How does 4 stroke outboard engine internal lubrication work?
How does 4 stroke outboard engine internal lubrication work?
Engineering Question:
Premise:
A 2-stroke outboard engine is a fairly simple machine.
The engine lubricant is in the fuel.
The fuel / lubricant mixture has an induction path which allows it to lubricate the crank shaft, connecting rods, etc.
And though it's a bit smokey, it seems to be a fairly durable system. The horsepower to weight ratio of 2-stroke engines is pretty good.
But one of the main advantages of the 2-stroke design is that the crankshaft can operate on the vertical axis.
This simplifies the transmission; spline to drive shaft, to lower drag unit, some gears to align the shaft rotation to the thrust vector. Done.
But 4 stroke engines are a different matter.
Most automotive 4 stroke engines I've seen have the oil sump below the horizontal crankshaft.
Up-end the 4-stroke, and the sump runs dry.
Reposition the oil intake, but the bottom cylinder's connecting rod and piston would churn the oil into a froth. The lubricant would fail, and shortly thereafter, the engine.
Yet there are several well established brands of 4-stroke outboard engines commercially available.
How do they work?
Does the engine crankshaft actually rotate in the vertical axis?
Or is there an additional gear-box to send the torque down to the prop.?
If vertical, how does the bottom cylinder machinery avoid frothing up the oil in the sump?
Premise:
A 2-stroke outboard engine is a fairly simple machine.
The engine lubricant is in the fuel.
The fuel / lubricant mixture has an induction path which allows it to lubricate the crank shaft, connecting rods, etc.
And though it's a bit smokey, it seems to be a fairly durable system. The horsepower to weight ratio of 2-stroke engines is pretty good.
But one of the main advantages of the 2-stroke design is that the crankshaft can operate on the vertical axis.
This simplifies the transmission; spline to drive shaft, to lower drag unit, some gears to align the shaft rotation to the thrust vector. Done.
But 4 stroke engines are a different matter.
Most automotive 4 stroke engines I've seen have the oil sump below the horizontal crankshaft.
Up-end the 4-stroke, and the sump runs dry.
Reposition the oil intake, but the bottom cylinder's connecting rod and piston would churn the oil into a froth. The lubricant would fail, and shortly thereafter, the engine.
Yet there are several well established brands of 4-stroke outboard engines commercially available.
How do they work?
Does the engine crankshaft actually rotate in the vertical axis?
Or is there an additional gear-box to send the torque down to the prop.?
If vertical, how does the bottom cylinder machinery avoid frothing up the oil in the sump?
30 character limit on sigline?
- Dan Rowden
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Re: How does 4 stroke outboard engine internal lubrication work?
$5 says this thread gets less that 6 replies.
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Re: How does 4 stroke outboard engine internal lubrication work?
£10,000 it gets more.
Re: How does 4 stroke outboard engine internal lubrication work?
These first 3 don't count.
I'm guessing you guys aren't engineers.
I'm guessing you guys aren't engineers.
30 character limit on sigline?
Re: How does 4 stroke outboard engine internal lubrication work?
$100 says it gets more than 5.
- Dan Rowden
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Re: How does 4 stroke outboard engine internal lubrication work?
<considers locking the thread to collect the dosh>
Re: How does 4 stroke outboard engine internal lubrication work?
I knew that was coming
- Dan Rowden
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Re: How does 4 stroke outboard engine internal lubrication work?
Well, it was kind of inevitable.
Re: How does 4 stroke outboard engine internal lubrication work?
You should've bet that there'd be less than six on-topic helpful replies.
So far there's zero.
So far there's zero.
Re: How does 4 stroke outboard engine internal lubrication work?
...
Last edited by xerox on Wed Jun 17, 2009 1:38 pm, edited 1 time in total.
Re: How does 4 stroke outboard engine internal lubrication work?
What gave it away? =)sear wrote:These first 3 don't count.
I'm guessing you guys aren't engineers.
It's just a ride.
Re: How does 4 stroke outboard engine internal lubrication work?
I'm betting sear doesn't realize this forum is not populated by the usual sort of egghead Geniuses.
Good Citizen Carl
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Re: How does 4 stroke outboard engine internal lubrication work?
Just the kind with the cracked shellCarl G wrote:I'm betting sear doesn't realize this forum is not populated by the usual sort of egghead Geniuses.
Re: How does 4 stroke outboard engine internal lubrication work?
With an "interest in probability and statistics" (a euphemism for gamblers)."the usual sort of egghead Geniuses."
No wonder I feel so at home here!
btw:
If I may be forgiven an on topic comment:
I've been to a few outboard motor web sites.
They don't give details. But simply looking at the profile of the power units doesn't suggest they add a whole lot of space at the bottom of the vertical block for a sump. 4 stroke & 2 stroke power-heads seem roughly the same.
30 character limit on sigline?
Re: How does 4 stroke outboard engine internal lubrication work?
PS
Looks like Jason is the Genius in this thread.
He's found a link to some diagrams.
I still can't quite figure out what the physical relationship is between the crankshaft and the oil pan.
But the diagrams provide some detail.
Thanks one and all.
It would have been an even more boring thread if you hadn't joined in to keep me (us?) company.
I can't afford to pay for the party in Las Vegas.
But here's a little cyber-treat:
[said to buxom waitress with name tag:]
"Sally? How cute. What did you name the other one?"
Thanks for the link Jason. Sorry I didn't recognize it as a link before.
I guess I should have clicked it.
Looks like Jason is the Genius in this thread.
He's found a link to some diagrams.
I still can't quite figure out what the physical relationship is between the crankshaft and the oil pan.
But the diagrams provide some detail.
Thanks one and all.
It would have been an even more boring thread if you hadn't joined in to keep me (us?) company.
I can't afford to pay for the party in Las Vegas.
But here's a little cyber-treat:
[said to buxom waitress with name tag:]
"Sally? How cute. What did you name the other one?"
Thanks for the link Jason. Sorry I didn't recognize it as a link before.
I guess I should have clicked it.
30 character limit on sigline?