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junglejustice · Post by **junglejustice** » Mon May 23, 2005 9:52 am

Thought that I would post this for clarification of this piece. It's simple, but it works.

You can see that the bolts that come out of the flywheel go into rubber and then stop with just a nut on the other end and nothing holding their tips aligned (other than the rubber) They have the ability to flare under torque and at higher rpm the ends spread - this is what tears up the front donut.

The bolts that go through the holes in the donuts and to the shaft don't move as there the go through those metal strips and metal reinforcement/locator pins molded in there. Their ends can't flare...

This simple little plate keeps the flywheel bolts similarly in place and aligned.

junglejustice · Post by **junglejustice** » Mon May 23, 2005 8:28 pm

Don't know why the original post would not log the pics...? Any way, here they are...

zambon · Post by **zambon** » Mon May 23, 2005 9:18 pm

thanks JJ,
I will try to get one or my own in my car since I am replacing my donuts right now anyway. Looks like a great low tech improvement that I wouldnt have thought of on my own.
James

DaveH · Post by **DaveH** » Tue May 24, 2005 5:18 am

JJ,

Can you explain how the flywheel bolts flare? Don't the bolts tightly capture the spacers/sleeves molded into the donut?

From what I can recall from looking at a broken donut, dounts (and guibos ;-> ) are not just 6 spacers molded into a rubber disk. 3 of the spacers are attached to a 3-pointed spider with a big hole in the middle for the nose bearing. Not sure if the flywheel bolts fasten to the spider spacers or not though, but I suspect they do since these spacers are without locator pins.

Reale · Post by **Reale** » Tue May 24, 2005 10:02 am

The 3 lugs that attach to the driveshaft yoke are free-floating.
The 3 lugs that attach to the flywheel are joined centrally to the middle of the donut. However, JJ has evidence that the driveshaft bolts are able to flare outward despite this.
I was considering using a plate like this on BOTH sides of the donut.
I think that the 1-piece driveshaft tends to really stress the front donut. I am tracking front donut lifespan now.

Octopussy · Post by **Octopussy** » Tue May 24, 2005 10:27 am

My front donut recently fell apart at about 4000rpm causeing a fragment of it to put a nice hole in my exhaust( it sounded like a gunshot when it happened). When my mechanic showed me the donut the only thing left was the 3 holes for the driveshaft bolts. So I'm wondering if this plate would've helped prevent this from happening

zambon · Post by **zambon** » Wed May 25, 2005 9:37 pm

JJ

I talked to my machinist today and arrived at a small dilema: what hardness/thickness of steel is needed to optimize this modification? If the steel is too soft or too thin, the holes for the bolts will become ovaled in time, right? Your photo shows steel that looks fairly thin, but what do I know?

James

junglejustice · Post by **junglejustice** » Wed May 25, 2005 9:52 pm

You don't want it to be too thick as (in theory) you would be moving towards a solid coupling again and maybe compromise smoothness... In theory...

Thin. No problem. Just to support that forward rubber a bit. There isn't too much moving around up there once it is all bolted tight.

It time, yes, it may oval the holes and then you just replace it when you do donuts... It's not a cure-all; just a little extra help for high-powered cars...

More intended for a high-powered application that gets opened up regularly any way.

Maurizio · Post by **Maurizio** » Wed May 25, 2005 10:37 pm

You actually could just use a good quality aluminum plate of 1 mm thick.
You want to add stiffness in the radial direction of the bolts and a low stiffness in the nut direction so that the plate can form and take tolerances when assembling. The trick is that the plate has a in plane stiffness which is very large and makes sure the three bolts have to work together against the torque of the engine. It even changes the bending profile of the bolts, which makes the 4x stiffer.

Saluti,
Maurizio

Mats · Post by **Mats** » Wed May 25, 2005 10:54 pm

You should probably stay away from aluminium...
This kind of fastener needs a very stable material to not relax with time, alu will just not do.

In my opinion you can use whatever gauge steel you can fit in there and it won't affect the function of the guibo at all unless the steel plate touches any other part then the guibo and the nut.
The flex occurs between the screws in the guibo and linking the three screws fron the driveshaft won't upset anything, they're already linked on the other side remember...

Maybe keep in mind that you want a perfectly symmetrical part as a heavy part would upset the balance of the shaft.

Maurizio · Post by **Maurizio** » Wed May 25, 2005 11:43 pm

This kind of fastener needs a very stable material to not relax with time, alu will just not do.

A good point, on the nut side & washer side not a problem but the guibo has not such a nice contact surface.

Was thinking of making some supports for a long time.
Now I have the TS drive shaft out, it might bea good time to design something

Mats · Post by **Mats** » Thu May 26, 2005 5:00 am

Not to rub it in or anything but the contact area isn't really the point, alu will relax with time even if it had a very large contact area and a static environment.
That's just alu... You maybe can find a useful heat treated alloy but steel is so much easier.

Maurizio · Post by **Maurizio** » Thu May 26, 2005 5:18 am

I'm just plain stubborn, (that's why I stick with alfa's) so for me it just depends on the applied N/mm^2 .
A plain example, how about alloy wheels.......
But one thing is true looking at fatigue steel wins!

But I don't want to start an huge discussion so guys take the easy and safe route use steel .

Mats · Post by **Mats** » Thu May 26, 2005 8:13 am

I retorque my wheels... you don't?

junglejustice · Post by **junglejustice** » Thu May 26, 2005 11:18 am

Use 2mm to 3mm thick steel, not aluminum

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