V-4

[riff_raff]

xpensive,

A flat, opposed (180deg V) 4 cylinder engine and a conventional (less than 180deg V) V4 engine differ mostly in how their crank pins are arranged. A flat 4 will normally use 4 crank pins, with adjacent pins spaced 180deg apart in order to achieve dynamic balance. On the other hand, a 90deg V4 might use only 2 crank pins spaced 180deg apart, with rods from opposing cylinder banks running side-by-side on a common crank journal.

As for the differences between a conventional V12 and a flat 12, the cranks are usually identical. This is because both engines are essentially two in-line 6 cylinder engines with a common crank. Since an in-line 6 with equally spaced crank pins has perfect dynamic balance, the V angle of a V12 is not so important with regards to balance.

Hope that was helpful.
Terry

[ISLAMATRON]

I think you missed the "joke" Ronald... the original question was what was the difference between a flat 4 and an exactly 180* V-4... here's the quote...

A flat 4 and a 180* v 4 are completely different. The crank shaft design being the main difference.

Can someone please xplain the above, was a Ferrari "flat-12" of the 70s not just a 180 degree V-12?

Apparently it was Flat-V engines.

Or maybe its me missing the "joke"

[xpensive]

xpensive,

A flat, opposed (180deg V) 4 cylinder engine and a conventional (less than 180deg V) V4 engine differ mostly in how their crank pins are arranged. A flat 4 will normally use 4 crank pins, with adjacent pins spaced 180deg apart in order to achieve dynamic balance. On the other hand, a 90deg V4 might use only 2 crank pins spaced 180deg apart, with rods from opposing cylinder banks running side-by-side on a common crank journal.

As for the differences between a conventional V12 and a flat 12, the cranks are usually identical. This is because both engines are essentially two in-line 6 cylinder engines with a common crank. Since an in-line 6 with equally spaced crank pins has perfect dynamic balance, the V angle of a V12 is not so important with regards to balance.

Hope that was helpful.
Terry

Thanx Terry,
How many "cranks" on a Porsche flat-six engine anyway?

[tok-tokkie]

xpensive,

A flat, opposed (180deg V) 4 cylinder engine and a conventional (less than 180deg V) V4 engine differ mostly in how their crank pins are arranged. A flat 4 will normally use 4 crank pins, with adjacent pins spaced 180deg apart in order to achieve dynamic balance. On the other hand, a 90deg V4 might use only 2 crank pins spaced 180deg apart, with rods from opposing cylinder banks running side-by-side on a common crank journal.

As for the differences between a conventional V12 and a flat 12, the cranks are usually identical. This is because both engines are essentially two in-line 6 cylinder engines with a common crank. Since an in-line 6 with equally spaced crank pins has perfect dynamic balance, the V angle of a V12 is not so important with regards to balance.

Hope that was helpful.
Terry

Honda are upgrading the V4 800cc VFR motorcycle to 1200cc later this year. The 800 was a 90 degree engine but they are narrowing to 78 degrees for the larger engine because of packaging considerations. To retain dynamic balance the engine has just 2 crankpins but each with journals at 28 degree offset so the motion of the pistons is as if it was a 104 degree v-four.

Link to Wiki on new VFR http://en.wikipedia.org/wiki/Honda_VFR1200F

Link to interesting article on twin cylinder engine balance which may explain why Honda went to 104 degrees instead of 90 degrees. http://www.xs650.org.au/smoothness.htm

[marcush.]

with the common pins for opposed cylinders you have a distinct advantage in having a
smaller offset between both cylinderbanks in fact just the width of the big end of the conrod.
With two separate crank throws the offset is inevitably larger ,as you need to have a
main bearing or a big slope or crank throw to connect the two conrod bearings.