Correct pressure plate bolts

[wesk]

Thanks Keith,

To sum it all up:

Question # 1?
What are the correct dimensions for the clutch to flywheel bolts PN 630129?


NOTE!: Length does not include the thickness of the head!

What has Brian found to be available?

The previous chart referred to three bolts I took measurements from.
I had to renumber them below to match up with the lengths.

Below is a photo of four bolts.
#1 is an offering from RJ Fitzpatrick under WO-630129.
#2 is a Mr. Gasket offering #911.
#3 is an Army Jeep Parts offering under WO-630129
#4 is the takeout bolt from my M38.

http://willysmjeeps.com/v2/modules/gall ... .sized.jpg

Note: Brian's overall lengths have been converted to the standard length used in bolt dimensioning to match the blueprint.

Bolt #1=
Total length=.835 (27/32") (-7/32")
Thread length=.625 (5/8") (-1/16")
Grip length=.215 (7/32") (-5/32")
Grip length in flywheel=.0325 (21/64")
Length of threads in flywheel=.38 (3/8")

Bolt #2=
Total length=.98 31/32" (-3/32")
Thread length=.66 21/32" (-1/32")
Grip length=.32 21/64" (-3/64")
Grip length in flywheel=.1375 9/64"
Length of threads in flywheel=.53 17/32"

Bolt #3=
Total length=1.01 3/16" (-1/16")
Thread length=.665 21/32" (-1/32")
Grip length=.335 21/64" (-3/64")
Grip length in flywheel=.1525 5/32"
Length of threads in flywheel=.53 17/32"

Bolt #4=
Total length=1.08 1 3/32" (+1/32")
Thread length=.68 11/16" +/- O.O
Grip length=.4 13/32" (+1/32")
Grip length in flywheel=.2175 7/32"
Length of threads in flywheel=.61 39/64"

Based on the above comparison the closest bolts are #2 & #3. This is because bolts 1 & 4 grip lengths are quite a bit outside the maximum in the blue print. A slightly shorter grip length is allowable but any length longer than listed in the blueprint is out of the question.

[4x4M38]

Thanks for that drawing Keith!

And thanks for summing it up more clearly than
I did Wes.

Again the critical dimensions are what's under the head.
Although bolt 1 is close as far as thread length the grip
is shorter, thus the length under the head is also shorter,
Putting fewer threads in the flywheel.

Note none match the Willys specs shown.

Thanks for listening,

[wesk]

I wanted to make your decimal/inch measurements which were not used much back in the 40's/50's comparable to the blueprint from the 40's that uses the full fractional system. The two key ingredients in bolt dimensions are thread length and grip length. The grip should never be so long it contacts the first thread and the threaded part of the bolt must have at least 1 1/2 threads showing on the other side of the threaded device it was screwed into. The rest makes no difference. Bolts that meet this criteria but have way to may threads showing after fastening them can easily be shortened and the first thread area can be re-camfered on a grinder.

[4x4M38]

That's my key takeaway. My used flywheel is .988? if I remember correctly?

A new flywheel I am assuming would be close to 1" thickness.

I think the only bolt to come even close to showing threads out the back are the 1-1/4" G503 bolts, which appear to be unobtanium.

Willys has been specifying a bolt since the late 40's that will not show any threads out the front of the flywheel. Keith's factory data substantiate that.

I guess they had their reasons.

[4x4M38]

One other clarification.

The total length shown in my data above is from the end of the bolt head to the end of the threads. That is not length under the head.

The bolt shown in Willys document is 1-5/16" long total length,
1-1/16" under the head.

If one compares that total length dimension and length under the head to the examples only one meets that length. Bolt 4.

Length under the head is critical for the reasons Wes posted, and especially in light of the fact you have to subtract the thickness of the pressure plate cover and the lock washer from that dimension. What is left is all of the bolt that will go into the flywheel, whether a portion of grip length or threads.

I'm still puzzled that no one has asked about these bolts before. I guess everyone just sticks their old ones back in.

[wesk]

The bolt shown in Willys document is 1-5/16" long total length,
1-1/16" under the head.

This is what creates the chaos and misunderstandings. Try using the standard bolt dimensioning system. Length is effective length always. from under the head to the tip of the last threads. The length you are using is overall length and is seldom use when describing a bolt. I will now go back and apply this standard dimension system to your figures and correct my chart to prevent un-neccessary confusion to the masses.

[4x4M38]

Thanks Wes.

I have labeled "total length"
and "length under the head"
in my data.

I have the lengths under the bolt head in my posted data here.

I was trying to show the difference as I'm convinced that's how we ended
up with bolts that don't meet Willys own specs.

I appreciate you clarifying and making it easier to understand.

[wesk]

I'm convinced that's how we ended
up with bolts that don't meet Willys own specs.

Actually Willys no longer produces this bolt nor do they procure it. The reason you are only finding bolts that don't measure correctly is that particular bolt is no longer produced and the ones you are being sold by MV Vendors have the Willys part # assigned to the bolt by them. They did not procure their bolt copies from Willys/Kaiser or Chrysler. They procured them from a standard hardware supplier in a size that was close to the Willys spec in the ORD 9.

[WillysMotors]

They procured them from a standard hardware supplier in a size that was close to the Willys spec.

I would have said that they procured them from a standard hardware supplier in a size that was similar to the description in the SNL and parts list but never had access to the original factory design specification. (or figured it was close enough)[/quote]

[4x4M38]

Thanks for the replies.

But hasn't the CJ in one form or another been built and sold into the 60's? I guess to really complete my investigation I need to see if a jeep dealer sells me these bolts and what their measurements are.

I limited myself to some of the military suppliers as that's where many of us would look first. My guess is the after market civilian suppliers would carry the same bolt as Kaiser Willys. They probably all get their parts from the same source(s). The dealer might be another matter.

[mdainsd]

The most important dimension, is the one no one is talking about. The Willys drawing has it. It is the diameter of the "grip length" of the bolt. Notice it has a TIGHT tolerance (.002"). That dimension is what makes it a "special cap screw"

*edit: Wes alluded to this, but the importance of the tolerance on this portion of the bolt cannot be understated.

That diameter is a precision fit, both through the clutch but more importantly the counter bored holes in the face of the flywheel. This is done so that the bolts operate in shear mode. If they were say threaded all the way, or sloppy in the grip length fit, the action tries to bend the bolts at the point of thread engagement. Bending puts the bolts into tension at the thread minor just outside of the flywheel threads, this is a no-no. The tight tolerance fit keeps the forces on the thickest part of the bolt and those forces are shear, much stronger.

[wesk]

Good point to accentuate better than I did above "

You will be best off with grade 8 bolts of the proper dimensions with at least a rating of -2 on close dimensional tolerance.

" It is not just the shear function that the close tolerance found in a -2 bolt gives. It limits unwanted movement between the parts that are fastened together.

Note that in the above posts where the question of bolts includes a part dimension number they all fail to show the -2 for tolerance that is listed in the ORD 9 for that bolt. The ord ( shows 630129, 7324841, screw, cap, hex-head, 5/16-18NC-2x 1 1/16.

[4x4M38]

In my original attached documentation I
noted the grip diameter for bolts 1, 2 and
renumbered 4 were between .306 and .308.

Take care,

[wesk]

But not the relevance of the diameter or it's importance. Had you listed the full ORD 9 description of the bolt originally then one of my first impressions would be that it was a close tolerance bolt.

[WillysMotors]

Thanks for the replies.

But hasn't the CJ in one form or another been built and sold into the 60's? I guess to really complete my investigation I need to see if a jeep dealer sells me these bolts and what their measurements are.

I limited myself to some of the military suppliers as that's where many of us would look first. My guess is the after market civilian suppliers would carry the same bolt as Kaiser Willys. They probably all get their parts from the same source(s). The dealer might be another matter.

This could/should be a subject all it's own.
From the 50's through the 1980's there were only about 8 actual surplus dealers that specialized in 'Jeep Parts'.

You will read on the "G" stories of surplus guys contacting a guy named Rudy in Toledo and getting the names of the 600+ suppliers to the Jeep plant, and buying parts directly from the sub contractor. Eventually, after Willys stopped buying the large quantities, the suppliers started substituting crap that was universal.