B&S 28Q777 crankcase vacuum line sucking oil up to fuel pump

[Scrubcadet10]

My kawasaki Mule uses a vacuum pump, i have the clear line on it and it works great.
Polyuerthane

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[lefty2cox]

Did we do a leak-down on this?

 

[Sdmcarlson]

So your engine crankcase is getting pressure inside it from somewhere. As oil is splashed around inside, that increase in pressure is pushing oil through the breather line that goes to your fuel pump. So, where can the pressure come from? Well, as the piston moves up and down, it creates positive and negative pressures in there. This is usually relatively low pressure differences because the size of the crankcase and the distance of the piston motion. Any oil usually goes through breather and back into engine through galley.

So, in your case, I'm guessing as the piston goes to top of stroke to compress fuel/air mixture (or exhaust stroke as well), and some of that is getting by and pressurizing the crankcase - loss of power also. If that engine has a oil filler tube, you may feel the blow-by. How does it get past? Either the, as you said, the head gasket, valves not closing, or the rings. Harbor Freight has a cheap cylinder pressure tester. I dunno the specs but seems 90 to 120ish psi should be good.

I'd do a leak down test next.

Good luck

 

[warreng5995]

I had two mowers that had oil coming back to the carburator and in each the float valve was stuck and the gas was filling the crankcase and forcing the oil out.

yep, as I said that in some previous posts, I thought about that at one point. But the oil isn't being thinned down, don't see or smell any fuel in the oil either.

 

[warreng5995]

Reading the posts, couldn't find any reference to the having done a compression test. When the new rings were put in, did the cylinder show scoring? As someone suggested, I would hook up spark tester and run it. Look for any signs of missing or poor ignition. Also, I would check for oil breather for blockage or sludge.

So your engine crankcase is getting pressure inside it from somewhere. As oil is splashed around inside, that increase in pressure is pushing oil through the breather line that goes to your fuel pump. So, where can the pressure come from? Well, as the piston moves up and down, it creates positive and negative pressures in there. This is usually relatively low pressure differences because the size of the crankcase and the distance of the piston motion. Any oil usually goes through breather and back into engine through galley.

So, in your case, I'm guessing as the piston goes to top of stroke to compress fuel/air mixture (or exhaust stroke as well), and some of that is getting by and pressurizing the crankcase - loss of power also. If that engine has a oil filler tube, you may feel the blow-by. How does it get past? Either the, as you said, the head gasket, valves not closing, or the rings. Harbor Freight has a cheap cylinder pressure tester. I dunno the specs but seems 90 to 120ish psi should be good.

I'd do a leak down test next.

Good luck

As I said in previous posts, my Dad bought this mower from his nephew who bought it from an auction.... We ran it for a couple seasons, but there always seemed to be something I had to fix all the time to keep it running. Fast forward, I basically have rebuilt the entire mower. Including a complete full engine rebuild, hasn't been run maybe an hour.
When I first broke it down, yes there was a lot of sludge in the bottom of the sump pan. But after breakdown I spent several days cleaning **everything**, including the whole crankcase, nearly spotless. So no sludge now.

I also have replaced crankcase breather, fuel pump, air filter, fuel filter, oil filter, fuel lines, rings, all gaskets and seals, sparkplug, valves lapped, complete rebuild on carb, and probably some more things that I can't remember right now. All parts are all B&S OEM. (except the fuel pump that I just replaced a few days ago while troubleshooting is an Oregon)
The fuel tank was also removed and cleaned out.

After I readjusted the valves again this last time, and spent like an hour doing so before I was completely satisfied.The power was decently improved from what it was, but its not 100%.

Did we do a leak-down on this?

The problem is these engines have an ACR which limits the compression to 60-90 psi. In order to get a valid compression reading ti would require adjust the vavle clearance until the ACR is no longer effective. But there is one problem that as the electric starters are too weak to turn the engine through the compression stroke. Briggs recommends doing leak down tests instead when a compression problem is suspected.

Yep, what StarTech said above, Can't do a compression test on this engine, as it has a compression release built into the camshaft to make it easier to start. That compression release doesn't move out of the way until centrifugal force overcomes it when the engine is running. So using a compression tester only gives a false reading at best.

Leak down test is possible, haven't done that yet. Might try it when I get time.

Also Cylinder and piston were clean, no scoring at all. New B&S rings.

I'm pretty sure there's a Reed valve under the flywheel that goes bad and that's why you have oil in the vacuum tube.

humm... don't remember seeing any valve or opening under the flywheel, other than the crankshaft seal of course. The vacuum line goes to the crankcase breather, which I also just replaced, but it is on the side of the case down toward the bottom behind the carb.

The clear fuel line you are using going to the fuel pump might be some of your problem! This line will collapse and therefore won't work for the fuel pump correctly! That fuel line should be a ridged black double core rubber line. If it collapses it will not operate the fuel pump correctly!

Snowmobiles use the same type of fuel pump and they will not work correctly with the clear fuel line either.

The fuel line I am talking about comes off the Engine. It is the pulse line to the pump. This must be dual core rubber line. The other lines can be clear line

I know the vacuum line. I thought about that, watched and felt of it with engine running and didn't see any flexing of the line at all. If I didn't have a clear line on there, I wouldn't even know there was any oil in the line to begin with. Further, with the engine running, the oil seems to stick back only on the walls of the line, fuel pump runs fine. I may change the line to a regular black fuel hose just to see if there is a difference in running, have no way to see inside a regular black fuel line to see if the oil is still present though.
At this point I think this is a non-issue, and was mostly just my observation of not seeing it before because I had been running a regular black hose fuel line previously.

At this point my main issue is, it will start when engine is cold every time, it will continue to run even after engine is hot and up to full temp. But once you turn the engine off, and leave it off for around 5 min or so, it won't restart. Doesn't even hit, and I've ruled out "not getting fuel". And it is getting air. So its either compression or spark.

With that said I believe it is a weak ignition coil. Although its working, and will start a cold engine, when the coil itself is also cold. Once the engine gets hot and the coil is hot, when the engine cools down some the coil is still too hot and has a weak spark. And therefore doesn't have a strong enough spark to restart the "cooler" engine.
It will however restart a Hot engine. As in have the engine running up to full temp. Turn off engine, wait only a few seconds, restart engine. But if the engine sits for 5 min or so, it won't restart until its basically cold.

So a weak coil is my theory. We'll see what happens. I don't have a spark tester at the moment, but I am getting one. I have removed plug previously and reconnected the coil wire to it, grounded plug back to the block and cranked the engine, it does have spark. Just how strong of a spark when the coil is hot is the question..?
As soon as I get time I'm going remove cover and etc, remove coil and go buy a new one. I've replaced about everything else anyway, might as well replace the coil too as it may even be the original for all I know.

When I get time, I will try to do a leak down test and see what results that gets.

Thanks Everyone for All the Info and Replies! ?
Will update when I have more

 

[RMD]

That's High crank case pressure due to blow by on the rings. So its worn rings, or ring clearance. That would account for the oil leak from the dipstick as well. Oil cannot travel up the vacuum line to the pump any other way. It also accounts for the oil on the intake as well from the crank case breather. Oil would only pass here if the breather valve was stuck open or crank case pressure was raised.

You also must know you cannot replace rings in a worn barrel as the barrel will be oval and the rings round. Hence blow by. So unless you have checked the barrel for round, honed the barrel even new rings will not seal.

 

[Brian - Modern Mower]

HOLY COW. I am surprised by the responses.

I run a repair shop, and am a Briggs master technician. you are describing a typical problem. so typical, i could not believe the responses. you have too much crankcase pressure. normally, at a shop, we hook up a crankcase pressure gauge at the dip stick to see what the pressure is. the tool is called a manometer. the crankcase needs to show negative pressure (a vacuum) and, you are describing all of the typical symptoms of positive pressure. there are a few things that cause that, but the most likely suspect is a blown head gasket. second would be a breather valve that's not working, and third would be blow by past the rings, but that's the most rare.

BTW, i have worked on perhaps 1000 machines in the last year.

the crank case is building up pressure, and forcing oil out of all sorts of places. if i was a betting type, I'd bet its a head gasket.

 

[lefty2cox]

HOLY COW. I am surprised by the responses.

I run a repair shop, and am a Briggs master technician. you are describing a typical problem. so typical, i could not believe the responses. you have too much crankcase pressure. normally, at a shop, we hook up a crankcase pressure gauge at the dip stick to see what the pressure is. the tool is called a manometer. the crankcase needs to show negative pressure (a vacuum) and, you are describing all of the typical symptoms of positive pressure. there are a few things that cause that, but the most likely suspect is a blown head gasket. second would be a breather valve that's not working, and third would be blow by past the rings, but that's the most rare.

BTW, i have worked on perhaps 1000 machines in the last year.

the crank case is building up pressure, and forcing oil out of all sorts of places. if i was a betting type, I'd bet its a head gasket.

I think he said in the original post that the head gasket and breather were both replaced.

 

[warreng5995]

Thanks for the replies and info guys, will take all into account ?

Here is my Update: Over the last several days when I had a few min, I made a leak down tester. So this morning with the engine cold, put the engine to TDC, placed vice grips on the crankshaft against the frame so the engine could not move. Pulled the spark plug and it was a bit wet, appeared to be oil.
Screwed in my compression hose, and with the air compressor regulator set at 100psi, the leak down gauge showed about 80psi or so. And I could hear the air coming out somewhere.

So I got to searching, first thing I did was pull the dipstick and put my ear up to the fill tube. But the air leak wasn't any louder. So I kept searching and found the sound was louder on the other side of the engine around the carb/intake area. At first I thought it was coming from around the head gasket, but it sounded higher up. So I pulled the air filter cover and filter off, and the sound was definitely louder, and I could see a film of oil down in the bottom of the air intake "tube" where its takes in the air through the filter.

So, I put everything back together, put my spark test on and started the engine. Good steady spark.
Turned off engine, took off spark tester, restarted and went and mowed for about 20 min to put a load on the engine and get it up to full temp.

Brought it back in, shut it down, pulled spark plug. Plug looked clean and dry this time (of course engine was hot too). Reinstalled Leak Down tester, removed air filter. When I connected the tester to the compression hose, once again tester showed 80psi. And I could hear air coming up through the intake, and saw some smoke this time coming up through the intake, and once again there was oil in the bottom of the air intake "tube".

So that's a 20% loss of compression. But a hot or cold engine didn't make a difference in pressure loss, it was the same both times. Which to me would appear its not the rings???

With the engine still hot, I then reinstalled the plug with spark tester again, and the spark was still strong and steady, the same as it was with the engine cold. So I was wrong about a weak coil apparently.

With that said, after engine was at full temp and shut down. When I attempted to restart, the engine will chug a bit at first, but then comes up to speed, when it does I did notice it puffed smoke for a second or so. It did this every time except the first time when I first shut it down, that time it would not restart. But I even went back out and mowed for another 20 min, brought it back in and shut it down. But once again it would chug for a few hits but then come up to speed with a couple puffs of smoke.

So I couldn't figure out why I couldn't replicate the the hot-no start issue now when it would do it every time last week.

Today I checked the oil again when it was cold before I did anything this morning and it was at the full mark.
After running it and the engine was hot, after I shut it down and did the leak down tests and etc. I once again checked the oil level and this time the oil was Over Full. If the "low to full" mark is 8oz as is written on the stick. Then it appears it may now be another "8oz" OVER full.
Which must mean fuel is getting into the oil/crankcase. And if so, this *may* be why the engine restarts now even when hot, as there is enough fuel in the oil to make it combust easier?? IDK
OR would the oil expand this much simply due to the engine being hot/overheated due to the intake valve leak? I wouldn't think so and haven't seen this before personally, nor heard of it before either. But you all would know more. I will have to go back and check oil level again once engine is cold to verify its still showing over full.

In any case at the very least, this currently seems to show that the intake valve is leaking. The only way that I know of to verify this would be to pull the head and do a "liquid leak" test, with the head upside down and held in a vice or etc, and cover the valves in a liquid (such as gas or carb cleaner) and see if the liquid would leak past the valve. If so, then it means the valve is not sealing and it also show which valve is leaking. Which again if this is the issue it would have to be the intake.

But I'm not sure how this would be forcing a film of *oil* back up into the air intake? (the new intake valve seal???)
And also apparently getting fuel into the crankcase?? (will recheck oil level to verify this)

I got to thinking about the intake valve as I was walking back over the house, and this may have been what was wrong originally before I rebuilt the engine. As if the intake valve was not sealing, and somehow this was forcing oil back up into the intake, which would then mean it was also being drawn into the combustion chamber where it would be burned. Would this not be the cause of why the intake valve, piston and inside of head had such a thick coat of baked on oil/carbon?? The exhaust valve I might say had some carbon on the face of the valve, but not much around the seal or the back of the valve. The intake valve on the other hand was really bad, as well as the intake port in the head.

So with all that said, I have a 20% pressure leak through the intake valve. Some oil coming up through the air intake and apparently being burned in combustion. And very possibly fuel going into the crankcase.

What do you guys think???

EDIT: Just wanted to add, as I stated in previous posts, I lapped the valves during the rebuild and they appeared to have seated well all the way around. BUT could the valve be bent just slightly enough to cause this?? Or maybe I just thought I had them seated good. Been a while since I lapped valves on a car engine.

EDIT 2: Rechecked oil level after engine was cold. It is back down to the Full mark.

 

[lefty2cox]

You indicated that you checked the oil after doing a leak down. This may sound like a dumb question but did you clean the dipstick and then check it? Or just pull the stick and check it? Some air always gets by the piston during leak-down and pressurizing the crankcase will force oil up the stick.

Most on here are wiser than I am but if you have fuel in the oil and are losing air through the intake, you have two problems. The intake valve and leaking carb, I would think. Did the oil smell like fuel? 8 oz is enough to make a stink I would imagine.