Joined: May 12, 2014 Posts: 47 Location: Frisco, Texas
Posted: Tue Sep 22, 2015 11:44 am Post subject: Correct length for crankshaft pulley guard bolts
1952 M38, 24 volt, L134, #65666, North Texas. I'm in the process of buttoning up after replacing the rear main seal. I used the seal from Midwest Military. When I removed the pulley guard, I noticed that the previous owner had used two bolts as spacers. I ordered the correct spacers from Midwest. The previous owner used 6 Hex bolts, 1 1/4" long, on the pulley cover. Is that the correct length for those bolts? Using the correct spacers, I'm only able to only get 3-4 turns when trying to tighten these bolts. This vehicle had some serious oil leaks, from the pan as well as the rear main. Thanks in advance for your help. _________________ Mjfire
Thanks Wes. ORD 9 SNL G-740 is the one manual I have not purchased. I didn't realize it had that many pictures. I will be ordering it this week. Thanks again for your priceless knowledge. _________________ Mjfire
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Wed Sep 23, 2015 6:57 am Post subject:
In length alone a bolt has a larger tolerance for nominal length
which can vary widely as opposed to a machine screw who's length is measured from the bottom of the head and has a much tighter tolerance.
In the case of installing in blind holes and other critical
fits the machine screw is preferred as the designers can specify
the required length and know it will be within their manufacturing
limits.
I will assume then that you meant to add that a bolt can have a round screw driver head and a machine screw can have a hex head. Just to keep from confusing those not as versed at you in hardware engineering philosphy!
Otherwise a lot of folks will look for a screw driver head because you told them a machine screw was used. Also in this case the term "machine screw" was not used. "Bolt, machine" was the term used.
Rather then increase the level of confusion I prefer to point folks who need to know to a well organized written product explaining the entire program rather then extracting a wee bit of the info and bending it to fit a post. The difference between bolt & screw alone is very complicated and not universally defined.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Wed Sep 23, 2015 10:20 am Post subject:
Wes,
I appreciate you clarifying a couple of possible confusing
things.
Please note in the Ord740 page above you posted the two items
you highlighted were Bolt which was then superseded by
Screw, machine.
As you have pointed out many times in the past, the Military
changed or superseded items for good reason.
I would speculate, for what it's worth, that motor pool folks
found themselves in similar circumstances as MJ, where the
item would not fit up correctly, maybe due to varying degrees
of bolt lengths available, yet still within bolt tolerances.
Then they changed the spec to a machine screw to ensure the length
would fit the hole.
My purpose of this reply to MJ's post was to draw a distinction
between bolts and machine screws and one should buy
a machine screw where called for versus grabbing a like sized
bolt from the drawer down the aisle.
Perhaps this should be in it's own page, but thought it relevant
to his query.
Joined: May 12, 2014 Posts: 47 Location: Frisco, Texas
Posted: Wed Sep 23, 2015 11:32 am Post subject: Message below the picture.
Yes Wes, I know the manual is free to download. This is the best forum type vehicle web site I've ever seen. I just want a hard copy to keep by the head when I take my daily constitutional. Thanks again. _________________ Mjfire
Joined: Jun 15, 2014 Posts: 268 Location: Cambridge, Ontario, Canada
Posted: Wed Sep 23, 2015 5:06 pm Post subject: Re: Message below the picture.
Mjfire1949 wrote:
Yes Wes, I know the manual is free to download. This is the best forum type vehicle web site I've ever seen. I just want a hard copy to keep by the head when I take my daily constitutional. Thanks again.
exactly my thoughts. I would rather keep my eyes in a book than a computer screen. I find it easier to flip around different sections and pages. _________________ 1952 M38 project
Brad
The "Screw, machine hex head" was on a different part not germane to this discussion. Using the term "Machine Screw" under the conditions you cite in my ord 9 page without the "hexagon head" part of it's printed description is confusing for folks not as well educated in fastener engineering as you are. My goal is to make this site reliably informative for everyone without confusing anyone. Sometimes we need to make longer posts and reduce the language level to a point that we are all on the same page.
The more stringent dimensional tolerance levels are actually shown by the dash # after the thread type. IE 5/16-18NC-3x 3/4 the -3 is the indicator that a more stringent dimensional tolerance has been required beyond the tolerance of the previous -2 fastener it superseded.
The term "Screw" is still not fully agreed upon anywhere in the industry as anything other than a course threaded tapered screw such as wood screws and sheet metal screws. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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