getting a knocking/tapping at idle after enigne warms up - Team Camaro Tech
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post #1 of 11 (permalink) Old Feb 12th, 07, 09:42 PM Thread Starter
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getting a knocking/tapping at idle after enigne warms up

I just set the timing on my new (rebuilt) 454. I ran it about 15 mins at idle, but then a slight nocking near/under the valve covers started (hard to tell exactly where)....its not very loud or metal-to-metal clang (as other posts describe). When I gave it a little gas it went away, but then once the RPMS dropped it came back again. I let the engine cool and started it up again, took about 15 mins for the knocking to start again. The engine is a stock 454 and was just rebuilt (professionally) and has new edelbrock fuel pump (and push rod), water pump, intake and carb. Also just put in new flywheel (with new ARP bolts) and havent installed dust cover to bellhousing yet. Doesn't sound like what others have posted about what rod knock sounds like. It sounds more like a tapping. I would check about whether it was hitting the valve covers, but it only happens after the motor warms up. Nothing seems to be loose or vibrating. I checked belts, power steering pump... Maybe this is an impossible question to answer, but I was wondering if anyone knows what might be happening.
Thanks, Mike
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post #2 of 11 (permalink) Old Feb 12th, 07, 10:27 PM
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Re: getting a knocking/tapping at idle after enigne warms up

Since the flywheel was changed, I'd look for something inside the bellhousing,..perhaps a foreign object or the throw-out bearing is making some racket.
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post #3 of 11 (permalink) Old Feb 13th, 07, 05:04 AM
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Re: getting a knocking/tapping at idle after enigne warms up

It reads like when the oil heats up and becomes thinner, a lifter is not staying pumped up, has too much clearance and bleeds down. Or maybe the idle is too low. Listen carefully to find/locate the noise. Most important step. Crawl underneath to listen for the flywheel noise, it will be louder there than listening over the fender.

One way to find out, heat the engine up, listen for the noise, try to localize it to a cylinder about the valve cover using either a stethescope or screwdriver, remove the valve cover, and turn the engine over to bring the suspect cylinder up to compression, and check the pushrods for being able to spin by two fingers and NO clearance or excessive play.

If the suspect cylinder appears to be good, check the other three cylinders by the same method. If you find a loose pushrod, then a lifter swapout is the next order of business. as long as you have good oil pressure, lifters should not be noisy, nor should the rest of the engine, for that matter.

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post #4 of 11 (permalink) Old Feb 13th, 07, 12:38 PM
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Re: getting a knocking/tapping at idle after enigne warms up

Like Everett...
Get a mechanics stethescope..it is like a Doctors but has a long rod.
Listening on tappet covers one can find farely close if not the actual rocker tapping, or any tapping on the covers.
Inspection of the inside of the tappet covers with a magnifing glass will show any interference marks.
Messy, if u dont have cutout tappet covers, a stethoscope to each of the rocker studs will locate a rocker or lifter.
Elimate all the easy stuff...I did have an ebgine yrs ago that tapped like this.
In the end we stripped it down and found a cracked piston...we suspect someone must have dropped the box or something like that.

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post #5 of 11 (permalink) Old Feb 13th, 07, 04:28 PM
 
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Re: getting a knocking/tapping at idle after enigne warms up

i had this same problem after doing a head job on a 454...the machine shop set the spring pressure up heally high on the heads and the lifters were giving up under the pressure when the engine got hot...i put hard seat crower lifters in it and the noise all but went away...the mechine shop guy said if i wanted to run that cam with those heads and big valves, i`d have to deal with it...its almost unnoticable, so thats what i did is just live with it...my thing is that theres no chance of spring bind or valve float with it set up this way...
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post #6 of 11 (permalink) Old Feb 13th, 07, 09:01 PM
 
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Re: getting a knocking/tapping at idle after enigne warms up

Same thing just happened to me in the shop with one of our 454 1 tons. New factory motor, I guess I didn't pre-lube quite long enough, got a stight valve train "tic" after running for about 10 min. When I shut it down for a while it went away after I re started the motor, then came back after 5 min. or so, but if finally went away after a half hour or so and has been fine. "it has about 700 miles on it now" Dont know if it was the same problem but just thought I should let you know.
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post #7 of 11 (permalink) Old Feb 13th, 07, 09:09 PM
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Re: getting a knocking/tapping at idle after enigne warms up

Everett's sounds right...

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post #8 of 11 (permalink) Old Feb 13th, 07, 09:19 PM Thread Starter
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Re: getting a knocking/tapping at idle after enigne warms up

Tim, what you describe sounds kinda like what I have happening. Hopefully mine might go away also. I spoke with the rep at the place I got the engine and he suggested to remove the valve covers and check the pushrods for slack. He figured if any were loose, then about a 1/4 turn tighter would do it. I think I am going to first, as was suggested here, try and isolate better where the noise is coming from (inlcuding from underneath). If it is from the valves, I'll try and home in on the cylinder. Then, I'll pull the valve cover and inspect the inside for any marks. I'll then check for any slop in the pushrod. Does that sound like a good plan?
Mike
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post #9 of 11 (permalink) Old Feb 13th, 07, 09:23 PM
 
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Re: getting a knocking/tapping at idle after enigne warms up

on the money...sounds like if you follow everetts get-up, you`ll be right on point...
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post #10 of 11 (permalink) Old Feb 13th, 07, 10:47 PM
 
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Re: getting a knocking/tapping at idle after enigne warms up

If it is the same problem, it should be gone once you run it for 30 min. or so. I just pre-lubed my 502 with the rockers off and it took a long time to get oil up to two of the pushrods. When I did the 454 motor at work I was lazy and did not remove the valve covers,"and didn't pre-lube as long" so I am sure one or more rocker arms may have been a bit dry. Chevy may pre lube the new motors or test run them (?) but going by the build date the 454 sat in a wherehouse for almost 2 years. Make sure to let us know what you find out..........Tim
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post #11 of 11 (permalink) Old Feb 14th, 07, 11:44 AM Thread Starter
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Re: getting a knocking/tapping at idle after enigne warms up

thanks Tim. I am hoping that is all it is. My engine sat for about two years also, so maybe it is just dry under there. I am going to take a closer look this weekend and I'll post about what I find out.
Mike
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