Knocking? Tapping? Loose flexplate? Video...

This past Sunday night I fueled up. Shortly after that I started hearing a faint, random "knock" or "tapping" coming from the motor (I would "estimate" that the noise is coming from the lower rear of the motor...but that is not verified) mostly when the motor is at idle or lower RPM, at least below 1000 rpm...mostly in the idle range.

Today I did some testing and noticed that the tapping or knocking is most pronounced when the vehicle is in gear and when the brakes are held....or the ebrake being used while the vehicle was in drive for my video.

Originally we were thinking it was spark knock due to bad fuel (since it just started happening randomly after I filled up the tank) and not thinking a bearing or a rod being the cause of this noise, and I am still guessing they are not the cause as the noise is not constant. Is it possible the flexplate is making this noise? I know the flexplate bolts sometimes loosen up causing the flexplate to make noise.

If the vehicle is idling in park it will not make this noise constantly, just an occasional faint tap or knock will occur.

Here is the video from this afternoon:

http://s20.photobucket.com/albums/b210/bbugaski/Videos/?action=view&current=XJNoise.flv

I have a 1995 Cherokee with the 4.0 and AW4 automatic transmission, and I just pased 208,000 miles. Yes the exhaust manifold is cracked but the tapping/knocking is quite pronounced and I believe you should be able to hear it quite clearly.

I am just curious if anybody can identify this noise. I am crossing my fingers that is just a loose flexplate and nothing more serious.

Thanks in advance

Check the bolts for the torque converter. I bet they are loose at the flex plate. Seen this on 3 Xj's I've bought cleaned up tightened them and resold for a profit.

Does the transmission have to be detached from the motor or can this be accomplished by removing the inspection cover or whatnot?

I'm not particular familiar with the internals of the trans or the bellhousing.

Thanks.

sounds EXACTLY like my engine. welcome to the world of piston slap. drive it and enjoy the noisy engine.

I checked my torque converter bolts out too- I recommend that first. There are 4 bolts securing the inspection plate to the bellhousing and this can be done without removing the trans or anything other than the plate, hence the term inspection plate.

once you verify your TC bolts are tight you may search on here and find results suggesting combustion chamber cleaner etc. your mileage may vary here. Did me no good. I have also dropped the oil pan and changed the connecting rod bearings with no improvement.

An engine builder told me the 4.0's pistons distort over time and mushroom, and the only remedy is new pistons/rings. may as well rebuild the whole thing at that point IMO.

I am running mine until it pukes and replacing the entire engine.

good luck and I hope that yours is a simple fix but that sounds exactly like my noisy beast.

On a side note. To fix the flex plate right, you must back off all four bolts at once more then one turn, then retighten. Just tightening bolts on it will do you no good. I've fixed a knock before doing this

I ran some seafoam maybe 2 years ago. Would piston slap just show up so sudden from none?

Also do the flex plate/torque converter bolts need to be tightened in a specific sequence? I assume in an alternator pattern.....and does the transmission have to come back off of the motor or can you leave it bolted up and just remove the inspection cover? Like I said I never tore into a trans or this bellhousing area prior.

You do not need to remove trans. Just remove the inspection cover. To turn over the flexplate have someone either bump the starter or manually turn the engine over. Not by the flexplate bolts. Alternating is what I do to tighten them although I do not know if it is required.

Very well! Maybe I will get around to doing this tomorrow.

Just curious how do you access the torque converter bolts as well?

Remove the cover bolted to the bell housing.

Nick

Well I just got done. The 4 torque converter to flex plate bolts were only finger tight. Removed them, loctited, and reinstalled; no more tapping/knocking!

I wasn't able to see the flexplate to crank bolts, and I assume the transmission must come back to access them? I just removed the lower inspection cover, I did not remove the starter but I don't think you'd be able to access them from there either.....

Thanks

Glad to hear it helped. I love buying Jeeps like that for cheap. In fact I even tell the buyer that's what it could be. Yet nine times out of ten they still sell it to me for less then $500.

Hey, i get a hollow tapping noise in low RPM's when my engine is in stress.. 1st 2nd 3rd gear. it sounds like tapping a piston almost. any suggestions? just wait till the engine goes out i guess?

Try the flex plate fix. It's easy insurance. I've also seen cracked flex plates. Usually between two bolt holes.

I love when it turns out to be just loose Flex-plate to converter bolts, But twice I've had the fleck plate brake all the way around the crank bolts. Not as an easy fix but still not as bad as an engine rebuild.

where is it located exactly? and what all do i have to remove to gain access to it?

Note: ive never torn into an engine, tranny, or transfer case. but intend on doing it all for the fun of learning and experience.

also, how much knocking should i allow my lifters and rockers... before i should be worried?

What Torque should the torque converter to flex plate bolts be tighened to?
Or do you just tighten them up good?

I saw the torque recommendations somewhere a few days ago but it would be difficult to get a 1/2" torque wrench in there. I just applied loctite and used a 3/8" ratchet and tightened them pretty good, although not to the point where I would be worrying about snapping the bolts.

I still haven't got the inspection cover back on, I can get you some pics Sunday evening if you'd like if you still haven't found it by then. I've become sidetracked with other Jeep related projects and haven't given reinstalling the cover much thought yet.