I have a 96 ford ranger that has broken to new flex plates in a years time. It is broke down again and needing it replaced again. the truck has over 300,000 on it. The transmission is newer though.Jasper engine rebuild.
what could be the problem? Has anyone been through this and found a solution? how to check crank end play with motor still in truck?

 

Welcome to the forum

Flexplate is called a "flex" plate because it can absorb some engine transmission misalignment, but not too much.
No engine and transmission will line up exactly, but the center lines of crank and input shaft on transmission need to be within .008 of an inch of centered

First thing is to make sure DOWEL pins are in place so bell housing is PRECISELY aligned with engine block when bolted together, missing dowels means broken flexplate over time.
The dowels are used specifically to align crank and input shafts, they need to be there AND need to be a snug fit on both engine and bell housing

Too much end play of crank can cause broken flexplate, in and out movement is expected, but should be limited, misalignment is the more common problem

You can push in on the front pulley and then push it back from rear of engine to check end play, thrust washers on the crank set end play, you would have to look up your engines specs to see what range is acceptable.

If torque converter bolt holes don't line up perfectly in the center of flexplate holes then alignment is off, even if you can get bolts to thread in, its still misaligned and will give you trouble.

I think the flexplate also used a spacer on the crank that wasn't used with flywheel(manual trans), make sure that is in place

And broken flexplates were not all that uncommon on 1996 and earlier Rangers and Explorers, in 1997 Ford changed 4.0l crank to an 8 bolt version, I assume because of this problem.

When you place a bell housing on an engine it should push on and be flush, no gaps.
If you have to use bolts to snug it up.......STOP!!!
There is something wrong, and it will come back to bite you
On an automatic the torque converter should be free to turn when bellhousing and engine are snugged up, it will slide forward to be bolted to the flexplate and holes should lined up centered

 

Local transmission shop has put it in twice already. They are really good. Can I order the 8 hole crank and put it in?

 

I take it you are not an "engine guy"

Yes, you could put in an 8 bolt crank but it would cost less to change the flexplate 5 more times
Requires almost a full engine rebuild to change a crank shaft.

This was not a 100% failure on all Rangers(or Explorers) with a 4.0l and 6 bolt crank with automatic trans.
Just a "known" issue.

Doesn't matter how good the shop is, all mechanics "go to school" on customers vehicles.
If transmission was rebuilt the input shaft maybe be off center a bit, more than the allowed 0.008"
Have them or someone else check that before new flexplate goes in.
And the dowels

The flexplate DID NOT BREAK for the last 20 YEARS(1996-2016) so ask yourself what is different now?
I don't know but you probably do,if you have owned the vehicle for at least 2 years
So what has changed between engine and transmission?