Drilling a Fidanza

[Ccmano]

So I’m about to drill the pressure plate mounting screw holes deeper and tap for the longer bolts. Is there anything special about this process I need to know before I start?
H
:cheers:

[Jagdpanzer]

Be sure the drill bit you use does not cut back the existing threads and use a depth stop so all are the bore depths are uniform. Make first pass with a regular 3/8-16 starting tap then finish with a bottoming tap. Use aluminum thread cutting oil.


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[Jagdpanzer]

You may also have to slightly countersink the bore entry with a 3/8” drill bit or end mill cutter to allow the bolt shank to seat deeper.


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[Jagdpanzer]

And best to do these steps on a drill press.


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[A26B]

My Fidanza was drilled tap size, all the way through from Fidanza. All I had to do was run the tap through.

[Ccmano]

My Fidanza was drilled tap size, all the way through from Fidanza. All I had to do was run the tap through.

By “all the way through” do you mean the hole came through the back?

Good stuff, guys. Thanks
H
:cheers:

[A26B]

By “all the way through” do you mean the hole came through the back?

Good stuff, guys. Thanks
H
:cheers:

Yes, drill holes went all the way through the flywheel. It was only tapped deep enough for the standard bolts. All I has to do was start the tap into the existing threads and thread them deeper. My Fidanza was purchased in 2003. Looks like I got lucky....hope you are too.

[Ccmano]

Yes, drill holes went all the way through the flywheel. It was only tapped deep enough for the standard bolts. All I has to do was start the tap into the existing threads and thread them deeper. My Fidanza was purchased in 2003. Looks like I got lucky....hope you are too.

Interesting... mine is not drilled all the way through. However the treads do go all the way to the bottom of the holes. Just not far enough for the longer bolts.
H
:cheers:

[WVZR-1]

Interesting... mine is not drilled all the way through. However the treads do go all the way to the bottom of the holes. Just not far enough for the longer bolts.
H


Is there not a specialty bolt available that might make life wonderful? What is the actual depth of the holes?

[Ccmano]

Is there not a specialty bolt available that might make life wonderful? What is the actual depth of the holes?

Not that I am aware of, but I already found a set of the recommended SRP bolts. (Thanks to Jagdpanzer). If you do a search in the Tech section there is endless discussion of this over ther years. These (no longer available) SRP bolts are best solution. It should be noted that they are simply shortened versions of an existing ARP bolt. Why SRP didn’t make them just a bit shorter to fit the exiting hole, I can’t say. From what I can see the regular bolts utilize about 60% of the thread in the Fidanza. Utilizing all the thread would be sufficient. The difference between the SRP bolt length and the depth of the hole the Fidanza is only about .25 inches. I will check shortly. Shortening the bolts my actually be the most expeditious solution.
H
:cheers:

[WVZR-1]

Not that I am aware of, but I already found a set of the recommended SRP bolts. (Thanks to Jagdpanzer). If you do a search in the Tech section there is endless discussion of this over ther years. These (no longer available) SRP bolts are best solution. It should be noted that they are simply shortened versions of an existing ARP bolt. Why SRP didn’t make them just a bit shorter to fit the exiting hole, I can’t say. From what I can see the regular bolts utilize about 60% of the thread in the Fidanza. Utilizing all the thread would be sufficient. The difference between the SRP bolt length and the depth of the hole the Fidanza is only about .25 inches. I will check shortly. Shortening the bolts my actually be the most expeditious solution.
H


Why wouldn't a bore from the back-side to allow the use of the bolt "as is" be maybe much easier? If you've sufficient threads and depth I'd think I'd rather that than risk destruction of existing threads when attempting to bore and thread.

Through the years there's been much discussion but I believe it's actually maybe "what's required for each individual" - yours is very different than what some have experienced and it could actually change I'd think dependent upon "BRAND" of flywheel.

Balance? I'd think regardless of drilling/threading or back-side relief you'd certainly re-balance.

[A26B]

The entire concept of the "special" bolt is to provide more thread engagement. Yield strength is greater in iron than aluminum. Less engagement can result in stripped threads & loose bolts.

Working with blind holes requires attention to detail, to insure the shank of the Special PP bolts is engaged in the flywheel counter-bore, below the surface of the flywheel. Achieving maximum engagement without binding on incomplete threads or hole bottom can be tricky. The LT5 crankshaft tapped holes for the flywheel bolts are also blind. Caution must be exercised when using after market bolts here as well. If the bolts bind or bottom out, the flywheel may not be clamped sufficiently to the crank flange.

The OEM & aftermarket bolts for the pressure plate are designed so the "major" diameter of the shank engages the counterbore to provide the maximum torsional shear resistance. The "minor" diameter of the bolt thread "root" is also a stress riser. Both factors are undesirable for the application.

The other function of the bolt is clamping, placing the bolt in tension.

In summary, the aftermarket "special" pressure plate bolts are purposely made with a longer thread. Cutting them off defeats the entire purpose.

OK.... just how necessary is it to use the "special" PP bolts anyway. It's a valid question. To my knowledge, a catastrophic failure has not occurred from using the stock PP bolts with an aluminum flywheel. Loose bolts have been known to occur.

I'm old school, having been hot rodding since before scatter-shields & when flywheel/clutches sometimes exploded at high rpm. It's something you never forget. So for me, the special bolts are an exercise in good judgement and an inexpensive investment for the insurance. Engineers with experience in this area could calculate the requirement for thread engagement in this application. It's not my area of expertise so I tend to compensate by over-engineering to be on the safe side.

Your choice..... Choose wisely grasshopper.....

[Ccmano]

Jerry,

Concept of shortening the SRP bolts was simply a potential expedient to utilize the existing fully threaded FW holes without drilling. It would have resulted in thread length longer than the standard bolt but shorter than the SRP bolt. Roughly splitting the difference of the two.

As you know, Haibeck for example, simply uses the standard bolts with the Fidanza and has had no issues that I am aware of.

Nevertheless I decided to go ahead and drill the FW since I already have the SRP bolts and be done with it.

Thank again for all the input guys! This is what make this group so special!
H
:cheers: