. Unless there is a better sprag clutch out there, I think just kickstarting is the best way to go as replacing the srag is just going to fail in a short period of time anyways. Mike

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