oil stopping up air filter

[olddude 10]

I have a 520 H that will stop up the oil filter in a real short time. I can change the filter and cut the grass one time; maybe 2 hours running at most. I had a oil drain pipe leak that I thought might have been the cause but I fixed that with no help. That pipe had been loose since the day I got it but I fixed it anyway just to be sure. It just started this at the end of last season all of a sudden. I always change the air filter several time a season and about mid season I put a new one in and the old one looked good with no excess oil. When I changed it the next time it was oil soaked. It seemed to run alright eventhough it was pretty much completely soaked. 

 

I've checked the oil fill cap o-ring and it seems good. I change the oil at leaste twice a year and as far as I know it has never been over-filled. It doesn't use any oil other than what it loses through the air filter. The oil always stays in within the hash marks between changes. It hardly ever smokes unless I leave it parked on a slope for awhile and once started it clears right up it just gives off a little puff on startup. I changed the plugs not long ago and they looked good, no oil fouling at all and I probably didn't need to change them but I did anyway. Those plugs had probably had a little over a hundred hours on them.

 

I haven't done a compression test yet because the dang thing runs so good, has plenty of power but it does develope a slight miss between mid and full rpm when the filter really cloggs up. I can not see any other oil leaks at all. When I noticed the oil leaking from the oil drain it did pull oil up into the fan area but I pulled the cover off the air intake and cleaned it out good. There was quite a bit of oil and dirt built up around the fan and cover. 

 

I'm thinging it could be the air breather tube but I haven't been able to find out just where it is on the engine. That will be the next thing I'll try to adress if I can find it..

Also I have never adjusted the valves on this engine, I just never saw the need to as it starts and runs so well. The engine has roughly 1600 hours on it. I would like to get this fixed. filters are not that expensive but every little bit helps with gas prices the way they are it now cost me almost $40.00 to cut my grass every week and that adds up pretty quick.

[Snoopy11 5,717]

Sounds like rings to me... or maybe valve guides are worn...

 

Don

[Jeff-C175 7,203]

1 hour ago, olddude said:

breather

 

 

My first suspect in cases like this.

 

 

[olddude 10]

Thanks to both of you. I went out and started digging around and found the breather. A pain to get to but I managed to remove the top cap assy to get a look. The mesh screen looked good and clean and dry. The little check balls were free and clean. I did look at a parts diagram and according to that there is another screen in the top cover but I could not find it. I don't know if that matters though because it's never been taken apart until now.

 

I took  compression readings on both cylinders and the back one was 105 and the front 103 psi. Not sure what they are supposed to be but I do know this, take a reading with 3 different testers and you will get three different readings so true numbers are somewhere in-between. The main thing is that they read pretty much the same. Two pounds one way or another should not be an issue, at leaste that's what I'm thinking anyway. 

 

I would think that if the breather was the fault it would be soaked with oil but it was pretty darn clean so I still don't know. There was a rubber o-ring between the top and bottom piece that seemed a little hard to me, maybe that's normal I have no clue. It seemed to fit together tightly and there was no oil residue around the to pieces all that looked dry.

[lynnmor 7,579]

You don't judge the need for a valve adjustment by how easy it starts.  Valve lash decreases as the engine heats up, so you adjust periodically to prevent burning the valves if the clearance goes to zero.  You are way overdue.

 

Are you using a foam prefilter over the paper air filter?  If not, the paper will become plugged quickly.

 

Your compression is pretty good but 115+ would be better.  Doing a leakdown test might turn up a cause for excessive crankcase pressure, it may be that the rings are worn enough to cause the problem.

 

There are two different types of breathers used depending on year, be sure that you are looking at the parts diagram for yours.  I have never seen a breather clog, they are rather trouble free unless the engine is well worn.  Just be sure it is assembled correctly and all the parts are there, you mentioned a missing parts so again, check for the proper parts list.

[olddude 10]

Yes always use the foam pre filter. This is a 1996 520H tractor and I looked at the parts diagram that I got with the tractor when I bought it. It shows a screen on the top section but I guess it could be on the inside where the little check balls are. I didn't take it apart any further than just separating the two pieces. 

 

Is there a page somewhere that explains what has to be removed to get to the valve adjustment and how best to do it?

[Jeff-C175 7,203]

I think the only way oil can make it's way into the air filter is via the breather tube.

 

That breather tube is akin to the PCV valve on automobiles, it's purpose is to 'recycle' the pressure in the crankcase by directing it back through the carburetor.

 

NORMALLY, the only thing that comes out of that tube is fumes... oily fumes.  Over time, the oil in those fumes can tend to deposit oil.

 

It should never be so much that it actually clogs the filter up.

 

The breather assembly has 'check valves' in it that should only exhaust, and not breathe IN.

 

There is always going to be SOME pressure in the crankcase from a little bit of 'blow by' past the rings.  If a ring goes 'bye-bye' that pressure will increase and more stuff will come out the breather tube.

 

If the breather assembly is OK, then I would be looking for causes of excessive blow by.

 

If you pull the oil dipstick when the engine is running, is there more than the usual amount of pressure escaping?

 

 

[lynnmor 7,579]

1 hour ago, olddude said:

 

Is there a page somewhere that explains what has to be removed to get to the valve adjustment and how best to do it?

I did write up some information several times over the years, perhaps you could do a search.

It is a project, you will remove exhaust and intake and then the valve covers, start applying penetrating oil on all fasteners now.  Take photos as you go, especially of the linkage.  Be sure to work clean and keep debris from falling inside, a shop vac is your friend.  I always suggest inspecting the intake for leaks and notches cut into it from the heat shields.  Also this is a good time to glass bead and paint the exhaust.  Use only Onan gaskets, the cheap ones can fall apart.  Use a torque wrench to tighten the bolts, see the Onan Service Manual for specifications.

If you are unsure of anything, stop and post here.

[ineedanother 1,459]

1 hour ago, Jeff-C175 said:

There is always going to be SOME pressure in the crankcase from a little bit of 'blow by' past the rings.  If a ring goes 'bye-bye' that pressure will increase and more stuff will come out the breather tube.

I believe that the pressure in the case is from the piston moving down the cylinder and there should be essentially no blow-by.

[Jeff-C175 7,203]

20 minutes ago, ineedanother said:

should be essentially no blow-by.

 

In a perfect world! Always gonna be some, albeit a small amount.

 

 

[olddude 10]

16 hours ago, lynnmor said:

I did write up some information several times over the years, perhaps you could do a search.

It is a project, you will remove exhaust and intake and then the valve covers, start applying penetrating oil on all fasteners now.  Take photos as you go, especially of the linkage.  Be sure to work clean and keep debris from falling inside, a shop vac is your friend.  I always suggest inspecting the intake for leaks and notches cut into it from the heat shields.  Also this is a good time to glass bead and paint the exhaust.  Use only Onan gaskets, the cheap ones can fall apart.  Use a torque wrench to tighten the bolts, see the Onan Service Manual for specifications.

If you are unsure of anything, stop and post here.

 

Thank you...........I have the worlds worst luck when it comes to searching for stuff like this. It seems that everything pops up but what I'm looking for but I'll try.

I looked at it again yesterday and yes it does look like a project. I think I'll just put it back together for now because I need the mower badly, if I miss a few days cutting my weeds now it will take the rest of the season to get back in control. I do have 7000 feet of Zosia that can take a few missed weeks of mowing but I also have 21/2 Ac of crabgrass, goose grass, black medic, and who all knows what else that gets out of control real fast. 

 

I've been looking for a service manule for this motor but haven't been able to come up with one I guess I will look some more maybe something will come up.

[olddude 10]

17 hours ago, Jeff-C175 said:

I think the only way oil can make it's way into the air filter is via the breather tube.

 

That breather tube is akin to the PCV valve on automobiles, it's purpose is to 'recycle' the pressure in the crankcase by directing it back through the carburetor.

 

NORMALLY, the only thing that comes out of that tube is fumes... oily fumes.  Over time, the oil in those fumes can tend to deposit oil.

 

It should never be so much that it actually clogs the filter up.

 

The breather assembly has 'check valves' in it that should only exhaust, and not breathe IN.

 

There is always going to be SOME pressure in the crankcase from a little bit of 'blow by' past the rings.  If a ring goes 'bye-bye' that pressure will increase and more stuff will come out the breather tube.

 

If the breather assembly is OK, then I would be looking for causes of excessive blow by.

 

If you pull the oil dipstick when the engine is running, is there more than the usual amount of pressure escaping?

 

 

That's kind of what I was thinking but when I pulled it apart it looked clean with very little oil residue anywhere. But that was after it had sat for a couple days maybe if I pulled it apart right after it has been run it would be different. Let me ask you this..........In the top part there are three little plastic looking check balls that I can see but there are 4 holes, is there a chance that one of the plastic balls is missing? I've never looked at one that I know is working so I don't know if this is right or not. If there is supposed to be 4 balls rather than three I'm thinking that might be the problem. I've looked at parts diagram but that piece is not broken down to where I can tell what is there.

[RED-Z06 2,480]

Run it with the filter off...in a clean environment, if the breather is a problem yoy should see oil blowing aggressively out the hose.

[olddude 10]

Dang!! I was just looking for something else and found a service manual. In looking at it I think I have found the problem. There is a pic of the top part of the breather and it shows that there are 4 balls and a screen. There are only 3 balls in mine and the screen is missing. Now I'm wondering how, why and where they went missing. I don't see how they could have ended up in the chrankcase because I can't see how they could have gotten past that ball of mesh wire in the bottom part of the breather. I know for a fact it has never been pulled apart so I guess the screen was never in there when it was built and over a period of time that ball just worked it's way out and went somewhere??? It looks like that screen is there to keep the balls in place in case one gets loose in it's seat and prevents it from falling out. Just a guess on my part.

[Jeff-C175 7,203]

2 hours ago, RED-Z06 said:

if the breather is a problem yoy should see oil blowing aggressively out the hose

 

And out the dipstick hole.

 

 

[Jeff-C175 7,203]

3 hours ago, olddude said:

Let me ask you this

 

I'm speaking generically about small engines in general.  I've never messed with an OhNo.

 

 

[olddude 10]

23 hours ago, RED-Z06 said:

Run it with the filter off...in a clean environment, if the breather is a problem yoy should see oil blowing aggressively out the hose.

 Blowing out the hose LOL well, hell yeah it was ......it would stop the filter up compelety in about an hour of run time

[olddude 10]

I have a old 316-8 out back that I have been trying to find the time to get going and I robbed the upper part of the breather to see if that would fix the problem. Sure enough there are 4 balls in there along with a screen. I put it on the 520-H and started her up and everything seems ok. I didn't get to run it long because I got tied up with something else but I will this afternoon when it cools down a little. I did notice a different sound it wasn't making before and I'm pretty sure it's the breather working like it should. You can hear it from the drivers seat but standing beside the tractor you can hardly hear it.

 

If anybody is looking for a 16, 18, 20, 24 hp onan service manual I can post a link if that's ok. that is if one of the mod's say it's ok.

[Snoopy11 5,717]

The Onan oil issues go back to a Willy Wonka quote:

 

"You should never, never doubt what no one is sure about."

 

There are 3 universal reasons for oil showing up in the air filter... those reasons are "universal" to most engines. Those universal reasons are mentioned in this thread.

 

@olddude... If this was my engine... I would still pop the head to see if the piston top has oil on it... as well as the valves. I tend to be proactive, rather than reactive. Just my advice.

 

Don

Edited July 28, 2022 by Snoopy11

[Jeff-C175 7,203]

10 minutes ago, olddude said:

If anybody is looking for a 16, 18, 20, 24 hp onan service manual I can post a link if that's ok. that is if one of the mod's say it's ok.

 

If it's not already in the "Manuals" forum here, I don't see why you couldn't upload it.

 

But it appears that it's already here:

 

https://www.wheelhorseforum.com/files/category/14-onan-service-manuals/

 

 

Edited July 28, 2022 by Jeff-C175

[olddude 10]

10 minutes ago, Jeff-C175 said:

 

If it's not already in the "Manuals" forum here, I don't see why you couldn't upload it.

 

But it appears that it's already here:

 

https://www.wheelhorseforum.com/files/category/14-onan-service-manuals/

 

 

Thanks....... I just went there and saw that. There is a lot of new stuff there since the last time I checked.

[olddude 10]

44 minutes ago, Snoopy11 said:

The Onan oil issues go back to a Willy Wonka quote:

 

"You should never, never doubt what no one is sure about."

 

There are 3 universal reasons for oil showing up in the air filter... those reasons are "universal" to most engines. Those universal reasons are mentioned in this thread.

 

@olddude... If this was my engine... I would still pop the head to see if the piston top has oil on it... as well as the valves. I tend to be proactive, rather than reactive. Just my advice.

 

Don

Thanks Don, I used to be like that but now it seems like there is so little time and so many projects to get to. Now I just go by the don't mess with anything that's still making smoke.LOL These things are almost as hard to work on as these newer cars now days. I can't complain at all about this tractor it's been a good one. I wore out 6 or 7 of those box store mowers in a few years time and I've run the heck out of this ol girl since 1997. It has done everything I ever asked of her and dang!! I'm ashamed to mention some of the stuff I have put her through. The only thing I ever had to do to it is put 4 tires on it, change the oil and filters on a reg basics, I did replace the spark plugs one time a couple years ago and I wore the first deck completely out a few years back and found a good used on on Craig's List to replace it with. I still have the old one that I put on in the fall to chop up leaves and clean up the woods around the house. I know I will have to retire her in a couple years then I might tear the motor and hydraulics down and do a overhaul just to sit in one of my sheds to have something to look at on cold rainy days. I might even take her out for a spin around the hood every now and again. That is if I could ever find something to replace her with. Whatever that might be would have some really big shoes to fill.

Another thing, a lot of people like to fuss about those Onan engines. The only complaints I have with the ones I have had is they like gas, and maybe parts are a little hard to find if you need them but other than that I ain't complaining.

Edited July 28, 2022 by olddude

[olddude 10]

Just thought I would post a follow up on how everything worked out. I'm back in action, I cut grass for around 3 hours yesterday evening and when I pulled her back into the shop and let it cool down a bit I pulled the covers off the air filter and everything was dry as a bone. I'm glad I finally took the time to find out why it was doing this. Hard to believe one little ball the size of a bb could cause that much trouble, I guess it makes sence though every time one of those pistons bottomed out it turned into a oil pump. 

 

this winter I think I'll pull the motor out and fix that still leaking oil drain tube. It stopped leaking for awhile but I noticed yesterday that it still is leaking a little. I never did get it tight because of the elbo and the way it lays in the frame. the only way to get it tight is to pull the motor out so you can turn it so It don't hit the frame. Does anybody know what type threads are machined into the block. Is it a straight thread or is it a tapered pipe thread?

[lynnmor 7,579]

1 hour ago, olddude said:

 

this winter I think I'll pull the motor out and fix that still leaking oil drain tube. It stopped leaking for awhile but I noticed yesterday that it still is leaking a little. I never did get it tight because of the elbo and the way it lays in the frame. the only way to get it tight is to pull the motor out so you can turn it so It don't hit the frame. Does anybody know what type threads are machined into the block. Is it a straight thread or is it a tapered pipe thread?

It is 3/8 tapered pipe thread.  You can remove or considerably loosen the four engine mounting bolts and put something under the engine to gain enough room to fix the drain pipe.  The pipe nipples and elbow are available at any hardware store, that style of pipe cap is harder to find.

 

I drain the engine oil completely by lifting the right front corner, then lower it to run a 3/8 NPT tap in till it just starts to cut new threads.  Clean the threads with parts cleaner and then install a new 3/8 pipe nipple using red threadlocker.  Use the same threadlocker on the elbow as well but on the pipe cap use Teflon tape for easy removal.  If you ever need to remove the drain pipe, it should come out of the block without trouble, but if it turns too hard, warm the pipe with a propane torch.

[olddude 10]

21 hours ago, lynnmor said:

It is 3/8 tapered pipe thread.  You can remove or considerably loosen the four engine mounting bolts and put something under the engine to gain enough room to fix the drain pipe.  The pipe nipples and elbow are available at any hardware store, that style of pipe cap is harder to find.

 

I drain the engine oil completely by lifting the right front corner, then lower it to run a 3/8 NPT tap in till it just starts to cut new threads.  Clean the threads with parts cleaner and then install a new 3/8 pipe nipple using red threadlocker.  Use the same threadlocker on the elbow as well but on the pipe cap use Teflon tape for easy removal.  If you ever need to remove the drain pipe, it should come out of the block without trouble, but if it turns too hard, warm the pipe with a propane torch.

Thanks, that is pretty much what I did accept the part about running the pipe tap through it. I thought about red 271 lock tite but used a blue thread sealer that pipe fitters use on pipe fittings. I thought I had gotten it tightened enough but when it started to tighten up I had almost a whole turn left to get back to where it needed to be and I was afraid to turn it any more for fear I couldn't get that full turn. It is really hard to get a small pipe wrench in there where you can get leverage enough to get a good grip on it. I tried but it tightened up pretty tight about half way around so I stopped there and ran the drain out the other side. It didn't leak for awhile but now it is starting to leak a tiny bit and I don't like that. That's what it did before started with a little residue on the side of the block and then got worst over time. I never saw a drip on the floor but I hate all that oily mess all over the base of the motor and frame. I think I'll pull the whole motor out this winter where I can get to it and fix it like it should be. I just hope it hasn't worn the threads down in the block from all that moving around like it was doing.

The way it drains is really in a bad place with the deck setup the way it is. It's hard to drain the oil without it getting all over the place. I made a drain pan that would fit under the foot rest but still clear the top of the deck and that worked pretty good but you still have to be careful. I put a small valve on the new drain pipe with a short nipple sticking out where I can slide a piece of rubber line on. Now I just put the pan on the floor slide the hose on then open the 1/4 turn valve and drain it that way. Then I pull the hose off and put the cap back on the nipple just to be safe in case something was to get up there and turn the lever by mistake. That works pretty good with far less mess.