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Rebel 450 Knocking

2109 Views 42 Replies 3 Participants Last post by  DD23
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

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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!
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
If you can correlate the knock to a flywheel position, that would help...
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