M38 Crankshaft Pulley - Timing Marks

RICKG · Post by **RICKG** » Wed Oct 12, 2022 7:34 pm

note the 3 rivets on the black pulley, none on the green.

RonD2 · Post by **RonD2** » Wed Oct 12, 2022 7:41 pm

Thanks!
More inconsistency with government parts (not surprising).

See TM9-8012 paragraph 142.d. on page 176.
Says there's supposed to be a hole (for 5-degrees BTDC).
No mention of the notch.

RICKG · Post by **RICKG** » Wed Oct 12, 2022 7:45 pm

the green came off a MC core I've had since the 70's so i'm fairly sure it's original, the black is off a recent acquisition RMC core, mebbe its a repop?
either way, notch or hole, they align with the cover marks on my stand L134.

RonD2 · Post by **RonD2** » Wed Oct 12, 2022 7:52 pm

I didn't post a photo of the pulley off mine that I suspect is a repop because I didn't want to muddy the water with this topic.

Although it has both the hole and notch correctly aligned with the key-way for 5-degrees, the rivets are crudely done and the two sheaves aren't butted against each other like they're supposed to be. There's about a 1/8-inch gap between them (this is why I'm shopping for a replacement).

The mis-marked one in primer (the subject of this post) is for my spare RMC engine that came with a mangled CJ pulley on it.

Post by **wesk** » Wed Oct 12, 2022 8:28 pm

Ron,

If it is a defect, I see no way to tell if the factory did it or an Army mechanic did it, or both.

Try to not forget the Military had the M38 the first 10-12 years and then local governments and private owners got them. These jeeps are a over a half century old. They are actually 70-72 years old so the civilians have owned them around 60 years. That plenty of time for probably a dozen civilian owners, mechanics and engine rebuilders to add notches as well.

See TM9-8012 paragraph 142.d. on page 176.
Says there's supposed to be a hole (for 5-degrees BTDC).
No mention of the notch.

Actually it divided it's statement in that paragraph for the early with flywheel mark alignment with pointer in timing hole (in bell plate). Then they mention Late series you align the hole on the back of the pulley with the timing cover 5 Deg mark. What we should keep in mind that between Sep 1950 and Jun 1952 there were several shops that often tried to get away from that hard to set up flywheel hole who made their own marks or notches or holes on that pulley to be able to time up front. Both military and civilian. In reality we can all try to guess when a certain pulley in our hand was made and mounted on our engine but the truth is there is no way to prove our guess is correct.

You mentioned two bulletins:

Incidentally, this TB and MWO (both issued after M38 production ended) are pertinent:
TB ORD 547, 18 DEC 1953, 1/4-ton, 4x4, utility trucks M38 and M38A1, Prevention of crankshaft pulley failures
MWO ORD G1-W54, 15 SEP 1954, ¼ ton 4x4 utility truck M38 & M38A1, Installation of new engine timing indicator

I have never been able to locate a copy of either. Do you have a copy?

RonD2 · Post by **RonD2** » Wed Oct 12, 2022 8:59 pm

wesk wrote:You mentioned two bulletins:
Incidentally, this TB and MWO (both issued after M38 production ended) are pertinent:
TB ORD 547, 18 DEC 1953, 1/4-ton, 4x4, utility trucks M38 and M38A1, Prevention of crankshaft pulley failures
MWO ORD G1-W54, 15 SEP 1954, ¼ ton 4x4 utility truck M38 & M38A1, Installation of new engine timing indicator
I have never been able to locate a copy of either. Do you have a copy?

No.

Post by **wesk** » Wed Oct 12, 2022 9:32 pm

Have you ever read them?

RonD2 · Post by **RonD2** » Wed Oct 12, 2022 9:36 pm

No.
If I had, I'd have (or make) a copy and share them with you.
I pulled the titles off the list (yours I believe) on this site.

RonD2 · Post by **RonD2** » Wed Oct 12, 2022 9:48 pm

I'm just guessing from memory, but believe the TB added the rivets to the pulley and the MWO added the Type IV Timing Pointer to the timing cover (shown at the bottom of page 55 in the M38 Reference Guide).

Might've got these ideas from ancient PS Magazine articles, but failed to make a note of which edition(s). They're hard to search.

Post by **wesk** » Wed Oct 12, 2022 11:31 pm

I just thought you may have had an opportunity to read them in the past. And perhaps recalled some details. I agree the rivet repair for those that had the pulley's spot welds shearing was probably the issue but I think the timing bulletin only addressed the cover and pointer not the pulley.

Yes the PS Mags are hard to search. I don't know of any available index for them either. Ryan & I managed to round up most of them that covered the M38's duty life but indexing them would take months. Mainly because their individual TOC page is extremely vague with it's article descriptions.

Kendall · Post by **Kendall** » Thu Oct 13, 2022 7:41 am

Here is the article from the 1954 PS Magazine #18 page 837 for the pulley repair.

Post by **wesk** » Thu Oct 13, 2022 9:02 am

Would you email a larger file size copy?

Kendall · Post by **Kendall** » Thu Oct 13, 2022 9:37 am

RonD2 · Post by **RonD2** » Thu Oct 13, 2022 9:41 am

Here's the entire copy: http://psmag.radionerds.com/images/3/36 ... h_1954.pdf

Here's the complete PS Magazine index by issue number: http://psmag.radionerds.com/index.php/Index_by_issue

And here's a PS Magazine master index issue: http://psmag.radionerds.com/images/1/1b ... _Index.pdf

The master index issue is kind of searchable if you do a "Ctrl-F" and enter the search term, for example "M38". Still clumsy.
Much of the M38 article topics are grouped together on pages 227-230.
Look under "Timing" on page 229.

RonD2 · Post by **RonD2** » Thu Oct 13, 2022 11:29 am

Back on the topic --- here's the front side of my pulley in question.
It looks like the rivets might be improperly located compared to the PS Magazine #18 article.
I can't think of a practical way to tell if the pulley is balanced or not except to take it to a machine shop, which would make it a lot more expensive than it already was, and nothing to do about it anyway if not balanced.