I think it's done for. There's got to be something wrong with the cylinder somewhere in the stroke. Crankcase is full of pressure and the oil is contaminated just getting it warmed up. I still can't figure out why it would be doing that and seem to pass a leakage test. Start of compression stroke.
Is there something I'm missing? I think the oil in the intake is a blow-by problem, but what should I do about it?
- Thread starter bshr49
- Start date
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 65
- Messages
- 24,995
Nothing inside your engine makes a 100% seal over time
The rings only seal tight when the piston is moving and even then there is a gap between the ends.
I went to the effort of writing a full description of the mechanism in my previous post
If you want to know then read it
If you don't then ignore it
The forum works a lot better read from your browser than as messages on a phone.
The rings only seal tight when the piston is moving and even then there is a gap between the ends.
I went to the effort of writing a full description of the mechanism in my previous post
If you want to know then read it
If you don't then ignore it
The forum works a lot better read from your browser than as messages on a phone.
Richard Milhous
Well-Known Member
- Joined
- Aug 2, 2021
- Threads
- 6
- Messages
- 173
1. I know that the cylinder is not going to be 100% sealed. Perhaps in my "hobbyist automotive background", I should have mentioned that I've rebuilt engines before. I am familiar with how an ICE works, ring gap, and that some amount of blow-by is always going to be present.
2. I'm going to have to disagree that rings only seal when they're moving. They may seal better in motion, but they still seal when they're not.
3. I know it takes time/effort to respond to questions on a forum, especially when it's a question that could easily be answered with a quick search. All of my previous searching has not led me to an answer, which is why I joined here.
4/5. I read your posts and understand what you're saying. Perhaps it's that I don't know how much crankcase pressure is to be expected from a single cylinder with a relatively small small crankcase vs. an automotive engine that would have a larger volume available/cylinder. While running, the pressure is enough to make the oil cap jump like an exhaust flapper and spray oil if the cap is just sitting on top of the fill tube.
6. I am on a browser on this forum. I should be getting email notifications (that I would see on my phone) when a comment/reply is posted because I want to stay engaged and avoid ghosting my own thread, but I'm not getting any emails.
It still seems like the oil is getting contaminated with fuel a lot faster than it should be. The links in my last post were after about 5 minutes of run time after replacing the carburetor and draining/refilling the oil. The picture in the post before that (oil draining out of the filler tube) was what the oil looked like before I started working on it this time. I haven't drained/refilled the oil multiple times as Scrubcadet10 has suggested, but I wouldn't think a small amount of still-contaminated oil would make the oil look like that within 5 minutes.
If you think I'm ignoring your comments/advice, I'm not, I'm just trying to understand the root cause of the problem to see best how to fix it, or if it's even worth it. If the oil "mist" is instead a "fog", the WHY is what I want to know. I thought I might have a leg up having prior automotive experience, but apparently no. Sorry if I'm frustrating you, thank you for your time.
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 65
- Messages
- 24,995
There is only 2 places where fuel can get into the engine
1) fuel pump
2) carburettor
leaking fuel pumps are easy to find because they drip fuel or have a diaphragm that can be seen.
If you want to see this happening then set up a cylinder head off with fuel dripping slowly into the cylinder
It will pass right through as if the piston was not there.
now pour the fuel into the cylinder and it will pool for a long time because for the fuel to get into the crankcase, the air has to get out and the petrol sitting on top of the piston prevents this happening very quickly.
If you really want to understand engine breathing then buy Rex's eBook and read it.
If you want the research numbers then go to the University of Auckland & buy the research papers.
Excessive blow by is a two way street and usually will cause carbon fouling of the plug
Fuel leaking usually does not do that .
1) fuel pump
2) carburettor
leaking fuel pumps are easy to find because they drip fuel or have a diaphragm that can be seen.
If you want to see this happening then set up a cylinder head off with fuel dripping slowly into the cylinder
It will pass right through as if the piston was not there.
now pour the fuel into the cylinder and it will pool for a long time because for the fuel to get into the crankcase, the air has to get out and the petrol sitting on top of the piston prevents this happening very quickly.
If you really want to understand engine breathing then buy Rex's eBook and read it.
If you want the research numbers then go to the University of Auckland & buy the research papers.
Excessive blow by is a two way street and usually will cause carbon fouling of the plug
Fuel leaking usually does not do that .
Not gas that is water. Take a lighter to it and see if it burns. If so it is gas if not it is water and hold lighter to it long enough it should spatter and sputter. Don't burn up the dipstick though.
If it was water cooled, I would agree and start looking at a blown head gasket. It does not ignite immediately, but will eventually produce a short-lived weak flame, but that could be the oil igniting, I don't know at what temperature that would start to happen. It does not show signs of boiling water out (I'm assuming that is what you meant by spattering and sputtering).
It has only sat for 12 hours today after me getting it started. The plug is not carbon fouled as far as I can tell, it has some light grey deposits on it, not black, as I would expect with carbon fouling. I was going to take a look at the breather valve, too, and have run into my next problem, the holes to be used to loosen/pull the flywheel are not threaded.
Edit: I forgot to add that once I checked the breather valve, I was going to fill the fuel tank and just let it sit for a week. If fuel is leaking through the carb (even though this one is brand new), it should cause the "oil" level to rise.
Last edited:
The valve does not sit flat against the block. Bad valve? Just guessing, but I would think it should normally stay in a closed position. Thinking back on everything now, if he completely filled the crankcase, there would have been no place for the oil to go except through the valve, likely with a lot of force, that could have easily bent it.