Thrust..flex..convertor questions

[joe schmo]

How true should the flexplate be when turning?

I've been chasing a "knocking" noise right at the convertor area.

I do have an 1/8" clearance between the flex & convertor..using washers as shims.

I checked the end play on the crank with a dial indicator..it's at .008.

I hope that rules out the thrust bearing.

Drained the oil & saw no flakes in it..also cut open the oil filter..looks fine.

With the convertor disconnected..the noise is still there..but..it's much, much less audible. I mean you can hear a pretty loud rapping/knocking noise with it connected..not so with it unbolted from the flex.

You've actually got to get under the car there to really hear it.

Using a screwdriver..it's hard to locate it..the oil pan & block were checked this way.

I'm hoping beyond hope the flex is to blame..although I can't see any cracks in it..also "rapped" on it & the "ringing" seems uniform..therefore eliminating that as the culprit.

The noise is there right at startup..cold or not.

The flex..car running..does have a little walk in it..should it be this way at all?

 

[441120]

Your flex plate should run true and not need shims for the torque convertor.
I hate noises, good luck.

 

[joe schmo]

I should have mentioned that I had a thrust failure on a new motor after 500 miles.

I had to pull it & had it rebuilt again.

I suspected the convertor and shimmed it according to what I had learned here & from others.

I did read this from Lee Thompson recently..

The noise could very well be one of the crank counter weights hitting a main cap. This could happen if the crank is moving back and forth far enough.

This was in reference to Mad Turbo's thread.

The thing is..I've checked the end play with a dial indicator..it seems ok.

Based on the previous failure though..it all points towards the flex and/or convertor..correct?

I did not remove the flex yesterday..just looked at it closely & "dinged" it & it did have what seemed like a uniform ringing sound.

It's a JW flexplate..new.

All I know is that with the convertor disengaged..car running..the noise is almost gone..but there's still some.

I guess the weight of the convertor on the crank magnifies the noise big time.

Any help is greatly appreciated.

I simply cannot afford to take this motor out again because of a thrust failure.

 

[joe schmo]

This may be a silly question..but I'll ask it anyway.

Is it possible that piston slap resonates louder with the convertor attached?

I suspect my piston to wall clearance is a bit much..sounds like a deisel to me. Wisecos..from what I hear, are louder than some others.

I will attempt to find out exactly what it is..but..noises do resonate throughout a motor.

I did remove the serpetine belt yesterday as well to eliminate any accessory causing the rapping noise..ruled that out.

Just now..I watched the flex spin at idle & now it does seem to spin true..no descernable "wobble" at all.

If I have to..I will buy a different convertor..& maybe another flexplate..& swap em' out.

When I unhooked the convertor..I still heard something..but maybe that was just piston noise..maybe the convertor is to blame.

 

[joe schmo]

Well..my most recent builder just told me that the piston-to-wall clearance was .002.

Dave Weber actually built the motor & bored the block the first time.

I then had the thrust bearing problem & had a local guy rebuild it again.

The G.S.C.A. tells me that .004-.005 is the recommended clearances on these Wisecos.

My builder tells me .002 is good.

 

[441120]

0.002" pistons to wall clearance seems tight. If they're forged pistons that's real tight. Piston slap is usually cold and as the piston heats up the clearances tighten up. This is usually with forged pistons.

 

[joe schmo]

I agree..it sounds tight.

Maybe the old guy is going senile.

I'll worry about that later..the convertor noise comes first.

I called Chris today at CK Performance about their Pro Torque 12" convertor.

I'm leaning toward ordering it & seeing if that fixes it..I can't keep driving this car with that noise.

Thanks for responding 441120.

 

[VadersV6]

If you pull the washers out and move the converter back and forth, you have 1/8" converter thrust? If so, why would you try and eliminate all clearance and basically bottom the thing out with washers? You want that clearance because the converter is going to expand, and under load, its going to want move rearward, and it needs to be able to move. The flexplate is designed to do just that...FLEX. If you bottom out all the clearance with washers, the flexplate cant do its job. Plus washers arent exactly a high tolerance shim. Remove the washers and bolt the converter up direct, unless you have excessive clearance that you're trying to eliminate. 1/8" is fine. Going smaller than that, and you may trash your thrust bearing.
As for the P/W clearance, going with the recommended clearance isnt always necessary. .002 is on the tight side, but not so tight that I would worry, as long as you're running cool. You can go .001 with hypers cause they dont expand much and dont require thermal expansion to reach proper clearance. It all depends on the alloy and how much its designed to expand, and how hot your engine runs. If you're running at 190-200 degrees, yes, .002 is too tight for forged pistons. If you're running 160-170, you're fine. Alot of people will go big on the clearance with forged pistons, and then never reach the operating temps that the piston manufacturer had in mind when they recommended their clearances. Then you have piston slap...the piston rocks excessively and then the skirts crush more than they should, and you end up with slap. Ontop of that, you have so much clearance that you have a crapload of blowby and leakdown. The piston to wall clearance is determined by the alloy and the intended operating temps of the engine. With hypers you can run a tight clearance and run the engine at pretty much any temp. You dont have to even warm the motor up. If you have forged pistons and had alot of clearance machined, you need to always warm the motor completely up before going WOT. When the motor is cold, you have so much clearance that you will crush the skirts too much if you throw too much load at it. All it takes is 1 time and you'll permanently have slap and alot of blowby. Basically, if you run a 160 thermostat, go tight with forged pistons. If you run normal factory temps, go with the recommended clearance and always warm the motor up. With hypers you can pretty much do anything but detonate.

 

[joe schmo]

I have 1/8" clearance between the convertor & flexplate bolted up.

I had the convertor bolted up directly to the flex..& was told I needed an 1/8" gap inbetween the two..so I used the washers.

When I unbolted the convertor from the flexplate..I was able to slide it back a bit..I'm guessing that's what you were wondering..correct?

 

[VadersV6]

I have 1/8" clearance between the convertor & flexplate bolted up.

I had the convertor bolted up directly to the flex..& was told I needed an 1/8" gap inbetween the two..so I used the washers.

When I unbolted the convertor from the flexplate..I was able to slide it back a bit..I'm guessing that's what you were wondering..correct?

When he said an 1/8" gap, Im sure he meant that the converter should be able to move forward and rearward 1/8" with the converter unbolted....which is how it should be. You're asking for trouble by bottoming out the converter. I know there are a few people doing this with washers, but if the clearance is so excessive that you have to use washers, then something else is wrong. If you have 1/8" movement, thats how it should be, and just bolt the converter up directly to the flexplate.