Closed crankcase engines, etcetera---

[Brian Rupnow]

I have built six i.c. engines in the last 5 years and I am happy with all of them and how they run. What I am not happy with is the constant mess of oil that I have to contend with every time I run them. For one thing, I don't have an oil-can capable of reaching into hard to access areas and dispensing one or two drops of oil. I am going to research a hypodermic syringe with a long steel needle that can reach in and dispense only one or two drops where I want them. I will probably build another engine sooner or later, and would like to consider a closed crankcase engine. Like, how hard can it be? I would probably use sealed ball bearings on the crankshaft main bearings, and probably have the camshaft extend through a boss on the side of the engine housing, with external cam gears and an oil seal on the shaft where it exits the engine case. The engine case would, of course, have to be split with a gasket between the two halves, an oil drain, and an oil filler cap, positioned so as to prevent over filling the crank-case. I don't know exactly what I would do to lubricate the con rod big end or small end. If I partially fill the crank-case with oil and use splash lubrication, that would probably work, but then I might have to have an oil control ring on the cylinder. My engine would be a four stroke, not a two stroke, so mixing oil with the gasoline and having the gas/oil vapour circulate thru the crankcase on the way to the carburetor would not be an option.--But then again, perhaps it would be an option, especially if I run a Viton o-ring on the piston, as they do require some lubrication to prevent premature wear. I would like to hear suggestions, points of view, etcetera from other i.c. engine enthusiasts in regards to this issue.---Brian

 

[mu38&Bg#]

If you have sump oil, oil control rings will be required or it will burn off oil. Depending on what you're doing with the engine, adding oil occasionally isn't a big deal. Pulling premix through the crankcase in a four stroke is common practice, many production model aircraft engines are designed this way and it works very well.

Greg

 

[Brian Rupnow]

Well, I have answered one part of my question. I had to go up to my local drug store and get a prescription filled. I asked the druggist about a hypodermic needle, and they have all kinds of them, very inexpensive. The needles are sold separately and come in various lengths and diameters and attach with a "twist/lock" motion to the syringe itself (which is made of plastic). The druggist knows I'm not a diabetic, so wanted to know what I wanted the syringe for. I told him that I made miniature engines and needed to reach into tight spots to apply small amounts of oil, which made him laugh. The needle is the largest one he had, at #18 gauge x 1.5" long. The total cost---40 cents!!!

 

[Brian Rupnow]

If I did build such an engine, it would be all machined from bar stock, no castings. If it is true that it is common practice to route the fuel (an air/oil/fuel mix) through the crankcase enroute to the combustion chamber on 4 cycle model aircraft engine, this would lubricate both ends of the con rod, and also the cam shaft and gears if they were in the internal cavity. Of course, you would end up requiring oil seals around the rocker arm push-rods (I am assuming overhead valves), and probably a sump drain plug. I will have to find out more about routing the air/oil/fuel mix from the carburetor through the crankcase on its way from the carburetor to the combustion chamber. Sounds like it might be the way to make a home made (unintentional) bomb!!!

 

[Rustkolector]

Brian,
I can tell you that most model engines require much less lubrication than we usually give them, but it does depend on how fast we run them. Slow to medium speed engines don't need much oil. As has been said a little thin oil in the fuel is usually adequate for the top end. Much of this oil ends up in the crankcase as well. Many high speed RC 4 strokes depend solely on fuel/oil mix for both top and bottom end lubrication. You could gain some good experience on wet sump enclosed crankcase engines building either Bob Shores Silver Bullet or his Hercules engine. These have proven to be good engine designs that run quite well.

Also, forget about the plastic medical syringes for oiling. The rubber seal in the syringe will swell up on first exposure to petroleum based fluids making them useless. Look for a glass syringe, or make your own plunger for the plastic syringe out of aluminum or delrin, and fit a metric O-ring to it.

Jeff

 

[aonemarine]

you know, you could make the engine without a oil pump and rely solely on splash to fill a trough that could gravity drain back to the mains...no oil pump necessary, windage is wonderful LOL

 

[Gedeon Spilett]

oil from a small outside tank (pressurized or not) is guided by a piece of tube just above the running conrod head and fall drop after drop (10/min), then by simple splashing reachs all the parts that have a small conduit to drive oil as it is usually designed.
Oil sump requires oil rings, yes, in my hands, otherwise my engines burn a lot of oil or refuse to start when over filled, probably I'm not good enough at making piston rings.

 

[Brian Rupnow]

It seems to me that the simplest oiling of the bottom end would be achieved by a splash oiling system, utilizing a "beak" on the bottom of the con rod, similar to the old 1930 Model A Ford engine. If the con rod was drilled full length, that would also look after the small end of the con rod. If the actual "dipping trough" was kept relatively narrow so that only the "beak" dipped into it and not the entire bottom of the con rod, then oil splash would be kept to a minimum. I think some kind of "sight glass" would be necessary to prevent overfilling the sump with oil. If I follow John Stevensons advice and put a "windage" tray with a slot for the con rod at the bottom of the cylinder, then most of the oil would be kept off the cylinder walls. That way I could probably get away with one compression ring (Viton) and one scraper ring (again, Viton). I would use sealed ball bearings for the crankshaft main bearings. Probably I would keep the camshaft and gears in the sump as well, so they would benefit from the splash lubrication, so that I only needed to put oil seals around the rocker arm pushrods.

 

[Brian40]

Hi Brian
I am refining the design of my 32x40H gas engine as i go along and have reached the conclusion that I am going to have to go for a splash lube system
The intention to go for gas as a fuel, deprives me of the ability to mix oil in the fuel, so splash lube and a metal piston ring it has to be.
As this is a horizontal engine I intend to make a removable cover over the crank.
The intention is to put a dipper on the rod to push oil up into the big end. the splash it makes will travel up into the cylinder.
To keep some control over the amount of oil delivered, the dipper will pass through a small trough containing the required amount , delivered by a controllable plunger pump in the sump, any excess. in the trough will over spill back into the sump well out of the way.thus stopping over oiling.
Main bearings are to be sealed ball races, Cam gears are on the outside, but I am considering A notched timing belt for this job. cams to be lubed by a felt pad under the camshaft.
I hope this all makes sense. every time I sit Down to look at the drawing I seem to end up modifying it
Brian H.

 

[Brian Rupnow]

A little research shows that I did buy a set of cast iron rings for my 1" bore Odds and Ends hit and miss engine. I couldn't get them to seal properly, so I removed the ring closest to the combustion chamber and replaced it with a Viton o-ring. This cured my compression problem and the engine ran fine. I still have the one cast iron ring that I removed. If I built a new engine with a closed crankcase, I could put one Viton ring at the combustion chamber end and use the cast iron ring about 1/4" behind it to use as an oil scraper ring.--Might even drill a series of 1/16" holes around the skirt of the piston on the crank-case side to let the scraped oil run into.

 

[Brian Rupnow]

It just happens that a buna-n 1/4" x 1/16" cross section o-ring will fit right onto the end of the plunger where the original rubber one was. I have just filled it with light lubricating oil. Will wait for a few days now and see if the oil eats the o-ring.---Brian

 

[TimTaylor]

Brian,

The buna-n (nitrile) should work fine, as it is rated excellent for both static and dynamic applications for petroleum based lubricating oils, ATF, etc.