Yet another 'How To' is a bit specific to the Honda CB125 'Twin', that probably applies to most of the other 'Benley' series engined bikes as well. But also applies to a number of other 'small' Hondas using the same clutch arrangement. So, the CB100N & CB125S & RS singles, and the CG125, and all its derivatives, the XR125, City Fly, and all the Chinese 'clones'.
Clutches on small geared bikes tend to work hard for a living. Without much power to play with, gearboxes have to be worked hard, which means lots of clutch work. worse, when the small bike is a Learner Legal, and the owners are getting to grips with clutch control! This tends to wear the clutch plates rather thin, with lots of clutch slipping practice finding the biting point , and plenty of time spent holding the bike on the clutch, the springs compressed, hunting for neutral!
When they wear, they get difficult to adjust and you can find that it can 'drag' with the clutch lever fully in, but when you are riding, it can actually slip. On 'derelict' bikes that have stood, also common for the clutch to seize, the plates corroding together or silting up. But in either instance, its an often neglected assembly, that can frequently benefit from this simple, and relatively cheap bit of overhauling.
There is only one significant 'hassle' to the job, and that is that the clutch assembly is held on with a recessed castellated nut, which needs a special socket or spanner to undo and do back up. The Haynes manual provides instructions on how to make your own, so we did, from an old 3/4 socket, cracked ruing a Land Rover cylinder head removal, using an angle grinder!
Anyway, THESE are the bits inside the drum, that we are going to replace, the clutch friction plates, and the clutch springs.
Chinese, e-bay specials, this is less than £20 worth of parts.
To fit them, we need to drain the oil, and remove the primary drive gasket. So you need to add a couple of litres of oil, perhaps £6's worth, and a gasket, we made out of an old cerial packet, in time honoured fasion! (see The Cornflake Packet Gasket Trick!)
Since the oil had to be drained and the primary drive cover removed, we took the oportunity to also clean the oil strainer, as described in HOW To: (Honda CB/CD/CM 125/200 'Benley' Series Engine) Oil Strainer Clean, and for the most part much of the job is the same.
Step 1 (as Oil & strainer)
Locate and identify the Sump Drain Plug. It is on the right hand side of the engine. If you find the Generator Rotor nut cover, the round slotted one in the middle, (missing in this photo!) and go directly down, it is recessed just ahead of an beneath the Engine Number boss, in front of the gear shift assembly.
Start and warm the engine, if possible. Warm oil is more runny than cold oil, so if you get the engine warm before changing the oil, more of it will come out, more easily. Once warm, be careful of hot exhausts and 'stuff', and turn the engine off before going any further! Often worth removing the battery lead, so you cant accidentally turn the engine over with no oil in it.
But, now you can put plastic washing up bowl, or you preferred container under the sump plug. Undo the sump plug, trying not to drop it in the container, and as it comes out, in a gush, get oil everywhere but in the container!
Sometimes helps if you can tilt the bike a little when its coming towards the end of draining. If you have a side stand you can prop it on that. If not, just tilt the bike, it wont take long to drain, there's not that much oil in there.
When the oil has cooled down.... you can undertake the oil change ritual of fishing for the sump plug in the ice cream tub!
REPLACE SUMP PLUG. it saves it getting lost and answering stupid questions later.... like "Why's it taking so much oil to fill it up?" and "Oh!? I seem to have an oil leak, where's that coming from?" Before you put two and two together, and remember, you forgot to put the plug back in!
And dispose of old engine oil in an environmentally friendly manner. Here its being tipped into an empty oil can, where it will be disposed of in an environmentally friendly manner, mixed with a little old stale petrol or something, and probably used to environmentally dispose of ants nests in the garden. You may prefer to simply take it to the local tip, and put it in one of their big reclamation tanks!
Step 2 (as Oil & strainer)
On the other side of the engine, we have one casing, covering the oil pump and primary drive. You will need to disconnect the Tachometer Drive, and the clutch cable. Then you can undo the bolts around the flange of the casing to remove it.
Step 3 - 'Doing' The Clutch
Inside the primary drive case is the clutch release shaft. On this shaft is the release arm, which pushes the release pin, poking out of the middle of the clutch. DO NOT try and press this pin in with your hands, or worse hit it with a hammer! I had a comment on a forum from a lad the other day with clutch troubles and that was what he had done, commenting that it didn't seem to move! No it wont! Its pressing against four big springs, and you wont easily move it, but hitting it with a hammer can easily bend it!
Sensibly, inspect the release arm and shaft as indicated here for any signs of damage or wear, and make sure that the lever is secure on the shaft.
Then remove the release pin.
Now the four spring cage retaining bolts can be slackened off with a 10mm spanner or socket. It's important to undo them evenly, each half a turn or so, going round opposites until they are undone. There will possibly still be some pressure on the springs when the screws are completely undone, so be careful they don't 'ping' on you. It may be necessary to hold the clutch drum to stop it turning with teh spanner. Easiest way to do this is to put the bike into a high gear and hold the rear brake pedal down.
with the bolts removed, the entire cage can carefully be lifted away from the springs. The centre of the cage contains a bearing and the release pin sleeve.
The springs can now be removed. Note how much shorter the 'old' spring on the left is compared to the 'new' spring on the right. This is how much the spring has 'relaxed' through being under constant tension. a spring this relaxed is unlikely to provide the clamping force to hold the friction plates tightly together to transmit drive, especially if the plates are old worn and thin as well.
Step 4 - 'Doing' The Clutch
This is NOT how the Haynes manual suggests the clutch pack be removed. It suggests that you remove the release pin sleeve and bearing, then use the special castellated spanner to undo the clutch shaft nut, and withdraw the entire clutch basket as a single assembly. However, we didn't have a castellated nut spanner, and we needed to get AT the nut to work out how to make one!
Here it is between the four springs. Curiouse little blighter ent it? this is what the Haynes Manual suggests:
"This tool is available as Honda Service tool, 07716-0020100. If this is not available, fabricate a suitable tool from a length of thick walled tubing. Refer to the accompanying illustration for details, cutting away the segments shown with a hacksaw to leave four tangs."
Thick walled tube of the right diameter was unfortunately in short supply, and experience following similar instructions has crafted a beautiful tool in mild steel that instantly mangles on use. Scratching around the 'strange tools' box found a peg spanner for an angle grinder that was 'close' but didn't really fit, giving ride to the idea of drilling a bit of plate, and bolting through to make a four peg, peg spanner to fit the slots. However experience of similar ventures suggested not. So an adaptation of the Haynes suggestion was executed. It wasn't PRETTY but it worked!
A 3/4" socket, (previously featured in these pages! It was split, trying to undo the cylinder head bolts on Wheezil the Diesel's engine!) in the 'junk' tools box, was found to be just the right diameter, and a close approximation to a 'thick wall tube', with a convenient 1/2" socket drive to fit onto a breaker bar in it. It is also (laughable quality, but still better than mild!) hardened tool steel. which was promising, but did mean that it would defy attempts at cutting it with a hacksaw. However, I own an angry grinder. And it that dont work, a BIGGER angry grinder!
I marked roughly where metal needed to be removed, then set to with the cutting disc, roughing out the shape then, more carefully working each tank in turn until it fitted.
I told you it wasn't pretty, but look, it worked, and any tool that does the job, is a good tool!
So, with improvised tool 07716-0020100 on the end of trusty breaker bar, the engine in gear, and the rear brake held down hard.... the castle nut was stormed!
Step 5 - 'Doing' The Clutch
With the Castle Nut loosened, it could be removed by hand, followed by the washers.
The Clutch 'Pack' will then slide out of the basket off the shaft.
And can be taken apart to fit the new friction plates
The Clutch pack constitutes the hub, five 'friction' plates that tank into the clutch basket on the outside, four plain plates that go between each of the friction plates, splined onto the hub, and the 'master plate' on the end.
With the 'Pack' disassembled, the old friction plates can be removed, and the new ones fitted. It's advised that the new plates are allowed to soak in clean engine oil, over night before use.
Fist friction plate is fitted and bears on baking plate of drum. Plain plate, splined on hub fits next, with another friction plate on top, alternating until you run out of both plain plates and friction plates, and can fit the master plate on the last (5th) friction plate to complete the stack.
Clutch pack reassembled, and the old friction plates can be junked
Step 6 - 'Doing' The Clutch
And the pack reassembled into the basket
We reassembled the same way we disassembled it. Without the springs or release cage fitted. They Haynes provides that the pack be completely assembled with the springs and cage before fitting. this holds the pack together and prevents the master plate falling off the splines on the hub, while fitting into the basket. But that hampers access to the caste nut with our improvised tool 07716-0020100. It does however make refitting the pack something of a faff as that master plate WILL keep falling off the spines, and when it does, you have to take it all apart again to get it back on, or the clutch just wont work! You have been warned! But, making life hard for ourselves.....
Pack fitted to basket, castle nut can be refitted, same way it was removed with improvised tool 07716-0020100, and holding the transmission locked on the rear brake.
And the NEW clutch springs can be fitted. They are longer and stronger than the relaxed old ones taken out, so they will take a bit more force to compress into place.
Release basket can be screwed over the springs, again, carefully compressing the springs evenly working around the four bolts tightening opposites about half a turn a time, so that the basket is clamped up 'square' on the springs.
Release pin sleeve and bearing fitted squarely in the release basket, the clutch is fitted, ready for the cover to go back on.
As Haynes method, the release basket and springs would be fitted to the pack before putting the pack into the clutch basket. The clutch shaft washers and castle nut, would be fitted through the release bearing housing, and tightened up through the same hole. This can make assembly a LOT easier, but only if you can get your improvised tool THROUGH the clutch release bearing housing! If not, then this can work, but you have to be careful to keep the plate pack together while fitting, and expect to have to 'jiggle' it a few times to be sure it works.
If you HAVE used this method, its worth trial fitting the primary drive cover, before fitting gaskets and filling with oil or anything, and checking that the clutch is operating properly, in case you have to strip it back and jiggle the plate pack again!
Step 7 (as Oil & strainer)
Before putting everything back together, the casing faces need cleaning up to remove all the old gasket material, before they can be put back on.
A lot of the old gasket may simply tear off by hand, but more stubborn bits will probably need carefully scraping. Care needs to be taken not to damage the gasket faces. A carpentry chisel can make a good scraper, as they are often wider and stiffer than Stanley blades, which can often gauge and scratch the soft aluminium.
Both the crank cases And the faces of the primary drive cover have to be cleaned. The sump could do with a bit of a wipe out with tissue, and something soft and pokie, like a lollipop stick to get any gloop or debris out, incase you have dropped any old gasket material in there while scraping. Then a new gasket may be fitted, and the primary drive cover put back on..
DO NOT USE ANY KIND OF GLOOP!
Silicone sealant, hylomar, RTV, 'Squeezee Gasket' are NOT a good idea here, instead of a paper gasket. first you have just cleaned that strainer, and any gloop you use to glue the casing back on with will squeeze out the joint and bits of it will float about in the new oil, and get dragged to and clog that nicely cleaned mesh! NOT GOOD! Worse, one of the oil pump galleries is formed between the crank case and the primary drive cover flange. if you use gloop, its likely to squeeze into that gallery and clog THAT up starving oil flow to the top of the engine! EVEN more NOT GOOD!
NEW GASKET..... bolt cover back on, re attach clutch cable and tacho drive, refill with oil, and jobs a good'n and the clutch should work nice and smoothly and adjust easily for many more miles to come.!