Knocking on front cylinder - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 11-20-2011, 11:36 AM Thread Starter
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Knocking on front cylinder

OK So here we go. I was riding down the highway when all of a sudden that soft rapping sound I had assumed was the Cam Chain, all of a sudden got much louder, and I lost power from the front cylinder. SO I'm hoping this could be an ACCT fix? But would I have lost power. I had figured I would only have heard the rapping noise.

From many different people I've heard many different things.

Everything from, ACCT problem that caused the timing to go haywire, broken/twisted rod/bearings.

Today I'm taking off the tank, and going in, if it's not immediately apparent, I am pulling the engine and doing a complete tear down and rebuild. My question to you, the wise people of VN750.com, is, what should I look for directly?
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post #2 of 8 (permalink) Old 11-20-2011, 12:28 PM
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First things first. Before pulling the engine, I would do a compression test. It will probably be very low, but at least then you will know you actually need to pull the engine. Not likely an ACCT thing, that would not cause a loss of power on the front cylinder unless the chain broke or jumped teeth. And the cam chain tends to make a rattling sound. A rapping or knocking sound is more likely to be a con rod bearing or piston slap. If you have completely lost power on the front cylinder, you have lost the ring seal, or a valve is stuck open, or worse, you have a broken rod.


Since it is the front cylinder, I would start the teardown with the front cylinder. It may or may not be necessary to split the cases, but if you have any doubts about whether it has lower end problems or not, then you will literally have to completely disassemble the engine. If you go that far, I would not buy any parts until you find out the condition of everything. There could be more wrong than the engine is worth, considering what Kawasaki charges for parts.

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post #3 of 8 (permalink) Old 11-20-2011, 12:45 PM
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We might disagree on alot, but not this. Jerry is right, "knocking" is likely a rod bearing or some piston related issue (I had a piston with a loose wrist pin that " knocked"... It backed out one side of the piston, tore a groove down the cylinder wall and thereby destroyed the rings, removing all compression)

If you jumped timing you likely would have sucked a valve, which I think would make more noise than just a knock.

A bent valve might not hit the piston, but wipe out power. Do as Jerry says and if needed just pull the offending cylinder.

I would ask if you been hearing a "soft rapping" from the ACCT why you been riding the bike without addressing that.....

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post #4 of 8 (permalink) Old 11-20-2011, 01:31 PM
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The way this occurred is exactly what the previous owner of my bike described to me. As the bike (2002) had under 4700 miles on it, I had a hard time convincing myself that the "rapping" sound was a rod knock. Turned out to be a spun connecting rod bearing. I think the first thing you should check is the is the filter screen behind the side oil drain. Look for any specks of metal. A copper/silver color would be a bearing problem. Note: If you get to a point of ordering a connecting rod bearing, you will have to order 2 of whatever the part number is to get both halves. Kinda crazy, but Kawasaki sells them 1/2 a bearing at a time. Check out my post about dealing with engine knocks. Good Luck.
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post #5 of 8 (permalink) Old 11-20-2011, 02:27 PM
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agree its not the acct, sorry. my toc spring I replaced the original with broke after a month. at low idle knocking was loud, higher rpms it would quiet down, at all rpms it did not lose any power!

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post #6 of 8 (permalink) Old 11-20-2011, 02:44 PM Thread Starter
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Wow, so many responses so quickly.

I originally didn't think it was the ACCT. When the engine went down, I was actually riding to see what sounds I may hear. boo
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post #7 of 8 (permalink) Old 11-20-2011, 05:09 PM
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That's too bad man. I hope that you can repair it without splitting the cases.
X2 on what Jerry and Knifemaker suggested. Seems to be the best plan. Good luck
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post #8 of 8 (permalink) Old 08-22-2014, 12:33 AM
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Hey I have I believe a cylinder knocking? I have video if anyone could help
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