Honda Twins banner

Rebel 450 Knocking

4K views 42 replies 3 participants last post by  DD23 
#1 ·
Hello all. I have been trying to pin point this knocking that came out of nowhere with my 86 rebel 450. It’s been a dreaded journey for the last week or so trying to trace this and figure out this knocking sound I have. The chain of events that happened that day before it started to knock :

1: I changed the exhaust and was told to re jet the carbs so it wouldn’t run lean. Changed slow jet from stock 35 to 40 and main jet went to a 130 from I think was a 112. I changed the exhaust and rejetted the carbs then rode the bike and tested out the jetting. The oil may have been contaminated with gas also because I smelt So there’s that possible problem

2: came home and pulled the plugs after bike started to act up while riding. Plugs were black and sooty. While checking The bike out….

3 bike fell lightly into the dirt on left side. (Kickstand was in soft dirt) Peg and shifter lever went into the dirt
4: started the bike after it dropped and it started knocking
5. After it started knocking I was told to check out the valve clearance to make sure that wasn’t the problem. I adjusted the valves which didn’t make a difference in knock and returned the exhaust and carbs back to stock. Was told that it may be the top end. It’s very hard to figure out where the sound is coming from because the sound is equally loud at the bottom end and the top end of the motor. I also synched the carbs thinking the knock could be from unsyncd carbs. Knock was still there
I’m chasing down top end but trying to think out of the box maybe it’s not top end but bottom end from the the shifter hitting the dirt. I’m shooting in the dark but just trying to think logically. Nothing was bent shifter wise though and the shaft that the shifter bolts onto seems to be okay. It does move in and out slightly though but I think that is normal .
Other things I’m thinking about if the spark plugs were black and sooty it could be loaded with carbon and having a pre detonation problem but I really don’t know. It’s so hard to pin point where the sound is coming from. I’m going to get a stethoscope from harbor freight today and see if that helps alittle more. The shifter didn’t bend or nothing just had dirt on it from hitting the ground. Things that were also brought up after I had the valve cover off was the cam adjuster larger wedge doesn’t spring downward. It’s stuck up so maybe the cam chain is not adjusting? But then when I start the bike with plugs out or even in with plugs in and the wires not attached there is no knocking at all. If there was something internal of the top end it would be still knocking I would think. The bike only knocks when it is running at idle speed. If you rev it the knocking goes away. So now I’m thinking pre detonation? maybe the new cdi I bought is not functioning properly or the ignition coil. It does get spark though. I have just been a hamster wheel going nuts about this noise. Was looking for some insight or maybe if anyone has had this knocking before …
Thank you!! Here is a video of the knocking

 
See less See more
#28 · (Edited)
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 adjuster.....is 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.

Feedback.....

I will listen again to the knock vidio...

Organism Newspaper Font Line News
 
#29 ·
Thank you for all that info. A closer inspection of the brand new oil I just drained out shows metal flakes. A lot of them so I think it’s time to seak professional help and or give up on it and sell it. I have a couple of motorcycle mechanics at work that may be able to rebuild the engine but than again I paid 1500 for the bike. Don’t even know what they would charge me.
i did run the bike with the covers off only to find I still cannot locate where it’s coming from. Also the oil light and neutral light does not illuminate at all anymore since running it without the covers. Feeling way beyond defeated right now. Not happy at all. Have to think of what to do now. Not sure if it’s a top end piston problem/ low end crank shaft problem/ or oil system not working correctly. Would hate to pay to have a engine rebuild and not have the oil system not up to par and repeat the whole process over again with lack of lubrication. I don’t know. I really don’t know at this point. I’ve tried what I can. I think myself digging into the engine with limited knowledge of these engines and lack of information from a online manual is a no go for me. This is the oil I drained out before I pulled the clutch cover off. It was brand new oil and the oil pan was very clean before I drained the oil.

Astronomical object Circle Tints and shades Metal Serveware

Liquid Tableware Dishware Ingredient Fluid
 
#30 ·
Glitter.....

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 there.....you can do it.

Anyways, enough for today, go have a beer or two, but not 3.
 
#33 ·
Update to the one problem of the oil light and neutral light not illuminating. Both bulbs have blown out. I verified that with a good bulb into the oil and neutral sockets. Oil light goes off when engine is started so that crisis has been avoided. That makes me feel better. Engine still with problem makes me feel worse 😩😂. Atleast I know that there is oil pressure !
 
#34 ·
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....

Over.....

Dd23
 
#35 ·
i will try some of your suggestions tomorrow. I put the clutch cover back on and filled with oil. Not many videos at all on YouTube about this rebel 450 engine. Was wondering what the closest engine would be to it. Maybe I can find more videos on those? I think the cm400 engine is close. Are there any others. I see the cb engines are different.
 
#36 ·
DD I tried what you said but no I don’t hear any knocking or any weird noise. I’m only able to look through the small piston hole though. The cylinder head is not off. I’m just probling the top of the piston with a long screw driving trying to see if it moves or not. But no I don’t hear anything weird.
 
#37 ·
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 ?

Good.

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.

Feedback
 
#40 ·
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...

Feedback

Over....
 
#41 ·
The bike made the noise with the other exhaust and now with the stock exhaust back on. The only exhaust I see come out of the pipes are at the bottom where the I guess drain holes are.

I do have a strobe light. I will have to see if it still works. I already have the t marked in white.
I could do this and take a slow motion with the iPhone I have. That’s a good idea.
Yes I have a test tank. I can take off the valve cover tomorrow and check
I will also check the right side. I’m guessing this will get messy?


Do you say the engine knock was noisey more at the bottom of the engine ? Yes. But sound the same from bottom and the top. I will take a video of the right exhaust rocker also. I’ll get the video tomorrow Thank you for all this. I really appreciate it! I know it takes a while to type all this out!
 
#42 ·
I just tried the timing light. Problem is my light has a adjuster that can advance timing from 0degree to to 60 degrees. The knob goes below 0 so I don’t know if it’s actually on 0 when the knob is at zero. From what I can see if I adjust the knob to 21 degrees The t on the flywheel lines up with the mark on the case. If I rev it up the t does not line up with the mark on the case at all. Even when I adjust the knob either way. The T (white mark shows on the light at a revved up speed about 1 1/2 inch to the right of the mark on the case. I also recorded a slo motion vid of the timing light at idle (set at the 20 degrees on the knob again not sure if the knob is correct). With the exhaust quiet the knocking happens from what I can is at tdc when the white mark is at the mark on the case
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top