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Hi all! I’m chasing down a knock in my 350 that seems to come and go. The knock is a bit of a hollow knock, and kind of sounds like a knocking on the inside of a valve cover, which doesn’t look to be the issue. When the knock comes around, it goes up and down with RPM, and seems to quiet down when the car is warmed up, being the loudest when cold. Although I can hear the knock, I can’t seem to locate it with a stethoscope. I’ve tried the valve covers, which I’ve removed, inspected, and adjusted the valves, oil pan, block, etc. Also sounds louder from underneath the car versus the engine bay.
Oil pressure is very good. 60psi at startup, 40-50 psi shuffling thru gears, and 12-14psi at idle, running 10w40 Mobile 1. Temp is also good, running 185 degrees all day long. Car runs great with tight acceleration and starts right up, hot or cold. Timing is at 10 degrees BTDC and has a very mild cam.
I took a couple of videos from underneath and one from up top. Can’t hear much except the wind on the engine bay video, but the knock is audible from the 2 videos underneath. I was hoping someone might give it a listen and possible direction. I haven’t checked the fuel pump,as of yet, but it is new. Someone recommended putting some washers around the base of the dizzy. Not sure what that spacing would accomplish?
Any insight would be appreciated!
http://s30.photobucket.com/user/cv2065/media/IMG_0711_zps30af77ce.mp4.html?o=0
http://s30.photobucket.com/user/cv2065/media/IMG_0712_zps93314848.mp4.html?o=1
http://s30.photobucket.com/user/cv2065/media/IMG_0710_zps21fe836d.mp4.html?o=2
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Check the spring under the fuel pump arm and see if it’s still there. You can tell very quickly if the fuel pump arm is loose (slop in it.)
If it’s an automatic transmission make sure the converter bolts are tight and not touching the inspection cover.
I have also heard that noise it the converter bolts are too long.
Thanks for the replies guys. I have 4 on the floor, so no converter. I do however need to check the inspection cover. Thanks for the suggestion. I tried to get the car to duplicate the sound this morning, from cold to operating temp, it was a no go. Ran perfectly. Getting a bit aggravated with it as I know its there somewhere waiting to come out. I’ll try again tomorrow. I did put the stethoscope on the fuel pump and sounded normal.
[quote=”barneyb” post=113518]Is this a built motor with forged pistons?[/quote]
Built yes, but not by me, which adds to the uncertainty. I would be highly surprised if it had forged pistons.
Was the oil psi fluctuating when you checked it? If the needle was bouncing it could indicate excess clearance in one or more of the bearings which may be the cause of the noise. More info on finding noises here.
http://www.ericthecarguy.com/faq/diagnosing-noises-in-your-car
Keep us posted.
I don’t believe so Eric. Oil pressure starts at around 60 when cold, and settles to 12-14psi at idle. Might slowly go between those two markers, but nothing that I would consider wild fluctuation. Great video library by the way!
[quote=”Macmaven” post=113526][quote=”barneyb” post=113518]Is this a built motor with forged pistons?[/quote]
Built yes, but not by me, which adds to the uncertainty. I would be highly surprised if it had forged pistons.[/quote]
A knock that goes away with temperature could be piston slap. This is common with loose built engines with forged internals.
You will hear piston slap more when the engine is cold.
Maybe…loose piston wrist pin??? Who rebuilt the engine? I would let them listen and see what they think. …
[quote=”JTF” post=113643]You will hear piston slap more when the engine is cold.
Maybe…loose piston wrist pin??? Who rebuilt the engine? I would let them listen and see what they think. …[/quote]
Good plan, but the engine was already in the car when I bought it, and let’s just say that the guy who built it is a bit of a tool, so that’s a no go. If it continues, I can bring it in somewhere and get a second opinion, problem is getting it to do it.
With a wrist pin issue if you disable the ignition to a particular cylinder and the noise goes away, it usually indicates a wrist pin issue problem. It might also be an indication of piston slap but I believe that would be difficult to prove since that wouldn’t react the same way. If nothing else, you would be narrowing down the source of the issue with this ‘test’.
Thanks for that Eric. Next time I hear it, I’ll pop the hood and start pulling plugs at the dizzy. Again, great video by the way!
As a follow up, was taking her out today, and didn’t hear the knock again, but noticed the oil fluctuation between 14-16 psi at idle. I can hear/feel the idle fluctuate, even though its only fluctuating 2psi. As I mentioned before, it has done this before, but thought that it might be a part of the total equation like Eric mentioned before. I’m in hopes that i don’t have clearances issues, because I suspect that can spell the end for the crank. I also use a little oil between changes. I’d say about a full quart, but nothing crazy.
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