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Old 05-09-2011, 10:50 PM   #1
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Default Honda 82 VF750C loud knocking in engine. Please Help

Here is my story. Any help would be highly appreciated as I'm a poor college student, and somewhat mechanically inclined.

I got my Honda 82 VF750C up and running again for the summer and its been about 3 weeks of riding. My bike sat for 2 days and i went to start it and it had a very loud knocking noise coming from the engine. There was no sign of this the last time i rode it. I shut it off with about 30 seconds of idle, and tried again, same problem. It more sounds like a piece of aluminum is violently pinging on another piece of metal.

Things to note:

Starter was having difficulty turning and would jam a few days prior and especially the time i heard the knocking. I thought my starter was just getting jammed or going bad.

A week before i dropped a small piece of rubber in my gas tank. I was thinking my fuel filter would catch it, as i was about to replace that.

I have had a small leak in my left crankcase where the alternator is. I was working on replacing the gasket, but i maintained a good oil level and checked it every day.

The oil filter hasn't been changed for probably a couple thousand miles.

My carburetors probably need a good tune up.

My conclusions:

Hoping to god its not a rod.

Maybe my oil pressure failed and my engine isn't getting the appropriate oil.

Carbon build up from the piece of rubber.

Please tell me its not a rod!

Thanks in advance for the info, i highly appreciate it. This is my only mode of transportation for work and i have no money.
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Old 05-10-2011, 05:02 AM   #2
Morbo the Destroyer
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"sounds like a piece of aluminum is violently pinging on another piece of metal"

Honestly, I don't see how that can be anything other than what it sounds like. The question now is: is the sound in the top end or the bottom? If it's in the top end, you might have a valve train failure. Bottom end is most likely a rod.

The bike is almost thirty years old. What is the service history on the bike; do you know, or has it been handed around? Has it had regular valve checks and adjustments? Has the oil been changed, if not right on schedule, at least regularly? How about riding attitude, treating it well or beating the crap out of it? (Be honest)
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Old 05-10-2011, 06:03 AM   #3
Easy Rider 2
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Originally Posted by nihilomni View Post
This is my only mode of transportation for work and i have no money.
Well, I hope you have a bus pass.......or a bicycle. Seriously.

1) You should not ride it......or even run it for that matter.
2) I think you are gonna have to scrape up $150 or so to get it trailered to a shop for an official diagnosis.

Alas, almost any repair inside the engine/starter/flywheel etc. is gonna be more than the bike is worth, probably.

Nobody can really tell you what the cause of the noise is without being there.
Your little piece of rubber has nothing to do with it.
You might be able to tell a little bit more about the situation by running the starter with the plugs out but someone with engine experience probably should be there for that too.
'11 Kawasaki Vulcan 900 C

Last edited by Easy Rider 2 : 05-10-2011 at 06:06 AM.
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