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Engine noise - Piston slap vs. lifters vs. flexplate

kellen

NAXJA Forum User
Location
Seattle
Well I am just trying to figure out which one I can rule out, if any. 89 4dr 4.0 4x4 Auto

During the early parts of a trip, ie when the car is warming up, I can hear my exhaust leak, which sounds like a ticking that shows when engine under load and goes away until engine is warmed up. The noise seems to go w/ the gas, ie more gas, more noise. Haven't seen the crack, but due to their history, I am sure thats what it is.
Now my real prob. is after the Jeep is warmed up, I get a weird noise, almost like rocks or something in a can being rattled. It seems to be from the engine, from what I can deduce. I may be making this up, but it seems that I get this noise when I back off the gas or just lightly get on it, but it doesn't seem to be there under full load.
The Jeep hasn't loss power or mpg. I have searched and heard flexplate (cracked or 4 bolts loose), lifters, or just the 4.0 piston slap. Anyone of these ruled out w/ the info given?? To check the flexplate, do you just unbolt the cover and look up to the flexplate. Anyone have a picture of this cover under the car or where it is at?


Thanks in advance,

Kellen
 
I am going to say flex plate.

Minor piston slap normally goes away when the engine it running at temp, and the lifter tick would be constant with throttle like the exhaust sound. Flex plate noise will dissipate when the engine is under load. Check the torque on the flex plate bolts to spec- 40 ft-lbs I think but don’t hold me to it, also, check the plate for a crack, they will generally start at the center or one of the bolt holes and work outward.


if no picture has shown up by the morning i will snap one for you
 
see my reply on Jeepforum. I agree with NCSU though, sounds like mine did with the flexplate went out. When I removed mine a light tap with a hammer and the center fell out. That was scary!!
 
Being this vehicle is my DD, what would happen if the flexplate was to go out?? Would I just be stranded or would the repairs be even more expensive?? If it was cracked, what am I looking at price wise or I guess hour wise to have someone do it, unless a weekend mechanic can get it done w/ a chiltons.

Thanks,

Kellen
 
I did a flex plate. Bought a Crown, which IIRC cost me around $65. I did it myself in an unheated garege at night during the cold part of the winter, so progress wasn't very efficient, and I encountered a lot of other things the previous owner had "fixed" that significantly affected my flat rate time.

The basic noise was similar to the rod bearing -- a RAP RAP from down low in the engine when idling in neutral. Put it in gear, hold the brakes and give it a little gas to load the tranny, and the noise would disappear.

In my case, the crack was about 60% of the perimeter. The crack formed around the outer perimeter of the reinforcing ring that the flex plate to crankshaft bolts go through. By dropping the inspection cover on the bottom of the bellhousing and prying on the flexplate with a pry bar, you could see the crack opening up.

Yes, if it lets go on the road you are standed. Whether it would cost any more to repair depends on whether or not anything else is damaged when it fails completely. At the least, you're looking at a tow bill.
 
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