Bolts for a Fidanza Flywheel

V12-Engine
1

I have converted from an automatic to a manual transmission and in the process also opted for a Fidanza aluminium flywheel.
Going through the parts manual I discovered that the auto flexplate with spacer ring have different bolts than the bolts for the flywheel. 2 different part numbers. Can anyone tell me the difference ?
I’m guessing that the flywheel bolts are longer. But what is the correct length.? The Fidanza flywheel is thicker than the original steel flywheel, so should I not go for bolts that take that into account ?
Can I simply measure the crankshaft flange, the flywheel thickness and maybe the lock tab ring and ad up the three to get the correct length ?
Are they Grade 8 bolts or something completely different ?

Thanks … Ole

2

Is C4855 not the part number that you require?

If that’s the correct part number for a manual e type, flywheel to crankshaft bolts then will it not suit your application with the Fidanza flywheel?

Rgds.

Andy.

3

Andy, that is indeed the correct PN. There are two reasons for my questions. The Fidanza flywheel is thicker than the steel FW and I would think that the bolts should therefore be longer to grab the entire thread in the crankshaft flange.
Secondly one of the usuals have them listed at either $5.02 or $8.40 a piece and at boltdepot I can all 10 (grade 8) for roughly the price of one.

4

I have converted from an automatic to a manual transmission and in the
process also opted for a Fidanza aluminium flywheel. Going through the
parts manual I discovered that the auto flexplate with spacer ring
have different bolts than the bolts for the flywheel. 2 different
part numbers. Can anyone tell me the difference ?

Yes, the flywheel bolts are longer, because the flywheel is thicker.

But what is the correct length.?

I’m sure you could just measure the thickness difference between flywheel
and flexplate + spacer ring.

The
Fidanza flywheel is thicker than the original steel flywheel, so
should I not go for bolts that take that into account ?

How much thicker? And where do you suppose you’d find exactly the right
length bolts? If it’s no more than 1/8" thicker, I’d probably just use the OEM
flywheel bolts. If it’s a BUNCH thicker, yeah, you’ll need to find suitable bolts
– and if the heads aren’t the right shape, you might need to find different lock
tabs, too.

Can I simply
measure the crankshaft flange, the flywheel thickness and maybe the
lock tab ring and ad up the three to get the correct length ?

Both the flexplate and the flywheel use the same lock tabs, so those won’t
make a difference. But yeah, adding up the thickness differences is the way
you should go.

Are they
Grade 8 bolts or something completely different ?

They LOOK more special than that, but I don’t see any good reason regular
Grade 8 wouldn’t work. You might look around at Chevy flywheel bolts or the
like and see if any just happen to be the right size. When you’re doing all
this, lay your clutch disk on the flywheel and check out the clearance
between the center hub of the clutch disk and the heads of the bolts,
remembering that the clutch disk gets compressed a bit in actual operation.

You haven’t mentioned the two drive pins. The flywheel uses longer ones
than the flexplate, and for the same reasons you might need longer ones yet
for your thicker flywheel. If so, I think you’re in for having them custom
made.

Frankly, I’m a bit surprised that Fidanze doesn’t make their flywheels exactly
the same thickness there so you could use the OEM hardware. That, or
provide the needed hardware with their flywheel.

– Kirbert

5

Kirbert, I will get the longer drive pins, as I noticed they are different as well. Thanks for pointing it out.
I’ll double check the actual thickness of the two flywheels and consider your 1/8" guideline.
I did think about the bolt heads as well, but not whether they would interfere with the clutch plate. The flywheel/flexplate bolts seem to have a shallower (if that’s the word) head than your ordinary bolt from the hardware store.
Thanks for your inputs.
Engine, gearbox and car body will meet up soon and I plan to be on the road in April/May time. Or later. :slight_smile:

6

The flywheel/flexplate
bolts seem to have a shallower (if that’s the word) head than your
ordinary bolt from the hardware store.

You can fix that, of course, but if you take to grinding bolt heads you might
want to weigh each one and make sure they all end up the same.

The clearance issue for the clutch disk depends not only upon the thickness
of the flywheel hub and the height of the mounting bolt heads, but also the
overall thickness of the flywheel. Basically, the key issue is the depth of the
recess in the middle of the flywheel. When Fidanza made the hub thicker,
did they also locate the clutch face farther away from the crank flange? This
all starts to get into stack height issues and making sure your throwout
assembly has the correct range of travel.

Back in my college/co-op student days (mod-1970’s), a guy where I worked
showed up one Monday morning in a brand new DeTomaso Pantera. We all
said “We heard those cars were unreliable.” To which he replied, “That was
the original model. This is the Mk II, they fixed all the problems.” That
Thursday, the car failed to make it to work. Turned out somebody had
installed the flywheel bolts incorrectly and a couple of them backed out and
prevented the clutch from engaging. He had the car towed back to the
dealer, where of course they had to pull the engine/transaxle combo and
separate them to retorque (and presumably re-tablock) the flywheel bolts.
They then reassembled the engine to tranny and reinstalled it in the car, but
somewhere in all that they dented the oil pan. When they went to start the
car, the crank ripped a hole in the oil pan and dumped all the oil on the shop
floor. When they finally got THAT fixed, the guy picked up his Pantera and
drove it home and parked it in the garage and we never saw it again.

– Kirbert

7

I think you’re taking all the necessary precautions Ole. FWIW my used Fidanza appears to have been assembled sans lock washer plate as the alloy is visibly compressed around each bolt hole. 0n the AJ6/AJ16 manual flywheels they use 12-point bolts with a thinner wider flange but the oattern is different and I think they use 8 set screws and a pair of dowels. By working from first principles and using thread lock and a lock washer plate you should be OK.

8

And that’s how you “create” a future barn find :slight_smile:
I actually just bought a jewelers scale so I can “adjust” all the clutch bolts to the same weight, so I’m prepared for potentially having to adjust the flywheel bolts.

9

Thanks Pete. I have a new lock tab plate. Would you use Locktite as well ?

10

One summer in HS I worked for a guy who put vinyl tops on cars. My job was to drive back and forth to the dealers delivering one POS with a new top and picking up the next victim. On a Friday afternoon I arrived at the Ford dealer and turned over one car and while waiting for instructions I noticed a guy in a tux who looked like he was about to walk the “green mile”. A few seconds later the “bride” returned from somewhere in her very white dress which of course was becoming very dirty in the shop. In retrospect she may have been calling a lawyer. So I asked the manager what was up? He pointed to a Pantera (remember they were sold partly under a flag that your local Ford dealer could work on them) that was in an advanced stage of being taken apart. So “what is wrong with it” I asked. It is the alternator and we have the SOB in stock–the problem is we can not figure exactly how to get the old one out and the SOBs at Ford are gone for the day. Wonder where that car or that couple are today? I know where the cars are we put tops on–they are the ones that let go and inflated going down the road!

11

It is the alternator
and we have the SOB in stock–the problem is we can not figure exactly
how to get the old one out and the SOBs at Ford are gone for the day.

Exoticar with a Ford V8. My understanding is that things were very tight
under the hood indeed.

When I worked at P&WA, there was a guy there, a playboy type, who owned
a Pantera and drove it hard. Hard enough that the front lower A-arms failed
on a regular basis, he had taken to keeping spares on hand and had
become adept at replacing them. I didn’t actually work with him, dunno what
kind of work he did there, but if it were me I woulda become adept at
MODIFYING them so they wouldn’t break any more!

– Kirbert

12

I have a new lock tab plate. Would you use Locktite as
well ?

I’d use anti-seize compound. But that’s just me.

– Kirbert

13

Ole
Just make sure the bolts are a few millimetres SHORTER than the “bottom out” distance. When I converted my xjs to manual I was under the car. Torqued the clutch pressure plate onto the flywheel. All torqued EXCEPT the bolts were slightly too long and were torqued against the bottom of the thread hole. Clutch shudder until I discovered the problem.
In fact…it is only the first few turns of thread that do any work in a bolted connection …the rest of the bolt is relatively unstressed so going a few millimetres shorter is not an issue.
Regards
Matt

14

I cut the bolts so that they would just bottom out without the clutch pressure plate installed, avoiding the scenario you describe. My newly purchase jewelry scale will allow me to trim the bolts to within 1/1000 of a gram. That should help avoiding imbalance :slight_smile:

15

I also had an aluminium (I think Fidanza) flywheel fastened without the tab washer and the bolts had “eaten” out the Ali.

The data I have on the bolt is that it is 7/16-20 x 7/8" with 5/8" thread length and 11/16" head size. The head is 9/32" thick with a thrust face beneath it. Stamped GKN ABL X

I am not aware of any clearance issues with the thickness of the bolt head.

The objective is to evenly spread the clamping force around the face of the flywheel where it clamps against the crank flange (with minimal deformation around the bolt holes). I suspect that Ali flywheels are poor in this regard and therefore benefit from the use of the broad tab washer. The location dowels should take zero shear force, therefore I do not see a problem with using “shorter” dowel pins in the thicker ali flywheel.

You want the highest coefficient of friction practical between flywheel and crank. You can even buy special friction washers to go between flywheel and crank which are covered in diamond dust. I believe the Corvette uses such a device.

The coefficient of friction between a steel flywheel and the crank is given as 0.5-0.8 and for an ali flywheel is 0.61. If there is oil or grease present then your coefficient of friction drops to 0.16. That would be very bad.

Flywheel Bolt 1.jpg1141×863 74.3 KB

16

> The location dowels should take zero shear force, therefore I do not see a problem with using “shorter” dowel pins in the thicker ali flywheel.

The location dowels are supposed to take 100% of the shear force. If they don’t cross the joint between the flywheel and the crank flange, they’re doing nothing, might as well leave them out. If you can’t find location dowels long enough, I’d take the flywheel to a machine shop and drill recesses into those two holes so the dowel head can fit down into the flywheel flange and under the locking tab.

> You want the highest coefficient of friction practical between flywheel and crank. You can even buy special friction washers to go between flywheel and crank which are covered in diamond dust. I believe the Corvette uses such a device.

Nuts! We didn’t design things that way at P&WA – but P&WA is a far cry from GM.

I recall one turbine disk for which the torque requirements were so high that there was a dowel pin about every 4th bolt all the way around, and that’s a flange with perhaps 60 bolts. At P&WA, the design presumption was that 100% of the torque was taken by the dowels, none at all was taken by friction and none at all was taken by the mounting bolts. The fact that this Jaguar flywheel assembly even HAS a pair of dowels tells me that’s the thinking here, too. If it was intended to rely upon friction, there wouldn’t be any dowels.

– Kirbert

17

> I also had an aluminium (I think Fidanza) flywheel fastened without the tab washer and the bolts had “eaten” out the Ali.

Are you guys installing these things without the locking tabs? You need SOME sort of flat washer under a bolt head tightened down onto aluminum – always – but I would have expected the locking tabs to suit that purpose.

If you’re getting this sort of wear through the locking tabs, if I were installing one of these Fidanza flywheels I’d be tempted to install that spacer ring from the flex plate under the locking tabs. That, of course, would require the bolts to be longer still, and raise yet more questions about clearance to the clutch disk.

– Kirbert

1 Like
18

I run a Fidanza aluminum wheel, and the pressure plate bolts sent with the Keisler kit it was part of were defective: one of the bolts somehow escaped the threading process during manufacture. I ended up buying pressure plate attachment bolts in a specialty pack from a speed shop (high strength, right size, etc.). I used a locking washer (don’t recall the type- probably a star or some such).

I you are speaking of the pressure plate, just get highest strength bolts and ensure they are long enough to engage more than the diameter of the bolt in threads, more if possible, and that they DO NOT bottom out in the flywheel. I know one other Jag lister who fitted a Fidanza wheel, and his bolts bottomed out in the wheel just at the point that the bolt face was touching (but not squeezing) the lock washers. He got the torque OK, but the pressure plate could move, and he could not fully release the clutch after getting the whole mess back together. Only after a VERY long and frustrating disassembly (multiples, actually, as I recall) did he finally see that the bolts had bottomed out in the wheel.

I want to recall that I used the OEM jag bolts and a fresh locking tab set to fit the new wheel, but I may also have used new bolts (been about 9 years since I did this).

19

Thanks to all for your inputs. I had a couple of A-ha moments and will do some additional measurements and test fit this weekend.
Just to satisfy the general curiosity (perceived) I plan to post my findings, once I have everything worked out.

20

s. The fact that this Jaguar flywheel assembly even HAS a pair of dowels tells me that’s the thinking here, too. If it was intended to rely upon friction, there wouldn’t be any dowels.

Kirby
No quite. The dowels ensure exact alignment which you don’t get unless you have fitted bolts…which are not used here. So the dowels ensure concentricity but they can also absorb shear force. Aluminium is quite soft I would hope that the Fidanza Engineers calculated the bearing load from the shear pin at failure to make sure the alloy would hold it. The friction grip also provides torque capacity that is significant. An m10 can provide 3-4 tonnes of clamp force X 6 ( I think there are 6 bolts)= about 20 tonnes…even greased this would require 2 tonnes to slide the surfaces. I am surprised to hear that an aircraft engine doesn’t make use of the friction grip. It’s available for free and reduces the amount of components and therefore weight…
Matt