Drained Oil Smells of Gas

[rmaynard 15,434]

I rebuilt an older K-161 with the small bore last year. I had the cylinder bored to the new standard size, replaced the piston and rings. I ran the engine for about an hour before bringing it (on a 701) to the Wheel Horse show, where my grandson put lots of time on it over 3 days. It has not been run but a couple of minutes since. The engine runs great. So, on Thursday I drained the oil and it appeared thin. It also smelled of gasoline, but I could not light it. I removed the fuel pump (pulse-type) and looked for leaks. Found none, but replaced the diaphragm anyway. So, any ideas why I would have gas in the oil? As a point of interest, my first 701 also had a mix of gas and oil when I drained it for the first time, but I've had no problems since rebuilding it's engine.

 

[stevasaurus 22,717]

How does the spark plug look ??  Could be the break in period.  

[squonk 41,067]

2 ways gas gets into the oil. Thru the pump or washing by the rings with a flooding carb. You would have noticed the carb issue right off the bat. You can bypass the pump and run it gravity feed to a half tank and recheck the oil. If the oil is ok reconnect the pump. Run it some more and if the oil gets gassy it's the pump.

 

Also new tight bore with increased pressure and vacuum could have overwhelmed an old previously good diaphragm.

Edited June 8 by squonk

[stevasaurus 22,717]

Let me ask this ??  If your Grandson was shuting the tractor off at a high or medium idle...might that accound for that??

  

[lynnmor 7,305]

23 minutes ago, stevasaurus said:

Let me ask this ??  If your Grandson was shutting the tractor off at a high or medium idle...might that account for that??

  

Many people do just that, I cringe whenever I hear it.  Any engine should be slowed to an idle before turning off the ignition so that a minimum of unburned fuel is left in the engine cylinder(s).  That said, I doubt that is the real issue and the gas is slowly leaking past the needle valve in the carburetor or the fuel pump is defective.

[stevasaurus 22,717]

I'm just thinking, Bob is really knowledgeable about engines.  I would not sell him short knowing that he did the rebuild.  It would be the simple explaination that I would look for.  

    Change the oil and run it...do it so you know the history.

   Bob, did you really try to light the gas on the oil??  Can you burn leaves in New Jursey?? 

[ranger 1,750]

You could try shutting off the fuel tap and running the carb dry when finished with the tractor? Perhaps the latent heat of the engine when stopped is causing the gas to expand and flood into the inlet tract via the main jet? If the inlet valve is open then it will seep into the crankcase past the rings.

I suppose it’s also possible that a slightly leaky float needle could allow a form of siphon to occur, especially if the pump valves are on the weak side? With gravity feed I suppose we should always close the gas tap when not using the tractor. Or fit a check valve as @peter lena  recommends?. Look at all the comments folks make about the time it takes to crank the engine to raise the fuel from a rear mounted tank. So it’s draining back, or going somewhere else. If it’s draining back, something is leaking!

[TonyToro Jr. 1,415]

7 hours ago, squonk said:

2 ways gas gets into the oil. Thru the pump or washing by the rings with a flooding carb. You would have noticed the carb issue right off the bat. You can bypass the pump and run it gravity feed to a half tank and recheck the oil. If the oil is ok reconnect the pump. Run it some more and if the oil gets gassy it's the pump.

 

Also new tight bore with increased pressure and vacuum could have overwhelmed an old previously good diaphragm.

 One or the other

[rmaynard 15,434]

20 hours ago, stevasaurus said:

How does the spark plug look ??  Could be the break in period.  

Didn't check the plug. Will do that today. 

[rmaynard 15,434]

15 hours ago, stevasaurus said:

Bob, did you really try to light the gas on the oil??  

Yes. I poured about two tablespoons into a metal pan and tried to light it with a propane torch.

[rmaynard 15,434]

I know the visible signs of a sticking (open) float valve. That is not an issue. I never had a flooding issue. The pulse fuel pump was off of a K181 that I bought 10 years ago. Though it works fine, I suspect there could have been a little leakage at the diaphragm around the screws. The check valves in this pump seal better than any pump I've seen over my years of dealing with K-series engines. I dressed both pump half surfaces with 400 grit on a flat surface, and then replaced the diaphragm. Another interesting thing is that I put 2.5 pints of oil to start with, and when drained, I only had 2 pints. When in the shed, I keep plastic trays under all my engines. There was no leakage, nor was there any oil on the bottom of the engine or the frame. I'm not sure where that oil went. I guess it could have burned off in the break-in process, but I never saw smoke.

Edited June 9 by rmaynard

[peter lena 8,608]

@ranger  hello ranger ! thanks for the reference ! as usual when encountering a problem , I also add any possible detail and try / test it for function , with additional improvement , have that fuel check valve on al my small engines , clear fuel line to it / from it  to verify quick starts /  also have a small fuel filter before check valve . another detail I use  , is  STA BIL fuel storage additive . add 1oz , to all my fuel top offs , after tractor use,at that time , also check trans fluid , full / clean / solid shift boot , also touch up engine for oil / any issues ?  getting the picture ?  on that soon after run check , might possibly find a lead  to what' is going on ? noise ? leak ? etc ? been using that regularly for years , like the reliability / solid running , interesting , usually when ever I see another unit , its loaded with things to improve , thats what I do , because it works . your carb based problem , sounds like a rebuild kit , also clean out tank , STA BIL fuel storage additive , insure rank cap / vents , would also replace tank fuel line , breaking down ,  clean out tank , remove every possibility , nothing sarcastic , everything implied  is in steady use in my stuff , solid runners , thats what I want , pete

[rmaynard 15,434]

Thanks for the replies so far. I will address a few things.

I have been rebuilding engines since I was 14 (60 years) when I rebuilt a Volkswagen engine. Since 2009, I have been involved in strictly rebuilding K-Series Kohler engines. Everyone of the engines on all of my current tractors and those of which I sold, were rebuilt by me. Though I don't do the machine work, I have one of the most reliable small engine machinists at my disposal. When asked if he needed for me to leave a copy of the engine specs, his reply was "no,  if I don't have them in my head, I have them in my book. Just leave your new parts". 

As a precursor to any conversations about fuel, This is not meant to start an off-track conversation, but I don't use any snake oil.    I only use ethanol-free gas. Enough said about that issue.

This is a 701 with a K-161. The fuel tank has a glass bowl strainer, new fuel lines, and an extra see-thru fuel filter. 

The fuel pump was inspected prior to installation, and the check valves functioned better than any pump I've worked with in the past. Pressure testing showed no leakage either forward, backward or past the diaphragm. 

The carburetor was thoroughly rebuilt by me. It is a Carter carb, original to that engine. The float valve functions properly.

There is no siphoning into the bowl when the engine is stopped, as all fuel components sit lower than the intake of the carburetor.

 

21 hours ago, stevasaurus said:

How does the spark plug look ??  Could be the break in period.  

 

 

Steve, here is the plug. Looks pretty normal to me. I think you are probably on to something with break-in. A little blow by at the piston rings as they are seating could account for the gas smell.

I am going to refill the crankcase with SAE 30W non-detergent oil later today and see if it happens again.

Also, the grandson always throttles down before shut off, at least when I see him. 

  

[squonk 41,067]

Gas doesn't get into the crankcase because of magic. It was from the carb leaking by (unlikely) or the pump (likely) There  may even be a pinhole in the pump casting itself. If the problem persists, run the engine by gravity feed and I bet the issue goes away. 

[wallfish 16,994]

Another vote for fuel pump.

Curious about how many hours are on the engine if the break in oil hasn't even been changed out. Maybe there isn't a problem at all, change out that oil and check again.

[rmaynard 15,434]

5 hours ago, wallfish said:

Curious about how many hours are on the engine if the break in oil hasn't even been changed out. Maybe there isn't a problem at all, change out that oil and check again.

I'm going to say 8-10 hours.

[Alrashid2 165]

@rmaynard, did you ever figure this out? As you saw on one of my previous posts, I bought a 1985 312-8 with a Kohler K301. Changed the oil, and 2 weeks later noticed it was overfilled slightly and drained a bit, to find it smelled badly of gas and seemed much thinner. 

 

Similar to your case, my pump seems fine but it sounds like the most likely culprit, so changing that this week. I couldn't find any leak or tear or hole in my pump, but it is an aftermarket one installed by the PO, so hoping that is what it was. Checked my carb too and all seems good on it. 

 

Old engine but I have zero smoke from exhaust when running so I didn't think the rings were bad. We'll see

[rmaynard 15,434]

My issue was a hole in the oil pump diaphragm.

 

FUEL, not oil. Sorry.

Edited November 12 by rmaynard

[953 nut 55,188]

1 hour ago, rmaynard said:

My issue was a hole in the oil   FUEL  pump diaphragm.

 

[Alrashid2 165]

I figured that's what he meant!

@rmaynard was the hole obvious to you? I looked at mine up close and couldn't find any hole 

[rmaynard 15,434]

34 minutes ago, Alrashid2 said:

I figured that's what he meant!

@rmaynard was the hole obvious to you? I looked at mine up close and couldn't find any hole 

Yes. The diaphragm was ruptured.