Flywheel modification - would you be worried??

[MWP]

Get over the fact there is clearance around the bolt holes. Bolts are not designed to drive things. They sould only be used for clamping. Look at a race cars quick release wheel. It drives on pins and then just has one nut holding the wheel on.

Normally yes... the problem here is the lack of metal between the bolt hole and the dowels.
If the bolt holes were properly filled, the lack of metal would be less of a problem.
... well, by my thinking anyway.

[oldeskewltoy]

I'd strongly recommend that when you do final assembly you use a thin layer of anti-seize on all of the dowel pins.

[allencr]

I would have been more comfortable with them either milling all or some of the dowels down to the surface of the crank face or milling the non-threaded section of the dowels down...

?????????????????
The dowels are dowels, they are not threaded, they are in a crankshaft that's been reamed to a heavy/light press or sliding fit.

[Roundy]

Slot the holes the 1mm and use the 10mm with 12mm shoulder ARP bolts (4AGE i believe)

Given at the moment the dowels are holding all the shear force it is an effectively weaker solution than 8 x M10 bolts

[Xauterus]

How is it weaker?
What do you think the root diameter of an M10 bolt is? Its going to be weaker than a Dowel pin.
Bolts are designed to clamp.
How will this be weaker ?

This is a good engineering solution to your problem.

[Roundy]

Yep ignore me, didn't realise just how much effect the clamping has on the flywheel, i assumed that the majority of the strength was provided through shear in the bolts, hence the poorly fitting bolts weren't going to do much in that regard.

[hemi twofifteen turbo]

I understand the difference in PCD between the crank and flywheel, but would it have been possible to drill/tap the crank to take a larger bolt? From the pics it looks close. The other option would have been to fill the bolt holes with thread, then re drill. Being a steel flywheel should be strong enough with the current solution though. In diffs, I often see 'small bolt' ring gears fitted to a 'big bolt' carriers. This results in about a 2mm gap the whole way round each bolt, logic would suggest the ring should be slopping around on the carrier with all that free play, but I have NEVER seen one that has budged. Testament to the clamping force I guess, but the bolt holes in the fly are much closer to the center than they are in a diff carrier.

[MWP]

How is it weaker?
What do you think the root diameter of an M10 bolt is? Its going to be weaker than a Dowel pin.
Bolts are designed to clamp.
How will this be weaker ?
This is a good engineering solution to your problem.

Yes, thats fine, ARP M10 bolts and the dowels are plenty strong enough... thats not the problem.

My concern is with the metal removed from the fly wheel, and the reduced clamping area due to those dowels.
There is bollocks all metal left around those dowels and bolt holes on the flywheel and on the end of the crank there isnt much clamping surface there.
If there isnt enough clamping effect, and those dowels are put under a shear load (the bolts wont be because of the gap around them), the flywheel might crank between the dowel and bolt holes.

[TTV8RA23]

Im with xauterus. Im fitter turner by trade and i see no problem at all here. Only in the very worst case scenario should there be any drive on the sides of the dowels the pressure of the two faces held together by the properly torqued bolts will do all the driving in 99% of conditions if the bolts come loose etc then the dowels will be driving it. Even then i would not be concerned at all about it shearing between the holes if bolts are torqued properly with high temp medium strength loctite on the threads and a light smear of copper/nickel coat on the dowels. Imagine the forces it would take to break that, it would be in the hundreds of tons to tear 8 neatly fitted 10mm dowels out of that flywheel.
Ideally new flywheel yes, but failinjg that i wouldnt be too worried. I could machine you a billet 4140 to suit you exactly right for about $500 NZD
Cheers
Simon

[MWP]

Imagine the forces it would take to break that, it would be in the hundreds of tons to tear 8 neatly fitted 10mm dowels out of that flywheel.
Ideally new flywheel yes, but failinjg that i wouldnt be too worried. I could machine you a billet 4140 to suit you exactly right for about $500 NZD
Cheers
Simon

But thats the problem, the M10 bolts are no where near neat fitting.

Think im going to tell the engine builder im not happy with it, and ask them to press some hard steel plugs into the M12 holes and redrill so the M10 bolts do fit snuggly.

I sent an email & photos to ACS (Xtreme Clutch) asking them what they thought about the mods:

Our workshop manager and I have had a look at the photos you sent. From our point of view we would have favoured a milled or ‘notched’ approach for the bolt holes- keeping them the same diameter but widening the PCD only- that way only one dowel would be required, keeping more material on the crank flange. That said, **** have been in business for a long time and have a well respected name for doing this sort of work. As the engine builder they would know what output the engine will be rated at, and the material requirements to cope with the associated forces. They also will know what works well with cast and what works well with billet materials, so I am sure that they have carefully considered all the options before using this approach.

[SHEPPO3930]

my $0.02 - you could get a 3mm steel plate laser cut into a "ring" that goes under the bolt heads. the plate would only have the 8 bolt holes in it to suit the crank's PCD and bolt dia. make sure the dowels sit below the flywheel's face, fit the laser cut plate to act as a washer, then fit the ARP bolts. this way the bolt heads are 100% supported underneath (will achieve correct torque when tightening), and the clamping force can act on a larger area.

if it was me i'd have slotted the bolt holes in the flywheel inwards with a 10mm dia cutter in a mill. it's a popular thing to do when fitting an EJ series engine to an early subaru with an EA82 (or similar) engine. http://i26.photobucket.com/albums/c1...x/PICT3429.jpg i would however go one step further and add a laser cut plate as i mentioned above.

if you do plan to use the set up your engine builder has done, please let us know how it goes. i'm curious to know if cracks will start forming between the dowel holes and the bolt holes due to flywheel flex and the banging nature of 2-step limiters.

[MWP]

my $0.02 - you could get a 3mm steel plate laser cut into a "ring" that goes under the bolt heads. the plate would only have the 8 bolt holes in it to suit the crank's PCD and bolt dia. make sure the dowels sit below the flywheel's face, fit the laser cut plate to act as a washer, then fit the ARP bolts. this way the bolt heads are 100% supported underneath (will achieve correct torque when tightening), and the clamping force can act on a larger area.

Yup, was already thinking this, and i already have it
The engine originally had a flex plate with an extra plate like you describe in front & behind it.

[Supra967]

maybe try not to look at the photo of just the fly wheel? Does look thin around the holes but looks ok assembled.

[Xauterus]

I would just use it and stop worrying

[MWP]

I would just use it and stop worrying

Have you seen what can happen when a flywheel lets go???