Dart373

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At what size 4 cycle will a true crankcase oiling system need to be put in place? How well are the Saito gas 220's holding up? I know it has to be hard on them because you are not going to get much blowby with the compression(very sealed rings to support their compression) they run... just curious.

krayzc-RCU

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w8ye

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Back in the old days of more than 55 years ago, some car engines didn't have pressurized oiling system either.

Hobbsy

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There will always be blow by, how much or how little compression has nothing to do with it. Even the OS .70 ABC fourtroke has blow by.

Dart373

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I understand some car engines had dippers, that would sling crank case oil up to the rotating assembly.
Hobbsy? ARe you joking? I did not see a smiley, so I think you are serious. More compression means better sealing, which means LESS blowby. Take a 10:1 compression motor and run it, then take the rings out, now it is 6:1 , which has more blowby? Blowby comes mainly from the rings and some down through the valve stems. I am just asking at what point or size cyliner is it not enough oil from blow by? For example you could take the rings off of a Briggs 5 hp tiller motor and losen up the valve guides, and it will not run long. It really needs the crankcase oil. That's what I am asking. At what point should a motor have an internal oil bath system of some sort?

Hobbsy

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Dart, the compression ratio is a fixed value determined by the cylinder volume and the combustion chamber volume, no amount of sealing or unsealing will change it. An engine that is in excellent shape has blow by but a worn engine has more of it, the compression pressure stays pretty much the same no matter the engine condition, that is running pressure not cranking pressure. As the engine wears and the blow by increases you compensate by opening the throttle more keeping compression pressure the same in order to make the same power as when the engine was in good shape. No joke.

Dart373

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You missed my point. A higher compression motor will most definately need to seal better or it will be easier to get blow by, or at least on multi cylinders. If you have a high compression motor, and poor sealing rings, the cylinders will presssurize the crank case to the point where the ventilator can't keep up, and it blows the oil up the cylinders or valve guides. Back to the original question, that does not seem to be answered?

Hobbsy

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Most people avoid running engines with leaky rings by re-building them so your question is moot.

Dart373

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You really don't have much to add to the original question. Please reread post#1. You obviously know a lot. At what size motor will you no longer be able to keep it alive with blow by oiling only? Pretty simple ehh?

Hobbsy

My Feedback: (102)

That would require a true engine designer expert, most likley not found here and even then it would be a best guess because I doubt that its been done. I had a Ryobi 26cc fourstroke weed eater that had oil in the crankcase, it was an anemic loser of an engine that I only kept one year. Anything we say will be pure speculation until somebody actually does it.

Dart373

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It took you 4 postings to say "i don't know".

Sport_Pilot

You can make an engine as large as you want with oil supplied by the fuel. In WWI full scale rotery engines had the oil added to the fuel. They were not four stroke, but they were not normal two strokes either. I see no limit other than the economics of not reusing the oil.

Dart373

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I sure can't see a small block Chevy lasting long on gas/oil mix...

Hobbsy

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Then you already know your answer.

Dart373

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No, I know that a small block V8 can't take the lack of oil... I am curious as to about where the cutoff line is... you don't know.... I know that. Get off my thread if you don't have value to bring....

Campgems

No, the rotary engines were four stokes. There is no way to pressurize the crank case as required for a two stroke to run. The largest two stroke I am familiar with are outboard motors. They use a reed valve system so each piston has it own sealed crank case setup. These are inline or V engines that allow a bearing and seal between each cylinder. The four strokes use one Master rod and the the approiate number of slave rods off the master. The whole assembly fit in one chamber. I have plans for a 9 cyl Prat & Whitney Jr. radial of 88CC size. No oil pump. Only blow by. A bigger problem is getting the oil out of the crank case. If you have ever seen the preflight on a plane with the big radials, you will see the crew hand crank each engine over three or four revolutions. The oil will seep into the low cylinders an hydro lock them so they have clean this oil out prior to hitting the electric starter. Some of them had bypass valves in the low heads so the 'venting' could work. They are a very interesting engine. A blast to ride behind also.

In answer to Dart's question, if the Chevy small block was designed to work on blow by for oil, it would probably last as long as the pumped oil one does. It all depends on the design.

Don

Dart373

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I respectfuly diagree.... you could not get enough oil to the cam/wrist pins/main/and lastly, rockers. Not to mention the distributor shaft. Much more oiling is required than you think on a complex engine such as a V8. I am really kind of shocked to see so many people thinking a blow by system of oiling is as good..... strange.

Hobbsy

My Feedback: (102)

I suspect the upper limit would be set by the EPA who would say this is the largest engine we will tolerate spewing used into the ecosystem. As you can see in this Saito .80 there is no lack of oil at all and there is more down in the hollow crankshaft.

Dart373

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Looks rusty down there to me.....

Campgems

Perhaps they think it is good because it works so well. Like I said before, it depends on the design of the engine, not the size. I think a couple others have told you the same. A car engine is not designed to run upside down. Most airplane engines are, so you need to throw the chev v8 comairson out the window. It won't fly

Don

Broken Wings

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Dart, you may want a 1/4 scale Knuckle Head.....

Replica prides itself on the fact that all its engines are oil-pressure lubricated, as opposed to some running models that rely on oil blow-by to lubricate bottom ends. Oiling-system components are incredibly tiny, as you'd expect. For example, the Harley Knucklehead oil pump uses a 0.125-in.-diameter drive shaft with a 0.0625-in. square machined on its end to mate with a pump gear. A broaching operation cuts the tiny square hole in the gear, no easy task.

It Might smoke a little when you go inverted....Might smoke a little if you don't.......

It uses a gear driven pump and the engines crank case is designed with a wiper that collects the oil off of the fly wheel. A gear driven scupper collects the oil and returns it to the pump and then to the oil tank. It's a three line system, feed, return and vent. There's a check ball in the feed line of the pump that keeps the crank case from filling up with oil. When they're new they seal pretty good, after about a thousand hours the check ball drips (maybe one drop per hour) into the crank case. If you don't start the engine for a week and you fire it up the scupper can't keep up and it burps oil out of the breather on the ground. The cure was to pull the filler plug out of the oil tank so it could breathe a little easier.

The top end is oiled through the push rod tubes and it drains back into the case through a hole that runs along side each cylinder.

It would have major cool factor at the flying field....

Campgems

I keep looking at the work needed to complete one of these scale enines and I guess that's why I have plans and not an engine. An aquaintance is just about finished with his P&W Wasp Jr and at last count he had well over 2000 hours and and at least that many dollars invested.

I heard through our grapevine that one of our local Reno Racers is looking to pull the Lycoming from his plane and use a highly modified Corvette V8. Talk about oil issues. First, unless he is going to use a gear or chain drive to the prop, the engine will need to be inverted as the prop line is the radius of the spinner from the top of the fuselage. He is also going to have to go with a radiator for cooling.. A full pressure oil system with scavenger pumps in the rocker covers would also bee needed. I'm very interested in the progress, or lack there of, on this project.

Don

Campgems

Where are you going to get the little guy to kick start it?

Don

daveopam

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Hobsy, Have you seen the Honda 4C weed eater? Very interesting design. The crank has rubber straps on it. It beats the oil into a foam that lubes everything. It can run in any atitude.

David

Dart373

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There are several auto motors being used in planes now. I think they are using Ford V6 motors. I am not really getting what you guys mean by the motor "is designed for blow by oiling". What is that much different? Looking at a Saito, It appears to me to be similar to most single cylinder 4 cycles.