FLYWHEEL MOVES FORWARD AND BACKWARDS

I've been driving my xj after i rebuilt it for about four weeks now. It developed some ticking but wasnt coming from the oil pan. I narrowed it down to the flywheel and it appears the dust shield was hitting it. While down there i took the time to double check the fly wheel bolts and looked around to make sure it wasnt cracked. I had my brother start it up and shift between reverse, neutral, drive and third. At first I thought i was seeing things but when it engages the converter the flywheel actually moves forwards an 1/8 to 1/4 inch then slides back. I checked it again with a flashlight and I could actually see the whole flywheel, and crank all move forward than back. IS THIS NORMAL? I havent had any mechanical or other running issues with it.

4.7 stroker
aw4 tranny
231 t case

Wait a sec. The crankshaft moves too? Are you absolutely sure about that? Check and make sure, you should be able to see the harmonic balancer move as well if it does.

Did you replace the thrust bearings when you "rebuilt" the engine?

And it is a flexplate or "Plate, converter drive" with an auto trans, flywheel with a manual trans.

? Wrong bearings, missing the thrust surfaces???? or wrong locations?

That is a LOT of movement.

Like the man said, look at the harmonic balancer. The flex plate is just that.....flexible.

Crankwalk much? To truly verify it I would pull the oil pan itself and with a set of feeler gauges, measure for any play between the mains and the crank. See if you can gently pry the crank all the way towards the balancer. Not sure how it is for Jeeps but I'm guessing play shouldn't exceed .005".

The main bearing did wrap all the way around to the thrust surfaces. and the crank went in snug. Good idea on watching the harmonic balancer. Ill go do that. Not flex plate... flywheel. Its an auto so it shouldnt flex. that thing is thick!

redrider2911 said:

The main bearing did wrap all the way around to the thrust surfaces. and the crank went in snug. Good idea on watching the harmonic balancer. Ill go do that. Not flex plate... flywheel. Its an auto so it shouldnt flex. that thing is thick!

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If it is an automatic, it has a flexplate, not a fly wheel.

I thought only a manual had a flex plate. Its all a gamr of words. lol Anyways I watched the harmonic balancer and it does move but just barely which i assume is normal. So im guessing its just an optical illusion since the whole drive train does shift a little.

the 4.0's spec only show 0.0015 to 0.0065 in. of endplay. which isnt much so you shouldnt be able to see it that easy. id get a dial indicator to the harmoic balancer then use the prybar to push/pull the crankshaft to measure how much endplay you're dealing with.

its possible that the thrust bearings are toast, its the only thing that keep the end play in spec.

when i pry on it it really doesnt seem to move. I ran out of light so ill look at it more tomorrow. as for the thrust bearing being toast, I only have like 300 miles on the engine. Broke it in with gtx 10 30 and the lucas zddp addative. Thanks for the input guys. Im starting to think that maybe watching the flywheel while it revs up must create an illusion like how sometimes it looks like spokes on a wheel are moving backwards at certain speeds.