Starter clutch keeps on falling apart...

**Anonymous** · 01-17-2005, 12:34 AM

over kill

if done right it should be ok but if you used thread primer and cleaned every thing and used red loctite it should not have came loose, and you have to use the correct tensile strenght bolts, they don't break unless they come loose, if you rebolt it be sure the threads in the housing are not distorted making for a loose fit

**Dink** · 01-17-2005, 02:53 AM

Consider having holes drilled to mount roll-pins into to absorb some of the punishment the bolts normally take. Be certain to use at LEAST grade 8.8 bolts.
Dink

**SqDancerLynn1** · 01-17-2005, 06:56 PM

Someone also made the sugestion to drill & tap the holes for a larger dia bolt

**crayonjota** · 01-17-2005, 08:44 PM

...I taught the thing a lesson with the biggest press you ever did see and some cold rivetts.. now I dare it to loosen up again.... Cost me $1 each for the rivetts and $5 for the use of the pedistal drill and hydraulic press...

Has to be the best $8 I have spent in a long time, not only did I fix the problem but got to play with some of biggest tools I have seen..

CJ

**robinjo** · 01-18-2005, 12:30 PM

Keep us informed how it holds up.

**crayonjota** · 01-21-2005, 06:32 PM

Originally posted by robinjo

Keep us informed how it holds up.

For the first couple of hundred miles everything was sweeeeet... All tight as a drum.. Now I get a telltake rumbling that there is some slop down there on the overrun, but nothing like as bad as before.. Maybe I should keep the revs down but it doesnt really sing till deep into the red zone and it doesnt sound or feel like it will self destruct again, and I am tired of cutting gaskets for the thing!!!

CJ

**Anonymous** · 01-21-2005, 06:38 PM

Rivets aren't as strong as socket head cap screws.....much lower tensile strength....

Grade 12.9 SHCS will be around 180,000 psi. Far above any rivet.

Make sure they're 12.9 since grade 8.8 is only 120,000 psi. That's a big difference.

**massakins** · 01-21-2005, 09:19 PM

Guys, I don't know everything, but I have had some experience with this issue and will try to share it with you. First, the bolts are not the problem, so efforts taken to strengthen them may only delay a repeat failure. Second, the range of failures to correct the root problem range from not starting the engine to catastrophic failure of the crankshaft/engine cases and cylinder block; I have seen examples of each.

The problem as I understand it resides in the starter clutch. This simple device consists of a ring gear, three rollers, three spring loaded plungers, three 8mm socket head cap screws, a tin cover and a hub. The ring gear floats on the crankshaft via dual roller bearings and has a precision machined surface that contacts the rollers. The rollers are held in contact with the machine surface on the ring gear by the spring loaded plungers. All of this is held in place by the bolts through the tin cover and hub, threading into the backside of the charging system rotor. The taper on the inside of this rotor maintains a solid connection to the crankshaft.

In operation, the ring gear floats freely clockwise, as viewed from the left side of the motor, and engages solidly when turned counterclockwise. The starter motor drives the ring gear via the idler gear to start the engine; once it starts it overspeeds the starter motors motion and disengages the three rollers. I think this is referred to generically as a Sprague clutch.

So, the problems arise when the surface of the rollers and machine surface of the ring gear start to develop flat spots. These flat start as barely visible and progress to 1/16" or more wide. Trust me, it happens to them all. Quicker if you have an out of tune motor that requires a lot of cranking, or one that backfires, or one with high compression/big bore/high cams/HD valve springs, etc. Once these pieces start to develop flat spots the situation escalates quickly due to uneven loadin gon the rollers and the higher contact pressure presented by there uneven shape. The contact of these spots doesn't always align in the same place so the ring gear starts to move off center when the starter is engaged; the loose fit on its roller bearings to the crankshaft allows a lot of misalignment here. However, the idler gear does not, so once the ring gear "locks up" with the rollers in a misaligned condition the idler gear exerts an enormous force on the gear teeth each time this tight spot comes around. This is sufficient to stretch or fatigue one or more of the bolts and cause it to loosen. Its a downward spiral from here. I've never seen a bolt failure that didn't include flat spots on these pieces as well.

If the rollers and ring gear are in good condition there is no excessive load on the three bolts. I've seen the starter hub welded to the flywheel, inside of the bolts welded, gap around the outside of the heads of the bolts filled with epoxy, plus more done to avert this condition.

Sometimes this condition can also cause the flywheel to spin off of its taper and damage these surfaces. Minor damage can be carefully cleaned up with a hand file, emery cloth and finally lapping compound, but its a very arduous task.

The worst outcome I saw was a starter clutch on a dragbike that didn't release once the motor had started; with the rider staging the bike at 7500-8000 rpm the dual reduction of the starter caused the eletric motor to see many multiples of this speed until it came apart. As I said, ruined the cases, crank, cylinder block, etc. plus sent the rider to the hospital to have the metal removed from his left leg.

The three rollers and ring gear have to be completely smooth and free of flat spots. Rollers used to be available separately but the ring gear came only as a kit. No idea what today's prices are. Starter clutches and clutch hubs are the Achilles heels of many of our beloved rides.

My apologies if this doesn't read clearly but please send questions or comments sharing your experiences.

**Jethro** · 01-21-2005, 09:53 PM

Ok....

So how do we prevent this from happening?

**massakins** · 01-22-2005, 10:46 PM

Jethro, et al, for what it is worth, I have never had to install a second starter clutch into any of my bikes, that is, after replacing the original on these used units. I think this is because these were mostly race bikes that had well tuned engines, good fuel, decent weather conditions, fully charged batteries, etc.

The situations that seem to be most damaging to this component are cold weather, weak batteries, damaged/worn/poorly tuned engines, dirty fuel systems, etc. All of these conditions dramatically increase the amount of time that the starter motor is required to operate and many of them increase the possibility of a backfire.

If you're experiencing starter problems, replace any flat spotted rollers or ring gear and ensure everything else that is manageable can be optimized. Not only is this best for your starter, but its also the most enjoyable way to ride the thing as well.

For those that are interested in improving the OEM pieces, here are my thoughts. It would not be too difficult to make rollers that are harder than the OEM ones; basic machining and heat treatment using a high alloy steel should suffice. But, unless the ring gear was suitable reinforced, this would just accelerate its deterioration. And the rollers are available separately from Suzuki, while the gear comes as part of an expensive kit. To reinforce the wearing surface of the gear you could either coat it with a material or treatment that would make the surface harder or possibly shrink a hardened sleeve over it and tack it into place. Surface finish must be maintained and diameter is critical. Not sure if either is feasible or cost effective. Hardness of all pieces would be a compromise between improving the existing pieces and risky failure due to being too brittle.

The stock unit will survive if all else is in order. Once it starts to deteriorate it rapidly escalates. Hope this helps.

**crayonjota** · 01-23-2005, 02:42 PM

Thanks for the very well conveyed and informative coverage on the subject. I took a ride this morning with the superbike Club and found my self in the red for the most part of the trip out. The starter fragged once again and wouldnt engage to restart for the trip home. Kinda akward as we went to a beach.... Anyway, I wasnt alone as a gixxer had a similar issue (his solenoid was down) and after a bit of a push onto some concrete we both restarted, however my bike sounded really rough and I came home at no more than 5000rpm as the vibration was killing me..

As luck would have it it all held together well, the rivetts were good, but the dampers had pushed themselves back out of the clutch and fell out with the crankcase off...and of course the free play was back and the rivetts loose.. Tomorrow I am looking for a used unit complete from a 750, and if that doesnt go bikebandit wants $150 for a new replacement, which I cannot really afford, so I may well drop the lot out, put the generator back in and push start it till I save up enough gold for replacement. I cannot see any problems with doing this, but as always input would be nice...

CJ

**crayonjota** · 01-25-2005, 08:11 AM

I learned something that may be of interest yesterday. I went out looking for a good used starter clutch and found a GS750 crank with everything intact. The starter clutch is about half the size and weighs half as much, and get this the needle roller bearings are the same size (crankshaft) but a little thicker, so I have to fit the ringgear from the 750 too, but is identical in diameter and no of teeth. The idea of less weight and bigger bearings seems like a winner to me. I will hook it all up today if I get time and contine my saga..

Starter clutch keeps on falling apart...

Starter clutch keeps on falling apart...

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