Thread: Engine Balancing? - Broken Flexplate

The most common cause of broken flex plates is due to misalignment. In the LR V8's sometimes one of the engine-to-bell housing dowels is lost during removal.

I had a full balance done on mine when it was rebuilt. Cost under $400.

When the torque converter is removed, have them check the nose of the TC and the matching hub aligner on the crank. Mine was damaged and probably caused the second flexplate failure.

I had a new hub aligner fitted and the TC repaired.

ewww, hammery.....

to check them for round cut a piece of carbon paper to exactly the circumference of the inner race and install it then face the TC up to it on some long guide bolts.

bring it home replacing the bolts one at a time till its just touching evenly (you still want it to slide) then very slowly turn the engine over by hand.

remove the TC carefully and eyeball the witness marks the carbon paper has left, if you see very distinct lines that run forwards and back (that you cant attribute to getting it in and out) clean it up and install the TC in a different position and go again. (and with the crank in a different starting position)

If the marks come up in the same way in the same position relative to the crank then the crank is potentially damaged. If the marks come up the same relative to the TC then the TC is damaged. IF you get 2 new sets of marks that look similar to the first lot then both are gone.

Careful Repetition of the test adjusting the start position of the crank AND the relative position of the TC is important to ensure that its not misalignment on installation thats causing the problems

Probably not so easy to do in the car, Dave.

still doable. you have to pull either the box or the engine to get to the TC... It'd be a lot of a bugger to do on your back on the floor under the vehicle with the Box out.

IMO Its a check that you should do IF youve had a damaged flex plate but dont have obvious signs (like the photos you put up) of hammering on the TC and the Spigot) I think its especially important if you're thinking about reusing the TC.

Thanks Ron, i had seen your photos, and looked the first time the plate broke. I'm just concerned why this has happened again. Last thing i want is to fix the flex plate, then have to replace it again in another 20K.

Sorry, I left a bit out....

When the gearbox was done, the gearbox builder knew that the flex plate had broken, so they double checked alignment, and also installed a new spigot. Plus they also found that one of the dowels was missing, so it was reinstalled. I also went through all this the first time the plate broke.

My question is in regards to the vibration.. Does anyone think it could be a badly balanced engine, that has caused the plate to break again. Ever heard of this before?

Stu

yes, but not so much overall engine balance but the harmonic balancer. It was stiffer than an alcoholics nightcap. changed that and no more weird drone at certain RPMS and AFAIK it hasnt done a plate since.

Well, finally got around to gettting the motor out. The poor old girl has been sitting in the driveway for 6 months

And this is the result



The big thing i have noticed is that the Cracks are directly between the bolts.

Thoughts, Suggestions? I'm considering VCAT as this motor has been a disaster from day one.