Running Rough - Rattle Above Idle - Team Camaro Tech
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post #1 of 19 (permalink) Old Mar 8th, 10, 10:07 AM Thread Starter
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Question Running Rough - Rattle Above Idle

Late last fall my 69 with a HEI 350sb started running rough. The weather here has been beautiful so I'm back to trying to figure out what the issue is. I have a rough idle, like it is missing on a cylinder. Then above idle there is a very loud rattling or clanking sound coming from the engine bay and a lot of vibration for sure. No oil smoke or antifreeze in exhaust. This is all with the car in park.

I checked the resistance on the 2 year old wires and thought I found a dead one. Replaced it and no difference.

I'm not sure where to look next. I don't think it's a timing issue with detonation. I haven't adjusted timing in a few years and never had this rough running issue before. Maybe bad gas? It's been sitting all winter without Stabil. I use 93 but may have put in 89 by mistake - but I don't think so.

I've had a consistent problem with the valve train rubbing the valve covers, but it's never effected the performance, just made a ticking sound. I loosened a cover and the rattling sound is there there above idle.

I'm thinking it's a spark problem, maybe bad cap or rotor. I pulled and they look OK - no cracks. But that does not explain the rattling above idle that was not there before.

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post #2 of 19 (permalink) Old Mar 9th, 10, 12:46 AM
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Re: Running Rough - Rattle Above Idle

Try a new set of plugs, first take the car out and drive it normally, give it a couple of good runs, then shut it down without idling long if you can help it, pull them and read them.
You may need to go a step or two hotter than what you are currently running.

What are the specs on your timing, initial, total?
Vacuum advance?

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post #3 of 19 (permalink) Old Mar 9th, 10, 06:35 AM Thread Starter
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Re: Running Rough - Rattle Above Idle

I pulled the plugs when I first experienced the rough running, and they looked OK. Brown. But I am not an expert. I'll try your method and do a good analysis with some loupes. Do you know of a good link or thread that explains reading plugs?

I have my timing specs at the house. I will post.

Thanks!
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post #4 of 19 (permalink) Old Mar 9th, 10, 07:36 AM
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Re: Running Rough - Rattle Above Idle

Rattling or a steady tap?Tapping my be something in the valvetrain.Check the valve springs,pushrods ect.You can check the springs by pulling the valve covers and pushing down on the valve side of each rocker arm.After you check the rockers on all the valves that are closed,rotate the engine 1 full turn and check the remaining valves.A broken spring will be very weak,but will still function at idle.With stock or stock size springs you may be able to push all the springs a little bit,but a broken spring will just press down practially with your fingertips.Broken pushrods or lifters usually clack when the engine is idling,but you might not be able to hear it until you get the engine speed up.Bottom end problems like broken piston skirts and spun rod bearings make lots of noise but dont typically make the engine run very rough.

Rattling from detonation could be caused by a vacum leak,particuarly one in a vacum port located directly over one intake runner such as the rear vacum port on many intake manifold located directly on the top of one of the intske runners.You should never use the port for a PCV valve as that cylinder will go lean.

Good luck.
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post #5 of 19 (permalink) Old Mar 9th, 10, 08:55 AM Thread Starter
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Re: Running Rough - Rattle Above Idle

I'd call it more of a rattling than a tapping. It sounds like a metallic gargle, or what I hear detonation sounds like. What I don't understand, I guess, is how I'd have detonation now, when the timing has not been changed in years?
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post #6 of 19 (permalink) Old Mar 9th, 10, 10:03 AM
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Re: Running Rough - Rattle Above Idle

Try adjusting the valves. If you have one (or more) that needs tightened more than the others, it very well could be cam failure. I know of at least one vehicle that started out making a lifter noise. They readjusted the valves and it wasn't long before the noise was back.
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post #7 of 19 (permalink) Old Mar 9th, 10, 10:08 AM
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Re: Running Rough - Rattle Above Idle

Wow... I hope you don't mean that you haven't CHECKED the timing in years!

Parts wear, things loosen up, moisture and dirt..... you should check everything a couple times a year. The timing isn't going to stay where you set it indefinitely, even if you change the cap, rotor and plugs\wires once a year. I guess that also depends on how much it's driven.
The timing chain stretches, the distributor experiences wear, the cam wears, etc.
But from the sounds of it, you may have something mechanical internally that's wrong. Spun bearing, broken valve, dead lifter.... something like that.

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post #8 of 19 (permalink) Old Mar 9th, 10, 09:27 PM
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Re: Running Rough - Rattle Above Idle

Jonny - I owned a Pontiac once that exhibited the same symptoms you're describing. It had a cracked flexplate. It wouldn't cost ya anything to pull the inspection cover and take a look-see....

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post #9 of 19 (permalink) Old Mar 11th, 10, 12:12 PM Thread Starter
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Re: Running Rough - Rattle Above Idle

All sound like great ideas to take a looksie over the weekend. I'll get back with an update.

I've seen vacuum leaks on this engine before. Would that contribute to sudden detonation?
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post #10 of 19 (permalink) Old Mar 13th, 10, 06:40 PM Thread Starter
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Re: Running Rough - Rattle Above Idle

OK, so I had a couple hours to mess around today. I think I had a combination of a number of issues going on adding to the disturbing sounds and what I thought was rough running.

First issue was I think I did not have the engine up to temperature in a few months. Once I let it run for a while it seemed to run much better at idle. So at higher RPM I was still having a lot of rattling, etc. I thought it might be bad gas, but runs very good now.

One issue I continue to battle is a rocker arm rubbing on the valve cover. Fixed this. And checked out the valve train visually and it looked OK. Ran it with the cover off on what I thought was the problem side and all looked OK. So with this interference fixed I now hear another quick tapping sound we can focus in on.

I originally thought it was detonation due to the "rattling", but I think this was the combination of the valve cover and something else. Without the valve cover noise, it is definitely a tapping sounds that comes and goes, sometimes with load, sometimes without.

After running around and under the car, I think it's coming from around the flexplate. I'd guess it's possible interference between the flexplate and starter? It was too hot underneath to get too close to check it out. But I did take a look for cracks and the flexplate looks OK. Maybe the starter has drifted towards the plate? I replaced the starter maybe 2 years ago...and have a feeling it may have shifted.

The sound now is a very quick metallic "gargle", almost like dropping a 2x4 on concrete repeatedly very very fast. And it comes and goes every couple seconds. So this is my next item to search out.

What else could this be? The valve train sounds good under the covers with a makeshift stethoscope. Like a quiet sewing machine.
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post #11 of 19 (permalink) Old Mar 13th, 10, 06:56 PM
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Re: Running Rough - Rattle Above Idle

I wounder if that HEI distributor you put in before all of this, may have wiped the gear off the distributor...

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post #12 of 19 (permalink) Old Mar 13th, 10, 06:58 PM
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Re: Running Rough - Rattle Above Idle

Check the torque converter bolts. They can make an awful racket if they get loose. So can the dust cover.
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post #13 of 19 (permalink) Old Mar 14th, 10, 12:30 PM
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Re: Running Rough - Rattle Above Idle

That was going to be my recommendation as well.

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post #14 of 19 (permalink) Old Mar 14th, 10, 04:43 PM Thread Starter
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Re: Running Rough - Rattle Above Idle

Indeed, 2 of the 3 torque converter bolts were loose!! Very loose in fact. But still there. Problem solved! Runs and sounds like a champ! Thanks guys!!
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post #15 of 19 (permalink) Old Mar 14th, 10, 09:32 PM
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Re: Running Rough - Rattle Above Idle

Quote:
Originally Posted by The Beerboy View Post
Indeed, 2 of the 3 torque converter bolts were loose!! Very loose in fact. But still there. Problem solved! Runs and sounds like a champ! Thanks guys!!
Outstanding! Glad you see you got it fixed.

69 RS, Hugger orange/black, Deluxe interior, Sony AM/FM/XM/CD, PS & PB. 355, forged pistons, Eagle rods, balanced, Iron Eagles, 9.4:1 CR, .038 quench, XR270HR Cam, Z28 intake, FAST-EZ EFI 2.0, Thorley Tri-Ys, TCI 700R4, 2400 stall, 3.42 posi
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