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M/C Mechanics - HOW2:

Adjust Tappets & Camchain Tension in the Honda CB125T/Benley

This and cleaning the oil strainer, are pretty much all there is to an engine service on the Benley series engines, apart from checking or changing the spark plugs, and possibly adjusting the carburettor. This Handy How to, created for you by Donna, following the instructions in the Haynes Manual.

Haynes Manual, under 'Routine Maintenance', Page 28: "Four Monthly or 2,500 miles" (just for reference) Tef says that's every other oil change, that should be done at about 1,250 miles. But Tef reckons should be done every 1000, to be on the safe side, and worth doing Tappets & Cam-Chain tensioner, with each oil change, at least for the first few thousand miles of owning the bike, to tell how much adjustment they need. We've also had a couple that have 'wound off'; so worth keeping an eye on. So, what the book says:-

Haynes - 1 Adjust Valve Clearances: the engine must be cold for the valve clearances to be checked accurately. Place the machine on it's centre stand on level ground, then raise or remove the seat, withdraw if necessary the side panels & remove the petrol tank.

CB125 Sump Plug Location

Simple enough; seat up, petrol 'off'; disconnect petrol hose at tap; pop the side panels; undo tank bolt, carefully lift the tank off, lift the plug caps off the spark-plugs and tuck the leads up out of harms way.

Haynes: Remove its two retaining bolts, then remove the cylinder head cover with its thick rubber gasket.

THIS is the fiddly bit!

CB125 Sump Plug Location

Two chrome bolts on top of the rocker cover are easy enough (10mm AF Spanner. A cranked one helps; or a socket, but a 6 sided one is reccomended. A 12-point socket can 'slip' as the chrome nuts are a bit rounded on the corners, being 'cosmetic)

CB125 Sump Plug Location

There isn't much room around the top of the engine to get the rocker cover out, and with the rockers inside, it can be rather annoying, and the ignition coils and brackets all get in the way! TRICK: is to 'roll' the cover forwards over the rockers, so that the curvie bit in the front of the cover goes around the frame tube...

CB125 Sump Plug Location

THEN, you can rotate the cover out of the gap, sort of pivoting around the frame tube. EASY! (when you know how!)

CB125 Sump Plug Location

Haynes: Disconnect & remove both spark-plugs.

Oh! Already taken the leads off! Meanwhile, removing the spark plugs is the topic of another How2: Remove & Refit Spark Plugs!

CB125 Sump Plug Location

And out they come. Remember to do both sides, and worth checking them against the book, while they are out. (Page 115!)

CB125 Sump Plug Location

And giving them a quick clean, & checking the gap.

CB125 Sump Plug Location

Haynes: On CB125T,T2,TA&TB models, remove the two contact breaker inspection cover screws and remove the inspection cover and it's gasket. On CB125TD, CD125T & CM125C models, unscrew both inspection plugs set in the crankcase left hand cover.

CB125 Sump Plug Location

Simple enough.

Haynes: Rotating the engine anti-clockwise by means of a spanner applied to the alternator retaining bolt

CB125 Sump Plug Location

OK, A deep socket then! & A torch to see all these 'ere marks theyz babbling about.....

Haynes: watch the machined slots in the camshaft left hand end and timing marks visible through the aperture in the contact breaker backplate (CB125T,T2,TA&TB only) or through upper inspection aperture (CB125TD, CD125T & CM125C). When the T1 mark (CB125T,T2,TA&TB,CD125T & CM125C) or TL mark (CB125TD, only) is aligned with the fixed index mark on the crankcase left-hand cover, and the camshaft slot is in the 3 o'clock position, the left hand cylinder is at TDC on the compression stroke, and the valve clearances are ready to be checked.

Marks?! TL, TF, TR, TLDR!?!?!?!? WHAT! "TEF! Wazaal this mean?"

Teflon-Mike: You need to rotate the engine round its cycle so that the valves are closed, and the cam has taken all pressure off the valve before you check the tappet clearance; what's called 'on the rock' where the rocker can actually be wiggled a bit..... So, you rotate the crankshaft, until the T1 or TL marks can be seen in the little window at the top; That means that the piston is at top dead centre, only it can be at top dead centre between the compression & power strokes, or top dead centre between the exhaust & induction strokes, so you also have to watch the timing marks on the cam shaft to tell which one it is. You want it to be between the compression & power strokes, because that's when the valves are both closed, and the tappets 'on the rock' the gaps at their widest point, where you can measure them. THEN you wind the motor on 180 degrees of the crank, or 90 degrees on the cam, which puts the right hand cylinder at top dead centre between the compression & power strokes, so you can check that cylinder's clearances.

Yeah! "TEF! Wazaal THAT mean?"

Teflon-Mike: Look at the slot in the end of the cam-shaft. When its pointing towards the back of the bike, like THIS

CB125 Sump Plug Location

Teflon-Mike: Check the tappets on the Left Hand Cylinder. When it is pointing straight up, like THIS

CB125 Sump Plug Location

Teflon-Mike: Check the tappets on the Right Hand Cylinder.

Oh, RIGHT! Why didn't you just say that to start with! Jeez!

Err... what about the CD & CM's though, they the same?

Teflon-Mike: Book gets to that in a minute. Doesn't say anything about the cam-slot again; just says on the CB rotate the crank half a turn, on the CD & CM a full turn.. so that would have the cam-slot pointing forwards on them, I think.

OK... I can do this bit, now. THANK-YOU! Bugger off back to your camera and take photo's!

Haynes: Using a 0.05mm (0.002") feeler guage, check the clearance between the top of each valve stem, and it's corresponding rocker. The feeler guage must be a light sliding fit with the rocker and valve stem just nipping it.

CB125 Sump Plug Location

OK, so got the cam shaft slot pointing the right way; give the rocker a little 'wiggle', check that it's 'on the rock'. If it's tight, then either the tappet clearance has closed up, which isn't good, or you haven't got the timing marks set straight! So wind the crank round again and try again, wiggling the rocker until it does go loose, or you are sure you are at the right 'timing'.

CB125 Sump Plug Location

Sliding the blade between the tappet & valve, it's sort of a 'feel' thing, you cant explain. Blade ought to be kind of 'stiff' to tug through the gap. If you aren't sure; pick the feeler gauge blades a size up and a size down from the one you need, and the smaller one should slide really easily, larger one not go in at all.

Haynes: If adjustment is necessary

On this occassion it wasn't; so I adjusted some tappets on an engine we had 'lying around' that wasn't in a frame!

CB125 Sump Plug Location

Haynes: slacken the locknut.

CB125 Sump Plug Location

Haynes: and turn the small square headed adjuster to obtain the correct setting

I did this with the feeler gauge under the adjuster. Make sure that the rocker is all the way up, then screw the adjuster down. & you will feel when it grips the gauge.

When its 'set' wind the lock nut back down with your finger, then slide the feeler gauge in and out to make sure it is properly set.

Haynes: Tighten the lock-nut, holding the adjuster at the same time to prevent it from moving

CB125 Sump Plug Location

Haynes: Rechecking the gap after tightening the lock-nut

WARNING: the adjuster has a VERY fine pitch thread and it is VERY easy to over tighten it and strip the threads. It is also very easy to not tighten the lock nut enough and for them to work loose.... Tef says; its easier to fix a loose nut, than a stripped one! After adjusting the tappets, go back round them all and do a final check-tighten. Then after a hundred miles or so, it IS worth lifting the rocker cover again, and again, just checking non have wound off.

So, inlet, on the Left Hand Side checked; can check the exhaust on the LH-cylinder.

CB125 Sump Plug Location

Then, rotating crankshaft to the timing mark for the other cylinder; inlet on the Right Hand Side:

Haynes: When both inlet & Exhaust valves are correctly set, rotate the engine one full revolution (360 degrees) and realign the marks on the CD125T and CM models and rotate the engine through 180 degrees on the CB125 model, to align the T2 mark (CB125T,T2,TA & TB models) or the TR mark (CB125TD only). The right hand cylinder will now be at TDC on the compression stroke.

Right! Yeah! What did Tef say? slot in cam pointing straight up on my CB125, forwards on a CD or CM.....

Haynes: Check & if necessary adjust the valve clearances of the second pair of valves.

CB125 Sump Plug Location

Then the Right Hand Cylinder's exhaust.

CB125 Sump Plug Location

And THAT is the tappets checked!

Haynes: Refit Cylinder head cover, checking that the sealing ring and sealing plugs are in good condition, and fit and tighten the bolts. If a torque wrench is available, tighten the cover retaining bolts to a torque setting of 0.8-1.2kgf m (6-9lbf ft). The petrol tank, side panels and seat can now be refitted unless thier removal is necessary to complete some other maintenence task. Do not fit the inspection covers or spark plugs

OK.... Tef says DONT do this! Do the cam-chain tensioner first! You'll see why!

Haynes: Adjust the Cam-Chain tension: With a spanner applied to the alternator rotor retaining bolt, rotate the engine anti-clockwise until the T1 mark (CB125T,T2,TA & TB, CD125T & CM125C models) or the TR mark (CB125TD only) is aligned with the fixed index mark on the crank case left hand cover. Slacken the cam-chain tensioner lock-nut which protrudes from the rear of the cylinder barrel, then retighten the locknut. The tensioner assembly should position itself automatically to provide the correct tension as soon as the locknut is slackened. Note when retightening the locknut, the adjuster stud must be prevented from rotating. Do not touch the tensioner bolt which protrudes from the rear of the cylinder head.

Yeah, err... OK! THIS is what I did!

CB125 Sump Plug Location

THIS is the bolt at the top, between the carbs that Haynes says "don't touch"! So I touched it! It holds the Cam-Chain Tensioner in place inside the engine, BUT, Tef says that the bit that needs to move to let the tensioner take up slack, MAY be pinched in place by this bolt... so to LOOSEN it SLIGHTLY... like as in maybe 1-Turn MAX.

CB125 Sump Plug Location

This is the Cam-Chain Tensioner stud & lock-nut they are talking about, between and beneath the carburettors.

CB125 Sump Plug Location

Loosen the lock-nut, not the stud. In THEORY, the spring in the tensioner mechanism, should pull the tensioner blade down and take up the slack in the chain, as soon as the stud is unlocked, and you may 'feel' it 'tug' as you undo the nut. BUT!

CB125 Sump Plug Location

Known 'niggle' on these engines, and THIS was why we undid the bolt they say 'do not touch'; the tensioner mechanism 'sticks'! So we slacken off that 'Do-not-touch' bolt, then give the top of the tensioner blade a 'little wiggle' to make sure it is 'free'.

CB125 Sump Plug Location

THEN with a spanner on the square of the tensioner stud, to hold it still, the lock nut can be retightened, and THEN, don't forget to nip up the 'do-not-touch-bolt'!

Haynes: If repeated attempts to adjust the cam-chain tension fail to quieten a noisy camchain, the engine must be removed from the frame and the cylinder head and barel removed, as described in Chapter 1 of this manual, for the tensioner components and cam-chain to be examined for signs of excessive wear or damage.

Tef Says: If the cam-chain is noisy after repeated attempts to adjust it; its probably Donald-ducked. Tasking the head off and fiddling with it wont tell you much, and you'll have to split the crank-cases to loop a new (endless) Cam-Chain over the crank! DON'T think "Oh! Well, I'll put up with the rattle!" It can be rather nasty when they SNAP!

CB125 Sump Plug Location

NOW: we can put the cover back on like Mr Haynes said to after doing the tappets!

CB125 Sump Plug Location

Check the condition of the Rocker-Cover seal. These do NOT have to be replaced every time the cover is removed, but they do go hard with age, and the rubber seals on the retaining bolts are often forgotten.

CB125 Sump Plug Location

Re-Assembly is the reverse of removal! FAFFING FIDDLY! As removal align the curvie bit of the cover around the front down tube of the frame,

CB125 Sump Plug Location

Then sort of twist the cover over the top of the engine. Tef says don't worry too much about the seal falling out of place, just yet, but don't let it snag or yank it, try and get it over the rockers with the cover.

CB125 Sump Plug Location

Then it can be tilted back over the rockers, careful to get the rubber seal between the case and the cylinder head.

CB125 Sump Plug Location

It will almost certainly be a swine, and fall out, but just be gentle.... and tickle it back into the rebate in the casing as you lower it into place

CB125 Sump Plug Location

paying attention around that curvie bit, where it likes to pop out when you're not looking!

CB125 Sump Plug Location

Then the cover bolts can be jiggled into place, screwed in, and then tightened down. The cover may need a little re-alignment to get the screws in straight. Don't force them.

CB125 Sump Plug Location

And then do the cover up evenly tightening down a little on each side in turn, so it goes down straight.

CB125 Sump Plug Location

Tef tells me THIS is what WD40 is REALLY for! (Not lubing chains, or loosening rusty bolts, but) Spraying onto the electrics inside the magneto cover, before we put the cover caps back on, to keep the damp out.

CB125 Sump Plug Location

Inspection caps back in. And refer to How2: Remove & Refit Spark Plugs!, if needed...

CB125 Sump Plug Location

To replace the spark plugs! HT leads can then be put back on the plugs, and the tank and side panels re-fitted, and the engine 'run up' to check for nasty noises or leaking oil. and JOB DONE.

See, even a GIRL can do this!

 

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