| planojc | -- 10-07-2011 @ 6:18 AM |
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Have a fresh rebuilt 24 stud that has a slight knock at idle and when under a load at low rpm’s. When driving at normal speeds the sound can’t be heard. I removed each spark plug wire one at a time and the knock is still there. Using a stethoscope all over the engine I don’t hear the knock. The engine at idle is a little noisy, and with the stethoscope, is loudest around the fuel pump stand. I’m open for suggestions as to what to check for. Thanks, John
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| TomO | -- 10-07-2011 @ 6:47 AM |
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Some fuel pumps make a sound that can be mistaken for an engine knock. Tom
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| supereal | -- 10-07-2011 @ 7:16 AM |
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It is also possible that you are hearing a valve with excessive tappet clearance. As you say the engine is a fresh rebuild, it could also be a poorly seated valve assembly retaining fork knock. A rod bearing or wrist pin usually gets louder as engine speed goes up, and a main bearing will thunk.
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| planojc | -- 10-07-2011 @ 8:27 AM |
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Super, if it is a valve issue, can it be detected with a vacuum gauge or compression test? Also is there a problem with just driving the car and making sure the noise doesn’t get louder? Thanks
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| Pauls39 | -- 10-07-2011 @ 12:03 PM |
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Try taking the fuel pump off and running the engine without it. Pumps and their pushrods can make a noise just like a rod knock. Check the pushrod for correct length, and check the pump mechanism for wear.
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| supereal | -- 10-07-2011 @ 12:16 PM |
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A compression test will usually not tell much, unless the valve assembly has come loose from the block. If your engine is running smoothly, I'd drive it a while and see if the noise changes. A valve with too much clearance between the tappet and the valve stem usually sounds like a ticking, rather than a knock. The other suggestions regarding the fuel pump and/or rod should be checked if the noise doesn't go away. A problem such as a broken valve spring will seriously affect operation. We always install new valve springs and keepers. Over the years, when we used to grind valve stems for clearance, it seemed that I always had at least one that ticked enough to hear at idle.
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| planojc | -- 10-07-2011 @ 4:24 PM |
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I'm now thinking it's the fuel pump or pushrod. I have a NOS pushrod still in the box to compare the length with. Will keep you posted.
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| alanwoodieman | -- 10-07-2011 @ 4:32 PM |
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I had a new fuel pump and it had a different pump mechanism and it made a sort of clunk sound when it was running, especially at idle, just a thought
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| supereal | -- 10-07-2011 @ 4:37 PM |
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I've seen those, Alan! And I don't yet know why they are an improvement!
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