M38 Crankshaft Bolts

[Naugha]

The crankshaft of my late model M38 came with two different bolt types on the plate that attaches to the flywheel. I think this is the proper setup.

Straight Dowel Bolts with shoulder (2)
1/2-20NF- 2x 1 3/16”
9SNL part 7371231 (or 7371232 ?)

Hex Bolts (4)
3/8 - 24NF - 2x 1 5/32”
9SNL part 7324840

But my machine shop guy feels certain that the four Hex Bolts (7324840) are not proper for that location. He insists those four bolts should be similar to the two Straight Dowel Bolts with a low profile head but not recessed. He points out that the edges of the four hex heads used on the crankshaft have left small nicks in the low collar on the shaft adjacent to the bolt heads. The technician working on the Go Devil has ordered what they consider to be the proper bolts from a shop that has a supply of vintage hardware. The parts are at the machine shop but I can get pics if needed.

Does any of this sound familiar and ... if the bolts he ordered fit ... does it make any difference to the performance of the crankshaft / flywheel?
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[wesk]

Early on the two dowel bolts were tapered with the same thread size as the other four. About mid 50's they made the change to the straight shouldered dowel bolts with 1/2" threaded bolts. The bolt heads are somewhat similar but there are only 2 dowel and 4 regular.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[Naugha]

So, is it two dowels (tapered = early / straight = late) and four hex heads for a total of six.... plugging up six holes.

My machine shop guy seems to think there is another style bolt with a thinner head that is used for the 4 non-dowel bolts. Maybe he he going by a civilian jeep repair practice that is not in the military book. Maybe there is more than one way to skin a cat and these fellows don’t always follow M38 manuals on cat skinning.

The engine and radiator in place will place will lift my spirits.
It’s starting to look like a jeep.
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[wesk]

Post photos of your original 4 flywheel bolts and the new ones they ordered.

The part numbers for the M38 engine's 4 regular flywheel bolts are ORD# 7324840, WO# 632157 (hex hd steel 3/8-24NF-2x1 5/32"). The part numbers for those 4 bolts in the 49-54 Willys CJ Parts Manual is GM-106286 (hex hd 3/8-24x 1 1/8").

When you cross reference the ORD# to FSN's & NSN's this is what we get:

[quote]NSN 5306-00-275-1597 355497S, 632157, 7324840
Product Details | MACHINE BOLT
________________________________________
5306-00-275-1597 An externally threaded fastener designed for insertion through holes in assembled parts and normally intended to be tightened or released by torquing a nut. The threaded and unthreaded portions are both of one nominal diameter of 0.190 inch (5 mm) or larger. The head is not designed to be held or driven with an inserted driver or by the thumb and fingers. A locking feature may be incorporated in the design of the head or threads. Head dimensions and sizes of threaded and unthreaded portions shall conform to internationally recognized fastener standards. For items having a grip length portion machined to a tolerance of 0.0015 inch (0.038 mm) or less, BOLT, SHEAR. See also SCREW, CAP, HEXAGON HEAD and SCREW, MACHINE.
Part Alternates: 355497S, 632157, 7324840, 5306-00-275-1597, 00-275-1597, 5306002751597, 002751597
Hardware and Abrasives | Bolts
Supply Group (FSG) NSN Assign. NIIN Item Name Code (INC)
53
01 JAN 1961 00-275-1597 01847 ( BOLT, MACHINE )

Drawings & Photos | NSN 5306-00-275-1597
________________________________________




Cross Reference | NSN 5306-00-275-1597
________________________________________
Part Number Cage Code Manufacturer
355497S 23040
FORD MOTOR CO FORD PARTS AND SERVICE DIV
355497S 57526
FORD MOTOR CO
632157 08018
BORG-WARNER CORP
632157 16460
MARINE ENGINE SPECIALTIES DIV OF MESCO TECTONICS INC
632157 34623
AM GENERAL, LLC
632157 79410
LIBERTY VENTURES INTI LLC
7324840 19207
U S ARMY TANK AUTOMOTIVE COMMAND AMSTA-IM-MM
Request a Quote
________________________________________

Technical Data | NSN 5306-00-275-1597
________________________________________
Characteristic Specifications
THREAD SERIES DESIGNATOR UNF
NOMINAL THREAD DIAMETER 0.375 INCHES
THREAD QUANTITY PER INCH 24
THREAD CLASS 2A
THREAD DIRECTION RIGHT-HAND
THREAD LENGTH 0.562 INCHES MINIMUM
FASTENER LENGTH 1.156 INCHES NOMINAL
MATERIAL STEEL COMP 4037H OVERALL
MATERIAL DOCUMENT AND CLASSIFICATION ASTM A304 ASSN STD SINGLE MATERIAL RESPONSE OVERALL
HARDNESS RATING 32.1 ROCKWELL C MINIMUM AND 39.1 ROCKWELL C MAXIMUM OVERALL
MINIMUM TENSILE STRENGTH 12000 POUNDS PER SQUARE INCH
HEAD STYLE C1 HEXAGON
HEAD HEIGHT 0.250 INCHES NOMINAL
WIDTH BETWEEN FLATS 0.562 INCHES NOMINAL
FEATURES PROVIDED CASEHARDENED AND UNFINISHED HEAD

[WillysMotors]

[RonD2]

Thanks for posting the drawing Keith!

Printed copy went straight into my notebook.
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[WillysMotors]

[Naugha]

Here are the bolts that were on the crankshaft.
The mechanic said the four regular looking bolts were wrong.



Here are the bolts that were ordered.
They did not come from a jeep and were too large in diameter.


Even after being turned the bolts did not do what he wanted
which was to catch and lock onto the CS ridge.....
but strangely to me, the other standard looking bolts did catch/lock.


We talked a little. Seems he has not worked on a GoDevil before.
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[RonD2]

An obvious question: do the bolts you removed match the dimensions on the drawings posted above? It sure looks like the ones you ordered don't. Curious why your machinist doesn't believe an original Willys drawing for the L134.

I'd be very concerned with a machine shop that never worked on a Willys L134 before. Not saying they aren't competent, it just means they sure need to read the engine rebuild TM very carefully.

The 2 dowell bolts in your photo are the early tapered style. The later style dowells are straight. Both are commonly available. There's a MWO/TB for a machinist to convert a flywheel from early to late dowells. See TM9-1804A (June 1951), paragraph 74 on page 83.

Good luck!
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[RonD2]

I'd add that you seem to think that these 4 bolt heads are supposed to "catch" or "lock" on that ridge on the crankshaft flange?

I'm pretty sure that's not the case. That ridge on the crank flange and the bolt head size aren't meant to interfere with each other. In other words, it's not some kind of "anti-spin" feature for the bolt. The correct bolt, nut, and lock washer (properly torqued) are what keeps those bolts from spinning. There's supposed to be plenty of clearance between a correct bolt head size and that ridge on the crankshaft.

The heads on the 2 straight (later style) dowel bolts are round with one squared side.

I can post photo's if helpful.
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[Naugha]

It was a Friday afternoon at the shop. I decided to get some feedback here about the pics before talking to the machinist/mechanic and the boss.

The machinist working on the block had voiced his desire to reassemble the engine. I was going to use a mechanic shop I had worked with before to do the job but then thought maybe it was wise to let the folks who worked on the block to follow through with the reassembly.

I now think it’s one of those rare occasions where I spotted something amiss. Both my civvy and MC GoDevil drive shafts had this bolt pattern with two ‘special bolts’ and four ‘reguler’.

Monday I will show them the bolt diagram/specs and get things straightened out..... maybe gently bring in a restoration guy I know who is presently working on a vintage jeep. I don’t know any speciality war jeep mechanics.

BTW. I watched the ‘‘Metalshaper’ videos several times, disassembled both GoDevil engines, bagged/tagged the parts and finally came to the conclusion that this was not the time to start a new profession...... and nothing goes easy like they do in most of the videos out there.🎥
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project