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Author Topic: Inline-four crankshaft  (Read 216696 times)

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Offline Rex Schimmer

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Re: Inline-four crankshaft
« Reply #30 on: December 05, 2011, 11:04:14 PM »
IO, you are right I did mean stroke, at my age I find it is easy just to blame being old but thanks for the correction.

One of the side affects of high "mean piston speed" is very high acceleration numbers when the piston hits the end of the stroke and is reversed. It increases by the square of the rpm change, i.e. going from 4500 ft/min to 6000 ft/min increases the acceleration load by 1.78 times. Studies have been done regarding rod failure and most of them fail in tension from these acceleration loads, which is a reason for light pistons and very high quality rod material. It has also been found that the back pressure from turbo charging can reduce this tensile stress in the rod a;though you normally do not have to turn a turbo motor at high rpm to get competitive power.

I attended a class a couple of weeks ago that was put on my Dema Elgin of Elgin Cams on racing engine design and it really put a light on really being able to define the parameters that you need for the type of competition that your are going to do to enable you to have a grip on how to build a competitive racing engine and also the huge number of compromises that are required to make real horse power. 
Rex

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Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #31 on: December 05, 2011, 11:23:28 PM »
... "mean piston speed" is 6000 ft/min, most engine designers and builders consider 4500 ft/min the upper limit for performance engines that need to run longer than 10 seconds...
Thanks for the heads-up. Apparently the 4,500 isn't a "hard" limit, judging by my hemi V8 experience. It's a full 3.75" stroke and it ran 9,000 almost every time down the track the last two seasons in competition. That's full power for as long as twenty seconds- longer than dragracing, but shorter than land-racing.
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline WOODY@DDLLC

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Re: Inline-four crankshaft
« Reply #32 on: December 06, 2011, 05:57:18 AM »
IO, you are right I did mean stroke, at my age I find it is easy just to blame being old but thanks for the correction.

Rex, at my age I just do rpm x stroke / 6!  :-D

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Offline Interested Observer

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Re: Inline-four crankshaft
« Reply #33 on: December 06, 2011, 07:52:45 AM »
Ref. Reply #29 - Centrifugal oil pressure
The other consideration is the pressure required to pump the oil “uphill” INTO the crank in the first place.

Offline RansomT

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Re: Inline-four crankshaft
« Reply #34 on: December 06, 2011, 07:55:50 AM »
Just to put things into perspective:  the new Kawasaki ZX10r has a piston speed of 5200 (a little more than 26 m/s) and comes with a factory warrantee to boot.  :roll:

Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #35 on: December 06, 2011, 11:57:17 PM »
The consensus seems to favor a flat crank.
So... the next crank concern is whether center throws (#2 & 3) should be at 0` or 180` to each other- comments?
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline jacksoni

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Re: Inline-four crankshaft
« Reply #36 on: December 07, 2011, 07:20:22 AM »
The consensus seems to favor a flat crank.
So... the next crank concern is whether center throws (#2 & 3) should be at 0` or 180` to each other- comments?
Just changes firing order making custom crank of course mandatory but also makes getting a cam ground harder as no standard cam core will work. Makes cost go up. I need a custom core, though one used in other engines also, but by the time I get done with the core, shipping, grinding,shipping etc etc is close to $1k. A lot more than your usual Comp Cams deal. Spend the money on better rods, lighter pistons or something else.
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Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #37 on: December 07, 2011, 11:52:58 PM »
The consensus seems to favor a flat crank.
So... the next crank concern is whether center throws (#2 & 3) should be at 0` or 180` to each other- comments?
I guess I should have emphasized that I'm asking strictly about vibration aspects. I've never attempted to delve into the analysis of a piston engine's vibrations. But I'm sure that the firing order of an inline engine will influence vibrations in at least one plane (probably the plane defined by the bore centers), and possibly in the other two planes.
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline wobblywalrus

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Re: Inline-four crankshaft
« Reply #38 on: December 08, 2011, 12:32:32 AM »
In reference to reply #34.  Just for perspective, the Hinckley Triumph Bonneville will rev to 9,000 rpm with Carillo rods, forged Arias racing pistons, special crank and rod bearings, racing valve springs, and careful assembly.  This is really pushing it and it is just over 4,000 fpm average piston speed.  The 5,200 fpm average piston speed, with street bike reliability, opens new frontiers of big horsepower.  I wonder how Kawasaki does this?
 

Offline Koncretekid

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Re: Inline-four crankshaft
« Reply #39 on: December 08, 2011, 06:03:20 AM »
The Triumph is a 360 degree twin, which like a single, cannot be balanced without a balance shaft of some kind.  I suspect that vibration may be more of a limiting factor than piston speed.
I'll bet some of the racers in AHRMA are spinning higher than 9,000.
Tom
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Offline RansomT

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Re: Inline-four crankshaft
« Reply #40 on: December 08, 2011, 06:19:56 AM »
In reference to reply #34.  Just for perspective, the Hinckley Triumph Bonneville will rev to 9,000 rpm with Carillo rods, forged Arias racing pistons, special crank and rod bearings, racing valve springs, and careful assembly.  This is really pushing it and it is just over 4,000 fpm average piston speed.  The 5,200 fpm average piston speed, with street bike reliability, opens new frontiers of big horsepower.  I wonder how Kawasaki does this?
  

They have kept the same bore/stroke (76x55mm) for several generations of the bike while raising the rev limit to 14k.  Here is an article that does give a little info on the engine design.

http://www.superbikeplanet.com/2011/Jan/110106kawza10.htm

Offline wobblywalrus

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Re: Inline-four crankshaft
« Reply #41 on: December 08, 2011, 11:27:46 PM »
I am not sure how useful this will be for the subject of this thread, but here it goes.  The Triumph is a twin with four main bearing journals and counter balancers.  There are two firing orders for these bikes, 360 degrees and 270 degrees.  The engines with 270 degree cranks are much smoother on the street than the ones with 360 degree cranks.  The race part suppliers have figured out the proper combinations of piston weight, connecting rod weight, and crank balance factors for the 360 degree engines.  I would need to figure everything out on my own if I use a goofy firing order.  With a 360 degree crank I am building on their experience.

The target rpm for my engine is around 7,500 rpm.  I gear for that.  There is always the possibility of a tailwind or me putting on too big a rear sprocket.  The engine is built to run safely at higher rpm if this happens.  Bearing shells are on the loose side of tolerance.  The oil hole edges on the journals are chamfered.  Carillo rods.  The gudgeon pins are offset 1 mm in forged racing pistons.

These engines can be built to run over 9,000 rpm.  This advice was given to me if I planned to do this.  Polish the crank and grind knife edges on the webs, enlarge the oil passages, and rebalance the crank for high rpm.  They told me the balance factor.  Also, I was advised to use a metal treatment that is also used on F1 car engines.  I did not do any of the things in this paragraph.  I would only go up to 9,000 rpm accidentally, or never.

It sure made sense to me to trust the experts on the issues associated with high rpm.  I am a low dollar guy and a crank break would set the program back.  Besides, that exploding motor would be right up close to a sensitive part of my anatomy.

Offline jacksoni

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Re: Inline-four crankshaft
« Reply #42 on: December 09, 2011, 07:37:08 AM »
The consensus seems to favor a flat crank.
So... the next crank concern is whether center throws (#2 & 3) should be at 0` or 180` to each other- comments?
I guess I should have emphasized that I'm asking strictly about vibration aspects. I've never attempted to delve into the analysis of a piston engine's vibrations. But I'm sure that the firing order of an inline engine will influence vibrations in at least one plane (probably the plane defined by the bore centers), and possibly in the other two planes.
I asked about this firing order (up, down, up, down instead of more usual up, down, down, up) on an engine building site and got this response:

It would introduce a first-order end-to-end rocking couple in the engine while providing absolutely no benefit whatsoever, and would need a first-order counter-rotating balance shaft. It doesn't change the 2nd-order vibration of a normal (up down down up) four-banger. There's simply no logical reason to do it that way.
Jack Iliff
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Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #43 on: December 10, 2011, 12:45:22 AM »
re: post#42
Thanks for a direct answer to the question! Up/down/down/up it will be.
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Offline sockjohn

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Re: Inline-four crankshaft
« Reply #44 on: December 12, 2011, 09:07:12 PM »
Last time I was at Van Dyne Engineering Stu had a 200 inch 4 cylinder based upon current midget motor technology, it had a hair dryer on it and ran gas with an intercooler, I think, anyway it was for some guys sand rail but it made over 1200 hp on the dyno.

I thought that older midget motors were V4's, possibly in the 60's?  V4's are somewhat prevalent in motorcycles and outboard motors, but I am uncertain the advantages and disadvantages to them.

Bub 7 streamliner used a V4.

http://seven-streamliner.com/engine/index.html