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  #1   IP: 72.220.83.31
Old 04-17-2010, 02:42 AM
Charles Taylor's Avatar
Charles Taylor Charles Taylor is offline
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Knocking / Runs Rough

Over the last few weeks, I have been pulling the valves and replacing their springs because of a sticking exhaust valve in #2 cylinder. I finished up last Sunday and the engine was running fine.

Today I went to clean up the boat and see if the engine was still running well. It was running fine while I warmed it up so that I could change the oil.

One of Murphy's Laws must have taken effect. After nothing more than changing the oil, the engine developed a pronounced knock and ran rough.

I tried adjusting the timing, checking the fuel filters and squirting MMO into the cylinders. I noticed no change.

I did notice that choking the engine has no effect at idle. The knocking decreases at higher RPM. There is no smoke. I also noticed that the manifold stays rather cool to the touch and the temperature gauge is in the normal range.

What could cause this problem that only chose to manifest itself after an oil change?

Thanks,

Charles Taylor
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  #2   IP: 38.118.55.125
Old 04-17-2010, 08:16 AM
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Don Moyer Don Moyer is offline
 
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Charles,

Assuming that your oil pressure is normal after the change, I don't believe your rough running has anything to do with the oil change. My first guess is that you bumped something during the oil change that is affecting the secondary ignition system on one or two of your cylinders.

When an Atomic 4 runs on only two cylinders it will emit a knocking sound and deliver considerably less heat to the manifold (addressing your other symptom).

Don
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  #3   IP: 74.92.224.177
Old 04-17-2010, 12:40 PM
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Qben Qben is offline
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I had the exact symptoms you describe when my engine was firing on only 2cylinders (due to water in them though). Try removing spark plug wires one at a time to isolate which cylinders are affected (the engine will immediately die if you remove the wire from a firing cylinder when only 2 of them are firing). You can probably also tell by feeling the plug wire boots where they attach to the plugs. The ones over the firing cylinders will be much hotter than the ones over the non-firing cylinders. After you isolate the cylinders that are not firing, you can start troubleshooting, by switching plug wires and plugs around (or replacing with new). Also check your distributer cap for cracks or blemished surfaces on the affected contacts (underneath).

You should also probably check cylinder compression and torque on your head nuts. Since you recently had the head off, this could also be a leak at the head gasket.

Qben Oliver
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