fuel in crankcase

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Yakov
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fuel in crankcase

Post by Yakov »

A few times now I've checked my oil only to find it murky, greenish, and smelling strongly of gas.
So I change it, reset the fuel pump diaphragm, because I know it leaks fuel to the outside, and I've even pulled the pump off and tried squeezing fuel in to see if it leaks to the engine side, and I don't think it does.

So that leaves the zenith carburetor.
I know that the pump check valve leaks (risks a fiery inferno, I've read :) ), but can that cause fuel to contaminate the oil? Would that cause the bowl to overfill? (and could that cause my problem?)
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heinkeljb
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Re: fuel in crankcase

Post by heinkeljb »

The most likely place fuel (GAS) can get into the crank case part of the engine is via the fuel pump. The carburettor will spill fuel on the outside of the engine if the float bowl over flows.

This will, in small amounts, make the outside of the carburettor "damp" and will show as damp and discoloured due to the dust that will stick to it. Engine bay will also smell of fuel every time you lift the engine cover. In larger quantities, you have yourself your fiery inferno scenario!

Any fuel that goes down the correct route through the carburettor will end up in the combustion chambers. If one of the inlet valves is open as this "overflowing" fuel comes down into the cylinder head, then the fuel will pool in the combustion chamber and if left will eventually find its way past the rings into the crank case and contaminate the oil.

THIS IS A VERY BAD STATE OF AFFAIRS if true, as the fuel will wash the oil from the cylinder bores and will result in rapid wear of both rings and barrel.

So I would suggest you look at your carburettor again and try and sort the pump check valve. I would also use the manual to check the fuel level in the float chamber and check that the two floats have not got holes in them.

It would also probably be worth while replacing the diaphragm in the fuel pump if you can. If you can't get a replacement, then you can go for a low pressure >4psi electric fuel pump and bypass the original one completely.

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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AustHaflinger
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Re: fuel in crankcase

Post by AustHaflinger »

Unless the engine is totally worn out and has virtually no rings, as John has said the fuel will can only get into the engine via the fuel pump. If if the engine is worn not much fuel will get past the rings via the carb.

My engine has been changed to an electric fuel pump with the mechanical engine driven pump removed so I do not have the issue.
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Goatwerks
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Re: fuel in crankcase

Post by Goatwerks »

Incorrect statement...............
Gas can enter crank case if float valve leaks. It will drip down throttle bores into intake manifold and wash out the rings. If the pump is not leaking, then the gas is from the carb overfilling.
Also look at the pump check valve, if it leaks, the bowl will siphon when sitting.

To verify, pull the carb and use a 1.5-2.5 psi pump to fill it and see if it drips, or elevate a small gas container(or 1lb coffee can)8-10 ft to simulate pump pressure.
Yakov
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Re: fuel in crankcase

Post by Yakov »

I think it must have gotten through the carburetor then, as I used a marine fuel tank that sits on the truck bed with a primer bulb, and I suspect the bulb must have kept the pressure up when the engine was off.

Speaking of carb check valves, when I disassembled mine for cleaning a year ago, I broke the check valve off inside the body and drillled/picked out its remains. The unimog carb kit I got had one, so I used it, as well as the 'mog accelerater pump. I know the pump is the incorrect length for the haflinger, but the other difference was the tip - a much smaller diameter with a lot more space between the metal and the skirt. (See photo) I couldn't tell what the difference was between the 'mog check valve and the haffie one because mine got destroyed, but I suspect they might be different as to the seating against the pump... Can anyone confirm this?
Also, does the check valve have any other pieces, like a rubber ring or fiber ring that I was supposed to replace? My kit has a lot of little fiber rings left over... I never thought much of it, since the truck ran okay, just leaked gas...

I just realized while writing this, that the skirt on the pump was lodged in the pump tube when I took the cover off. Would a pump skirt stuck in the bottom cause any serious problems?
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Goatwerks
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Re: fuel in crankcase

Post by Goatwerks »

Replace the pump seal, if it fell off it was only 1 issue , 2, float valve must have a sealing washer(.5mm copper or aluminum with thin paper cover gasket). The Unimog carb parts are fine, just move the pump rod to hole furthest out. Zenith float valves are the same length, the orifice varies (1.25, 1.50, 1.75, 2.0)
If you use the thick top cover gasket, you must use a 1mm washer on float valve. Make sure float ends are secure(loosen screws,when float drops, secure the screws). With these pre settings the float level should be perfect.
Yakov
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Re: fuel in crankcase

Post by Yakov »

So to finish the story, here's what I ended up doing:
I polished the indent on the float where the valve sits, and sealed the pump valve carefully with gasket sealer, and it seems to have solved the problem.
The fuel pump didn't appear to be the problem for me, even though it leaked enough to make puddles under the parked car. (Fixed that yesterday with a new diaphragm).

Thanks for the help, everyone!
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Goatwerks
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Re: fuel in crankcase

Post by Goatwerks »

What are you thinking!!!!(I envision massive flames) Never use sealant of any kind on a carb, always use the correct seal washer for each valve as needed. The kit usually has a diagram with it if you lack a repair or parts manual. Fuel eats all sealants.

Originally they used fiber washers and moved onto more durable aluminum washers over time. Either type will work.
You can download the repair pdf files from my website.
Yakov
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Re: fuel in crankcase

Post by Yakov »

Oh no! I couldn't think of any other solution. I tried new aluminum washers on the check valve and it leaked no matter what I tried. I mean, maybe the ones I got from HaflingerTechnik were the wrong size for the Unimog check valve I put in, they did seem a little larger than necessary.

I guess I'm back to the beginning with that. Glad I posted my so-called "solution" before I really put it into service and found out the hard way.
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heinkeljb
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Re: fuel in crankcase

Post by heinkeljb »

Do some measuring of parts and then order suitable washer from somewhere online if you don't have a good car accessory shop or motorbike shop that has a good workshop.

I hate to disagree, but there are sealants out there that are solvent proof - that includes petrol (gas) or diesel or any of the other volatile liquids.

Putting a stop to leaking fuel even with a sealant has got to be better than letting it leak. Just like anything to do with the fuel and / or brake system, regular visual checks should be done to spot such leaks and then remedial action can be taken.

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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Goatwerks
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Re: fuel in crankcase

Post by Goatwerks »

Rule#1 for sealants, If factory did not use it, you don't use it and never use it where fuel is involved!
I have been in automotive industry for decades and seen all the mistakes, some can endanger life.
Post up a pic or list the washers you need by breakdown #. I have a shit load of old NOS carb washers and small bits and valves.
Easy to put in an envelope.
Yakov
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Re: fuel in crankcase

Post by Yakov »

So it turned out that I'm still getting gas into the oil.

I can't figure it out at all. I pulled the fuel pump and pressurized it every day for a week and there's no leak past the diaphragm. I'm thinking that the fuel creeps up the side of the bowl and flows down the side. Every time I take off the air cleaner, the carb throat is wet, and theres gas in the tube that goes across the top of the carb top cover. Is that normal? What is that tube for anyway?

The float isn't sinking. I've adjusted the float valve to close at too low a level for normal driving (it hiccups on acceleration), so I know its not flooding and overflowing while driving.
My other theory is that fuel flows down the starter jet into the intake manifold. From the repair manual, it looks like the disc that the choke cable controls has some effect on fuel flow. Could the choke being left on while the engine is off let fuel into the cylinders?

I have no idea what to do. I've changed the carb cover gasket and float valve, and even pinched off the fuel line into the carb when I park. Nothing seems to help. Anyone have any ideas on what I should try next?
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heinkeljb
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Re: fuel in crankcase

Post by heinkeljb »

You could try removing the carb from the manifold, putting a cup / tray under it to catch any fuel that goes down the throat.

Remove ignition, turn engine over a couple of times to prime the system. then leave it to see how much fuel ends up on your sealing gasket.

That would at least prove it was your carb that is causing the issue. (It already sounds like it, but it would confirm your theory).

I take it you have a new air filter - blocked one would increase the vacuum which might make the float chamber fill over time.

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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