Just another knock thread...w/video

[GoldGTP]

Hello all!

First off, the knowledge in these forums is priceless! A plethora of info around here!

Well, to get directly on it, I believe this 3800 SC motor has a rod knocking.

My story -

Recently purchased this '03 GTP from a used car dealership less than 1k miles ago.

The car has 2 previous owners, 100k miles on it, and was $4900. Seemed like a good deal, so I slapped down the greenbacks...

I immediately did a fluid change. The oil looked rough, so I replaced the oil with Mobile 1 10w30, and a k&n oil filter.

The CEL came on with-in 300 miles of driving the car...I forget the number it threw, but turned out to be a bad thermostat...Replaced that with fluids as well.

I noticed a bad tensioner bearing on the acc belt, so I replaced both belts, both tensioner pullies, and the SC idler pulley...

I've also replaced the radiator cap and air filter fwiw...

I was getting around to servicing the plugs, and noticed the motor resonating a tap tap tap sound from the passenger side of the engine.

What is strange though is when I stand over the motor I don't hear it as much as when I stand about 4ft away from it.

I have been reading about "piston slap", but I might be kidding myself into believing it's that..

I have also read somewhere something about the harmonic balancer going bad making things wobble around down there.

The knocking seems to vary with RPMs. If I just flick on the throttle cable, I hear the knock fade out then resonate back...

With it idling, the tap seems to have a pattern to it - tap tap tap ----- smooth ---- tap tap tap ---- ect ---

I'm also thinking the motor mounts are shot...The motor seems to twitch around in the engine bay at idle. I haven't had much luck with solid motor mounts, so those I'll pass on...
Are there any nice sets the gurus can recommend?

I've also purchased a tranny filter and seal (Auto)... Any advice on performing this service?
Looks like Dexron VI is the way to go, correct?

Should I pull the plugs and inspect each one?

I don't mind replacing the block and pistons, are there any vendors to recommend on a remaned short block? Could I take a N/A block/pistons and swap it in? (Still new to GPs and blowers)

I plan on keeping it stock with regular maintenance and 91 octane.

Here are a few vids of the motor and the knock sound -

YouTube - CIMG3926.AVI

YouTube - CIMG3928.AVI

Here is another video of the motor "missing" at a high rev (not sure if this is normal) -

YouTube - CIMG3927.AVI

Glad to have found these forums, looks like a good place...

Thanks much for any thoughts/replys/advice!!

[kfish]

The missing at high rpm is you bouncing it off the rev limiter.

Did you try taking both belts off and running the motor for to see if the noise is still there? It doesnt sound like a rod knock to me.

[RegorHtims]

What Kfish said

[Scottydoggs]

3 rd vid you are hitting the rev limiter, keeps the car from over reving in park, and for-bidding neutral drops.

hard to tell what the ticking is, could be a exhaust leak or a s/c coupler. lets hope its not a rod knock.

[01gpgt01]

My cars been making the same noise for 5 years. My neighbors Buick regal does the same. Heres what mine sounds like 2001 Grand prix GT - Car Videos on StreetFire . I gave up and figured if it was a rod I would have seen it by now lol. This video is maybe 4 years old

[GoldGTP]

Thanks for the quick replys!

The missing at high rpm is you bouncing it off the rev limiter.

Did you try taking both belts off and running the motor for to see if the noise is still there? It doesnt sound like a rod knock to me.

I was wondering if there was a limiter doing that, thanks.

I have not tried taking off the belts yet, was thinking about trying that out with the S/C belt, but I wasn't aware you could test the acc side like that...

I did get under the car with a mech stethoscope and I can't hear the tap through the oil pan, but I can hear it when I touch the scope to the block...

Again, thanks for the quick replys and keep the thoughts flowing!

[99prixgt]

these motors tend to be on the noisy side. Pretty sure both mine make the same noises.

[Scottydoggs]

put the mech stethoscope on the sc snout, and see if you can hear it loud and clear there, if not start looking for black carbon build up around all the exhaust manifolds and down the pipe to the cat and so on.

sc coupler is less than a 50 dollar fix, YouTube - Replacing a worn out supercharger coupler on 3.8 GM engines

exhaust leaks are lets face it, more work.....

[99prixgt]

when it sounds like this

YouTube - GTP With Blown Motor

you have a problem

[SilvaMan61]

i just want to say this is how all trouble shooting threads should start off. thanks for being so informative.

i couldnt watch the videos since im working but i can say your motor mount may be alright, these engines like to dance around alot.

[GoldGTP]

Very much appreciated on the replys...

So the lower end tapping at ~55 seconds on the 1st video is a "normal" sound?

Any advice is hungrily eaten up on this side.

Again, thanks for the fast replys.

[Scottydoggs]

does any of the tapping go away after it warms up?

my sc makes one hell of a racket when its cold and once warm its all smooth, like its been said before these are noisy engines.

[torq455]

I have 72,000 miles and mine is smooth and quiet.

[GoldGTP]

does any of the tapping go away after it warms up?

my sc makes one hell of a racket when its cold and once warm its all smooth, like its been said before these are noisy engines.

It seems to be the opposite, and that is what has me nervous...

Last night I turned it over and it was about 35 degrees here in Sac, and it sounded smooth for about 30 seconds then the tapping ensued...

It seems to have started after I changed my belts and oil, because I dont remember this sound when I went to test drive the car...I took nearly 5 hours of checking this, listening to that before I laid down the cash...

A few more questions -

It seems like my new belts are "loose" or my tensioner arm is weakening...I can push on either belt and have the tensioner arm move quite a-bit...
Is this normal?

Also, a buddy at work claims I should just use some plain 'ole 10w30 oil instead of synthetic...He says regular oil has more "cusion" than the synthetic stuff...
Would it be a big deal if I ran some regular 10w30?

Thanks again fellas, much appreciated...

[offroadfury6]

LMAO man the first video sounds COMPLETELY normal.....

second video alittle effy but I'mma say normal.....

Drive it dude, sounds fine to me...can you hear the "tick" inside the car???

the first video, my car sounds the same since I bought it new in 2006...now with 91K
Wash it and take it for a cruise...

your tenioner is suppost to move, normal...duno how "bad" it's moving but yes they jump alil...
I really dont see changing from syn oil to normal oil making a differnce...I dunno what all this new crap out is about with synthetic and high mileage stuff but I usually run Valvoline or Castrol...non-syn...

[OrangeL67]

I replied on your youtube. I'd bet a left nut it's your flex plate. Anyone who has had a cracked flex plate will tell you they quiet down once you get on the gas. Plus the sound seems to be coming from under your engine. Probably warped or cracked.

Only thing that sucks is, it could last 10 years like that, or it could break in half tomorrow. You never know.

Big rims, 35 - 40 roll punches, and fat people will all help break that thing sooner or later (if it is the flex plate)

[Scottydoggs]

I replied on your youtube. I'd bet a left nut it's your flex plate. Anyone who has had a cracked flex plate will tell you they quiet down once you get on the gas. Plus the sound seems to be coming from under your engine. Probably warped or cracked.

Only thing that sucks is, it could last 10 years like that, or it could break in half tomorrow. You never know.

Big rims, 35 - 40 roll punches, and fat people will all help break that thing sooner or later (if it is the flex plate)

and thats easy enough to check out.

and fat people lol

[GoldGTP]

I replied on your youtube. I'd bet a left nut it's your flex plate. Anyone who has had a cracked flex plate will tell you they quiet down once you get on the gas. Plus the sound seems to be coming from under your engine. Probably warped or cracked.

Only thing that sucks is, it could last 10 years like that, or it could break in half tomorrow. You never know.

Big rims, 35 - 40 roll punches, and fat people will all help break that thing sooner or later (if it is the flex plate)

Thanks for the response man, much appreciated.

About the rims...Yea, I don't really like them, wish I could find a nice set of stock chromies...they were on the car when I bought it about a month ago...

Any recommendations on an oem flexplate?

Would it be easier to remove the motor or the tranny when it comes time to replace it?

Thanks again for all the replys.

[OH4CompG]

Removing the motor is easier in my opinion. I helped a friend do a torque converter by pulling the motor. We had it driven into the garage, and driven out in under 8 hours with beer breaks and a lunch break

[GoldGTP]

Sounds like a plan...

Just curious, is there anywhere online that sells a downloadable FSM?