-98 Sprag clutch tooth size, 51t or 53t?

[P3aK]

Hey guys!

Been lurking for quite some time, eventually signed up, but didn't expect this to be my first post really.

Well, it's a -98, sprag clutch busted. Engine out, opened up. Unfortunately I ordered parts before I tore everything opened and actually had a look. Doh! Idiot!

I was under the impression that I should select the biggest teeth sprocket size when I select the sprag clutch.
Seeing the the posts all over about the 93-96 (97?) had to grind a few millimeters out of their engine casings to fit the new replacement sprag. And knowing the 98s had already been outfitted with the new larger improved one from factory.

But as it turns out I had a 51t sprag clutch sprocket, and the one I ordered was a 53t. Huh?
Was mine NOT outfitted with the new larger improved sprag from factory? Or is this a third option? I'm thinking, was there originally a 49t that turned into a 51t and now it's evolved into a 53t?

My logic (which apparently might be severely flawed) was that the smaller electric starter sprocket (the 13t or 15t) should be as small as possible 13t, and the sprag clutch sprocket (51t or 53t) should be as large as possible 53t, to make it as easy as possible for the electric starter to turn the motor over. And that it would do it more slowly so the sprag clutch would have an easier time gripping the shaft.

But if we turn that around. If I go for a larger starter sprocket 15t and a smaller sprag sprocket 51t, then it would turn over the motor faster. That would mean the sprag is turning faster and it would be more difficult to keep the grip on the shaft, right?

Am I missing something here?

Where is the actual improvement of the new improved sprag clutch that Triumph replaced? That it spins the motor faster, or that it puts less pressure on the electric starter and goes slower?

Because as far as I can see that's the only actual difference between them.

I ask the above because I want to understand where my logic goes out the window.
But basically I'm wondering if I should return the 53t and go for a 51t which I had. OR if I should bite the bullet, order and change the starter sprocket as well from 15t (which I assume I have, didn't count it, gotta do that!) for a 13t, if that is indeed the superior choice.

And here I was thinking that I had everything figured out :(

[London_Phil]

Haynes manual says.
"Note: The starter clutch components and starter idler gear were modified in late 1995.
This modification was introduced on production models from engine no 23707 (four cylinder grey painted engines and all three cylinder engines) or engine no 23681 (four cylinder black painted engines) and the new components can be identified by the 15 tooth starter starter idler gear, and 51 tooth clutch gear.
On earlier engines, modified parts for the starter clutch and idler gear are available in the form of an assembly rather than individual parts: refer to a Triumph dealer for details and ensure you purchase the 13 tooth idler gear and 53 tooth starter clutch gear set"

Got to be honest, I never quite worked out what that means.
I suspect the 51 tooth sprag is the newer, modded one, and the "kit" for the 53 tooth sprag consists of a  51 tooth sprag and a 15 tooth idler, plus possibly a newer shaft with through bolt.
But I could be wrong.
It could just allude to the fact that the sprag is now an assembly only item, and you need to purchase the correct one to match your idler.
I'm assuming that if so, the ideal option is a new 51 tooth sprag and a matching idler gear, but the new 53 tooth sprag is possibly a better one than original too.

It would be great to actually know what is needed.

[London_Phil]

UPDATE..
Having found Triumph service bulletin 194, the mists clear.
You can no longer buy individual components of the sprag clutch, so the reference to the kit means the items
that create the finished sprag  ( Bill of Materials or BOM to demand planners).

There are TWO new sprags
13 tooth idlers need a 53 tooth sprag T1221030 ( still a modified sprag)
15 tooth idlers need a 51 tooth sprag T1221025 ( modified sprag)

So you can have an improved sprag with either  a 13 or 15 tooth idler and have improved "spragging"
OR you can upgrade to a 15 tooth idler and have improved "spragging" and probably a slightly faster crank speed
And don't forget whilst you in there to fit the improved alternator shaft with the through bolt, to reduce likelihood of DAR

Simple??

[P3aK]

Thank you, finally I talk to someone who's on my page. Darned dealer doesn't know jack and doesn't even wanna try be helpful.

Ok, so both 15/51 and 13/53 are updated sprags, finally confirmation on that suspicion. But then the question remains, which one is "the best". I'm thinking for longevity of course. I do NOT want to do this again.

I had owned the darned thing for less then a day and merely opened up the seat compartment (yes with the key) before all this. I can't say I'm appreciating the learning curve by any means :(

I've taken out the idler (finally know what to call that thing, thanks) and I had the 15t, together with 51t sprag. So do I order and change the idler as well for 13t/53t. OR send back the 53t I received and and go with the 15t/51t I had originally? I just don't know which one I should go with.

What's the real difference between them? And the sprag I had went to shits with 15t/51t.. could the same thing happen with 13t/53t? (Yes I know, nothing lasts forever.) But would it at least be better?

Scouring the internet about this for weeks I've never even heard or read about 13t/53t before I received my 53t today. So I'm thinking this has to be an even newer sprag replacement then the one they did in -95. Otherwise ppl would at least mentioned it somewhere.

I don't know where to turn with this question...

Oh btw, I am talking about the entire sprag kit, can't buy the separate parts of course.

I've read about the DAR, but haven't experienced any trouble (for the 5h I got to use the thing) so I haven't delved any deeper into that situation yet. But I did identify where it sits and made some mental leaps by chance when I removed the idler earlier today. So I will look into that before patching the engine up.

----------

EDIT: Ok I just re-read what you wrote 3 times now to make sure I understand everything properly. So you're saying (well actually Haynes) that the 13/53 is the what the OLD engines used, pre -95?

Why would they have to grind parts of the casing out then if the new sprag sprocket was actually made smaller?
Or have I gotten this the wrong way around and it was because of the idler that ppl had to grind their engine case? THAT would put my logic totally on it's head.

It would indicate that cranking the engine faster during startup would be better and put less stress on that spring holding the internal sprag teeth. But wouldn't the clutch also disengage easier from the shaft and make the sprag slip?

The problem of the whole sprag clutch is that the tiny spring holding the internal teeth elongates and it starts to slip. I figured if you crank it slower the teeth would hold on better and not make the internal teeth recede and let loose of the shaft.

But then again.. perhaps that would result in snapped springs, as most ppl seem to have experienced pre -95. So the choice would be between broken spring or elongated spring. End result is same, unable to start engine without pushing the bike.

Jesus Christ, I should have stayed in the sandbox. I've never dealt with engines before and these are some major leaps för my mind to get around. And someone please put a voodoo spell one the idiot that came up with this idea.

[London_Phil]

Remember that the modded sprag is fatter, not larger in diameter, so you may have to relieve the sides of the case where it fits, as it may rub.
The idea is the thing is beefed up for longevity.
The factory also decided with later engines that it would help to spin the sprag faster, to get a more positive lock of the sprag (its a radial clutching action, so more spin = more locking force).
The factory apparently changed the advance curve to reduce kickback on later machines.
The sprag is generally damaged, as you say, when the spring stretches or breaks.
This is mainly caused by the sprag rotating in reverse when the engine kicks back.
It can also happen if the crank speed is low, and the sprags can slip and wear.

Bottom line if it were me.
15/51 sprag
Best quality battery you can afford.
Don't crank excessively and don't crank if battery is low.

You have a 98, so you should have had all the latest kit from new, including possibly the shaft with through bolt, but the PO may have abused the sprag  to failure

I'm sure someone will be along to add some more to this.

Good luck

[P3aK]

Yeah I guess I can't really compare, since all I've seen with my eyes are the 53t upgraded and the 51t default/upgraded for my -98.

"(its a radial clutching action, so more spin = more locking force)." - This was the part that I got wrong. I figured it would be the opposite. But I still don't really understand the physics of it. But I'll continue reading until I do :)

So there we are, 15t/51t it is then. Thank you so much!!!

This makes me wonder if I can take one shortcut.
I spoke to the dealer about returning the 53t and exchange for a new 51t. This would likely take upto 4v and I'd have to pay some shipping costs.
But comparing the upgraded 53t I received to my default 51t. The only thing that seems to be different is the actual sprocket (or should that be called a gear?).

Seeing as my 51t sprocket isn't damaged, couldn't I just switch that part and toss the whole thing into the engine? Should only be the internal parts of the actual clutch part that is damaged.

Right?

[London_Phil]

Thats the $spragmillion euro question...
Only you can decide if you want to chance it.
I've no experience of the internals of these sprags. Its likely they would be  the same, but you only find out after you invalidate the warranty when you dismantle the new one.
Its a lot to chance, if you then have to take it all apart again, for the sake of a few weeks and some cost.
Maybe your braver than me....

[gcloys]

UPDATE..
Having found Triumph service bulletin 194, the mists clear.
You can no longer buy individual components of the sprag clutch, so the reference to the kit means the items
 that create the finished sprag  ( Bill of Materials or BOM to demand planners).

There are TWO new sprags
13 tooth idlers need a 53 tooth sprag T1221030 ( still a modified sprag)
15 tooth idlers need a 51 tooth sprag T1221025 ( modified sprag)

So you can have an improved sprag with either  a 13 or 15 tooth idler and have improved "spragging"
OR you can upgrade to a 15 tooth idler and have improved "spragging" and probably a slightly faster crank speed
And don't forget whilst you in there to fit the improved alternator shaft with the through bolt, to reduce likelihood of DAR

Simple??

You totally rock Hit my button with ominous sounds of spinning wheels. 210cca isn't enough it seems.  Thank you

[London_Phil]

And amazingly, they are in stock, and reasonably priced!!!!

[gcloys]

$300 in the U.S. I've seen posts on repairing the sprag with a fork seal spring? Haven't looked into it yet. My 1998 was flawless until parked last week before the blizzard. Went to start and just brief attempt at turning over before spinning sound.  Battery in good condition w 210 cca. 40k on the clock and only ridden 2500 miles since purchase in May.  She's a keeper so in I go. Gaskets and sprag may come from the UK if I can get delivery. Sprint only ships DHL to 2kg international. My wife was there for a wedding in October for her nephew and was going bring back a gasket set but I didin't bother because everything was sound

[London_Phil]

If you do open it up to do the sprag, dont waste time trying to fix the old one
I have posted here about the job, someone did  it on an Adventurer, and documented it. Not a small job.

[Sin_Tiger]

If there is nothing wrong with the cylinders, you don't need to touch them.

The casing halves are fitted together with sealant, no gasket, the sump and side cover gaskets are not that hard to make from proper material.

[gcloys]

If you do open it up to do the sprag, dont waste time trying to fix the old one
I have posted here about the job, someone did  it on an Adventurer, and documented it. Not a small job.

I read through his posts on Advrider and saw the pictures here.  I'll order a new one OUCH!!

[gcloys]

If there is nothing wrong with the cylinders, you don't need to touch them.

The casing halves are fitted together with sealant, no gasket, the sump and side cover gaskets are not that hard to make from proper material.

The lower gasket set from Sprint shows gaskets for the sump but I was going to use sealant anyway Tbond 1207b (Suzukibond) since I have a whole tube. The parts for the '98 should be the 51tooth sprag assuming 15 idler Vin 55,335. Do you know if the DAR kit is needed for that year or was it correct from factory? I've had no rattles or strange sounds proceeding the failure of the sprag

[gcloys]

UPDATE..
Having found Triumph service bulletin 194, the mists clear.
You can no longer buy individual components of the sprag clutch, so the reference to the kit means the items
 that create the finished sprag  ( Bill of Materials or BOM to demand planners).

There are TWO new sprags
13 tooth idlers need a 53 tooth sprag T1221030 ( still a modified sprag)
15 tooth idlers need a 51 tooth sprag T1221025 ( modified sprag)

So you can have an improved sprag with either  a 13 or 15 tooth idler and have improved "spragging"
OR you can upgrade to a 15 tooth idler and have improved "spragging" and probably a slightly faster crank speed
And don't forget whilst you in there to fit the improved alternator shaft with the through bolt, to reduce likelihood of DAR

Simple??

Is the Alt. Kit upgrade for all year models? Ia there a cheaper solution $168 U.S.Jan12023. Doing my sprag and gleaning all I can. My 98 should have a 15 idler and need a 51 sprag but I'll know soon