Broken Flexplate - again?

[p38arover]

My P38A is running very roughly at idle. It clears up as the RPM are increased.

I'm suspecting yet another broken flex plate between the flywheel and torque converter.

It's not that long (mid last year) that it was replaced. I wonder if engine balance has anything to do with it. P38A engines are balanced with the flywheel and my flywheel is off the original engine and still has the same balance weights attached.

I don't know whether to pull the engine and strip it to have it balanced or whether to pull the gearbox and just replace the flex plate. Removing the box is easier (on hoist). The former I can do at home for free (shades of a certain British comedy), the latter requires the use of someone's hoist.

Has anyone here had an engine balanced?

Another option I have is to rebuild my original engine (slipped liners) with top-hat liners and refit it. Then I can sell the current 4.6.

Ron

[rangieman]

Well ive heard its a fault with discos as well ive heard of a couple of auto Tdi,s breaking the drive plates:eek:
good luck mate :cool:

[Bigbjorn]

what we used to do with certain earth movers was to fit up the flex plate and trans with the flex plate to flywheel bolts a firm finger tight, turn the thing over manually a few revs to get everything to line up and then torque up the flex plate retaining bolts. This ensures everything is running round and round in the same circles.

[DarrenR]

Hi Ron,
I'm not familiar with newish Rangies, so my comments are general questions more than anything else.

If I'm reading this correct, the P38A has a flywheel and a flex plate?
Didn't it make a hell of a noise last time it cracked?

Most 4WDrives in the past where I've cracked a flex plate you certainly heard it. But this was on vehicles with only a flex plate and the torque converter and was generally caused by alignment and or balance problems.

Best regards
DarrenR

[Pedro_The_Swift]

"It's not that long (mid last year) that it was replaced. I wonder if engine balance has anything to do with it. P38A engines are balanced with the flywheel and my flywheel is off the original engine and still has the same balance weights attached."

It wouldnt have done it any good---

rebuild the old one,,
and get it all balanced properly this time,,,


or sell it to the daughter as is:angel:

[Scouse]

I wonder if engine balance has anything to do with it. P38A engines are balanced with the flywheel and my flywheel is off the original engine and still has the same balance weights attached.

I recall that you mentioned a while ago that you thought this was the case as your RR had a short motor fitted.
I don't know if this would be the cause of your problem. We've fitted dozens of new short motors into P38 RRs & I've never heard of a flex plate failure afterwards. I'm not saying that it can't be the cause, but we've never (to my knowledge) had an engine balance issue with a replacement engine.
Good luck with it Ron.


(I don't think I can offer $1000 for it anymore though - $750 tops now :cool: )

[discowhite]

if it were that out of ballance you would feel it through the whole car!
the flex plate shoud only be there for the starter motor. its the torque convertor that joins/drives the lot together.
if the flexplate is cracking ide put it down to incorrect fitment, ie to much play in the bolt holes maybe a bent flexplate, a bur on the mating faces??
something like that??

cheers phil

[discowhite]

My P38A is running very roughly at idle. It clears up as the RPM are increased.

could this be something else?? like faulty injector/s, sensor fault, temp etc etc...

cheers phil

[p38arover]

The original flexplate didn't break with the original engine.

The first breakage was with the replacement (current) engine.

I think we tightened it correctly - see
TSB 0003
CDS. ref: L8432bu
Issue: 1
Date: 06.05.98

I could have sworn I'd seen something about shimming the flywheel or flexplate.

Ron

[p38arover]

if it were that out of ballance you would feel it through the whole car!

You can. It's quite bad. It's almost like one cylinder isn't firing. At first I thought I had an ignition fault - it does it on LPG and petrol.

At start up, it's OK. Then as RPM drop to the correct idle, it's very, very rough.

Ron

[p38arover]

I've never heard of a flex plate failure afterwards. I'm not saying that it can't be the cause,

I know of at least one other bloke that had a new flex plate fitted and the new one failed in short order - just like mine.

I'll check the records and see how long they lasted on mine - certainly less than 30,000km each, maybe 20K or less.

Ron

[p38arover]

The engine is out of the P38A. Tomorrow I strip it to take the heads and inlet manifold to Bruce Davis for working over.

The flex plate is shattered. I'm surprised the car drove at all.

Pics will be taken tomorrow.

Ron

[DEFENDERZOOK]

have you done a bit of a ring around to different dealerships to see if they have found an actual cause
or a remedy for this problem.......?


its seems to be common enough.......




it could be something out of alignment.....or out of balance causing it.......
or maybe even the material used.......
there may even be a superseded flex plate available......

[loanrangie]

if it were that out of ballance you would feel it through the whole car!
the flex plate shoud only be there for the starter motor. its the torque convertor that joins/drives the lot together.
if the flexplate is cracking ide put it down to incorrect fitment, ie to much play in the bolt holes maybe a bent flexplate, a bur on the mating faces??
something like that??

cheers phil

Phil, the flexplate transmits drive to the torque converter, not just there to start the engine !

[p38arover]

the flex plate shoud only be there for the starter motor. its the torque convertor that joins/drives the lot together.

No. The flywheel with starter ring (called the drive plate in LR parlance) is solidly fixed to the engine.

The flex plate is a thin sheet of steel that bolts to the flywheel at the inner circumference and the torque converter at the outer edge.

The starter motor doesn't apply any starting torque to the flex plate.

The photos I'll put up later will explain it all.

Ron

[51jay]

Surely it has either a flywheel or a flex (drive) plate it can't have both

[Blknight.aus]

No. The flywheel with starter ring (called the drive palte in LR parlance) is solidly fixed to the engine.

The flex plate is a thin sheet of steel that bolts to the flywheel at the inner circumference and the torque converter at the outer edge.

The starter motor doesn't apply any starting torque to the flex plate.

The photos I'll put up later will explain it all.

Ron

Keh??????

you have a flex plate OR a flywheel...

all of the starting torque from the starter motor is applied to the ring gear which is firmly attached to the flywheel if you have a manual OR the flexplate if you have an auto. The flexplate (or flywheel) is in turn bolted to the crank.

What kills flexplates..... lots of things.

1. Over powering the engine and prolonged stall tests.
2. If the torque convertor cavitates it vibrates and will stress the plate (but youve got bigger more expensive worries if this happens)
3. incorrect tensioning of the ring gear or the torque converter to the flex plate
4. any misalignment between the gearbox and engine that causes the TC and flexplate to be misaligned
5. wear of the TC support bearings that allow the TC to sag (again if this happens you have bigger things to be worried about)
6. Age
7. poor machining and deburing
8. poor balancing of the plate and ring
9. Murphy.

[rovercare]

Keh??????

you have a flex plate OR a flywheel...

all of the starting torque from the starter motor is applied to the ring gear which is firmly attached to the flywheel if you have a manual OR the flexplate if you have an auto. The flexplate (or flywheel) is in turn bolted to the crank.

What kills flexplates..... lots of things.

1. Over powering the engine and prolonged stall tests.
2. If the torque convertor cavitates it vibrates and will stress the plate (but youve got bigger more expensive worries if this happens)
3. incorrect tensioning of the ring gear or the torque converter to the flex plate
4. any misalignment between the gearbox and engine that causes the TC and flexplate to be misaligned
5. wear of the TC support bearings that allow the TC to sag (again if this happens you have bigger things to be worried about)
6. Age
7. poor machining and deburing
8. poor balancing of the plate and ring
9. Murphy.

I've never worked on a P38a, but assuming its the same as in a classic, you have a flex plate with ringgear attached, then a machined boss, then and adaptor plate, the thin bit he's talking off, which the convertor bolts to, as in it bolts narrowly to the plate through the boss, then outwards to the converotr to give it some purchase on the torqued area

I.e the convertor doesn't bolt directly to the flex plate, there is an adaptor between the flex plate and the convertor, the convertor b

[Blknight.aus]

I've never worked on a P38a, but assuming its the same as in a classic, you have a flex plate with ringgear attached, then a machined boss, then and adaptor plate, the thin bit he's talking off, which the convertor bolts to, as in it bolts narrowly to the plate through the boss, then outwards to the converotr to give it some purchase on the torqued area

I.e the convertor doesn't bolt directly to the flex plate, there is an adaptor between the flex plate and the convertor, the convertor b

yep but you still dont have a Flywheel (as the type used in a manual) and a flex plate...

In the case that your desribing (IF I follow you correctly) you have 2 plates 1. the starter plate thar mounts the ring gear then running off the same boss as the starter plate the flex plate that hooks up to the torque convertor. in which case all the afor mentioned things still apply to the plate that holds the TC.

If you only have the one plate but you have an adaptor ring inserted to assist in distribution of torsional forces the same things apply, but you have an additional chunk of metal that has to be bolted up balanced and aligned correctly.

and with the second setup here any problems from misalignement would be amplified whenever the startermotor was doing its thing.

[p38arover]

Surely it has either a flywheel or a flex (drive) plate it can't have both

It can and it does.

Flex plate (broken). Inner holes bolt to engine/flywheel. Outer holes to the torque converter. The torque convertor has a spigot which fits into the end of the crankshaft boss - like a pilot bearing.

https://www.aulro.com/afvb/images/imported/2007/09/164.jpg

Below: Driveplate (Flywheel), engine side. The spikes are the part of the reluctor ring used by the crank angle position sensor to determine engine rotation asnd timing (missing tooth is 30 deg from TDC).

https://www.aulro.com/afvb/images/imported/2007/09/165.jpg

Drive plate (flywheel from flex plate/torque converter side. Note the wear from the flex late.

https://www.aulro.com/afvb/images/imported/2007/09/166.jpg

[Blknight.aus]

how thick is the main plate? AFAIK its only a few mm thick not the same sort of thickness as the normal type flywheel.

And why the hell would you put a normal manual type flywheel on with something as heavy as a TC thats going to do a better job (assuming its all bolted up properly) of being a rotating mass than the flywheel itself?

surely not just to mount the reluctor ring on...

edit--------

BTW I consider a normal type Flywheel to be one of those big thick heavy buggers you bolt a clutch up to and wouldnt want to drop on your foot.

A starter plate is one thats only there to mount the ring gear to let the starter motor do its thing

A flex plate (in terms of engine-Transmission) is the plate the TC bolts up to be it a full diameter plate like the broken one in the top pic of rons post or a smaller hub drive as mentioned by rovercare (usually just a smaller diameter plate that only extends as far as the coupling bolts on the TC)

[ladas]

Many cars (auto's) have flywheels and flex plates

Surely you should know this Dave ;)

[Blknight.aus]

so far Ive never seen one that has a full thickness manual clutch type flywheel and a Flex plate..

Starter plates and flex plates yes but never a proper flywheel and a Flex plate and AFAIK theres 2 very good reasons for it

1. Mass, sure more weight helps keep the rotations smooth but it costs you in terms of acceleration. A TC weighs in at as much as some flywheels when its empty, add all the oil to it and thats more than enough weight to do the job putting a flywheel in as well, cmon thats just getting way out there (although if i had to put an auto behind a 3.9suzi that I knew was going to do lots of sub 1000RPM work ID consider this a + not a minus)

2. space flywheels arent skinney by taking the guts out of one and making it a flex plate or a starter plate you have more room for A, a bigger TC or b, you can shrink the gap between the donk adn the box by the same amount

and as a cherry on top to mount up the TC youd have to bore holes in or cast holes in the Flywheel which is more work to be done in terms of finish and balance.

Ive seen plant gear with the TC coupled to the flywheel directly tho...

[p38arover]

The main plate is 3.25 mm and the thin one is 1.6mm - I just measured them with verniers.

Ok I just checked the LR parts catalogue. They call the the flywheel the "drive plate assembly" and the thin one the "drive plate - bare"

Ron

[ladas]

This is for a Ser II Auto Disco TD5

See

http://www.aulro.com/afvb/showthread.php't=40365&page=2

[Blknight.aus]

Many cars (auto's) have flywheels and flex plates

Surely you should know this Dave ;)


The main plate is 3.25 mm and the thin one is 1.6mm - I just measured them with verniers.

Ok I just checked the LR parts catalogue. They call the the flywheel the "drive plate assembly" and the thin one the "drive plate - bare"

Ron

so we're having a difference of terminology here...

The main plate that is 3.25mm thick some of you calling the flywheel and Im calling it a starter plate and the manual is calling it the drive plate.

Same poo different shovels.

but we're all agreed that the shattered one in rons pic is the flex plate yeah... :angel:

[ladas]

but we're all agreed that the shattered one in rons pic is the flex plate yeah... :angel:


:twobeers::twobeers::arms::arms::clap2::clap2::Big Thumb::TakeABow:

[rovercare]

so we're having a difference of terminology here...

The main plate that is 3.25mm thick some of you calling the flywheel and Im calling it a starter plate and the manual is calling it the drive plate.

Same poo different shovels.

but we're all agreed that the shattered one in rons pic is the flex plate yeah... :angel:

Yea, I'm with you on this one, got called of to a job before hence the abrunt end to the post:angel:

I'd call the ring gear plate a flex plate, mainly out of visualization habit (tis what most flex plates look like, and the shattered one a drive plate, but either way is good enough I guess, a flywheel creates rotating mass and is generally a big thick bugger, neither of those here i'd call a flywheel;)

There is an inch wide boss between the 2 here, its basically what you'd machine up when making crazy conversion, but done from the factory by rover:)

[rovercare]

Odd how they are shattering they, they are well spigoted:confused:

[p38arover]

This is the previous flex plate (on right)

https://www.aulro.com/afvb/images/imported/2007/09/162.jpg

[rovercare]

This is the previous flex plate (on right)

https://www.aulro.com/afvb/images/imported/2007/09/162.jpg

WOW:eek:

Its very unusual, as it really cant bind by being pulled apart, as the converot should slip towards the engine neatly, maybe the converor is out of wack, and need to be checked for square, referencing shaft to bolt face, and the boss aswell, some time on a lathe with a dial may be called for:(