piston slap / loose torque converter bolts

[siminsez01]

okay, what is the difference. my 97 xj is making the slap noise. When i'm under it i cant tell if the noise is coming from the bottom of the engine or the front of the transmission where the flexplate is.

i took the front tranny dustcover off and checked 2 of the 4 bolts on the flexplate. how do i get to the other 2 bolts? can i rotate the flexplate? does the engine have to be in neutral to do this? only asking bc i was trying like hell to turn it and it wouldn't budge!

also, how do you tell that these bolts are tight in that you cant see to the other side of the flexplate. just try to tighten them and if they dont tighten then they are tight?

i understand piston slap is something that an xj can enjoy for much of its life, loose flexplate bolts are common and cause the same noise. guess i just wanna make sure its one and not the other.

 

[8Mud]

I had one set of torque converter/flex plate bolts back out on me. OEM and never touched, it´s rare for them to back out. Reusing them and forgetting the loc tite is often the main cause. As a matter of fact, reusing them at all, is most times not recommended.
Piston slap, is kind of RPM dependant. I cured mine by changing the idle RPM. They may still be slapping, but you don´t hear it.
If the troque converter bolts are loose, they are often, really loose, almost finger tight. Loose torque coverter bolts often sound like a tick, tick tick, in the early stages.
You can rotate the flex plat, by BLOCKING the wheels/tires, puting it in neutral and gently prying the flex plate teeth, with a long screw driver. Also not a bad idea to make sure the key is in unlock, but not in the run position. If you have to have it, in the run position and turning the motor by hand, it´s recommended to disconnect the coil wire. One chance in a million anything is gonna happen, but why take the chance.
Many people confuse, exhaust manifold leaks for piston slap. Not as silly as it sounds, the exhaust manifold can and often does sound just like a faulty lifter or other mechanical problems.

 

[siminsez01]

okay well given that my bolts have never been taken out, should i be able to rule them out as being loose? (i've heard the opposite, that these bolts are commonly loose on xj's)

guess i'm gonna look into that a bit more this weekend. If it were piston slap (goes away as the engine warms up) what could i do to help this? run a more viscous oil?

what can i do to diagnose this problem better? the noise is definately from the bottom of the compartment, it sounds like the noisy lifters, but 10 times louder.

 

[8Mud]

I use a short piece of 3/4" copper pipe, helps you zero in on the noise. If the torque converter bolts are loose, a light slap on the end of a wrench will often move them. Like I said, the loose ones I´ve seen, were pretty much finger tight and were reused. Over torquing them, can stretch the bolts and make them loosen all the quicker.
I´ve got 3 XJ´s with a total age of about 40 years added together. No loose tourqe converter bolts yet. But heck anything is possible.
Get somebody to start the motor cold and run your hand lightly around the exhaust manifold, especially where it turns from 6 pipes to 1. Make a practice run or two, before someone starts the motor. You don´t want your hand in there for more than half a minute or so, it gets really hot, really quick. A pretty much sure sign your manifold is leaking, is an occasional pop, at start up.
Noises will fool you. I recently had a front hub, that sounded like a lunched transfer and a valve train rattle, that turned out to be a distributor gear.

 

[lloyd]

I agree with 8Mud. There's a very good chance it's the exhaust manifold. As manifold warms up, it expands and closes the crack.. and you don't hear it anymore. It seems like half the time I help someone work on their rig with the I6, I hear this. Sometimes it's quiet in less then a minute. They argue and say it's not an exhaust leak/crack, and 6 months to a year.. or 2.. later later it crack finally gets big/loud enough for them to have to admit it. Helped one guy 3 years ago find a good used XJ. Told him when we checked it out it had an exhaust leak.. but oh no... Well last week he asked me if I would help him change his manifold cus now it's leaking all the time... and getting pretty loud

Tell ya what, Is it louder on drivers side then on passenger side? If it is, probably exhaust.. if it's louder on passenger side.. probably piston slap.. My money's on exhaust

 

[Atl XJ]

Piston slap on the 4.0l is a much different sound than the sound a leaking exhaust manifold makes, you can't really confuse the two. Trust me, I've had both. It is also very common for piston slap to be much more pronounced when the engine is cold and quiet down as it warms up.

 

[8Mud]

Piston slap on the 4.0l is a much different sound than the sound a leaking exhaust manifold makes, you can't really confuse the two. Trust me, I've had both. It is also very common for piston slap to be much more pronounced when the engine is cold and quiet down as it warms up.

To somebody that has heard neather, it could be confused. I´ve watched guys my whole life, confuse an exhaust tick, with a lifter tick.
If it´s piston slap, not a whole lot you can do about it, unless the Jeep is still under warranty. Even then, chances are it might slap again after all the work and expence.
Best way is to get a stethiscope and find out exactly where it´s coming from, second best a pipe. Localize the sound and go from there.

 

[siminsez01]

thanks for the preliminary help guys. i guess i do feel kinda stupid trying to decypeher a noise when i haven't heard either. i'm definately open to the problem being a manifold leak. seems like narrowing down EXACTLY where the sound is coming from is the next step. i'll do that this weekend and post back.

 

[Eagle]

Besides torque converter bolts, a cracked flex plate also makes a noise. But that sounds more like a rod bearing type knock than an exhaust leak tick.