M38 L134 Short Head Stud

RICKG · Post by **RICKG** » Fri Apr 01, 2022 9:28 pm

Well done Gentlemen! I'll need to study this thread more in depth.

Post by **wesk** » Fri Apr 01, 2022 10:33 pm

There are a lot of opinions and varying interpretations of some facts and in some cases varying interpretations of someone else's opinions.

My interpretation of the author's comments on 6 of 8 threads does not refer to actual thread pitch but it refers to 6 out of 8 threads of the subject bolt/nut period.

The study sheet that Jake introduced seems to be the opinion of the author who ID's himself as an amateur mechanic and contains his interpretations of the two references he listed at the bottom of his report. If you try to research those two references you should notice one link does not work at all and the other hits the titled web site but says page unknown. When I search the Coburn-Meyers web site I found the specs pages did not mention studs at all.

I started building and racing cars when I was 14. I have spent 22 years in the Air Force as a heavy jet mechanic and helicopter mechanic followed by 32 more years in to present in general aviation as a technician and inspector. I have been active in this jeep hobby since 1971 and built over 20 of them. What I posted on this topic is based on my opinion and interpretations of available technical data and those many years of hands on experience.

Any topic can be selectively researched to obtain supporting data for one's opinions but you still end up with opinions and rarely any solid engineering reports, drawings or papers.

Finally I will reiterate that studs have threads at both ends and the stressors apply equally to both ends. The safest path to follow is maintaining the best possible thread engagement at both ends which means leaving the last couple of threads at each end in the open. One other point I think no one has brought up yet is that course thread torques are usually lighter than fine thread torques. What does this mean??? If the higher torqued fine threaded nuts are suppose to only load the first 6 threads in an 8 thread nut then you should research how this same principal is adjusted to compensate for the coarser threads which get lighter torques because they are more easily damageable threads.

[quote]E-mail me at bill@gizmology.net if you find a mistake!
Coburn-Myers Fastening Systems: Dimensional Specifications
This reference link goes to an unknown page,
Model Engineering Thread Data
This reference link leads to an empty page.
[/quote ]

RonD2 · Post by **RonD2** » Sat Apr 02, 2022 11:50 am

I'm still wondering if I'm the first to discover that all those ORD9's that call out 3-1/2 inch studs that our MV vendors sell are wrong.

Post by **wesk** » Sat Apr 02, 2022 2:00 pm

I doubt it. Several thousand the last 10 years have tried using those studs. The ones that turned them out a couple to cover the shortness usually found out that they later pulled the cast iron threads during one of the torque or re-torque attempts. There are dozens of post since 1996, when I first opened the M38 Yahoo group, on all the 4 cylinder powered jeep sites that discuss the pulled threads issue.

RonD2 · Post by **RonD2** » Sat Apr 02, 2022 2:03 pm

I'm confused by your answer Wes.
What do you mean by "I doubt it"?

Are you saying the ORD9 length for the short head studs are wrong ---- or are they right?

RonD2 · Post by **RonD2** » Sun Apr 10, 2022 9:10 pm

Well, if your search brought you here, it kind of looks like this post is yet another open-ended (unanswered) question about the accuracy of parts listed and described in the ORD9.

No help here. Look someplace else for answers.

Post by **wesk** » Sun Apr 10, 2022 9:28 pm

RonD, This is the first time this post appeared in my unread list since my APR 2nd 2:00 PM post above. So I HAVE NOT IGNORED YOUR SECOND QUESTION!

My statement "I doubt it" referred to the question part of your post: I'm still wondering if I'm the first to discover

Again my reply simply put means "No you are not the first one to discover it!

RonD2 · Post by **RonD2** » Mon Apr 11, 2022 6:34 pm

Ok, thanks for the clarity Wes. I'm not the first to discover it.

I've searched and read many many posts in this forum, some going back well more than 10 years, and I've yet to come across any hint, much less a clear statement, that the length dimension for the 12 short studs called out in several editions of the ORD9 is wrong.

Many members asking questions in this forum related to studs were often given advice and pointed to the ORD9 --- with no mention that the studs are the wrong length.

And yet, members have been rebuilding L134 motors for years and often report and show their good progress in this forum --- but not one post I could find says they used the the 12 short studs called out in the ORD9 and found them wrong.

With more than 6,000 members in this forum (ok, really only maybe less than 100 participate actively), and 75,000 posts in more than 15 years --- it's unusual not to find anything about it.
I guess I missed it.
And going by vendors selling them as "correct" even today, I guess I'm not the only one. Spent $35 on studs I can't use. Oh, well.

I have many notes in the margins of my manuals. Here's another.

Maybe there's a Willys Service Bulletin or a Willys engineering drawing update that never made it into the ORD9 because of the short service life of the M38.

Maybe the Army had enough spare RMC motors in stock that they never needed to rebuild motors in the field or at a depot --- and never discovered it.

I guess we'll never know for sure.

Post by **wesk** » Mon Apr 11, 2022 8:56 pm

The short wind of it all is can you confirm that the Ord 9 WO Part number 349368 for the 3 7/16" stud is too short??????????????? It is not uncommon for hardware to have a nominal length that is not the same physically when you measure it. I am very curious who first started calling the short stud 3 1/2"???

RonD2 · Post by **RonD2** » Mon Apr 11, 2022 10:11 pm

Wes,
At the top of this post I mentioned that I haven't started assembling my motor yet so I can't confirm for a fact that a 3-1/2 inch stud is too short. You might recall that I started this topic to not de-rail Don's project thread where his fresh experience proves that 3-1/2 studs are too short. I expect to have the same experience. I'm just trying to avoid having a torque wrench in hand and finding it out the hard way.

All I can tell you for a fact is that I have 12 studs in hand that measure exactly 3-1/2 inches long. I bought them some time ago from one of our venerable MV parts vendors.
You asked

I am very curious who first started calling the short stud 3 1/2"???

That would be me, quoting what I have in hand.

The ORD9 calls for 2 sizes of the "short" stud (used on different engine serial number ranges):
WO-349368, G503-7371137 at 3-7/16 inches long
and
G716-7348512 at 3-3/8 inches long (1/16 inch shorter than 349368). G716 is the PE-95 Generator.

Several of our vendors advertise the WO-349368 as 3-1/2 inches long.
Other vendors don't give a measurement, just calling 349368 and 7348512 as "standard" length.
Only one vendor I found gives 3-7/16 as the length for 349368.
Nobody advertises 3-3/8 inches as the measurement.
It's not hard to verify this by searching what's being sold on the market.
I didn't make any phone calls to ask vendors for measurements.

There's not much point to that because I'm about 99% convinced that 3-1/2 inches is too short to seat the stud finger tight in the block and still give 2-3 threads showing above the nut.

The next best solution seems to be the Dorman 675-013 stud (3-5/8 inch) that Don had success with.
Either that, or start custom cutting my own by hand as some talented folks are doing (but something I'd really like to avoid).

Naugha · Post by **Naugha** » Tue Apr 12, 2022 7:58 am

Pragmatism is reality’s looking glass.

Other imponderables.

Seven of my twelve ‘short stud’ head holes needed studs slightly longer than the 3.5” studs sold on line as proper for those holes.

Ah.... but five of my twelve ‘short stud’ head holes worked just fine with 3.5” studs.

More haha to the story. I bought the three M38 ‘long studs’ from KW, who’s ad says you only need two long studs on the M38.... and yep, I think those ‘long suds’ look too long. Oh, well.

To anyone out there who ended up with studs or other parts that don’t fit, are not correct for their jeep, are worn out junk or are repops that look like caca ..... or parts that get lost in the mail ....... well, heck.

RonD2 · Post by **RonD2** » Tue Apr 12, 2022 11:02 am

Hi Don,
Can you map which size stud you used in each hole?

Post by **wesk** » Tue Apr 12, 2022 11:05 am

Ron,

Which one of those two #2's is actually a Number 3?

RonD2 · Post by **RonD2** » Tue Apr 12, 2022 11:13 am

Hi Wes,
The number 3 hole is in between numbers 1 and 10.
That was the best illustration I could lift from the manual.
I think there's a better one in the Willys SM.

Ahh Just make your own:

Naugha · Post by **Naugha** » Tue Apr 12, 2022 1:07 pm

Ron.
Using your diagram, the seven 3.5” studs I replaced with the longer studs were in holes 15, 9, 5, 10, 2, 4, 14.

Been looking at M38 engine pics showing the head studs. Hmmm.

I see a few studs without the minimum 1.5 threads but probably not enough to suggest a problem pattern. Also think I saw a few heads with bolts rather than studs and one head with very tall nuts.

My nickel is on an oddball situation with my head, block or stud holes, a problem you spotted and has now hopefully been fixed.