M38 waterproof venting

Harleygaz · Post by **Harleygaz** » Mon Jul 13, 2020 3:42 pm

Hi. I understand how the pressurized system works. my Questions are:

1 - how long could the fording valves be kept closed without adverse results and what would the results be if kept closed for longer
2 - how long could the clutch housing drain plug be kept in place and what would be the result if the plug was left in longer
3 - typically what crankcase pressure would the one way check valve open at? The advert in the green book shows a check valve with 10psi operating pressure but that seems rather high
4 - when the system is not in use and the drain plug is not installed wouldn’t crankcase gases exhaust through the fuel pump vent line to the clutch housing and then atmosphere? Wouldn’t that bypass the PCV?
5 - in one post I saw it says that not having the one way check valve does not have significant impact on performance of the system. What impact would there be on the pump and/or deep fording system if the check valve was omitted?

Thanks
Gary

RonD2 · Post by **RonD2** » Wed Jul 15, 2020 7:47 am

Hi Gary,
Are you planning on submerging your M38 ?

OKCM38CDN · Post by **OKCM38CDN** » Wed Jul 15, 2020 8:58 am

Fording operations bring on special problems - Check out TM9-8012 for the list of after actions needed.

CHapter 3 Paragraph
70. Lubrication After Fording Operations
a. After any fording operation, in water 12 inches or over, lubricate all chassis points to cleanse bearings of water or grit as well as any other points required in accordance with paragraph 275, for maintenance operations after fording.
If the vehicle has been in deep water for a considerable length of time, or was submerged beyond its fording capabilities, precautions must be taken as soon as practicable to avoid damage to the engine and other vehicle components in (1)) (2)) and (3)
below.

(2) Perform a complete lubrication service (par. 66). Inspect engine crankcase oil. If water or sludge is found, drain the oil and flush the engine with preservative engine oil PE-30. Before putting in new oil, drain
the oil filter and perform maintenance operation (par. 111).
(3) 58
Note. If preservative engine oil is not available, engine lubricating
oil OE-30 may be used. Operation in bodies of salt water enhances the rapid
growth of rust and corrosion, especially on unpainted surfaces. It is most important to remove all traces of salt water or salt deposits from every part of the vehicle or equipment. For assemblies which have to be disassembled,
cleaned, dried, and relubricated, perform these operations as soon as the situation permits. Wheel bearings must be disassembled and repacked (par. 67d (3) ) after each submersion. Regardless of the temporary measures taken, the vehicle must be delivered as soon as practicable to the ordnance maintenance unit.

Post by **wesk** » Wed Jul 15, 2020 11:21 am

Very interesting set of questions, few of which have ever been asked here.

1 - how long could the fording valves be kept closed without adverse results and what would the results be if kept closed for longer Normal fording operations would generally be less than 200 yards but there may be needs to travel further. The engine will initially start running rough & will soon quit after 20 or 30 minutes of fording. All of this depends on the engine's overall condition.

2 - how long could the clutch housing drain plug be kept in place and what would be the result if the plug was left in longer With the fording valves closed see the reply above. With the fording valves open probably indefinately.

3 - typically what crankcase pressure would the one way check valve open at? The advert in the green book shows a check valve with 10psi operating pressure but that seems rather high The correct check valve operates at about a 2.5 PSI differential. The 10 PSI working pressure reference is the max limits of the check valve. The spring loaded ball in the check valve starts to crack open when crankcase pressures hits 2 PSI.

4 - when the system is not in use and the drain plug is not installed wouldn’t crankcase gases exhaust through the fuel pump vent line to the clutch housing and then atmosphere? Wouldn’t that bypass the PCV? The PCV system does not allow the crankcase pressures to exceed 1 to 1/12 PSI Diff. Therefore the check valve remains seated during normal driving.

5 - in one post I saw it says that not having the one way check valve does not have significant impact on performance of the system. What impact would there be on the pump and/or deep fording system if the check valve was omitted? None if you read Bob Westerman's presentation on this system other than not providing pressurized crankcase gasses to the tranny/transfer/bell during operation of the fording syste,. In fact the early M38 fording system fuel pump did not use this port.

I suggest you review Bob Westerman's Fording System Presentation:
http://www.cj3a.info/sibling/m38vent/vent.htm

Harleygaz · Post by **Harleygaz** » Wed Jul 15, 2020 1:04 pm

Many thanks for the replies. Not planning on really deep water fording but the local Jeep club does have some trails with creek crossings that would be deeper than the clutch housing drain hole and possibly above the diffs. Also really for academic interest thinking about how the system might have been used in a combat role.

Wes, I did read Bob’s presentation, that’s what triggered my questions, but I’ll read it again as I may have missed something. Nice nice to have given you something a little different to think about!

Post by **wesk** » Wed Jul 15, 2020 1:43 pm

and possibly above the diffs.

Keep in mind the early M38's (Read Most M38's) Sept 1950 thru Feb 1952 did not have as much water protection as the last 5 months of production M38's had. Also the differential's had no protection related to the fording systems. The 6 prototype M38's did have a the diff vents plumbed to the air cleaner but productions models ignored this little item.

Make sure you read the directions in the manual for "What to service & care for after fording operations"!

Harleygaz · Post by **Harleygaz** » Wed Jul 15, 2020 2:34 pm

Thanks Wes. Mine is June 1952. I have the correct RMC block and engine plate and the later venting system. Diffs have the vents on the cases. I’ll use your advice for sealing the rear engine plate using silicon lube on one face each side and gasket maker on the other. I was going to use permatex blue, would that be best?

Post by **wesk** » Wed Jul 15, 2020 3:16 pm

The bell housing adapter plate used two paper gaskets that did not require any added adhesives. I rarely recommend adding glues to paper gaskets where the manufacturer does not encourage any glues.

Harleygaz · Post by **Harleygaz** » Wed Jul 15, 2020 3:23 pm

Wes, I think your advice was in relation to not having the gaskets. Do you know if anybody makes those gaskets or if not what is the best material I can use to make my own?

Post by **wesk** » Wed Jul 15, 2020 3:27 pm

They were a very thin paper. Do you recall the old construction paper we used to do classroom artwork projects on? That material would come in large enough sheets to use for tracing the adapter plate.

Harleygaz · Post by **Harleygaz** » Wed Jul 15, 2020 3:30 pm

Thx Wes

RonD2 · Post by **RonD2** » Wed Jul 15, 2020 5:45 pm

Just a thought....

https://www.summitracing.com/search/bra ... t-material

These are large enough and treated for resistance to water and common automotive fluids.

Might be better for your submerged $4,000 motor than hobby-lobby paper?

Harleygaz · Post by **Harleygaz** » Wed Jul 15, 2020 6:16 pm

Thx Ron.

Wes - your thoughts on this material?

Post by **wesk** » Wed Jul 15, 2020 7:18 pm

Paper is paper. The originals were very thin. You can buy these papers in a few various thicknesses all very close to the original gasket's thickness. Have you googled the gasket using all part numbers listed in the IPL's?

RonD2 · Post by **RonD2** » Wed Jul 15, 2020 7:52 pm

The TM/IPL part number search was a dead end for me. Maybe better for you I hope.

Even though I'll never intentionally dunk my M38, I quickly came to this is what I'm using for those gaskets (installed dry as Wes said). Thin .063 thick. Well-known USA quality automotive gasket maker. Water, oil, and fuel resistant. Fairly inexpensive. How can I go wrong?

https://www.summitracing.com/parts/fel-3025

No intent to disrupt your thread Gary, and my apology...but I'm still digesting that "paper is paper".

Good luck!