Joined: Aug 20, 2010 Posts: 143 Location: Illinois
Posted: Sun Sep 29, 2019 3:06 pm Post subject: What have I done, what have I done,
Been wanting to check the compression on the m38. So I took all the plugs out and such as the tm said. Installed the compression gauge and only got like sixty pounds. Took the gauge out to see if it could have been plugged since it hasn’t been used in thirty years. It was ok. Put it back in and got zero compression. So here’s where I figured out what an idiot I am. The compression gauge has a couple of adapters on it. The one I used was longer than the short one that should have been used. So now I have no compression on number one and 110 on the other three. The piston doesn’t look like it has any damage so I’m pretty sick about being so stupid. What happened to number one? Did it break a valve etc. oh if it does start, it’s pop crackle stuff. I will check the manual when I’m done pouting. Stupid John jr, arrrgh _________________ 52 m38
Just about all the compression gauges I have ever seen (55 years worth) have only 5 to 10 threads. None of these would be long enough to strike the piston so what exactly did you stick in the plug hole? Post us a photo of this weird gauge. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Aug 20, 2010 Posts: 143 Location: Illinois
Posted: Mon Sep 30, 2019 4:08 am Post subject:
Wes the gauge is just a regular gauge. The longer adapter was definitely hitting the top of the piston as there is a mark not a dent from it. Also the bottom of the adapter shows that it was hitting. Can’t post pics so let me know if there’s some other way to get them to you. Thanks John jr
First off refer to the manual TM-9 1804A, graciously provided in the downloads above.
First off a long compression gauge adaptor cannot strike the pistons. Period.
Referring to the manual and looking at the cross section views (both). You can see that the spark plugs are located over the valves, not the pistons. You have bent a valve in cylinder number one. They actually bend fairly easily and since yo left a mark and you have zero compression that is what happened.
The good news is that most likely you will not need a full tear down to rectify. Follow the same manual and do the tear down as far as getting all the stuff off of the head and the valve side of the engine. The head will have to come off as will the tappet adjustment cover. But from there on you can replace the bent valve quite easily. _________________ '52 Dodge M37, '42 GPW, '48 FrankenJeep CJ2A/M38, '50 CJV-35(U), '51 M38, '42 WC-57 Command Car, '44 WC-51 Weapons , (2) M1941 Sperry 60" Anti-Aircraft Searchlights, John Deere M-gator, '44 White M3A1 Scout Car
Joined: Feb 06, 2008 Posts: 69 Location: Findlay, Ohio
Posted: Mon Sep 30, 2019 8:21 am Post subject:
Hum, I cannot reach the pistons from the spark plug holes on any of my engines. Sounds like number 1 exhaust vale is not closing to get the compression. I would loosen that tappet and readjust the tappets
And if you bent the valve the next step is removing the head. Then removing the side valve cover to expedite the valve change. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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