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Topic Summary

Posted by: athawk11
« on: October 06, 2017, 07:37:36 PM »

Quote

For the life of me I can't figure out why the change was made after WWII from 1-1/4" to 1-1/16".

Following the war, auto manufacturers like Willys understood that most post war consumers/farmers weren't going to have much disposable income.  They were motivated to cut manufacturing costs so they could sell a CJ2A for a reasonable price.  You can see the results of these cost cutting measures when you compare an MB to a CJ2A.   I don't know about you, but I would love to have a glove box and wheelhouse tool boxes in my CJ2A and 3As.  Fact is, it cost too much to keep them.

I assume a shorter bolt would cost less back in 1946.  It may seem an insignificant cost saving choice to use a 1-1/16" bolt in leu of a 1-1/4" bolt, but every penny adds up.  And if the engineers saw no failures using a shorter bolt, well, why not use the shorter bolt?
Posted by: 4X4M38
« on: October 06, 2017, 07:14:13 PM »

Thanks for the reply.

Does that have to do with bottom hole threads
or through holes and does that matter?

This is what the ASME says:
ASME B31.1 "135.3.4 Bolt Engagement. All bolts shall be engaged so that there is visible evidence of complete threading through the nut or threaded attachment."
Posted by: mtnman37879
« on: October 06, 2017, 04:51:59 PM »

If the female threads used are equal to the bolt diameter, it's as strong as it's going to get. example, a 3/8 bolt needs 3/8 of female thread and a 1/2 bolt needs 1/2 of female threads.
Posted by: 4X4M38
« on: October 06, 2017, 12:39:16 PM »

The reason I'm asking is while buying WO-630129 bolts for my M38 I found they were 1-1/16" overall length and only 3/4" long
under the head. Checking with another supplier they sell a bolt with that part number with the same dimensions.

Neither meet the two Willys CJ2A specs above nor the 1955 Ord 9
G740 or G758 specs, so I started looking for proper bolts, as well as trying to see if Willys or Jeep changed to 3/4" under the head.

Using my used, takeout flywheel and my takeout bolts which are 1-1/16" or as measured 1.08" under the head. Taking into account the lockwasher, clutch cover, and bore to thread in the flywheel,
that results in .61" of threads in the flywheel. A 1-1/4" bolt would seem to have .7795 threads available, which would protrude slightly out the front of the flywheel, and use all the threads in it.

Everything shorter would use fewer threads in descending order
and result in the 3/4" long bolt having only .38" of threads in the flywheel.

I'm trying to document if any change to the shorter bolt was done by the manufacturer, and if not, confirm my numbers, and perhaps contact the suppliers and let them know my findings.

There is at least one supplier so far that is selling NOS bolts which I hope to have specs for, and Mr. Gasket sells #911 bolts which are 1" under the head, do have the unthreaded grip portion of the shank, and have .53" of threads in the flywheel. They are available on the Internet and special order at auto parts stores.

For the life of me I can't figure out why the change was made after WWII from 1-1/4" to 1-1/16".
Posted by: athawk11
« on: October 06, 2017, 10:29:44 AM »

I would add to Oldtime...

You can get these special bolts from shops that resurface flywheels. (At least that's where I got mine.)  It's worth it to get the right bolts.  The shoulder on the bolt (mentioned above) acts like a dowel bolt, keeping the pressure plate centered on the flywheel.
Posted by: oldtime
« on: October 06, 2017, 09:05:53 AM »

Yes I concur on the 1-1/16" length.
Ideally they should have a very short section of untreaded shoulder.
Perhaps 1/8" or 3/16" was untreaded.
They were a specialty bolt in that regard.
Grade 5 should be near optimum.
There is no reason to have bolts that are way stronger than the flywheel itself.
Be careful not to over torque these bolts or threads will strip out of the flywheel.
Posted by: athawk11
« on: October 05, 2017, 12:56:43 PM »

The 2nd (1947) and 3rd (1949) Edition of the CJ2A parts list says:

Clutch to flywheel bolts... Qty: 6 ...5/16-18 x 1-1/16" .
Posted by: 4X4M38
« on: October 05, 2017, 08:37:23 AM »

The Ord 9 G503 specifies a 1-1/4" long bolt.

The Ord 9 G740 and 758 specifies a 1-1/16" long bolt.

Does anyone have documentation this length was changed to 3/4"
or 7/8" for the civilian jeeps?

FYI, screw and hex bolt length is measured from the bottom of the
head to the end, not overall length.

Thanks,
Brian