There is an apparent discrepancy in the lengths of the ARP and Mr. Gasket PP bolts. Page 178 of the Mr. Gasket catalog has them listed at 1 inch. Rodger reported that he measured the ARP bolts at .75 inch. Here is a length to the Mr. Gasket catalog. http://www.mr-gasket.com/pdf/Fasteners.pdf

EDIT -- I guess Mr. Gasket could be including the size of the head in their numbers....

According to Aaron at Fidanza, the Fidanza flywheel has three different bolt patterns, two for pressure plates with for 5/16" bolts and one for 3/8". The counterbore measurements are as follows:

- 3/8" bolt pattern, depth is .20 and width is .375

- 5/16" bolt pattern, depth is .20 and width is .312. This is the pattern my long style McLeod 360500 uses.

Aaron says these FE flywheel counterbore dimensions would have been derived from the original steel flywheel. I have my original R-code flywheel in the garage and I see absolutely no counterbore.

So I guess I will get the thickness of the McLeod pressure plate at the bolt hole, call ARP and do some math.

Just in case you were dozing when we went over that in math class...

D = Basic Diameter.
p = Screw Thread Pitch
Le = Length of Thread Engagement
A t = The screw thread tensile stress area
d p = Pitch circle diameter of thread
A ss =The thread shear area

The following formula for the Tensile Stress Area of the (male) screw

http://www.roymech.co.uk/images/formula_at.gif

The ARP 250-2201 bolts are 3/4" long. The shoulder is 1/4" long, the threads are 1/2" long. I still have them....looking at them...never returned them to Summit after determining they were too short. The 3/4" length was the problem...too short....not enought thread engagement. You can go back and re-read the details.

The Mr. Gasket bolts (p/n 911) are advertised as 1" long. Looking at the enlarged picture on Summit's website, it looks like the shoulder may be 1/4" long and the threads may be 3/4" long.

I don't know why they are different lengths, yet both are claimed to be Ford or OEM replacement?

Rodger

I didn't see this until after I called ARP but they told me the same thing. By the time you consider washer and pressure plate thickness, you have maybe 5/16" of both threaded into the flywheel. Doesn't seem like enough. I think I'd rather have my current setup over that.

In this particular case I have decided to work with this formula:

RR = Pexposed/Pnon-exposed ;)

Uh-huh. I think if that was my car with the Grade 1 K-mart bolts in it I would just leave them there. I think they're probably good enough. :p Seriously.

Yes, not having them in front of me the only thing I can guess is that the head itself is .25" and Mr. Gasket includes that in the 1", and the bolts are really the same size.

I was pointed to this by HST:

http://www.cncbrakes.com/mc.asp?grp=...712&subseries=

Thanks Jean!

There are five different bore sizes on that page -- you need to get the right one. Any chance you could snap a quick pic of the MC that is on your car and post it?

If the ARP bolts and your current bolts are the same length, then you'll have the same effective amount of threads with both bolts (but you get the additional benefit of the shoulder strength with the correct ARP bolts). Of course you could always forego the use of a washer for the additional thread strength, or do like I did and use a "skinny" washer. I don't know what the width of the ARP washers are, but Rodger has them sitting on the kitchen table so he can tell you. I think they're pretty fat.

http://www.clubcobra.com/photopost/d...ium/ppbolt.jpg

They said 3/4" for the clutch.

Using the ARP bolts with their washers doesn't leave enough thread in the flywheel in my opinion. The 250-2201 ARP bolts with some very thin washer/shims I have might work. I am still confounded as to where these bolts I have came from, and why I used them without washers. I didn't fart during this build without having either specific instructions or some pertinent reference from the build books or experience from threads here.

Uhh, maybe it was like in Dallas when we all thought Bobby was dead but then Pam woke up and it was all a dream.:JEKYLHYDE

Yes, exactly.

Late coming to the party
 

elmariachi Jim I missed the Dallas thing unless it was Football. Anyway, Couple of things here are not quite right
Pressure plate bolts rely on the first 3-4 thread for 90% of there holding powers on a clutch pressure plate to flywheel.
I have run an iron flywheel (40#) for 3 years and now run an Aluminium one. There are helicoils in the Summit one I have. Yours may also have them or a timesert for the clamping power needed. I have not had a pressure plate bolt come loose in any of my cars or the Vettes, GTO's, or trucks I have worked on in the last 10+ years. I allways used Loctite for flywheel and pressure plate bolts, RED not blue. You are worried about your bolts in your clutch, you should see the small ones now being used in the new stuff. 8 & 10MM heads on a 1/4" -5/16's thread.
If you are running a RACE clutch with a 3,800# and up clamping load and up I could see the issue with longer bolts. Most Cobras are running a 2,800# to 3,200# on the street. If you want more holding power of a clutch, multi disc is the way we are going.
I use the washer on my bolts and have no problem. I the old days there was a steel ring that the bolts of the flywheel went through to not gall the surface of the flywheel. I never found loose bolts on one of these motors with 20-50 thousand HARD miles.
There is alot of heat and expansion going on in the bell housing, also alot of stress on the pressure plate bolts. Having washer washers spreads out the load bearing on the heads of the bolts, they may even absorb some of the loading and unloading pressures. I believe in ARP bolts, nuts, washers, and other fasteners. I have used them on motors for more than 30+ years. I have broken everything in a block but have yet to have a bolt break of theirs cause the main failure.
Jim go with a longer bolt if you want, just make 100% sure that the other end doesn't hit the block, or block plate in a full 360 degree rotation. I have seen this happen a couple of times.:eek::CRY:%/ Rick L

The rule-of-thumb for thread contact is, 1.5 x diameter of bolt/stud. This is a generality, variables like hardness, materials, threaded hole depth etc impact on it. Bottom line, if you follow this you'll never come up "short".:rolleyes:

That was one of the first concepts I learned in the Navy's Machinist Mate "A" school back in 1970..

If anything, Rick tends to fall on the "alarmist" end of the mechanic's spectrum. For him to allay our fears of the ARP bolts speaks volumes. Just periodically stick a torque wrench in the fork hole and make sure they're snug -- that's all you need to do. And if you've been running non-shouldered Grade 8 bolts without a hitch for a couple of thousand miles, I don't think you need to change them out either. Rick is great -- Rick is my hero -- I love Rick.:D

Undy, if you had read this thread from the beginning (at least from the point where Tom Kirkham brought up the concern with the bolts), you would realize that you are repeating what has already been stated...and that this is exactly the concern. ;)

As previously discussed in this thread, with the ARP fasteners you very well may NOT have this thread depth. (Actually, ARP said 1.5 X dia. MINIMUM, and RECOMMENDED 2 X dia. when threading into aluminum.)

ARP has stated their pressure plate bolt sets are intended ONLY for OEM replacement and could very well NOT have adequate shoulder or thread length for aftermarket aluminum flywheels.

You guys jumping in at the end of this discussion need to read this thread from the beginning to get the whole story.

As far as Rick's statement: "Jim go with a longer bolt if you want, just make 100% sure that the other end doesn't hit the block, or block plate in a full 360 degree rotation." This too has already been discussed. Go back and read the entire thread. I did this and ARP explained in detail why that was the WRONG thing to do...unless you do some careful measurement concerning the shoulder length (and no, ARP says you should NOT use a shoulderless bolt....read their reason in my posts in this thread.)

I retired from a career as an engineer in the maintenance department of a major chemical production facilty where I learned the devil is hidden in the details. You may not realize the weakness of a component (or worst case, the failure thereof) until you look at it in the smallest detail. I've also been a gearhead/semi-pro racer all of my adult life. My hobby and my career complimented each other and each helped me to be better at the other.

OK....I'm off the soapbox. ;) Maybe we have taken this to a greater level of detail and concern than necessary. Maybe just using a suitable bolt (obviously Grade 8 minimum) of a length to obtain adequate thread engagement is all that's really important. Maybe the shoulder isn't even necessary. Maybe the advice from ARP is more detailed than we need to be concerned about. :confused:

Rodger

In the words of the great George Anderson at Gessford, "That's how the Ford engineers designed it, and in 25+ years they never saw fit to change it. That's good enough for me."