How the hell does this happen?

[Bazda]

Yea dont think there are any off the shelf flywheels for the 7afe/4afe.

Jeffrey Bruce From Precision Enginerring makes them for me. I actually have a 7afe flywheel that he can copy for you Matt.
But it doenst have a ring gear.

I can get a price for you, give me a pm.

[TRD Man]

TOM'S made a chrome-moly flywheel for 4 & 5AFE. But no longer. Price would have been about $800 ~ $850.

It's an interesting break. I've never seen one break so neatly before.
The proximity of the circumference of the break to that of the crankshaft end suggests that it has been pivoting on there and makes me wonder if it simply wasn't loose.

[Dell'Orto]

Also Collier Motor Engineers in Levin can make billet flywheels, but they will need one to copy.

[Malcolm]

the fact that the failure is an almost perfect circle seems to suggest it's a shear failure due to rotational torque applied between the crankshaft flange and the friction surface, but that is a very large area to shear, which would probably indicate that it's a fatigue failure rather than due to a single force applied.

I would think if the failure was actually due to bending of the flywheel due to a misalignment of the flywheel, clutch or output shaft that the fractuce surface would not be as circular - although attempting to drive after the failure would obviously smooth the two faces out. Any closer pictures of the fracture surface?

[CAMB01]

Id be pulling the sump off and checking the main bearings down that end of the motor, and get the crank cracktested just to be sure.

[matt dunn]

TOM'S made a chrome-moly flywheel for 4 & 5AFE. But no longer. Price would have been about $800 ~ $850.

It's an interesting break. I've never seen one break so neatly before.
The proximity of the circumference of the break to that of the crankshaft end suggests that it has been pivoting on there and makes me wonder if it simply wasn't loose.

I believe that the first flywheel problem we had a year ago was caused but the bolts not being tight enough,
but I know that the flywheel bolts were not loose this time,
as when I picked up the engine from wayne my engine builder,
I held a bar on the front crank pulley while he torqued the flywheel bolts,
and they were new ARP bolts.

Tha flywheel will have broken on it's 7th race weekend,
and also done one or two hours on a test day, and one dyno tune/run.
So not sure if you would call it fatigued.

A chrome-moly flywheel would be the go I think,
and If i'm going to go that far I may also go for a smaller dia. twin plate clutch too.

[sleeektoy]

Was the flywheel checked to be running true with the crank/block?
The slightest bit out at the crank makes a big difference at the clamping surface.
When clamping the clutch plate to the flywheel it can do 1 of 2 things...

1. flex the flywheel slightly all the way round as it rotates
2. bend the gearbox input shaft slightly.

either way it usually ends with a failure similar to what you have as it flexes the flywheel about the bolts once the plate is clamped to it.
A small bit of dirt/swarf/crap between the crank and flywheel surfaces could cause the flywheel to be out too.

thought it could be worth mentioning as std flywheels usually handle a bit more punishment than that before failing

[matt dunn]

Was the flywheel checked to be running true with the crank/block?
The slightest bit out at the crank makes a big difference at the clamping surface.
When clamping the clutch plate to the flywheel it can do 1 of 2 things...

1. flex the flywheel slightly all the way round as it rotates
2. bend the gearbox input shaft slightly.

either way it usually ends with a failure similar to what you have as it flexes the flywheel about the bolts once the plate is clamped to it.
A small bit of dirt/swarf/crap between the crank and flywheel surfaces could cause the flywheel to be out too.

thought it could be worth mentioning as std flywheels usually handle a bit more punishment than that before failing

The flywheel actually gets laped onto the crank like a valve grind and then cleaned and fitted, so would definatly be on square and flat.

[Mr Revhead]

the fact that the failure is an almost perfect circle seems to suggest it's a shear failure due to rotational torque applied between the crankshaft flange and the friction surface, but that is a very large area to shear, which would probably indicate that it's a fatigue failure rather than due to a single force applied.

I would think if the failure was actually due to bending of the flywheel due to a misalignment of the flywheel, clutch or output shaft that the fractuce surface would not be as circular - although attempting to drive after the failure would obviously smooth the two faces out. Any closer pictures of the fracture surface?

kinda what i was thinking
without seeing it in person you cant see how much metal has been lost.


prob casued by matts n00bish gearchanges
if he changed gear they way he did in his old KP60....

[matt dunn]

kinda what i was thinking
without seeing it in person you cant see how much metal has been lost.


prob casued by matts n00bish gearchanges
if he changed gear they way he did in his old KP60....

Hey, it was a 2k 4spd, they are designed for no clutch flatshifting.

There is almost no metal missing, there are no bits in the bellhousing,
not even really a lot of metal file-ings.
could probably just aboput glue it back together so ya cant tell!

[Bazda]

billet flywheel and twinplate ftw

Remember if you get a twin plate you need the thick disc versions aka rally pack. The std type twinplate discs are far too thin and wear extremly fast.

I've had mine for 1.5 years and I drive it on the road, never had any issues with slipping