Cracked flexplate

We have a 98 2.7 4cyl 4x4 with a automatic that we purchased a few months ago from a small local dealer. Don't know why but at some point someone has replaced the motor. We just put the truck on the road at the end of last year. After a couple of weeks it started making a noise and figured out it was a cracked flexplate. When I tore it apart it had a missing torque converter bolt. I also notice a new TC and what looked like a fairly new flexplate. Thinking they installed a new flexplate and TC when they changed the engine and that the missing TC bolt caused the problem. I just put in a new flexplate from Napa. I did notice that the reinforcing washer for the flexplate to crank looked like it had some dings in it from a hammer. I cleaned it up a little with a flat file then lapped it some on sandpaper and flat surface. Both bellhousing alignment dowels were in place and everything seemed to go back together very good. Well after about a month it compleatly sheared the center out of the new flexplate with no warning apparent to my wife who drives it. This is at least the second cracked flexplate. Now I think there is a balance or alignment issue and someone replaced the TC and flexplate before me trying to fix the problem. I need to come up with a game plan to dignose why this is happening before I put it back togeather. I'm going to check the motor mounts,tranny mounts and bolts. Check the runout of the TC and crank and that washer. Will checking the crank runout tell if the rear main bearing is good? I'm assuming the 2.7 is internally balanced. Any other ideas as to why this would be happening and what to check?

 

Got the tranny out yesterday. All the engine,tranny mounts and bolts looked good. Checked the crank endplay. With me prying as much dared on the front crank pully zeroing out indicator then prying backwards pretty hard I could get up to .003 play. Standard play is like up to .008 and max is like up to .011. So crank end play is good. Checked crank runout and indicator never moved enough to take note. I was wrong in my memory in OP. It was the spacer between the crank and flexplate that had the hammer dings on it. I smoothed it out some more. Have to wait for new flexplate to check TC runout. Anyone with any ideas?

 

At this point I think I have figured out the problem. I believe I have a bad bellhousing. Looks like its been peened out of square 1/16" on the pass side. Soooo! Anybody have A bellhousing for a 4cyl to A340F auto tranny they would part with?

 

I would check and make sure you are not missing the alignment dowells for the bellhousing bolts to the engine. One of the other mechanics I work with forgot to transfer them over to a new tranny on a car once and it came back in 300 miles with a cracked flex plate. Well, 2 flex plates later he figured out what was causing the problem.

 

Thanks for the heads up NT but I allready was aware of that and had that in my OP. I think whom ever replaced the engine in the past didn't tighten it down and over time it peened the alum bellhousing. Then it cracked a flex plate. Then whom ever replaced the FP before me didn't catch the peened bellhousing and tightened it down causing a alignment problem. The first cracked FP for me I ignorantly assumed the missing torque converter bolt was the problem so I missed the bellhousing problem. 2nd time I knew I had a issue and found the problem. It seems like the 2.7 to auto bell housing is a little hard to find.