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gotdurt

XR RFVC ENGINE NOISE (500, 600, 650L)

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Just wandering if any of you Honda RFVC riders have ever experienced a noisy, resonating clatter/ knock at higher RPM's under load. It only does it under hard excelleration or highway speeds above 70. Valves are adjusted, octane doesn't affect it. The current bike in question is a NX650, 10K miles, but my XR650L developed the exact same problem at the same mileage. Both lived hard offroad lives. I've heard that the RFVC motors had a tendancy for cam chain/ tensioner issues. Has anyone delt with this before? Has anyone replaced a cam chain and/or tensioner before? Could it be another culprit? :thumbsup:

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That almost sounds like the cam chain slapping around alot. I had a '91 Suzuki DR350 that made that noise, it had around 8000 miles on it. When I took it apart, the connecting rod and the piston pin were still good and tight, but the Cam Chain was loose big time!

Maybe that's what you're hearing? Not sure but could be.

Or maybe it's piston slap? You know a worn out piston rocking back and forth, slapping against the cylinder wall. But you would hear that even at idle I would think, or under a light load.

LL.

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Yea, the cam chain is the only thing that makes sense to me so far. The only thing is, it seems to me that cam chain issues would result in clicking or tapping noises. At first I thought it might be a rod knock, but this is a high rpm symptom, and every knocking rod I've ever had occured at low rpm's, especially on deceleration. If I let of the throttle at all, it stops. Plus, it seems to be a higher frequency, and seems to come from the top end. Also, it's mild when cold, and gets worse after it warms up. The motor is tight and quiet at start-up and idle, unlike a rod knock.

Any piston slap I've ever heard was accompanied by burning oil, and neither bike used oil at all.

It just seemed odd to me that I have 2 bikes with the same motor that develop the same problem around the same mileage. I thought surely somone would have had the same experience with a similar XR.

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Well in a vaguely similar situation, I had a 1974 CB360 that suddenly started spurting oil everywhere. Culprit was the cam chain, it developed excessive slack from a stuck auto-adjuster and started vibrating to the point where it could touch the sides of the cylinder wall. After that, the cylinder was done for. It wore a hole straight through and sprayed hot oil onto the exhaust headers... But there wasn't any obvious noises before doing this. I patched the cylinder with JB-weld and stainless steel inserts and tightened the chain, and it worked great ever since.

These RFVC engines are light-years ahead of the old CB motor both in terms of capability and complexity.

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I have the same bike with the same problem. It seems to get worse when the gearing is higher. With a 14 / 51 sprockets it only happens in top gear. With 15 / 51 it happens in third through to top.

If you solve this problem please post the answer as I am keen to solve it.

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Sounds like piston slap and detonation combined to me. I'd try richening the needles/main jet first to see if it improves. My 79 xl540 did the same thing til I put a richer xr carb on it. The rfvc motors are gear drive counterbalacer not chain so I doubt that would be it.

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ya dammit! i forget to look at the post dates! i hope he has figured it out by now!

Maybe you could PM him and tell him its a lost cause and you'll give $10.00 for the old clatter box... Those NX's are great commuter bikes...J/K

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LOL! i really would like to have one. my grandfather had an 88 NX650, i thought that was the coolest thing i had seen! wish he hadnt sold it. a few months back he gave me the owners manual for it!

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