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Sharp sound when working engine hard on AC716


jlasater

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Ever since I've had my AC716 (late model style) if I bump the throttle up quickly or suddenly load the engine (hitting heavy grass too quickly) the engine emits a rather loud metallic banging noise. Obviously that's not a good thing. I hit a gopher mound today and when it made the sound, black smoke came out of the exhaust pipe as well, obviously running very rich. Choke is adjusted so it's fully open with the choke control pushed in. I use 10w40 oil, have tried super unleaded, but it still makes the noise if I'm not careful. Any thoughts as to what the issue might be? Supposedly the tractor got a new Kohler shortblock a year before I bought it. Other than that noise (and a charging problem I've posted about), it's been an awesome investment. Have yet to see a John Deere product (or any brand for that matter) that does a better job of mowing.
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I don't like 10W-40. Anyway, if the noise is light metallic, like pre-ignition, check points, timing, and carbon build up. If the noise is "deeper", be careful how much you use it before determining the cause. Did you check the fins for debris (overheating)?
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I blow the cooling system out with air every couple of weeks and have never had a significant amount of grass or dirt come out. Think the oil could cause noises like this? I figured running a very light oil viscosity might, but not with heavier weights.
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I had a 16 hp Kohler rebuilt and while pushing dirt it would make the same noise. I thought maybe something had broken but it still runs and I am done pushing dirt????
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HI, I think you need to determine whether it is a mechanical problem or preigintion. If the engine is normally quiet and when under load on a hot day and it sounds on a hard pull like you threw a handfull of ball bearings in the cylinder, I would suspect pre-ignition, commonly called "ping" in older cars. I would first check the fins, then get some hi-octane gas, maybe at an airport for private planes. See if the problem goes away. Next I would be sure the timing advance it correct and the carb main jet is set rich enough. If they are OK and the problem is gone with hi-octane gas, I would then pull the head and check for carbon build up. About 10 years ago, we had several older [16hp k341] tractors with this problem. to fix them we took a die grinder and took about .025 of metal out of the combustion chamber. This dropped the compression ratio some and the problem left. If showed up when the gas was down graded. It seems like the later k341s have slightly lower compression ratios than the older versions. We had about 4 or 5 of these older tractors that we were unable to fix any other way. We tried a lot. Constant pre-igniton can and will break pistons, and can break rods and in a high performance verion even break the crank. Any little sharp point or chip of carbon can get hot and glow and cause ping also. Good luck, Al Eden
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Hi, I forgot to mention Kohler does not recommend multigrade oil in these engines. It does not stand up under extreme temperatures as well as straight weight. SAE30 is the recmommended oil except for cold weather. 10-40 is not as tough as 10-30 under extreme temperatures. These engines see temperatures far higher than automotive engines see. The portion of the cylinder next to the exhaust valve gets extremely hot and the valve is between the fins and the cylinder and all of the heat is extremely concentrated in a triangular area near the valve seat and narrowing down as it goes down the cylinder. These areas are where the oil breaks down. This may be why you may find a lot of carbon on the piston and in the head as the oil is breaking down and getting burned. When I first became a dealer in 1981 I had a 7117 demo when we set it up we put 10-30 oil in it and it used a ton of oil and after my Kohler rep told me to get that damned stuff out, I put in 30. End of oil consumption. Thought I would mention this. Good luck, Al Eden
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Changed the engine oil and hydro while I was at it. Used Chevron Delo 30w oil in the engine. Runs much better. Amazed that just changing the oil fixed the metallic knocking sound, but it did.
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