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Cylinder/crankshaft offset


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#1 Biggles

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Posted 25 March 2010 - 00:54

I have an interest in the 1932 Ford V8 engine, in the design of which old Henry insisted on following the so-called "desaxé" principle, for little gain but a complicated asymmetrical engine cross section (desaxé = offcentre/unbalanced).
The desaxé principle states that the cylinder centreline should be located some distance after top dead centre, so that the cylinder axis is not directly over the crankshaft, but offset in the direction of rotation. The advantages of this are reduced piston side thrust and longer duration (greater than 180 degrees) intake and power strokes, with the penalty of variation in inertia forces.

Can anyone here tell me who formulated the principle and when?

I believe the 2010 Yamaha YZ450F employs the idea.
Are there other modern applications?

Here's what old Henry did in '32:

Posted Image

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#2 Greg Locock

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Posted 25 March 2010 - 01:33

I would have thought this would result in a very similar gain to offset gudgeon pins/little ends/wrist pins, depending on which side of which ocean you are. As such it has a real effect on a modern engine. Of course F1 engines use it for different reasons.




#3 Canuck

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Posted 25 March 2010 - 02:10

Elaboration for us mushrooms?

#4 McGuire

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Posted 25 March 2010 - 07:33

Can anyone here tell me who formulated the principle and when?

I believe the 2010 Yamaha YZ450F employs the idea.
Are there other modern applications?


The idea is ancient, predating the IC auto engine back into steam engines. By ca. 1905-06 it was a common feature on American automobiles -- one thing it does is make hand cranking easier. I recall reading in a 1906 issue of The Horseless Age (but not at the time) in which it was proposed that ideal offset should be 1/6 the stroke, though it didn't say how they arrived there.

Seems to be back in vogue these days. Honda loves it, employs 13-14mm on its I4s.

#5 Pat Clarke

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Posted 25 March 2010 - 07:52

Biggles,

The Hyundai Gamma 1.4 and 1.6 engines which will be released soon in the i20 model in Australia has 10mm cylinder offset.

This engine will replace the 1.3/1.4/1.5 and 1.6 Alpha engines that have been used in small Hyundais and Kias since the X3 Excel.

The reasons given are the same as Henry's all those years ago =]

Pat

#6 gruntguru

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Posted 25 March 2010 - 08:09

The advantages of this are reduced piston side thrust and longer duration (greater than 180 degrees) intake and power strokes, with the penalty of variation in inertia forces.


Now this raises a poser. The power stroke occupies more degrees than the compression stroke. Obviously TDC and BDC no longer coincide with the crankshaft pointing "straight up" and "straight down" respectively.

Will the stroke remain the same?

#7 Biggles

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Posted 25 March 2010 - 10:08

I should have come here in the first place!
I'm most grateful for the interest and for examples of modern use of the principle, particularly the oblique reference to F1 engines ...

... it has a real effect on a modern engine. Of course F1 engines use it for different reasons.

... but some explanation would be valued, if you would be so kind?

Will the stroke remain the same?

The stroke in an offset cylinder is lengthened when compared to that in a "standard" (zero offset) cylinder.
This may help:
Posted Image


#8 D-Type

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Posted 25 March 2010 - 13:08

I don't get it. Surely the stroke must equal the "throw" of the crankshaft. Wouldn't any increase in effective stroke at TDC due to the offset be cancelled out by a corresponding decrease at BTC. Or is this an over-simplification of a complex issue?

If the offset does increase the stroke, is this taken into account when calculating the cubic capacity?

#9 malbear

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Posted 25 March 2010 - 13:53

I think that the sidethrust is reduced during the expansion and intake strokes but increased during the compression and exhaust strokes but in a normal configuration the greatest sidethrust occurs during the expansion stroke, so with cylinder offset a slight overall reduction in total friction occurs. displacement does not change but the piston TDC and BDC are further down the bore as offset is increased so the dec is trimmed to suit.

http://www.wfu.edu/~...fset/offset.xls
http://www.fev.biz/d...007-01-1248.pdf

cheers malbeare

Edited by malbear, 25 March 2010 - 14:10.


#10 Biggles

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Posted 25 March 2010 - 15:19

I don't get it. Surely the stroke must equal the "throw" of the crankshaft. Wouldn't any increase in effective stroke at TDC due to the offset be cancelled out by a corresponding decrease at BTC. Or is this an over-simplification of a complex issue?

If the offset does increase the stroke, is this taken into account when calculating the cubic capacity?

In referring to the diagram above it may help to open it in another window (right click, save picture as …, etc.)
An annotation is missing from the diagram: point a2 should be marked on line CD at the intersection of the arc from point a1 on AB.

The circle represents the path of the centre of the crankpin and is divided equally at points a, b, c, etc. The line AB represents the centreline of a standard cylinder. The line CD represents the centreline of the offset cylinder (offset exaggerated).
From each of the points a, b, c, etc., at a distance representing the connecting rod length on the same scale as the crankpin circle, the position of the standard gudgeon pin centre is marked at a1, b1, c1, etc. and of the offset gudgeon pin centre at a2, b2, c2, etc.

It should be noted that the positions of TDC and BDC of the piston in each engine are established when its gudgeon pin, crankpin and crankshaft centres are co-linear. In the standard engine those are at g and a respectively, diametrically opposite each other, so that the distance between them around the crankpin circle is the same in each direction and therefore the mean linear velocity of the piston is the same on upstrokes and downstrokes.

In the case of the offset cylinder the positions of TDC and BDC are at T and B respectively and it will be seen that the distance TB in the clockwise direction of rotation is greater than the distance BT clockwise. As the crankpin travels with uniform velocity around its circular path, the mean linear velocity of the piston on its upstrokes will be greater than that on its downstrokes, the variation being dependent upon the offset.

From the diagram it will be seen that the length of stroke of the offset piston a2g2 is slightly greater than that of the standard piston a1g1 although the perpendicular distance from the crankpin centreline EF to TDC of the offset piston is less than that to TDC of the standard piston.

Thus, all else being equal, the offset cylinder engine exhibits a slight increase in swept volume with reduced piston side thrust and reduced frictional losses. However, the variation in mean piston velocity between up- and downstrokes gives rise to variation in inertia forces which may be difficult to counteract if the offset is appreciable.

I hope that this helps.
Onwards and upwards,
Biggles.


#11 McGuire

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Posted 25 March 2010 - 17:50

The effect on displacement is tiny -- typically well less than one cubic inch. The effect on cylinder wall friction and wear is small, even debatable. SAE papers and other findings have come down on both sides. The difficulty lies in the methods required to quantify such a gain: generally, a motoring dyno (fraught) and a floating liner on strain gauges (more fraught). In general: the engine may feel easier to turn over by hand, may well show (instrumentally) a friction reduction up to around ~2000 rpm, and above that rpm the apparent benefit often seems to disappear.

#12 Biggles

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Posted 25 March 2010 - 20:54

The effect on displacement is tiny -- typically well less than one cubic inch. The effect on cylinder wall friction and wear is small, even debatable. SAE papers and other findings have come down on both sides. The difficulty lies in the methods required to quantify such a gain: generally, a motoring dyno (fraught) and a floating liner on strain gauges (more fraught). In general: the engine may feel easier to turn over by hand, may well show (instrumentally) a friction reduction up to around ~2000 rpm, and above that rpm the apparent benefit often seems to disappear.

I hear what you say and have sympathy with your viewpoint.
My continued interest in the topic stems from curiosity as to why Henry Ford would go to such lengths to accommodate the "principle" and why modern designers and manufacturers are still in thrall to it.

#13 Greg Locock

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Posted 26 March 2010 - 01:15

In a production engine we use gudgeon pin offset to control cold idle clatter, where basically the piston hasn't warmed up enough and tends to rock around too much just after TDC. This tuning is done with the help of the piston manufacturer, who can also affect things by redesigning the skirt.

It will also affect the friction, in theory, so if the engine designer has put cylinder offset in, it'll probably stay there. I can't see any significant extra cost to be honest, the machining of the bores is not 'developed' off the main bearing axis directly.


F1 cars use it to place the cylinders lower in the block than they would otherwise be, to reduce the cg height.



#14 Wilyman

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Posted 26 March 2010 - 01:36

The "desaxe" design has been used on Peugeot engines from 203? onward.
To install the pistons incorrectly results in a rattley motor.

If I can be indulged. In explaining the desaxe design to apprentices I would use a bicycle crank as an example.
With the crank positioned at 12 0/clock it is difficult to push to get going.
With the crank positioned ie at 1 O/clock it becomes easier to proceed.

Anyone??

#15 McGuire

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Posted 26 March 2010 - 02:37

I hear what you say and have sympathy with your viewpoint.
My continued interest in the topic stems from curiosity as to why Henry Ford would go to such lengths to accommodate the "principle" and why modern designers and manufacturers are still in thrall to it.


I don't really have a viewpoint about crankshaft offset either way except that it's interesting, both historically and technically. That it may not be especially effective does not deter my enthusiasm in the least. My personal opinion, for what it's worth, is that as the industry's instrumentality improves, a small but nonetheless measurable benefit will be firmly established. (Some mfg'ers like Honda believe they are already there.) Since there is little/no cost involved and every tiny bit of fmep counts these days, looks like a winner.


BTW, like you I am also a fan of the Ford V-8. Just bought this '32 roadster this week, bringing it back to my shop Sunday. Will be finished as an early '50s style hot rod with a '42 V8 I also picked up. Really looking forward to this project.

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#16 Allan Lupton

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Posted 26 March 2010 - 11:09

The stroke in an offset cylinder is lengthened when compared to that in a "standard" (zero offset) cylinder.
This may help:
Posted Image

I normally inhabit another place, where I posted the following, but perhaps the anonymous Biggles hasn't looked there.
It might also be too technical for the nostalgia crew, but should be understood here I presume.

Whilst it is true that the stroke of a desaxé engine is not the same as the crank throw, the difference (for real values of offset) is so trivial as to be irrelevant. If you understand trigonometry, I can point out that you are dealing with the difference between the cosines of two small angles.
I find the idea that there is some benefit if intake and power strokes are spread over more than 180 degrees a bit hard to accept. So far as the power stroke is concerned, consider the differences in the turning moment diagram that would result, and then consider if the area under them would differ, and if it did whether it was a beneficial difference.
The diagram above shows a hefty offset, and reducto ad absurdam think about what happens when the offset = half the stroke.

Edited by Allan Lupton, 26 March 2010 - 11:11.


#17 McGuire

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Posted 26 March 2010 - 12:47

Biggles and Allen Lupton, welcome to both of you. I'm sure you have much to offer to our little forum and look forward to chatting with you.

#18 Biggles

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Posted 26 March 2010 - 12:59

F1 cars use it to place the cylinders lower in the block than they would otherwise be, to reduce the cg height.

Hmmm, not sure about that.
All F1 engines are V8s so if one bank is lower the other must be higher, by the same amount.
Maybe the overall reduction in height is half that of one bank if the engine is canted?

#19 Biggles

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Posted 26 March 2010 - 13:18

To summarise from here and from the Nostalgia Forum (De Saxe Principle thread), the features of the offset cylinder design would appear to be these:

It’s an old and interesting idea that has modern adherents (Honda, Kawasaki, Hyundai at least),
it will quieten an engine at start-up and idle by reducing piston slap,
it leads to lower parasitic losses (piston side thrust, crankpin bearing),
it may lead to easier starting (bicycle crank analogy),
it improves initial throttle response (according to Kawasaki),
it reduces the height of an engine.

Have I missed one?

I’m most grateful to all who have contributed positively to this discussion and to my knowledge and experience.

Onwards and upwards,
Neil (Biggles) Bennett.


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#20 Allan Lupton

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Posted 26 March 2010 - 14:03

If I can be indulged. In explaining the desaxe design to apprentices I would use a bicycle crank as an example.
With the crank positioned at 12 0/clock it is difficult to push to get going.
With the crank positioned ie at 1 O/clock it becomes easier to proceed.

Anyone??

a) not many engines are expected to start from static these days - and when they were started "on the switch" it was the cylinder that was past TDC that fired and started the motor.
b) even if they were started from static, all that desaxé does is move the dead point (where con-rod and crank are aligned) round a little

#21 VAR1016

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Posted 26 March 2010 - 20:00

Despite my lack of training in the likes of engineering and applied mechanics, I have been familiar with the desaxé concept for many years; as I recall it was covered in a book I still have but sadly not here, called The Petrol Engine, published about 1925. (I also learned from this book that certain 1920s Bristol radial aero engines incorporated variable valve timing!)

I am taking a bit of a liberty here - if it upsets anyone, I'd be happy to start another thread but I feel that my subject might just be related.

I'll be brief.

I'm an enthusiast of the Lancia Fulvia. For those not familiar with it this car has a very narrow-angle V4 engine.

Using well-established Lancia inventions, the crankshaft has offset crankpins, nominally double the angle of the Vee although I cannot be certain as I have no drawings and I believe that the centreline of the crank is not actually at the theoretical apex of the Vee.

The two relevant versions are the 1298: 77 x 69.7, vee angle 12° 40' approx and the 1600 82 x 75 vee angle 11° 20'

A pal and I decided to build an experimental version: we used a Fulvia 1300 crankshaft and bored the block to accept a set of 82.4mm pistons giving 1486cc. Now we realised that the Vee angle is important but as the picture shows with overboring, one runs into trouble at the bottom of the bores with 'overlap'. My pal had the block bored to 11°20'. We expected the thing to vibrate...

Posted Image

All this was done on very little money, the engine included Kugelfischer mechanical fuel injection (ex BMW set up by guesswork), special camshafts, gas flowed head of course and a nice exhaust manifold designed and built by us.

We were amazed: first it had in particular really good torque, and obviously plenty of power (I was doing nearly 120 and he sailed past me!) but the big surprise was that the engine was so smooth all through the rev range - much smoother than my 1600 Fulvia. Sadly the block cracked (we had naïvely imagined that the bore walls would be concentric which they weren't).

Sorry about the long preamble but I would love to hear an opinion or two on this. I cannot grapple with the maths, but with the difference in the crank offset and Vee angle surely it should have been awful?

Thanks for your patience.

Edited by VAR1016, 26 March 2010 - 20:03.


#22 MatsNorway

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Posted 26 March 2010 - 20:39

Cool.

Just want to mention that saab also had/gas a offset on cyl and piston relative to the crank.

They also had a tilting block to variate the compression if knocking or anything else appears. (low octane++)

#23 D-Type

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Posted 26 March 2010 - 22:32

Now, what about Cugnot's engine?

Biggles, I went to the site that you referred me to and there was no mention of how the cylinders were aligned or even if the drive utilised cranks. Someone else (was it Alan L) said that the Cugnot vehicle used a ratchet to translate the reciprocal into rotary motion. So what do you have that you can share?

#24 Biggles

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Posted 27 March 2010 - 00:06

Now, what about Cugnot's engine?

Biggles, I went to the site that you referred me to and there was no mention of how the cylinders were aligned or even if the drive utilised cranks. Someone else (was it Alan L) said that the Cugnot vehicle used a ratchet to translate the reciprocal into rotary motion. So what do you have that you can share?

From across the pond (no blame attached) I was led to believe that the 1932 Ford V8 cylinder/crank offset principle derived from a Frenchman by the name of De Saxe.
From that starting point I researched and found that an inventor of steam locomotion, Nicholas Cugnot, had been sponsored by one Count De Saxe. Encouraged, that was my entry point to this forum. Since I could find no reference to De Saxe in relation to Henry Ford's V8 design I wondered if Cugnot deserved the credit and if more knowledgeable people could assist my research.
The first response from the Nostalgia Forum was a cryptic "desaxé = off-centre" which, I have to admit, went over my head. Now that the waters have cleared it is apparent that the cylinder offset principle has been known in some quarters as "desaxé", not De Saxe, for many years, but not to me. For ever more I will eschew "desaxé" in favour of "offset".
The point here is that Cugnot, for all his inventiveness, is irrelevant to the discussion on offset cylinders in modern internal combustion engines.
Pace?
Neil.


#25 Greg Locock

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Posted 27 March 2010 - 00:41

Hmmm, not sure about that.
All F1 engines are V8s so if one bank is lower the other must be higher, by the same amount.
Maybe the overall reduction in height is half that of one bank if the engine is canted?

Grins. Who said each bank has the same offset ? Well they do, but one leads and the other trails, if you get my drift.

#26 Biggles

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Posted 27 March 2010 - 01:01

Grins. Who said each bank has the same offset ? Well they do, but one leads and the other trails, if you get my drift.

Regret I don't understand "one trailing" in a V8 engine - surely each bank is built with the same offset from the "standard" crankshaft centreline, and in the same direction? Surely each (all) cylinders must exhibit the same configuration? And the whole idea is that each and every cylinder centreline is advanced beyond the "standard" TDC?
Help me if I'm wrong - just searching for truth.


#27 Greg Locock

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Posted 27 March 2010 - 04:41

Both banks are dropped vertically, so one has positive desaxe and the other has negative.

#28 gruntguru

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Posted 27 March 2010 - 08:21

A pal and I decided to build an experimental version: we used a Fulvia 1300 crankshaft and bored the block to accept a set of 82.4mm pistons giving 1486cc. Now we realised that the Vee angle is important but as the picture shows with overboring, one runs into trouble at the bottom of the bores with 'overlap'. My pal had the block bored to 11°20'. We expected the thing to vibrate...

All this was done on very little money, the engine included Kugelfischer mechanical fuel injection (ex BMW set up by guesswork), special camshafts, gas flowed head of course and a nice exhaust manifold designed and built by us.

We were amazed: first it had in particular really good torque, and obviously plenty of power (I was doing nearly 120 and he sailed past me!) but the big surprise was that the engine was so smooth all through the rev range - much smoother than my 1600 Fulvia. Sadly the block cracked (we had naïvely imagined that the bore walls would be concentric which they weren't).

Sorry about the long preamble but I would love to hear an opinion or two on this. I cannot grapple with the maths, but with the difference in the crank offset and Vee angle surely it should have been awful?

I wouldn't expect a noticeable increase in vibration levels. 1 degree error in crankpin phasing will produce a small primary imbalance and an even smaller secondary imbalnce - both would be much smaller than the secondary imbalnce inherent to in-line fours (and their near relatives the narrow-vee fours). Of course there would have been potential for ignition and valve timing to vary by 1 deg on 2 cylinders unless you made provision.

#29 VAR1016

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Posted 27 March 2010 - 12:08

I wouldn't expect a noticeable increase in vibration levels. 1 degree error in crankpin phasing will produce a small primary imbalance and an even smaller secondary imbalnce - both would be much smaller than the secondary imbalnce inherent to in-line fours (and their near relatives the narrow-vee fours). Of course there would have been potential for ignition and valve timing to vary by 1 deg on 2 cylinders unless you made provision.



Thanks very much for your reply. As I wrote the engine was extraordinarily smooth - comparable with the earlier 1200 Fulvias which were rather turbine-like.

We did realise that there might be ignition timing problems, but as the budget was microscopic we just went with the standard distributor. And the budget obviously precluded "scatter" camshafts. I suppose that with a bit of money to throw at it, the engine would certainly have been much better.

Edited by VAR1016, 27 March 2010 - 12:10.


#30 Biggles

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Posted 27 March 2010 - 14:18

Both banks are dropped vertically, so one has positive desaxe and the other has negative.

No wonder you were grinning!
My thinking was blinkered. Thanks for that.
Neil.

#31 Engineguy

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Posted 27 March 2010 - 19:49

Both banks are dropped vertically, so one has positive desaxe and the other has negative.


The GM 3.5 and 3.9L "High-Value" (i.e. cam in block) 60° V6s do this... they moved the bores outboard 1.5mm on both sides to allow bigger bores. The resulting cylinder bore intersection is 3mm below crank centerline. The alternative would be to raise the cam, and raise the deck height, resulting in longer rods, more weight, higher CoG and a taller and wider engine (albeit slight).

Observation on Yamaha YZ450F: The 12mm cylinder offset there is notable because the stroke is short. Looking at the offset as a percentage of stroke it's 20%... 40% of the crank throw (half-stroke)!

Posted Image
.

Edited by Engineguy, 27 March 2010 - 20:05.


#32 Biggles

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Posted 27 March 2010 - 21:54

The GM 3.5 and 3.9L "High-Value" (i.e. cam in block) 60° V6s do this... they moved the bores outboard 1.5mm on both sides to allow bigger bores.
Observation on Yamaha YZ450F: The 12mm cylinder offset there is notable because the stroke is short. Looking at the offset as a percentage of stroke it's 20%... 40% of the crank throw (half-stroke)!

Thanks for that - is a scaled cross-sectional drawing available of any of these "double offset" engines?

#33 TDIMeister

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Posted 19 July 2010 - 19:19

There was a recent discussion about this in the context of the VAG VR engine family over on eng-tips.com. In that context, each side bank of the VR engine is offset on opposite sides of the cylinder-crank centreline, ±12.5mm on the 15° VRs and ±22mm on the newer 10.6° variants, in the same way Greg describes the practice done on F1 engines to lower the CoG. The effect of the offset is more a function of the ratio with the con-rod length rather than of the stroke; mathematically it is expressed as such).

I calculated the profiles of the resulting motions for the ±12.5mm case, using the known dimensions of the 2.8 VR6 (90.3mm stroke, 164mm con-rod length).
Picture of the VR cylinder layout: http://bit.ly/are5NC
Displacement: http://bit.ly/aDqcPv
Velocity: http://bit.ly/bRyAmY
Acceleration: http://bit.ly/91Ri58

As you can see, the profiles are different for the left- and right banks of cylinders; note how they deviate from the profile without any offset.

Given the above geometrical data, maximum true stroke is 90.585mm (cf. 90.3mm crank throw diameter). On the right bank with positive cylinder offset (toward the anti-thrust side) the maximum stroke length occurs at 186° CA (referenced to TDC), and the pistons' closest approach to true TDC occurs at +3°CA (0.0016mm below true TDC). On the left bank with negative cylinder offset, the same maximum stroke length of 90.585mm occurs at 174° CA and closest approach to true TDC occurs at -3°CA (also 0.0016mm below true TDC). The expansion stroke is effectively extended/contracted, in terms of crank angle, by 3° CA respectively. Not much. It's greater value is in friction reduction, and there's even a range of research results showing substantial improvements to almost none.

Offset piston pins are primarily for NVH purposes and involve smaller magnitudes of offset, often around 0.5 to 2 percent of piston diameter. his is mainly achieved by smoothing out the transition of the piston skirt position, which wants to stick to the anti-thrust side on the upward portion of the stroke and to the thrust side on the downward part.

#34 TDIMeister

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Posted 19 July 2010 - 19:27

On the Yamaha YZ450F, the offset is toward the thrust side, which seems counterintuitive if the goal is to effectively lengthen the induction/expansion strokes and reduce friction... wonder why? Knowing the stroke, offset and rod angularity at crank TDC, it's a straightforward calculation to determine the con-rod length.

Edit: I guess I shouldn't take for granted that the crankshaft can only spin in the clockwise direction! Sorry!

Edited by TDIMeister, 19 July 2010 - 19:30.


#35 gruntguru

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Posted 19 July 2010 - 23:53

Edit: I guess I shouldn't take for granted that the crankshaft can only spin in the clockwise direction! Sorry!

All crankshafts spin in both directions. Depends which end you are looking at. :)

(Looking at the Yamaha drawing, all you can tell is that the camshafts turn anticlockwise. Add the knowledge that they are chain drive and deduce that the crank turns anticlockwise also.)

#36 malbear

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Posted 20 July 2010 - 06:00

All crankshafts spin in both directions. Depends which end you are looking at. :)

(Looking at the Yamaha drawing, all you can tell is that the camshafts turn anticlockwise. Add the knowledge that they are chain drive and deduce that the crank turns anticlockwise also.)

In that picture you are looking from the left side of the bike and the engine is turning anticlockwise . If you look at it from the right side then the engine is turning clockwise.
the engine is turning the same direction as the wheels.
some race bikes have the engine turn backwards in the reverse direction of the wheels so that the overall giroscopic efect of the engine to some ectent cancells out the giroscopic efect of the wheels thus making the bike easier to corner and more unstable . another shaft is required to reverse the output shaft to turn the chain the right direction for driving the rear wheel
cheers Malbeare

#37 cheapracer

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Posted 20 July 2010 - 11:35

FWIW and I haven't looked it up for a bit, twin crankshaft engines looked to be all the rage a while ago.

Thats 2 crankshafts operating the same piston/s. Counter rotating and zero piston thrust losses as well as lower friction because no skirts are required. Minimal vibes of course with each crank cancelling the other.

If I remember correctly one test motor was a 500cc Yamaha single that immediately lept from 35hp to over 50hp and revved like snot. At the expense of and extra crank and rod etc.

Ah ha, one I remember I just found - a German Suzuki based 750cc single engine raced in Euro Supermono running a staggering 115hp! Thats about 20 up on a single crank Supermono in the day. Not much more info on it though.

Posted Image

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The Diesel concept...

I just found the mob who did the bike engine above and I think they have a sound idea in a twin crank diesel engine. Claim 110hp for a 1.4 turbo, not bad.

http://www.neander-m...ny/index_en.php

Theres a test ride of the 1.4 motorcycle here...

http://www.motorcycl...ycle/index.html

Problems for diesel include vibration, high crank/rod weight and high thrust due to hi compression so the disadvantages in that area already belong to the twin crank engine with the advantages of lowered vibration and zero thrust. Sounds good to me.

Also conrod ratio has a more important role with the twin crank so dwell can be increased easier with no regard to increased wall thrust as well as the power stroke is operating on a much greater crank lever.


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One uphill battle they have is the engine looks like a 1960's Kawasaki W650 and if you know your bikes ... :lol:

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Edited by cheapracer, 20 July 2010 - 12:43.


#38 TDIMeister

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Posted 20 July 2010 - 14:16

I calculated that based on a 50mm stroke, 100mm rod length and +25mm offset, true piston TDC would occur at +12°CA and true piston BDC at 199°CA with an actual displaced stroke of 51.762mm. It would have a very long dwell near BDC and the instantaneous piston velocity would peak very close to 90°CA, both of which can help breathing as peak piston velocity would be closer to the maximum lift of the intake cam lobe. So a significant improvement in VE and power is believable.

#39 Lee Nicolle

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Posted 20 July 2010 - 22:51

A little off subject. In years past in Holden HQ racing it was a fad to put the pistons in backwards as supposedly it reduced drag hence making a little power. Though to me all it seemed to do was wear out pistons and bores and the engines rattled quite badly at idle too.
Most production engines have offset pistons ofcourse.
I once rebuilt a Falcon 6 for a customer, It had had 1 piston fitted backwards at the factory. The bore was badly scuffed, had broken a top ring and was generally sad. It had only done about 80000km. I patched it up, honed new piston and rings and it ran ok but would not have been a good engine. I told them to sell it soon!

Actually you could make a thread about this, production engine cockups that actually ran. I have seen quite a few over near 40 years.

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#40 Ray Bell

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Posted 20 July 2010 - 23:40

Engine builders have been doing that for many years, Lee...

At Bathurst in the sixties it was commonplace for 'blueprinted' engines to have the pistons reversed to get extra power. Wear, of course, wasn't an issue.

#41 TDIMeister

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Posted 20 July 2010 - 23:57

What is the actual mechanism for the reported improved power? The amount of piston offset, if applicable, is not sufficient in magnitude to have the friction reducing effect that its proponents claim. Maybe due to cam grinding, clearances of the piston are assymetrical between the thrust and anti-thrust sides? Or different skirt contact area on either side? Either of these would also seem to explain the reports of increased wear, scuffing and piston-slap rattles.

Edited by TDIMeister, 20 July 2010 - 23:58.


#42 gruntguru

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Posted 21 July 2010 - 01:52

What is the actual mechanism for the reported improved power? The amount of piston offset, if applicable, is not sufficient in magnitude to have the friction reducing effect that its proponents claim. Maybe due to cam grinding, clearances of the piston are assymetrical between the thrust and anti-thrust sides? Or different skirt contact area on either side? Either of these would also seem to explain the reports of increased wear, scuffing and piston-slap rattles.


"Reported improved power" doesn't need a mechanism because nine times out of ten it doesn't exist.

#43 Catalina Park

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Posted 21 July 2010 - 09:48

A little off subject. In years past in Holden HQ racing it was a fad to put the pistons in backwards as supposedly it reduced drag hence making a little power. Though to me all it seemed to do was wear out pistons and bores and the engines rattled quite badly at idle too.
Most production engines have offset pistons ofcourse.
I once rebuilt a Falcon 6 for a customer, It had had 1 piston fitted backwards at the factory. The bore was badly scuffed, had broken a top ring and was generally sad. It had only done about 80000km. I patched it up, honed new piston and rings and it ran ok but would not have been a good engine. I told them to sell it soon!

Actually you could make a thread about this, production engine cockups that actually ran. I have seen quite a few over near 40 years.

The dyno told us to fit the pistons the right way in our HQ. :drunk:

#44 Lee Nicolle

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Posted 21 July 2010 - 09:59

Yes i worked that out about 30 years ago when I first heard about it. Realistically an old wives tale. Though as a engine sealer I saw quite a few. Fast ones and slow. There was so much monkey see monkey do in HQs in the early days.And probably still is.What amazed me was the performance of some true 'gunker' engines that were running near the front.

Edited by Lee Nicolle, 30 July 2010 - 00:05.


#45 cheapracer

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Posted 21 July 2010 - 14:40

Yes i worked that ot about 30 years ago when I first heard about i. Realistically an old wives tale. Though as a engine sealer i saw quite a few. Fast ones and slow. There was so much monkey see monkey do in HQs in the early days.And probably still is.What amazed me was the performance of some true 'gunker' engines that were running near the front.


But tell us about the cheats you found, far more interesting .....


#46 McGuire

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Posted 27 July 2010 - 03:00

Reversed pin offset was a Smokey Yunick thing. I'm not a fan of reversed pin offset.

#47 Lee Nicolle

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Posted 30 July 2010 - 00:38

But tell us about the cheats you found, far more interesting .....

Lots, though often inadvertantly. I did see a lot of poor machining and assembly. A crank ground with different strokes, a couple short and a couple long by 2-3 thou, a few blocks that were decked crooked, end to end and side to side,heads the same, caught a few oversize valves, usually by a few thou with replacement valves, an engine assembled with a bent rod, heaps of blocks with pulled head stud threads and a couple cracked around head stud bosses. heaps of loose cam gears and one engine that had been reringed had a broken flywheel bolt that they had not picked up hence the flywheel was loose too!!

The artistic liscence in interpretation was with a head that had not been throated as per the rules which I knocked back but the elegibility officer then let through [with no consultation with me, the sealer] The car was on pole at the GP and i recognised the head. The **** hit the fan and I wasted my day!! though the head was removed and replaced. But I had a ding dong argument with the chief scrutineer for support events who could not see the problem but found other things that he thought were wrong but were ok. A scrutineer with whom I had had problems with as a competitor.
The joke of it was the illegal head was not as good as the legal one!

Another head had undersized stem valves, a couple hasd light weight retainers and aftermarket locks. I saw a crank that had been winning but after it broke which was a stroker. After that they went to stainless seals and used lockwire as the copper wire had been soldered together.
A lot of heads had had some serious work done on bowls and ports with sandblaster, bead blaster. But very hard to knock back as there was no grinding. And GMH on some of the worst castings had cleaned them up by hand anyway so very hard to interpret. I usually let them go if they were what GMH should have produced not the junk they let out there. 76-80 heads were generally the worst. Bowls with so much casting flash around the guides it was rediculous. Crank and rod prep was similar too, lots of bead blasting.