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Old 06-03-2005, 12:04 PM
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Knocking Sound above 1100 RPMs..

Alright,I am coming to you for help.For the last few weeks I have been getting a sound from my car. It is a sound that resembles a busted flex-plate.I pulled the tranny two weeks ago and inspected the plate.It is an SFI approved plate with no cracks,no broken ring welds and it is true and flat.Also no ring gears are damaged.I reinstalled the trans,while I was at it,I installed a 2500 stall.That has really woke things up.While I had the plate off,I checked my crank end play.It is fine
Oil pressure is steady at 40 psi when cruising at 2500 RPM's,and when ideling at a light in drive it is around 15 psi.I t never fluctates.The engine makes no sound until it has fully warmed up.At around 180* it will start to clatter.There is nothing making contact with flexplate,or the fan or pulleys.
I went to a buddies house who races Chevys since this thing has me puzzled.He suggested that maybe it was the fuel pump as it sounded like it was coming from the front.I am close to deaf in one ear and it throws off my hearing.So I pull the fuel pump off and swap it out,plus a new pump rod.Did not correct the problem.I also kept steady fuel rate before the swap.
Last weekend,I rechecked all the settings on my valves,it has a hydraulic cam and lifters and they were dead on still.I have had an exhaust leak taken care of also,but that was not the problem.I did find that my baffle had dropped a little on one of my valve covers,but there were no rub marks where contact was being made.
My timing does not fluctate so I have ruled out the timing chain.I removed the belt from my H2O pump and alternator to rule that out,it is not there.Tomorrow I am going t get it hot and pull plug wires one at a time to rule out wrist pin,or at least hope to rule out wrist pin.
There is no effect on performance here guys,None whatsoever.It will make the sound in park so it is in the engine/tranny somewhere.I can not pinpoint it with the stetoscope,but it does appear to be from the rear of the engine,but like I said,I can not hear well anyway.
Here is how it goes.Once warmed,around 180* and above 1200 RPM's.Only under a load,but when you blip it,it goes away,but comes right back.Sounds like a busted flex plate but it is not..I also plan on checking the starter bendix, in case the spring is wore and allowing the gear to slide out and make contact.I have seen weirder things cause a racket.
Any suggestions will be investigated.Thanx guys.

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Old 06-03-2005, 12:10 PM
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How old are the lifters? I just had a TBI 350 doing almost exactly the same thing, and it was a gummed up/wore out lifter. The setting was right on, but when the oil was hot, it wouldn't pump up. blip the throttle, it would go away fo a second and come right back. HTH

Freak
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Old 06-03-2005, 12:10 PM
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how loud is it? From what you're describing it sounds kinda like a rod...
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Old 06-03-2005, 12:15 PM
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The lifters are two years old.New when I rebuilt the engine.I am on the same train of thought as Killer,just hoping it is not though.
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Old 06-03-2005, 12:30 PM
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yep, as soon as you said "load" i kinda had a red flag go up. How about checking the oil filter for abnormalities?

K
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Old 06-03-2005, 12:39 PM
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Changing oil tomorrow anyway,will cut open.You know,I forgot to mention,that after I did all of the things,each time I did something,it seemed as though the sound got less noticeable.Or maybe my ear is just working less and less on a daily basis.I may need to go get that checked out to,huh?
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Old 06-03-2005, 01:08 PM
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I had a knock like that in my '62 Impala, I was convinced it was rod bearing but I was going to build a new motor so I figured I'd run that one until it finally went. My water pump started leaking so I got a new one and put it on. The belt got twisted putting it back on so I grabbed the bottom pulley to rotate it and get it rolled back over, the pulley moved about an 1/8th of an inch before anything else did. I rocked it back and forth and heard a quiet version of my "rod knock". The holes in the pulley were egg shaped and the bolts worn about half way through. I replaced the pulley and bolts and no more knock. It's worth checking. Good luck.
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Old 06-03-2005, 02:33 PM
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Hippie,will check on that also.I turned the thing over with the crank bolt and that was tight,but the pulley mounts seperatley from it.I did run the engine with the belt off,but with inertia holding the pulley with no drag may be a good call too.I will stay fairly busy tomorrow but will be checking on alot of these ideas and surely more. It is driving me crazy.
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Old 06-03-2005, 02:45 PM
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If you already experienced an exhaust leak, check for more... this sort of problem had me stumped for a couple months on an old engine, turned out to be an exhaust leak. especially under load it will make noise, then will quiet up a bit on deceleration.

good luck

the blonde weasel
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Old 06-03-2005, 02:48 PM
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I have searched for all the exhaust leaks and got them controlled.It is real good to know people in the exhaust buisness real well.I installed new collector gaskets when I had the tranny out.Of course I had to run it uncorked before I reinstalled the exhaust.SWEET sounds of a cam and open headers .I am not ruling that out as I will be under it again anyway.It has a metallic sound to it.


The best way I can describe the sound is if you had a bolt sticking out and it was catching a raised surface.On every revolution it would hit the raised surface and that is the sound,it is constant with the RPM's naturally.
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Old 06-03-2005, 06:15 PM
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If you have a knock the first thing you should do is pull spark plug wires one at a time while the engine is running AND knocking. If the knock is coming from the bottom end it will go away or quiet down when you pull the wire to the corresponding cylinder. Very simple yet effective.
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Old 06-03-2005, 08:03 PM
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is it a stroker?
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Old 06-04-2005, 06:52 AM
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No 56.Just a typical .030 350. I have three ball games this afternoon,after that I am gonna work with it.Unless I go get that other car.Then I will work on finding that sound tonight.I have been thinking wristpin since it started,just want things to check first.I would love to come on here later and tell everyone how "stupid" I was because it was something easy and cheap.
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Old 06-04-2005, 07:42 AM
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rod knock.

tom
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Old 06-04-2005, 08:42 AM
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Knock

Doc here,

My first vote...would be as said before...a damaged or loose harmonic balancer (the rubber worn out) Had it happen on a 350 Olds before, was gawd awful noisy on acceration....knock..knock...knock...If you backed off it, it went away...acted and sounded like a rod...for sure..

Never would have found it if I wasn't turning the engine over by hand from the belt...trying to simulate the noise and it turned about an 1/8 turn, without moving the crank... and went "Knock" real loud!

I then grabbed the belt and rocked it back and forth...it went knock...knock...knock....Replaced the balancer and it was all good!

BTW..If it is...I'm told these can do major damage when they come apart!! so you want to replace it right away..

My second Vote (and I just know you don't want to hear this...) Is for a bad insert...time for a lower end.

Have you tried some "acoustical sound checks" using a stephoscope..or wooden dowel OR better yet 1/2 piece of PVC water pipe , carefully while running it while it's knocking? to pin point the area? It will make the noise..and as you get closer.. it will get louder until you get right on or very close to the offending part...that should include/eliminate things.

Hope it helps...

Doc
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