Sprag Clutch Removal

Hi there,

Here is a step-by-step process to remove the sprag clutch. The sequence of disassembly is as follows:

1. Remove the Left side rider's foot-rest

2. Remove the Gear clip

3. Unplug the wiring coming from the clutch case (/dynamo)

4. Remove the Clutch case

5. Remove magneto's center nut

6. Remove clutch plates

7. Slide out (carefully!) the main sprocket connected to the crankshaft along with the primary chain and clutch plate holder assembly

8. Remove the center nut in the clutch assembly

9. Remove allen screws and bolt holding the clutch case

10. Remove the remaining part of the clutch case

11. Open the Allen screws to expose the sprag clutch

Unplug two connectors linked to the wiring loom coming out of the clutch case. You may need to remove the battery cover for this. Also, ensure that the clutch oil drains into the pan, or else it will be a mess, especially if you are doing it at home.

Not recommended though: Mech is using a rod to lock the primary chain/clutch assembly from rotating so that the screws can be opened. Use specialized tools if you have access to them.

Clutch plates are removed already. The remaining part of the clutch assembly will only come out only when the primary sprocket comes out. This may take time if it's very tight (thanks to RE's quality of manufacturing/assembly) like mine. Be patient at this stage, as any damage due to rush will be costly and painfully time-consuming.

Special spanner to remove the center bolt holding the magnet in place.

Magneto comes out.

Now is the pain part of this whole process. Didn't know it would be so tight. I was happy that it's been untouched to date and was a bit grumpy that the mech didn't have any specialized tool to remove a tight sprocket.

It hurts to watch him do this to my bike ;(

Arrrgghhh had enough. Asked him, and got an obvious answer, that there is no specialized tool and it is actually supposed to be easy to pop out. Well..whatever!

Finally, after the visual torture and a few scuffs inside my clutch case, the damn thing came out. Along with the main sprocket came out the primary chain and the other side connected to the clutch assembly

One more bolt to go before the remaining part of the case can be removed.

3 allen screws around the crankshaft and one bolt on the right-hand side of the gear shaft

It may need a soft head hammer to loosen the case from all sides, especially around the crankshaft and starter motor area.

Bit of a crowbar method. Make sure not to overdo it.

Comes out finally.

All the chain lubrication and dirt have been piling up around the drive sprocket which stays outside the case.

Inspect the case for any signs of unusual marks, etc.

Remove all the Allen screws on the sprag clutch case.

Again a light use of a soft head hammer would loosen the case.

The sprag clutch assembly is visible now.

Take out all the 3 sprockets and a stainless steel axle rod.

These two make the sprag clutch kit. One on the right-hand side slides inside the sprocket kept on the left side.

Notice the tooth structure of the bearing visible here.

In a completely damaged sprag clutch, the bearing loses those metal teeth (pieces) inside the clutch case. That's bad and it will cause further implications. Imagine the primary chain rotating at a high speed and these metal pieces fall all over it. 

This is the damaged part. The area near my thumb supposed to be smooth, but it was developed grooves in the shape of the tooth seen inside the other bearing. Hence it doesn't slide, during the reverse rotation of the sprag clutch. 

NOTE: After removing the complete sprag clutch set along with the main gear connected to the starter motor, the case remains completely hollow with no parts in it. So every time the start button is pushed the starter motor spins freely inside this case.

INSPECTION & CLEAN UP:

As it's not every day that you get to open the clutch box and get to see the primary chain, sprocket, etc, take this opportunity to inspect every part that you can. For example, I could notice the following:

1. My primary chain adjuster has run its best life and now there is a small packing underneath. Maybe in the next overhaul, I need to replace the set.

2. Sprocket internal locking thread on my bike is too tight (even after grinding it a bit). I need to compare it to a new spare if it's an odd one that came from the factory, then this also needs to go.
Note: Being tightly connected to the crankshaft is actually not a problem in the bike's operation, it's just difficult to remove when needed. Which is again once in a blue moon.

3. My main sprocket is in decent condition for the now but I better replace it (along with the chain-sprocket set) sometime after the ride.

4. My clutch assembly looks spankingly new :D Just bragging!!

Now while at it, I would prefer to clean up the areas visible. As once all parts are put back in place, certain areas of the bike (like the front drive sprocket) wouldn't be accessible from outside. So do the necessary clean-up at this stage.

RE-ASSEMBLY:

Follow the same process in reverse. Additionally, you may use glue (mostly fevicol) on top of certain washers to ensure there is no chance of oil leakage. In my case, we used a little bit of the washer around the crankshaft.

Fill 400-500ml of 20w50 oil once the clutch case is assembled.

TEST-RIDE & ADJUSTMENT:

After the bike got ready I did a test ride and the riding was fine, but I found the kicker was not working properly. Kickers basically felt kinda spongy. For this, I had to get the clutch cable adjusted. Then it was all fine and I could feel the kicker rotating the crankshaft (/piston) inside. After a few attempts to kick-start the bike successfully, I called it a day.

Sometime in the coming months, I am planning to put on the new sprag clutch myself. This guide will come in handy for sure.

Hope you enjoyed going through this photo guide and that it helps you not only to understand the mechanics of the bullet better but also to perform DIY jobs at a home garage.



Keep Rolling,

Sid

Sprag Clutch - Demystified

Hi,

To start this thread with the correct mindset about CI engine bulls (like mine), lemme make this very clear:

" Bullets break down. Bullets get back up again. It just gotta be with a person who is patient and knowledgeable. "

Now if you have been following my posts or have seen my bike, it's a no-brainer to guess this baby (forgive me for saying this about the Bull which enjoys a macho status in India) is taken care of well. Well.. just to brag a bit more about our relationship, lemme say we take care of each other well, through thick and thin. It never gave up on me during any big rides and I return the kindness by taking care of its needs at the right time. Actually, it's quite common if you consider any biker who loves riding. There, I said it :D

Last Year:

Now before the eyeballs start rolling, let's get back to the topic; Sprag clutch. Well, I got to know about it a year back when I was trying to switch start the bike for going to work. There was this loud (relative, to other noises I usually hear from the bike) 'clang' from the engine (wasn't sure from where) when the switch didn't really start the bike. Though knowing bullets are an ancient tech, a noise once in a while is nothing new. But a metal-hitting noise was a bit too much for me to ignore. So I called up my mech and got to know it could be the starter gear and its nothing to do with the engine. That was a relief. So I decided to continue with my day and get that noise checked once I get some free time.

During the next servicing, I got the following update from Sami (my previous mech):

The starter gear (that's what my then mech referred to it as) slipping mechanism is faulty and the noise comes when the engine backfires. So every time I switch to start (or even kick) and if it causes a 'kick back', the crank is trying to rotate the starter gear backward (which should ideally rotate in only one direction and slip in the other). As the slipping mechanism is not working, the starter gear is rotating during kickback. It has to be replaced, however, I can continue using it and in case of a breakdown, kick start can be used.

Upon searching online for more details on the sprag clutch I came across the following post which made some sense to me:

Royal Enfield recommends 420ml of oil in the primary case(clutch case). While this is the right amount of oil for a CI/AVL Bullet without an electric start, it is insufficient for Bullets with electric starters. The reason is the fact that bullets with electric starters need more oil to lubricate the sprag clutch bearings and gear assembly for the electric start. 

Bulleteers in the UK and the USA have been instructed by their dealers to use 1 liter of oil in the primary case since a large number of sprag bearing failures have been attributed to lack/insufficient lubrication. So, the Bulleteers abroad have been following this advisory with good results. 

As far as my little knowledge goes, Royal Enfield India for its part has not circulated this advisory in India either through the dealers or through any means of communication, amongst the large number of owners who own electric start-equipped CI/AVL Bullets. 

I had a word with a well-known and highly respected Royal Enfield dealer and mechanic from the US of A, who strongly advised the usage of 1 liter of oil in the primary case. Hence, I thought I'd let fellow bulleteers know about this as this could save many sprag clutch/electric start failures which otherwise could have resulted due to the lack of sufficient lubrication.

Note: This advisory does not apply to the Unit Construction Engined(UCE) bullets.


I brought this topic up with Nandan (my mentor in bullet maintenance, whom I approach occasionally when I need to know the engineering-centric explanation for certain bullet behavior, which is usually beyond a mechanic's cup of tea), and here is what he had to say:

What is good for preventing jamming, will be bad for gripping.
The sprag itself has to grip in one direction &  slip in another.
The clutch has to grip well, or else you may as well buy a 100cc bike
with mileage-problems!
And even with small amounts of oil in the bike, it leaks.
In my opinion, extra oil is too much headache for a very small problem!
The best way is to avoid the starter and learn to kick-start the bike.
You can buy an ignition unit...the OLD model TCI, which did not skip a
spark like the new models.
It will make starting even easier. This unit can be kept as a spare.


After the above discussion, I continued with my rides on my bike, and other than occasional 'clangs' nothing really happened. 

Last Month:

I was looking for a new mech (as the old one is no good for my work anymore), and I came across Nizam from BSK. Very humble guy and currently the chosen one to put their hands on my bike. Even he told the same fear of a defective sprag clutch. Better to remove it for my Ladakh ride or replace it completely. However, he would still have a look at the clutch during servicing and let me know of any hope of repairing it.

Yesterday:

As part of some fabrication work getting done for my fuel tank, I was speaking with Imran (a well-known bullet mechanic who also travels with groups as a support mech). Even he suggested removing the 'sprag clutch' for the trip and using a kicker. That's the safest thing to do and commonly done by other CI bullets as well. Apart from that he was quite impressed with my bike's looks and the condition of the engine ;)


Reference Links:
The best and simple description of detecting known behavior of a bad sprag:

http://www.royalenfields.com/2012/06/royal-enfield-sprag-clutch-starter.html

Parts Diagram of Sprag Clutch Assembly:

Picture of the spare parts:

http://www.bulletwala.com/index.php/vintage-royal-enfield-genuine-new-sprag-clutch-assembly-560042.html#.U8S5C_mSxdU

So I have decided to remove my sprag clutch assembly for my upcoming ride to the mountains. I will try and record the removal process for my own reference.


Cheers!!,

Sid