loud knocking noise

[terrydmorgan]

I have an LS1 from an '03 Vette (low miles) and a 4L60e transmission from an '06 chevy pickup that has developed a loud knocking noise. It happens at low idle, but goes away under 2 different conditions: 1) when engine revs, and smooths out; or 2) with the car is in gear and under load - like sitting in gear with the brake on. It sounds external, but i changed oil and pulled filter to make sure nothing was coming apart inside the engine - everything was OK. I also ran the engine with the serpentine belt removed to make sure it wasn't an accessory or an idler - everything OK here too.

I think I have isolated the noise to the torque converter/flex plate. I can reach through the access port and rotate the converter/flex plate back and forth about 1 or 2 degrees, but it does not move fore and aft and the torque converter seems to be firmly attached to the flex plate. So, it seems as if the flex plate is slightly loose and allowing a small rotational movement relative to the crankshaft, which I assume is a bad thing. The only reason I can think that this would happen is that the bolts holding the flex plate to the crank have loosened, or possibly are too long. Seems like the fix involves pulling the engine and checking/changing out the flex plate to crank bolts. Of course, this is going to be a PITA, especially if that's not the problem.

So, before I go to all that trouble, I'd appreciate any other theories, especially any that involve not pulling the engine.

The engine is running well, but we've only operated it for a very short time, probably well under 1 hour since putting it in the '69 Camaro.

[terrydmorgan]

No responses ..... I take that to mean that I should pull the engine. Dang.

[robertjra]

I have a 2006 Chevy and mine did the same thing but after it gets hot no more noise

[terrydmorgan]

Thanks for the info. My knocking is quite loud and does not abate even after the engine gets to operating temperature. It started off as a relatively minor issue, but has become progressively louder. I'm planning on pulling it apart this weekend.

[Moter]

Very common to crack the flexplate around the mounting holes to the crank. Try and upgrade to Sfi approved part. Less likely to crack. Hth

[robertjra]

Thanks for the info. My knocking is quite loud and does not abate even after the engine gets to operating temperature. It started off as a relatively minor issue, but has become progressively louder. I'm planning on pulling it apart this weekend.

good luck with the pull out keep us posted!!!!!

[terrydmorgan]

Pulled the transmission today. the bolts between the torque converter and the flex plate were properly torqued and there was no movement between these two parts. The bolts between the crankshaft and the flexplate were also properly torqued, but the flexplate was not tightly connected to the crankshaft - a small amount of movement was possible, and I believe this is what was causing my loud knocking noise. Now, why was the flexplate loose if the ARP bolts were properly torqued? I see two possibilities: 1) wrong bolts; or 2) wrong flexplate. It seems that the ARP bolts may be too long or have too long of a shoulder, either of which would allow me to torque the bolts and engage the crankshaft, but not adequately "pinch" the flexplate between the bolt head and the face of the crankshaft. Alternatively, perhaps I have the wrong flexplate, and it is too thin in the region where the crankshaft bolts pass through. The flexplate I'm currently using has a sticker with the number P1398 on it, and has the correct bolt pattern and engages the starter properly. Any other ideas?

I'm planning on buying and installing new flexplate, and will probably go with an aftermarket unit, perhaps TCI. Any thoughts, theories or recommendations? I don't want to spend another weekend doing this again.

[Moter]

Hmmm....well at least you have narrowed the noise down to a certain area. And at least its not internal.
How long has this setup been together? To me it sounds like the bolts are too long. Is this is supposed to have a spacer under the bolts?

[terrydmorgan]

The car has only been operated for about 1 hours so far. I agree it seems like the bolts are the problem. I'm thinking that they mistakenly gave me bolts for a flywheel, rather than a flex plate. They're either too long or the shoulder is too long, which would make either the bolts bottom-out, or the shoulder contact the crankshaft before the flex plate is tight.

[Moter]

Thats it. The bolts are wrong for the application. If they are for a flywheel they will be longer and will never tighten in a blind hole.

[GeoffP]

Yep, I agree with that too. Flexplate bolts are shorter than flywheel bolts.

[terrydmorgan]

The new TCI flexplate and ARP bolts arrived, and yes, it turns out I had the wrong bolts. There's no shoulder on these new bolts, so the new bolts pulled the flexplate tight against the crankshaft. Now, we just have to put it all back together again - no problem.

[terrydmorgan]

Put it all back together. Started it, and no knocking - sounds good! Put it in gear - nothing happens. No reverse, no drive. Not sure what's going on. I used a TCI flexplate that JEGS suggested (890-399753) - no adapter necessary. I'm assuming it is correct, but it acts like the torque converter is pulled out of the transmission pump and just freewheeling. I have an LS1 from an '03 Vette and a 4L60e transmission from an '06 chevy pickup. Anyone know if this is the correct flexplate?

[Moter]

When you were reinstalling the trans,did you have to pull the converter up a little to the flexplate? Or was it a tight fit? Did you get all electrical conections made to the trans? One quick way...kinda messy..to see if pump is turning, remove one trans cooler line at the cooler...and start the car for a couple seconds. It is full of trans fluid?

[terrydmorgan]

There was a small space between the flexplate and the torque converter. Good idea on the electrical connections, I'll check and make sure everything got hooked up, and double check fluid level ;).