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Discussion Starter #1
Hi Guys, I’ve been trying to figure out what is causing the engine knock on my father’s 99 Sportsman 335. Follow the link to hear the noise below.


THE FACTS:
-Engine has 650 miles on it (used for plowing by previous owner). Starts first pull/crank
-Noise Appears to be coming from top end of engine
-Timing chain has been checked and is tight. No slap
-Primary clutch has been removed to eliminate that.
-Valve Clearances both at .06
-Oil and Filter changed. Correct oil weight used
-Oil pump intake screen cleaned, and pump repri
-Knock stops completely when engine RPMs are increased (as shown in video)
-Knocking noise is still made when decompression lever is removed, however, it doesn’t seem to go away when the RPMs are increased.
-Noise seems to reduce as engine warms up, but is still present.

I’m not sure what is causing the noise at this point, but I have a funny feeling about the decompression mechanism. When I took off the cover to inspect it it was flapping in the wind. Even when I removed it, the engine still made the noise though.

Thoughts anybody? It’s driving me mad!!

thanks everyone!

OnePumpChump
 

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Discussion Starter #3
Exhaust leak - you can almost see it about 6 seconds into the vid
We were doing a test with the valve cover off and got oil all over the exhaust. That was it burning off, but i'll check again for an exhaust leak. Think that is causing the knocking sound though?
 

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I wasn't looking at the oil smoke rising off the exhaust - I was seeing what appeared to be air blowing through the smoke below the exhaust pipe - you didn't get far enough down on the RH side to see it from that angle, but to me it sounds like an exhaust leak.
 

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I wasn't looking at the oil smoke rising off the exhaust - I was seeing what appeared to be air blowing through the smoke below the exhaust pipe - you didn't get far enough down on the RH side to see it from that angle, but to me it sounds like an exhaust leak.
Oooo, good point. Didn't even think to check that to be honest. I'll check it out and report back.
 

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Ok, so I checked for an exhaust leak, but there was nothing. Not even a spall puff from the mating areas. Do you think this could be caused by the decompression ball?
 

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I don't think so - too loud for that - decompressor just makes a ticking - I hate to say it, but it needs to be looked at by an experienced mechanic. It may be piston noise due to a scuffed piston caused by overheating. My son bought a 2002 Honda VTX1800 new. He didn't wait to break the engine in properly before he tried it out to see how fast it was. Afterwards, the engine made a noise, but only at idle. The dealer told him (and I concurred) it wasn't bad enough to covered under warranty and to just ride it a see if it got worse. Two years later and out of warranty, he decided to get the engine customized. He had me take it apart so he could get the engine cases, cylinders and cylinder heads powdered the same color as the bike. He also had the cylinders and heads Diamond Cut. As I was reassembling the engine I pointed out to him a scuff on one of the pistons and told him this might be the source of the noise the engine made (it never did get any worse, but it never went away). I installed a new piston. When I finished the assemble, I cautioned him that the engine needed broken in again. Not as many hours as when it was brand new, but a few hundred miles of stop and go driving and no extended idling. The noise was gone and never returned. That was in 04 and he still has the bike today with no noise.

It might not be the piston, it might be a piston pin or crankshaft knock, but it's not something that can be diagnosed from a video and might need disassembly to determine the source of the noise. You might just use it and see if it gets worse if you don't want to spend the money to get it fixed right now. Being a 99, I suggest you just run it and get a newer one later on.
 
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