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Discussion Starter #1
Sprag clutch failure is almost certainly due to failure of it's inner workings, in particular the finger retaining spring. The spring of which I write is a tiny, mushy little thing, hardly capable of damaging anything in your engine, in the unlikely event pieces of it wander from its required location.

Why is this unlikely? The spring provides the initial frictional force used by the sprag fingers to bite into the shaft. Therefore, if the spring breaks at start-up, the engine will fail to start.

The mushy spring surrounds the sprag fingers comprising the inner gear. The inner gear is encased by an outer gear assembly of rather hardy construction. Triumph did a very good job of encasing the engagement fingers and inner hex heads. Also, they used "green" loctite on said inner hex head bolts which join the inner and outer gear assemblies.

If any other part of the sprag clutch let loose in your engine, you would most likely find shattered gears(not just teeth) in the oil sump.

The cause of sprag failure is most likely due to low battery starts. Other factors can hasten sprag failure, including: Starting without the choke, Starting in gear, using an oil of too low viscosity(the lower the viscosity = a higher viscosity number /// 80w is less viscous than 20w).

Another possibility:

When disassembling your engine, pay close attention when opening your clutch. Closely inspect your judder-plate. Are all the brass rivets still in place? Brass shards from your judder-plate can destroy a sprag spring, clutch plates, block oil passages...

Crappy thing too, as once those rivets separate from the judder-plate and migrate from the clutch housing, they like to hide in the engine. Then on occassion, they will fire off through the engine creating little phantom events, some of which include: intermittent clutch failure, inability to shift, a random clack-similar to the sound one might hear when dropping a metal tie wrap into a sink's grinder.
 

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Discussion Starter #2 (Edited)
Part II: Sprag Clutch Workings

Triumph and Haynes do not address the sprag clutch, except in overall assembly. I will attempt to delve inside and explain the sprag clutch parts, and their simplified function.

A simplified parts list comprising the sprag clutch:
  • Outer Gear: Receiving gear to starter gear.
  • Sprag Fingers: Oblong bearings of the Inner Gear.
  • Inner Gear: A ring of oblong bearings, and Sprag Spring.
  • Sprag Spring: A long narrow gauge spring, affixed at both ends, creating a ring.
  • Sprag Hex Bolts: Hex bolts which mate the outer and inner sprag gears.
When you hit the "Start" button:
  • Affixed to the end of the starter motor is a small gear, which begins to spin. The starter gear is in constant contact with the Outer Gear of the Sprag Clutch.
  • The Outer Sprag gear begins to spin. This motion combined with the Sprag Spring, forces the Sprag Fingers inward toward the Alternator Shaft.
  • This combined outward force, causes the Sprag Fingers "bite" into the Alternator Shaft. If sufficient friction is present, the Sprag Finger's bite will cause the Alternator Shaft to spin.
  • The Alternator Shaft then in turn, spins the crankshaft and ignition begins.
  • Upon ignition, the Alternator Shaft begins to spin faster than the Sprag Fingers. Centripital force causes the Sprag Fingers to recede into their housing and away from the Alternator Shaft.
  • The Alternator Shaft is now allowed to spin freely.
In reality it is a little more complex than this, but you get the idea.
 

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In my post (woe is me) i said i thought my sprag had gone.As it went
clunck and all i got when i pushed the starter after that was a free spinning startermotor.
going by your post you said startermoter goes by alternator and sprag to turn engine.Do you think it could be a brocken alternator shaft bolt that could be my ploblem ??
 

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Discussion Starter #4 (Edited)
Part III: Sprag Clutch Repair

Sprag Clutch Replacement will not be provided, as that topic has previously been discussed by others. I will discuss how to fix your busted sprag assembly.

The following will hopefully save you $200.00US in parts, and/or $1500.00US in service fees at your dealership. If you decide this is the way to go for you, please remember you do the following at your own risk.

It should go without explanation, that to repair your sprag clutch, you must first remove your sprag clutch.

Once removed, you will notice that the sprag clutch appears to be in working order. In other words, it will only turn one-way, and bind when attempting to spin the opposite direction. Trust me, it's junk!

Go to the auto parts store and get:
  • An M6 hex-head Allen Wrench.
  • "Green" loctite.
Do not attempt to use the hex-head wrench in a traditional manner, as it will most likely be futile. "Green" loctite creates a bond which is truly a pain to break free.
  1. Notice that there are (6) M6 hex-head bolts on the backside of the sprag clutch.
  2. Put the hex-head wrench into a vice, or small diameter pipe.
  3. Hold the sprag clutch in one hand.
  4. With the other hand, insert the hex-head wrench to one of the bolts.
  5. Now with both hands, push down on the sprag clutch, until the bolt unseizes from the loctite.
  6. Repeat 5x.
Carefully slip the outside sprag from the inside sprag. Do not dislodge the needle bearings in the inner sleeve. Now, remove the inner gear. It will look very similar to Losiu's picture @ advrider:


Remove the sprag spring, which surrounds the fingers. DO NOT REMOVE THE FINGERS. THEY GO IN ONE-WAY ONLY!!!

Notes:

  • Take spring to auto parts store, ask the parts counter to show you some shaft seals.
  • Most domestic shaft seal springs are 2 sizes (approx. 1,2mm-1,5mm) in width.
  • You are going to need the thinner spring(approx 1,2mm). The width is the most important measurement, as the spring must ride within the groove surrounding the sprag fingers. The one I used was for a Toyota (Sequoia?).
  • The spring can be too long, just unwind where it is joined, and cut it to fit-Just BE SURE to cut the fat end of the spring and not the skinny end, as you'll need that end to wind back inside.
  • I wound quite a bit extra spring into itself, and used green loctite on the ends to be absolutely sure of a tight fit. I had/have no idea what the original tolerances/lengths are, so I adjusted tighter than what I originally found, but not noticably stretched so that spacing was evident in spring coiling.
  • When done, my spring band initially stretched about 0,25cm over the wider part of the sprag fingers. Rolling it to the middle of the fingers, the spring band seated in it's groove with a snap.
  • Slide the inner gear into the outer gear.
  • "Green" loctite the (6) M6 bolts, and button the two-halves back together. I have no idea of torque spec, so i just tightened them down as tight as I could in a star pattern.
Results:
My Daytona's starting has never been so solid feeling.

(thank you to losiu from advrider for the good pictures)
You can get more pictures from his post here: http://www.advrider.com/forums/showthread.php?t=222515
 

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Discussion Starter #5
In my post (woe is me) i said i thought my sprag had gone.As it went
clunck and all i got when i pushed the starter after that was a free spinning startermotor.
going by your post you said startermoter goes by alternator and sprag to turn engine.Do you think it could be a brocken alternator shaft bolt that could be my ploblem ??
You're backwards. Rather, the starter motor engages the sprag. Then, the Sprag engages the Alternator shaft. To me, it sounds like the spring in the Sprag Clutch has slackened.
 

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Excellent post, Alterna.

Reading the advrider and the relative ease of pulling the KTM sprag, makes you want to tar & feather T3 designers. :)
 

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Discussion Starter #8
DJW: I see you're in Texas. What part?
I grew up in Big Bend, but now live just North of Galveston.

Yeah, our sprag removal could be on an episode of MP's Flying Circus.:D

Now I'm off to recharge the battery on my Indian Chief. Loaned it to a friend who forgot to turn the key to "off", and close the fuel petcock...Doh!
 

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DJW: I see you're in Texas. What part?
I grew up in Big Bend, but now live just North of Galveston.

Yeah, our sprag removal could be on an episode of MP's Flying Circus.:D

Now I'm off to recharge the battery on my Indian Chief. Loaned it to a friend who forgot to turn the key to "off", and close the fuel petcock...Doh!
Sadly, I'm the the dfw metroplex, but in a good part close to the exit sign. Was in Galveston a couple times last year, not much Galveston in Galveston now. If I find an excuse to move further south I might take it.

Yep, my TR7RV has real bike manual controls too most don't remember :D
 

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Discussion Starter #11
No worries, glad to try and help.

And, if rebuilding seems like too much of a pain, I can do it for you.
Just send me:
  • your busted sprag clutch (in one piece),
  • a replacement spring (or $ to buy one),
  • a tiny tube of green loctite (or $ to buy one),
  • return shipping label (or $ to ship it back),
  • and beer $.
 

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Gotta have beer $$. I home brew so i'm good to go, but I believe I am fully capable of handling this however, some may not. I made a little headway today. Almost ready to drop the engine. I'll be updating this in my post. thx
 

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Holy Cow.

Your a genius.

Great post Alterna, guess this answers the question I posted earlier and ask how the sprag worked out!

Cheers :D

Say if you want a place to stay in the Fl. Keys.......I am planning on motor installation in 2 weeks, wanna help?!
I've got beer!!! :beerchug:
 

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Great post on the sprag spring.

Good to have a cheap fix.

However I didnt quite understand what you did to the spring ie the bit about cutting and reconnecting. I bet if I try that it will snap when in the engine. Is there a special way of doing it? Or is it simpler than imagined?

Cheers
 

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Discussion Starter #15
Great post on the sprag spring.

Good to have a cheap fix.

However I didnt quite understand what you did to the spring ie the bit about cutting and reconnecting. I bet if I try that it will snap when in the engine. Is there a special way of doing it? Or is it simpler than imagined?

Cheers
It is actually that simple, and exactly what Triumph did on the original spring.

Look at the original spring very closely. You will notice that it is wound inside itself in one small area. It is very similar to, when as a child you may have joined two ends of a drinking straw. By creating a small end and feeding it inside the other end, you were able to create a loop.

You will notice that the two ends aren't identical. One end is consistently sized, while the other end is tapered to a point.

The original spring loop ends aren't adhered together by Triumph, neither are shaft seal springs you'll buy as replacement parts. All you have to do is unwind this union. If you have concerns about the strength at the rejoined ends, you can always loctite them together(I did). I also threaded mine twice the depth of that noted with the windings at the shaft seal ends.
 

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Brilliant, just brilliant. I love fixes that cost almost nothing. Too bad it is such a pain to get to.

I vote this should be made a sticky. :thumbsup:

Now,where is that immoderate moderator anyway?
 

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Very informative...

I like the price....we just got the sprag out...the spring you speak of is really weak. It curls when taken off. We have a spring off a seal from another bike, right width but about 1 1/2" diameter. It stretches around the sprag no problem but might be too tight. Should I look for something closer or will this do.

Mike
 

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Too late....owner decided he wanted it thrown back together over my objections. To make a long story short its fine, bike starts no problem. The spring we used was fine.

Thanks for the cheap fix. I was the one I was looking for.

Mike
 

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Discussion Starter #19
Seal Part Number

http://www.woodys-auto-supply.com/auto-part-details.asp?prod=NAT-225545
National Federal-Mogul Oil Seals
225545
2.165 x 2.953 x 0.394


There is a spring just inside the black lip. You can just make it out in the picture.
It will be a tad too long, so just uncoil cut @ big end, and recoil spring into itself.
I made mine a tight fit as well.
Approx 1000 starts later and all-is-well.
 
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