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As above, and was the flywheel cover on when the bike fell over ?

You rode it with thin petroly oil !?

How is the oil light behaving...not many cmx450 made it to UK but engine is sohc 6 valve shell bearing type.

Remove plugs and check for a "bright" ring on piston crown, or evidence of piston crown striking cylinder head...

Any difference in knock if clutch pulled in ( disengaged )....?

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1,887 Posts
Try not to use it but you may have to which I understand.

May be a gear selection mechanism problem but I doubt it, even cotton wrapped around a tyre can sound like a disaster happening at 30mph, ask me how I know...

Do your research, you know of

Find out if your balance system uses cush drive weights....any lumps of black rubbery type stuff seen in the oil.

Petrol in oil is not good, but it does "clean" the insides a bit.

Check piston crowns but as Mike says, balance system check.

Do your research.

Feedback and pictures to help others...

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The balance chain adjusting quadrant and shaft is spring loaded to turn the quadrant anticlockwise to adjust. So the quadrant slot would move in a downwards direct, not up.

Can you clarify and how much slot is left ?

You should just about be able to see the balance shafts DOT, which should be above the horizontal...

Could be an exhaust leak, makes sense, phone audio has a good mic, does exhaust leak ?

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No vidio opens...

Gear shaft flexing ?

In what way ?

Some, but not much, in and out is normal.

The gear shaft had a spring loaded " central position", to which it returns after each gear selection.

Up and down, or front and back gear shaft movement is not normal. How is the flywheel cover support bush for gear selector shaft.

First vidio showed flywheel cover off and knock at idle. Since cover was on when bike fellow over, the flywheel will not have "picked up" any gravel or similar.

Need to see shaft flex vidio...

The shaft will have some flexibility cos its quite long, but is made of relatively large diameter steel...

Will have another look/listen to the first vidio....

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1,887 Posts
Hi, please post a picture of the flywheel cover which the gear shaft goes thru...

It has a support bush for the gear shaft ?

The flexing is the gear shaft bending a bit which will not happen in service due to the cover support bush.

The shafts "arm" is not vertical when in its central position meaning a loss of mechanical advantage for changing down gear....

As said not many cmx450' s made it to the UK, so "finer details" not known to me.

As long as the gear shaft is not bent, or has no ( other than very slight ) "play" in the c/case, then no problems seen. No oil leaks from the oil seal ?

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Yes, watched initial vidio again, seen gear shift vdio as well. cmx450c rebel 1986 (g) USA California balancer exploded view shows solid balance wieght, so no cush drive problems to worry about.

Balance adjusting quadrant self adjusted to slot mid point so didn't go over centre, so not completely worn out, dot position will prove this if needed.

So, what is causing this bad sounding noise ?

You have ruled out a leaky exhaust.

I doubt if the cylinder head is loose or a head gasket problem....but check visibly....

A picture of the camshaft would help rule out camshaft problem. I assume both cam sprocket bolts are tight ?

Picture of camshaft please.....

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Look at your clutch basket thread...

Videos although informative are too jerky to see/check some things....

I keep forgetting this is a cm bring slightly different to a CB.......please forgive me for that, no oil pressure switch seen...well not in the same place as a CB.....

Watched clutch vidio again, can I see the clutch hub, the bit with the spring plate, wobble ?

Hold hub and basket between finger and thumb so they become one, any wobble ?

The hub should be solid as if part of gearbox input shaft.

The basket drive overun cush drives are always a bit slack by now, as long as rivets not moving.

See clutch basket thread...

There is normally some clutch basket in/out movement...see CMSNL exploded views for your exact bike and post a link in this and your other thread...

Two threads on the go at the same time can cause some confusion, so requests answered in your latest thread, the clutch basket one would be great. Try to quote your bike details at the begining of each new thread....

Cmx450c rebel 1986 ( g) USA California ?

Love the tash and two compressors ....

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Ok been having a good look on using cmx450c rebel 1986 ( g ) USA views.

Exploded views do not show enough finer details, and if part not in stock, no picture.

Looking at your slotted nut picture, I reckon the slotted nut has been off before, due to the "disturbance" at about 9 o clock. The stakeable nut, looks to have a clean "restake" at about 7 o clock.

Would you agree with that ?

How much in/out play in mm ?

Top cam chain adjuster bolt tight or loose ?

The petrol contaminated engine oil ( thin) would not do the engine any good, but oil light behaving ok.

Yours according to CMSNL is a shell type bearing crank, very similar to CB 400 n.

Cb400n and the 450 version ( 250 the same ) are prone to left cylinder big end failure, as it is the last shell bearing to get any oil.

No marks seen on piston crown.

You may be asked to return to that cylinder once the " onions outer layers" have been eliminated such as gearbox problem ( don't think so ), clutch problem ( a possibility ), cam chain adjuster problem ( check top bolt ) , balance system problem ( not ruled out yet, but CMSNL shows solid wieght rather than problematic cush drive type ) or anything else.

I assume electric start works all ok ?

Hope it's not a buggered big end .

Going down the clutch less engine run route would rule out, it in, Tete would rule out g/box/clutch basket cause, as would engine run with cam cover off.

A quick ten second engine run would be sufficient.....possibly ?

From memory does this bike make that noise when engine is cold ?

At least you have proved the slotted nut is not loose.


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Internet being a pita...


Clutch less engine run may eliminate or rule in a possible g/box clutch problem, as would cam cover off for top end...

Clutch basket removal to inspect rear of clutch drum. Check CMSNL for a missing washer but it's been like that since you have had bike.

Have you been attending to cam chain tensioner at all ?

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1,887 Posts
No NO NO in BOLD, no, the engine must have oil in it, even for a ten second run. Shell bearings DO NOT like no oil, nore do those rocker arms and many other things !!!!!

More about that later, back in a minute...

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Oh well, what's done is done and can't be undone.....

Thanks for the brilliant sharp pictures, 5 pictures, 5000 words, I will be brief...

As Mike says, SHORT OUT plug leads to kill a cylinder.

The ignition system should be considered to be FRAGILE, DO NOT disconnect a plug lead with the engine running !

Are your plug leads yellow and black ? Suggesting a non standard HT coil, no matter.....

Picture 1
DOT. More or less perfect position if already adjusted, auto adjusted by the spring loaded system. Good length of slot left as well.

Do not be tempted to help, over adjust that spring loaded auto adjust system. Over adjustment just wears stuff out quickly. The "slipper A" that sits between the balance chain is vertually unobtainable, it costs an organ. The "rubber" on it will be rock hard by now. Over tight engine chains make a sort of winning whizzing rustling noise, which I have heard in one of your videos when the throttle was blipped.

The dot is in a good position.

Picture 2
Make sure the oil pump chain does not touch that hexagonal tower, the oil pressure relief valve, that lives just under the oil pump sprocket. They very very very rarely stick open due to spring.

Picture 3
Cam area.
Right exhaust valve rocker arm looks a little "dry" and a bit discoloured at the cam end. The valve working clearance adjusting screw looks a bit deep in the valve end of the rocker arm. This suggests a possible lub problem, but that's for later. I suspect the rocker arm can contact pad may he quite worn. I will listen again to the knock.....after finishing this post but do not think this possible problem is your knock.

Check to make sure that the oil pipe is not contacting the camshaft, it looks as if it is quite close.

Pictures of valve springs and view from other side would be good. Do the valve springs have a yellow paint marking at the top, all of them ?

Picture 4
Slotted nut.

See my picture at bottom, these are "stakable nuts" from the car world. Does the slotted clutch nut look like them ?

CMSNL com. Cmx450c rebel 1986 (g) USA California, is this your exact bike ?

Slotted nut, is that a wire clip on that nut ?

No clip is shown on CMSNL exploded views....

The blueish washer under the slotted nut, can I see some writing on it, maybe "outside" it part of that word ??

To me the slotted nut looks as if it's on backwards.....

Picture 5
Cam chain there a rachet system on the two parts, lines going across from side to side to "rachet" ?

Also, a bright area, maybe steel wire or foriegn object, close to the cam chain adjuster ?

Engine run with cam cover off ( but clutch cover etc. On, oil to level ) This is easily doable but messy. You will see oil flow to camshaft ends. Oil flow should be good and about the same side to side, oh hang on, yours had external oil pipe, will have to check as oil flow may be thru those pipes only, I will come back with oil flow diagram for you.......but engine run and oil flow check easily possible, but Messy !

As Mike says, with clutch all together, clutch cover on and oil to level, in gear with clutch pulled in ( disengaged ), and back brake on, all gearbox and clutch hub will stop turning, but, the clutch basket will still be turning cos the crank is cos the engine is running.


I will listen again to the knock vidio...

Organism Newspaper Font Line News

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1,887 Posts

Close and lock your workshop door, go home, gave a beer, a good night's sleep.

Tomorrow is a new day.

You have a good looking workshop with a good amount of room.

These engines are not that complicated. A few tools needed like clutch nut peg spanner/socket which you could make, there is a thread on here about that, and a flywheel puller bolt.

What have you got to loose by taking this engine apart.

CMSNL views are very usefull, I am sure there will be manuals out can do it.

Anyways, enough for today, go have a beer or two, but not 3.

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1,887 Posts
That's correct, at least the oil pump is creating enough pressure to turn the light off, but how much pressure after that and when the oil is hot, and does the oil pressure relief valve work properly, and does the oil filter by pass work properly, and a few other oil system "functions".....

Is the clutch cover still off ?

CMSNL cmx460c rebel 1986 ( g) USA California, your bike ?

Exploded views show a proper sump and oil filter underneath the engine, at the front. If the sump has sufficient oil in it, just so it starts to dribble out from by the oil pump chain with the bike on level ground and on the centre stand, it is safe ( safe ?????? but lots of dangerous rotating gears, chain, clutch drum, when engine running !!! ) to run the engine oil wise, as the oil pick up pipe and filter is quite well submerged in oil.

If you did this, you could see if the oil pressure relief valve leaks, and opens at high pressure, about 70 psi.

Also view oil flow to head and cam and the rockers. Remember I said I suspect that dry looking discoloured right exhaust valve rocker arm being quite worn....

Remember with engine running, cam cover off, clutch cover off, a real oily mess will result, a real oily mess !!!!!

Anyways, have you checked behind clutch basket so parts touching, banging, knocking ?

There is quite a bit of play/slack in clutch basket both in and out, play with the damping springs.....

I would like you to do the following...

Engine off, plugs out, working from flywheel side, turn flywheel in normal direction until flywheel side goes over tdc with piston half way down the bore in one steady slow movement. This places the piston and con rod in the "power" region of its movement ish. This is the position where the big end would be most worn ish.

Any play would leave the piston "up", in relation to the crank.

Looking at the piston crown, and moving the crank backwards, does the crank move backwards with no piston movement at all, and any "clunk" heard, as if big end play has been "taken up".

Do this test many times, say ten times.

Any "play movement" seen or clunk heard ???

You say compression not so good flywheel side.

Feedback feedback feedback.

Two of my books have gone AWOL over Xmas, still not found them, want to check oil flow diagram....



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1,887 Posts
So, piston set as described, crank moved backwards slightly, piston moves up instantly as seen thru plug hole and no "clunk" heard as if play in the big end has been taken up ?


A slight variation next, turn crank in normal direction, watch piston go over tdc and go about half way down the cylinder. Push down on piston crown with some wood dowel, or your probe.

Any piston downwards movement with no crank movement when piston is pushed down, any clunk heard as if play has just been taken up ??

I hope that answer is no clunk and no downward piston movement with no crank movement.

Further downward pushing of the piston crown results in crank movement.

This is a very rough and ready "measurement" of big end play but there still may be a bearing problem.


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Ok, listened and watched your last vidio.

Are you sure there is no exhaust leak at all ?

If there is a slight leak, it is not the knock.

Do you have a strobe timing light and some tippex white correction fluid for typists ?

Mark in tippex the flywheel T so it's is really easy to see.

Use strobe at engine idle. It should be possible to identify where the tippex mark is when the knock occurs, a datum if you will.

Ben took a brilliant vidio of his engine noise, managing to slow the vidio play back down, but didn't explore that "info" further.

Establish where the tippex mark is when the strobe flashes and noise heard.

Even slow down the idle speed to help

Do you have a test tank, or, allow carbs to fill with fuel. Remove tank and cam cover. Start engine and watch the top of the cam chain adjuster. Anything happen ?

During this run is there good oil flow to the right side ?

That suspected badly worn rocker arm pad on the right exhaust valve may be noisey.

Do you say the engine knock was noisey more at the bottom of the engine ?

A vidio if the cam area particularly that right exhaust rocker please...


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