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Engine noise (with audio recording)


Guest tzartler

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Guest tzartler

Hello everyone.

I have read and searched the forum for 3 days trying to narrow this engine noise down, but have had no luck so far.

First off, this is not a Reatta (please don't flame me). It is the same engine and tranny though, but used in a Vixen21. I am posting here because I saw Padgett, a Vixen owner as well contributes a lot here, and the amount of knowledge I see in this Reatta forum is the largest I have seen on the internet in all my searching to diagnose the engine noise of the GM 3800 LN3 vin C engine.

Here is a recording of the noise:

http://woodcreststudio.com/temp/Engine%20Noise.mp3

The noise is sometimes (rarely) at idle.

The noise occurs if you tap the throttle and allow the engine to return to idle. When it returns to idle, the noise disappears.

This noise appears only to be localized to a certain rpm band, but not totally sure about that.

With my hand on the intake, I believe I can feel the moment the rattle disappears.

I removed the serpentine belt to rule out all accessories and the noise still remains.

I have examined the harmonic balancer and the rubber looks really good.

I have physically checked the harmonic balancer to be loose and it is tight, pulling away from the engine, pushing in, and torquing it by hand clockwise to counter clockwise.

During listens, it appears louder when I listen to the head area of the engine, on the side which I believe when in a Reatta would be facing forward.

The entire exhaust except the headers is new. Cat-back has been replaced.

All heat shields on the headers, crossover pipe and under are all firmly secure.

The transmission is about 3-4 years old.

The engine has about 120k miles on it and runs really strong.

I hope it is all right to ask this here. You all seem so helpful and willing of a community.

With sincere regards,

Tom

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Guest tzartler

I used a stethoscope moments ago and it is loudest where the transmission bolts to the engine. I can't right now listen to the timing chain cover because I have no one to rev the engine for me. When I say loud, it is 20x louder than any other spot I could probe, listen and rev. ( top and front of the engine on to the bell housing)

Thanks a lot for the replies.

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Guest Recian

if its loudest where tranny bolts to engine could be flex plate but that sounds alot like top end head noise. It could be traveling down the back of the engine. Use the throttle cables by the t-body to change rpm and narrow it to intake/head area, bellhousing or timing chain area. Try chnging your oil and use 4 qts 5w30 and a quart of marvel's mystery oil (best stuff ever. comes in a red bottle) and run it hard for a few miles and see if it changes any, if youre talking about the intermittent rattle like ticking sound in the clip anyway. If youre feeling it in the intake and can hear it more by the valve cover that would make sense. Ive had alot of v6 and v8s with pushrod system that sit for a long time and will get sticking valves or issues with the valvetrain that sound just like you showed and marvel clears them up almost instantly

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Guest crazytrain2

Tom,

Did you find out what was making that noise? If not you might want to check the tranny modulator (Assuming you have a TH440 trans). Make sure you have good connections and no cracks in the rubber vacuum lines - If you pull the line going into mod. and oil dribbles out then the mod. is shot. Did you notice any change in shift pattern ?

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Guest tzartler

It is a 440-t4 trans (according to the service manual that came with this)

I have not found the issue yet.

Other things I have checked:

-- I checked vacuum line at the modulator and it is sucking at 18in Hg. there is no change in noise level if it is or not connected. I do feel something engage once I plug it back onto the modulator. No oil or anything came out of the modulator. This is a rebuilt transmission, if that is of any concern.

-- I took off the trans cover by the starter and inspected the flex plate and flex plate to torque convertor bolts. The bolts were tight and there were no visible signs of damage or cracks on the flex plate.

-- I listened to the timing cover and the noise seems apparent there as well. Hard to tell if it is a loud as it is on the back of the engine. The engine was idling in a way where the sound was present, but not as loud as it is when I feather the throttle.

Thanks for all the help everyone.

I am thinking it may be the timing chain?? Out of coincidence, the cam mag just took a dump... I am thinking this is a sign to do the timing chain and tensioner. There are 120k miles on the engine.

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Guest crazytrain2

Tom,

Sorry but I have to ask, have you checked the fluid level in your tranny? That sure sounds like a noisy trans. to me, an easy check b4 going the timing chain route.

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Guest tzartler
I have heard of flex plates cracking at the bolt circle at the crankshaft.

I was able to see that and there are no signs of cracking.

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Guest tzartler
Tom,

Sorry but I have to ask, have you checked the fluid level in your tranny? That sure sounds like a noisy trans. to me, an easy check b4 going the timing chain route.

The fluid is at the right level. That was one of the first things I checked when I first hear the noise. Thanks for asking. You never know what people do and don't check so no sorry needed at all.

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Guest tzartler

Ok, everyone... I think I found the cause of the noise. I was able to get a friend to come over and initiate the noise by revving the engine while I was outside probing around the engine. The noise is coming from behind the water pump on the left side as you face that side of the engine. Looking at the exploded engine view in the timing cover section of my engine service manual, it looks like that is where the timing chain tensioner/damper is. So it appears i do indeed need a new timing chain.

My friend was funny. He listened around too as I initiated the sound and he thought it was the valve train as well. I had him listen to the same spot where I found it to be the loudest and he agreed that it was the timing chain. Get this: He told me "I would drive around until it broke." LOL! I replied, oh, sure, I am going on a 3000 mile trip in a few weeks and I want that to happen when I am on the road! I'll bring a spare and do it curb-side LOL.

So, here is my question: I did a search for the parts list for the improved timing set and couldn't find it in any forum posts in the Reatta section of the forum. Does such a list exist that has the damper, chain, sprockets?

Also, I should replace the sprockets as well?

Lastly, I am really gracious with the help I received from everyone here. If there is anything I could help you with, please PM me. I run an audio production studio and I also am an electrician. Both trades for about 20 years.

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Just that I remember a running change between the 88 engine you have (3800 cast in top of plenium) and the 89-90 (smooth plenium top) primarily concerning improvements in the chain tensioner. Looked in the TSBs for 88 and 89 and did not find it.

If going in you need to replace the chain, sprockets, and tensioners so ask for the later parts. I do not know if a new sprocket will include the cam interrupter (magnet).

The problem is that if it goes for long enough it may wear a hole in the side of the timing cover. I have never heard of a 3800 jumping time though that is possible also.

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Guest Mike_s

The audio clip reminds me of when my 88 had a odd engine sound best described as marbles ratteling around in a tin can, which I also had a difficult time locating. It was the timing chain tensioner.

There were 2 possible tensioners that I know of, one is for a counter bored mounting hole the other not. I don't know if there's a way (vin?) to tell untill you remove the failed unit.

I also replaced the chain, sprocket and oil pump since I had puchased the parts on line before hand, that said, the existing sprocket and pump did not look bad and probably could have gone on for a long time. YMMY

Edited by Mike_s
changed gears to sprockets (see edit history)
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Guest tzartler

All is good. :) Today the timing chain was pulled. The tensioner/damper was broken so the chain was flapping around causing the crazy ruckus.

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