Number of crank bearings
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Originally Posted By: expat
Are those Mains Huge, or is it just the picture?
I thought there was an optimal size for crank bearings, being Rod or Main?
Yeah they look huge. Huge mains benefits crank stability and stiffness and smaller rod journals for rotating mass savings, presumably
Are those Mains Huge, or is it just the picture?
I thought there was an optimal size for crank bearings, being Rod or Main?
Yeah they look huge. Huge mains benefits crank stability and stiffness and smaller rod journals for rotating mass savings, presumably
Lycoming IO-360 aircraft engine, 200HP, 4 cylinders, 3 main bearings. The front bearing is HUGE.
Shannnow,
This crankshaft has 2 dynamic dampers. You can see one with the gear on top of it. While they weigh the same, the bushing size is different for each one, giving a wider operational range.
State of the art, for "turn of the century",,,, that is the 19th century...! Hahahahaaaaa.
This crankshaft has 2 dynamic dampers. You can see one with the gear on top of it. While they weigh the same, the bushing size is different for each one, giving a wider operational range.
State of the art, for "turn of the century",,,, that is the 19th century...! Hahahahaaaaa.
Not really.
The cylinder bores can be exactly opposed if knife and fork connecting rods are used.
Production engines have been built this way.
IIRC, the early Lincoln V-12 used such an arrangement as did the RR Merlin.
It's pretty well accepted that the Merlin had a pretty short life in service as compared to a PW or Wright radial, which is why it made a lousy airliner engine after the war, although it was very fuel-efficient.
Harley twins also use knife and fork rods.
The cylinder bores can be exactly opposed if knife and fork connecting rods are used.
Production engines have been built this way.
IIRC, the early Lincoln V-12 used such an arrangement as did the RR Merlin.
It's pretty well accepted that the Merlin had a pretty short life in service as compared to a PW or Wright radial, which is why it made a lousy airliner engine after the war, although it was very fuel-efficient.
Harley twins also use knife and fork rods.
An air cooled VW 1600 has 3 mains and put out a sporty 50 hp.
back in the late 60s there was a cat that raced a 300 ci ford 6I. in a altered was VERY FAST. BUT he had a custom hemi head.
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morris, I've got a hot rod mag from the black and white days with a guy with a 300 in a drag car who made his own custom heads...out of 4V clevelands, brazing the single cylinder sections together into one head. (IIRC) the exhaust rockers couldn't be lined up with the pushrods, so he made little bushes that sat atop cshortened exhaust pushrods, then had a stubby pushrod to change angle to the exhaust rocker
Is this the hemi 6 you were thinking ogf ?
Is this the hemi 6 you were thinking ogf ?
Originally Posted By: fdcg27
Not really.
The cylinder bores can be exactly opposed if knife and fork connecting rods are used.
Production engines have been built this way.
IIRC, the early Lincoln V-12 used such an arrangement as did the RR Merlin.
A neighnbour had an old car manual from ages ago that had the V-12 and V-16 luxury engines, and you are correct there were forked rods to allow in line Vs on a lot of them (the 12 based on the flathead was different), and other manufactureras di both that, and have a "hinge" off the side of the rod, down near the big end for the V...nasty looking kit
Another option is the "skotch yoke", which a Kiwi innovator is using to make a flat four with three mains, and in placne cylinders...very short package, and effectively an infinte rod/stroke ratio (Smokey owuld like that) which gives the piston stroke a full sinusoidal movement.
Not really.
The cylinder bores can be exactly opposed if knife and fork connecting rods are used.
Production engines have been built this way.
IIRC, the early Lincoln V-12 used such an arrangement as did the RR Merlin.
A neighnbour had an old car manual from ages ago that had the V-12 and V-16 luxury engines, and you are correct there were forked rods to allow in line Vs on a lot of them (the 12 based on the flathead was different), and other manufactureras di both that, and have a "hinge" off the side of the rod, down near the big end for the V...nasty looking kit
Another option is the "skotch yoke", which a Kiwi innovator is using to make a flat four with three mains, and in placne cylinders...very short package, and effectively an infinte rod/stroke ratio (Smokey owuld like that) which gives the piston stroke a full sinusoidal movement.
Originally Posted By: Shannow
Another option is the "skotch yoke", which a Kiwi innovator is using to make a flat four with three mains, and in placne cylinders...very short package, and effectively an infinte rod/stroke ratio (Smokey owuld like that) which gives the piston stroke a full sinusoidal movement.
I'd love to see a picture of that in an actual engine. I can't imagine it would work well and be relatively free of friction.
Another option is the "skotch yoke", which a Kiwi innovator is using to make a flat four with three mains, and in placne cylinders...very short package, and effectively an infinte rod/stroke ratio (Smokey owuld like that) which gives the piston stroke a full sinusoidal movement.
I'd love to see a picture of that in an actual engine. I can't imagine it would work well and be relatively free of friction.
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Notice the Subaru crankshaft has 5 main bearings, in contrast to the Lycoming's 3 mains. This results in design compromises that have obvious consequences. There is a reason this design is not used in high HP aircraft engines.
to: shannow. i remember that modded ford 300. i think i had that mag. and / or saw the engine in Tulsa. cutting and brazing heads was big back then. my dad and i went to Tulsa to the world points finals from 1965 to 1969. back then the interest in super stock was really bigger than the AA / FD class.
Originally Posted By: Cujet
I'd love to see a picture of that in an actual engine. I can't imagine it would work well and be relatively free of friction.
Here's an article on it...
http://www.autospeed.com/cms/article.html?&A=0948
Look at the "big end arrangement"...even given modern mass production techniques, the clearances/tolerances, thermal expansions, deformation under stress are going to be all messed up as it warms up.
And to add another two locations of boundary lubrication (at the end of the big end stroke) is getting silly.
I'd love to see a picture of that in an actual engine. I can't imagine it would work well and be relatively free of friction.
Here's an article on it...
http://www.autospeed.com/cms/article.html?&A=0948
Look at the "big end arrangement"...even given modern mass production techniques, the clearances/tolerances, thermal expansions, deformation under stress are going to be all messed up as it warms up.
And to add another two locations of boundary lubrication (at the end of the big end stroke) is getting silly.
Originally Posted By: Cujet
Notice the Subaru crankshaft has 5 main bearings, in contrast to the Lycoming's 3 mains. This results in design compromises that have obvious consequences. There is a reason this design is not used in high HP aircraft engines.
I'm not sure I follow. What is the conclusion you're drawing here?
Notice the Subaru crankshaft has 5 main bearings, in contrast to the Lycoming's 3 mains. This results in design compromises that have obvious consequences. There is a reason this design is not used in high HP aircraft engines.
I'm not sure I follow. What is the conclusion you're drawing here?
Looks like pretty thin metal supporting the crank throws. Which is where it broke in the photo, one of the supports for the throws broke. This does look like, had they gone with just 3 bearings, the supports could have been more beefy. The downside would be a heavier crank though; and some of that weight would have been at the throws, which I'd think would make for more NVH.
Planes are a bit different though, a bit more NVH is ok as long as the crank doesn't shatter due to a bit of pinging. Quick throttle response probably isn't high on the list either.
Have to think though, that crank was not in a stock motor. Lots of Subaru's running around; and they usually die for something else (heads, turbo, rust, general wear and neglect).
Planes are a bit different though, a bit more NVH is ok as long as the crank doesn't shatter due to a bit of pinging. Quick throttle response probably isn't high on the list either.
Have to think though, that crank was not in a stock motor. Lots of Subaru's running around; and they usually die for something else (heads, turbo, rust, general wear and neglect).
Originally Posted By: Hokiefyd
Originally Posted By: Cujet
Notice the Subaru crankshaft has 5 main bearings, in contrast to the Lycoming's 3 mains. This results in design compromises that have obvious consequences. There is a reason this design is not used in high HP aircraft engines.
I'm not sure I follow. What is the conclusion you're drawing here?
The design is a 4 cylinder, horizontally opposed engine.
The Lycoming design uses 3 main bearings, the Subaru, 5.
The Subaru crankshaft is weaker in the web area between the bearing surfaces.
The conclusion is that 3 main bearings on certain designs is a more robust configuration.
Originally Posted By: Cujet
Notice the Subaru crankshaft has 5 main bearings, in contrast to the Lycoming's 3 mains. This results in design compromises that have obvious consequences. There is a reason this design is not used in high HP aircraft engines.
I'm not sure I follow. What is the conclusion you're drawing here?
The design is a 4 cylinder, horizontally opposed engine.
The Lycoming design uses 3 main bearings, the Subaru, 5.
The Subaru crankshaft is weaker in the web area between the bearing surfaces.
The conclusion is that 3 main bearings on certain designs is a more robust configuration.
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