oil bath air cleaner 42 GPW

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Re: oil bath air cleaner 42 GPW

Post by Rod Rushton » Wed Jun 03, 2020 7:45 am

I would not hesitate to convert it to a dry paper element air filter, they are pretty efficient and no oil is involved, I did mine 10 years ago and have never looked back. To change the element is a clean hands operation, and you don't have the problem of dismounting and de-.greasing the bowl, just a quick wipe over with a clean rag is usually sufficient.
I think you have to look at the original operating conditions during the war where there was often a huge amount of dust and "foreign" particles floating about, and the conditions of motoring today using our Jeeps.
I admit earth moving equipment would almost certainly require an oil bath filter - but they probably had service engineers on hand to look after them, just as the Army had Mechanics ( or "Technicians" in modern parlance).
Just my "Penn'orth" that's all.
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Re: oil bath air cleaner 42 GPW

Post by Marty, SoCal » Wed Jun 03, 2020 9:18 am

All the tractors and earthmoving equipment we have at my work use two stage paper elements, one large normal one on the outside and another final element inside the main one to prevent dirt from changing the main one getting into the inlet. Turbodiesels need a lot more airflow yet are sensitive to being "dusted".

I use a Nissan diesel truck/forklift air filter element in my GPW's air cleaner housing, there's an older post I made about it in the mods section. There's a few alternate ways of doing it. Ron has conversion kits, as does Rod in Great Britain.

Here's a link to one thread over there on the mods section:
viewtopic.php?f=10&t=119440&start=15

Here's a link to the post I made showing how mine is set up with the Nissan filter element:
viewtopic.php?f=10&t=208791&p=1222801&h ... r#p1222801
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Re: oil bath air cleaner 42 GPW

Post by JAB » Thu Apr 29, 2021 9:03 am

Was the original problem ever resolved or did the PO just convert to a paper element? Surely they didn't all do this (suck oil) in-service. My GPW is doing the exact same thing and I'd rather make it "right" than make it "better", so I was wondering what the root cause of the problem was.
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Re: oil bath air cleaner 42 GPW

Post by Greendot319 » Thu Apr 29, 2021 9:53 am

This is an interesting one, I run an original oil bath and this is not a problem so there is something else going on here here, most likely it is a crankcase ventilation/pcv problem because that is directly connected to the crossover tube!
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Re: oil bath air cleaner 42 GPW

Post by JAB » Thu Apr 29, 2021 10:40 am

Greendot319 wrote:
Thu Apr 29, 2021 9:53 am
This is an interesting one, I run an original oil bath and this is not a problem so there is something else going on here here, most likely it is a crankcase ventilation/pcv problem because that is directly connected to the crossover tube!
Exactly what I was thinking, but before I re-invent the wheel I thought I'd ask.
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Re: oil bath air cleaner 42 GPW

Post by '42 Peep's Motorpool » Thu Apr 29, 2021 3:09 pm

Usually the three most common reasons for an oil bath cleaner sucking oil into the intake is related to one of these conditions: the oil viscosity is wrong (too thin), the oil was overfilled, or the PCV system is not operating correctly. Never had that condition personally, but it crops up occasionally on a lot of old vehicles/equipment.

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Re: oil bath air cleaner 42 GPW

Post by JAB » Thu Apr 29, 2021 6:03 pm

I disassembled the PCV today and it's clean and clear. It's a metered check valve, but I don't have enough oomph to shut it so unless there's a backfire it seems to flow pretty freely in both directions. I would think that as long as it doesn't cause a lean condition that's OK, as far as sucking oil. I have to admit that I didn' tcheck the oil filter cup (never should have assumed!), I just assumed that's where the oil came from in the crossover tube. I need to verify that; I may be barking up the wrong tree. The oil may be coming up the breather and into the tube rather than from the filter.
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Re: oil bath air cleaner 42 GPW

Post by Greendot319 » Fri Apr 30, 2021 1:41 am

The PCV components are usually pretty oily when the system is working fine so if yours are clear it seem to me that the oil is going the wrong way round the system, I would check your PCV pipe for obstruction and confirm the valves operation. I suppose if your motor had excessive blow by it could overwhelm the PCV system and excess pressure vent up the breather pipe too. Unless your jeep has been upside down I don't see any oil coming from the air filter!
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Re: oil bath air cleaner 42 GPW

Post by JAB » Fri Apr 30, 2021 11:04 am

Well, shame on me for assuming something and posting about it prior to verifying. The air filter was over-filled, not from me, but from this issue. The accordian hose turned gooey from soaking in the oil. The oil is obviously coming up the dipstick tube through the little hose to the crossover tube. Some is backing into the air filter when at rest, or sucked into the carb when running. When I disassembled the (clean and dry) PCV I didn't notice that there's a small hole in the center because it was completely clogged with carbon. I cleaned out the hole and replaced the accordian hose and put the proper amount of oil in the filter cup. The crank case needed a little oil as well. The felt air horn seals are drying out (parts cleaner/solvent) and will be reinstalled. I'll be enjoying the unseasonably warm weather tomorrow evening by taking it for a ride. If clearing out that little metered orifice is all it takes to fix this I'm good to go and others should benefit as well. If the problem persists, then more investigating will need to be done.
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Re: oil bath air cleaner 42 GPW

Post by '42 Peep's Motorpool » Fri Apr 30, 2021 3:54 pm

That can definitely do it! I think you will have solved the problem. :wink:

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Re: oil bath air cleaner 42 GPW

Post by Greendot319 » Sat May 01, 2021 4:33 am

This old video of mine might be of some assistance, I will warn you though that it is an older one and I talk extremely fast in it!

https://www.youtube.com/watch?v=ouVKZE2OqE0
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Re: oil bath air cleaner 42 GPW

Post by JAB » Sat May 01, 2021 10:02 am

Excellent video!

Here’s a quick pre-test drive update: the Jeep started right up (choke out and throttle on “high idle”) but wouldn’t run without the choke out. 1st rule of trouble shooting, make one change at a time. Since the only change was opening up the hole it was obviously now too lean. Thus the requirement for the choke. I wish I had seen your video earlier. I thought the “needle” face was supposed to be dished. So there’s so much air passing through now that it won’t idle unless the air supply is restricted (choked) elsewhere. I had another take-off PCV valve in “the parts pile” so I disassembled it to verify that it wasn’t any worse than the original (it’s close) and installed that one. We’re up and running, but now there’s a noticeable “putt” at idle, very similar to the sound of the engine when compression braking or coasting downhill in gear. I’ll have to order a new PCV with my next order, but at least it’s ready for our evening ride today!

Sorry about morphing and hijacking this post but all these systems relate to each other. It’s all connected.
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Re: oil bath air cleaner 42 GPW

Post by '42 Peep's Motorpool » Sat May 01, 2021 5:36 pm

Hi JAB,

Try pulling out the choke a little, the putt-putt sound may go away. This is a fast and easy way to determine if your mixture is off or if it is valve related (poor seat, etc). If you play with the choke and the sound goes away, you need to adjust your carb.

I am not sure what you mean by "dished" but the piece inside the PCV valve is dished on one side by design (although to be fair, there are postwar models which are visibly different).

Fun fact, the engine will actually run with the the valve itself removed from the PCV housing (but the system otherwise installed correctly), but will exhibit symptoms of a major vacuum leak so it will run poorly and lose power. This system is essentially a metered valve, controlled by vacuum overcoming the spring pressure. That you are having to choke it to run, sounds more like the valve is either stuck open all the time, or you have a vacuum leak someplace in either the PCV system or the intake/carb. It would be a good time to break out the vacuum gauge and find out.

Remember the PCV is a closed system, meaning it is imperative that all connections in the system not break the air lock. If they do, they can admit too much air and affect PCV function. The crossover to oil filler tube hose and clamps should be tight and the hose free of cracking or splitting, the oil filler gasket should be a tight seal when the cap is installed, the PCV tubing from the valve cover to the PCV valve should have good condition (I've seen these rust out from the inside out before from moisture in the crankcase that hasn't yet made through to be burned, they look great on the outside however :lol: ) tubing and have good flares and fittings. Of course the valve cover should have a good gasket seal as well.

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Re: oil bath air cleaner 42 GPW

Post by '42 Peep's Motorpool » Sat May 01, 2021 5:51 pm

PS - there were different PCV valves out there (war time and post war too). One of the biggest design changes during the war was internal and involved changing the diameter of the internal hole on the threaded end. If you aren't sure the spring is right, or that the valve is operating, you can test it. The original specs called for the valve to open between 12 and 16 inches of mercury (vacuum gauge reading).

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Re: oil bath air cleaner 42 GPW

Post by JAB » Sun May 02, 2021 3:25 am

'42 Peep's Motorpool wrote:
Sat May 01, 2021 5:36 pm
Hi JAB,

Try pulling out the choke a little, the putt-putt sound may go away. This is a fast and easy way to determine if your mixture is off or if it is valve related (poor seat, etc). If you play with the choke and the sound goes away, you need to adjust your carb.
Agree, and good trouble shooting technique, but the putt, putt only started with the other used and worn PCV valve, so my assumption is that since it showed wear, it may not be operating correctly either, thus my comment about ordering a new one.

I am not sure what you mean by "dished" but the piece inside the PCV valve is dished on one side by design (although to be fair, there are postwar models which are visibly different). Check out Greendots video just up-post from here. The moving part in mine looked like his but the seat on the stationary part is pitted, preventing a good seal.

Fun fact, the engine will actually run with the the valve itself removed from the PCV housing (but the system otherwise installed correctly), but will exhibit symptoms of a major vacuum leak so it will run poorly and lose power. This system is essentially a metered valve, controlled by vacuum overcoming the spring pressure. That you are having to choke it to run, sounds more like the valve is either stuck open all the time, or you have a vacuum leak someplace in either the PCV system or the intake/carb. It would be a good time to break out the vacuum gauge and find out. Yup, as explained, opening the clogged hole caused those very symptoms so I knew immediately that the PCV valve wasn't seating properly and "repairing" it by cleaning out the hole only made it worse. I have 17-1/2" vaccuum at idle with the "better, but also worn" PCV valve. Not as high as I'd like, but the engine is still standard bore with "acceptable" wear. It hasn't been re-built even once yet, but has been very well maintained.

Remember the PCV is a closed system, meaning it is imperative that all connections in the system not break the air lock. If they do, they can admit too much air and affect PCV function. The crossover to oil filler tube hose and clamps should be tight and the hose free of cracking or splitting, the oil filler gasket should be a tight seal when the cap is installed, the PCV tubing from the valve cover to the PCV valve should have good condition (I've seen these rust out from the inside out before from moisture in the crankcase that hasn't yet made through to be burned, they look great on the outside however :lol: ) tubing and have good flares and fittings. Of course the valve cover should have a good gasket seal as well.Excellent points, but the tubes and pipes are good/new, as is the filler tube cap gasket. I too was suspicious about the cap gasket but I know it's good because when the oil was "all over" the inside of the intake tubes and hoses it was not leaking out of that cap until I removed the cap. I am missing the little baffle thing that goes half-way down the dipstick though.

PS - there were different PCV valves out there (war time and post war too). One of the biggest design changes during the war was internal and involved changing the diameter of the internal hole on the threaded end. If you aren't sure the spring is right, or that the valve is operating, you can test it. The original specs called for the valve to open between 12 and 16 inches of mercury (vacuum gauge reading).
Thanks for the spec. I can test that now that I have a spec to test to, but I suspect that I still need to order a new one. I've got a "shopping list" for Ron started and will add this to it, but he's not listing the A6895 right now. Thanx!!!
-Jeff

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