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J D engine design

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k martin

09-04-2007 20:27:32




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I was told that most all of the JD two cylinder engines fired 180 degrees apart instead of the common 360 on most four strokes. If this is true can anyone tell me specifically why this was thought to be preferable.




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B-maniac

09-07-2007 13:48:23




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
Correction on post right below. Glad I got back on here before anyone cought my misprint. It should read "fires every 720 degrees" and "each stroke is 180 degrees of crank rotation so 4 strokes X 180 = 720. So it should read "all 4 stroke/cycle engines fire once in 4 strokes or 2 complete revolutions of the crank or 720 degrees. It was late when I posted and the brain didn't keep up with the typer. So just substitute these figures below when you read the one below. Sorry.

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P Browning

09-07-2007 14:42:58




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 Re: J D engine design in reply to B-maniac, 09-07-2007 13:48:23  
B-Maniac -- You may think you got back in here before someone saw your earlier piece -- but not so! I saw it earlier. It is neat that you came back to make it right -- 'could have started yet another small war. (PatB)



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B-maniac

09-06-2007 18:33:50




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
After reading all the replies and then re-reading your question , I can see that your question itself is really asking two different things. First of all , ALL 4stroke cycle engines fire once in a complete cycle which is 360 degrees. Intake,compression,power and exhaust. Each stroke is 90 degrees X 4= 360. What you really want to know but didn't exactly ask is why the JD 2 CYL 4 cycle engine's 2 firing strokes on 2 seperate cylinders are only 180 degrees apart. Each piston,individually , still fires once then another 360 degrees of crank revolution fires again. The other piston does the same thing. It's the relationship between the two pistons firing that you are really asking about. Answer is , it's the only way it will work with both pistons going the same way on the same plane side by side with crank pins opposite each other for reciprocating weight ballance. Like the one poster said , "draw it out on paper and it will all make sense to you". What you have is essentially 2 single cylinder 4 stroke engines side by side with their crank pins 180 degrees opposite each other. Each one still fires every 360 degrees but the firing strokes of each are 180 degrees apart in relationship to each other. Clear as a bell right?? The way Harley gets away with using a single crank pin with both pistons connected to it is they split the cylinders up and made a "V" out of it so the weight isnt all going the same way and the firing stroke time can be put where they need it by the angle of the "V" between the cylinders. You could completely alter the sound and power characteristics of a V-8 engine just by changing the angle between the two cylinder banks from the traditional 90 degrees. A lot of V-6's are 60 degrees. So I assume it's the relationship of the two cylinder's power strokes that you are asking about and didn't really mean to say that it wasn't a 360 degree 4 stroke engine by design. Thanks for listening . This forum is a great learning tool.

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mjbrown

09-05-2007 15:47:03




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
Listen closely to a two cylinder JD and you will hear a plump plump plump plump not just putt putt putt putt. The pl and the ump are 180 degrees apart with the 540 between the plumps. If you pull off a plug wire you can easily hear the difference.



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almrm

09-05-2007 13:59:56




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
I realize the mechanics of the engine make it a 180-540 firing engine. This is an opinion - They just do not sound like I would think they would sound. When they are running I cannot notice the back to back exhaust strokes on a smooth ideling tractor or any fair running tractor under load. Also, when one is put on the dyno, the HP and RPM needle hop in a steady pace not two strokes on and two strokes off (before the smoothing is appiled to the dyno). It does not seem right but I am thankful it is right. I have been around them all my life and I just love the sound!

Mark

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55 50

09-05-2007 21:03:59




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 Re: J D engine design in reply to almrm, 09-05-2007 13:59:56  
If you can get them to idle slow enough, you usually can hear the two distinct firings.



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Dave Pearson

09-05-2007 09:35:02




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
I've always thought unusual designs were cool. Have you ever seen the Ariel four square? It has four cylinders arranged in the block in a square. It's an old british design.



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Gerald J.

09-05-2007 08:28:45




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
It has to do with the mechanical balance of the engine. With the pistons going in opposite directions mechanical balance is easy, but the 180/540 firing intervals presides. MANY 2 cylinder 4 stroke engines dating from long before the Waterloo Boy operated that way. Up through tug boat engines.

When a 2 cylinder 4 stroke engine is set up for even firing (which allows a smaller flywheel for smoother power) the pistons are traveling together and it takes a huge crankshaft counterweight to keep the engine in one spot. Engines have been made that way too.

There are no counter weights on the JD crankshaft.

Gerald J.

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k martin

09-05-2007 19:46:50




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 Re: J D engine design in reply to Gerald J., 09-05-2007 08:28:45  
Thank you for your complete, precise and clear reply. It was the only reply that actualy aswered my specific question out of 22 emails.

Congratulations you recieve a great big howdy and thanks again.

kent



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Bob

09-05-2007 08:36:29




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 Re: J D engine design in reply to Gerald J., 09-05-2007 08:28:45  
Don't forget, with the HUGE counterweights needed with the pistons traveling together in the horizontal plane, you would need balance shafts to cancel out the forces in the vertical plane caused by the counterweights.

Can you even IMAGINE how something like that would HOP!!!



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Gerald J.

09-05-2007 13:49:54




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 Re: J D engine design in reply to Bob, 09-05-2007 08:36:29  
I once saw an R at a consignment sale sitting there idling. The front axle was bobbing up and down 4 inches in time with the power strokes. I can imagine how it would move with the big counterweight.

I saw an R in the last couple weeks and it must have been idling just a bit faster because the front axle didn't move at all.

Gerald J.



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Bob

09-05-2007 18:16:55




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 Re: J D engine design in reply to Gerald J., 09-05-2007 13:49:54  
It helps reduce the bounce if the tire pressure is UP!

I spent MANY hours working with an 830 in my younger years, and, yes, they can bounce pretty good at idle!



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Pete in MD

09-04-2007 21:47:54




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
For every 2 complete 360 degree revolutions of a 2 cylinder, 4 cycle engine there are 2 power strokes followed by 2 non-power strokes. A 4 cylinder, 4 cycle engine has 4 power strokes. To compensate for the non-power strokes John Deere engines used heavier flywheels and clutch assemblies than a 4 cylinder of the same horse power.

The John Deere 2 cylinder engines used bigger pistons with longer strokes than their competitors to get approximately the same horse power as their competitors' 4 cylinder engines in comparably sized tractors.

I would guess the reason John Deere thought this was preferable for close to forty years was that 2 cylinder engines used fewer parts than a 4 cylinder engine and therefore were less expensive to build and overhaul.

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Bob

09-04-2007 21:16:29




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 Re: J D engine design in reply to k martin, 09-04-2007 20:27:32  
The two cylinders do NOT fire a "fixed" 180-degrees apart.

The left cylinder fires, the crank rotates 180-degrees, the right cylinder fires, then the crankshaft has to rotate 540-degrees before the LH cylinder can fire again.

It's NOT a matter of "thought to be preferable".

It's simply a matter of the way things work out with a 2-cylinder "flat" engine.

A twin clinder engine of this type needs a crankshaft with 180-degree offset crankpins to achieve some semblance of dynamic balance.

The combination of the 2 cylinders, the 180-degree offset crank, and a 4-cycle system dictate that one cylinder will fire,then 180 dgrees later the other cylinder will fire, followed by the first (left) cylinder firing again 540 crankshaft degrees later.

The only alternative would be to have the 2 crankpins in the same "plane", so the two pistons move forward and rearward as a pair. The two cylinders could then "fire" 360-degrees apart.

However, can you imagine the dynamic balance NIGHTMARE caused by those 2 huge pistons moving in the same direction, at the same time???

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Duane Larson

09-05-2007 08:49:08




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 Re: J D engine design in reply to Bob, 09-04-2007 21:16:29  
An example of a tractor with two large pistons moving together is the IHC Titan 10-20. Large counterweights are used, and IHC sold a bunch of them in the late 'teens - early 20's.



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Bob M

09-05-2007 10:30:49




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 Re: J D engine design in reply to Duane Larson, 09-05-2007 08:49:08  
Even with the counterbalances those old IHC machines were poorly balanced.

If you ever get the chance take a close look at a running IHC Titan 10-20 (or the smaller Mogul 8-16). While the engine power pulses are evenly spaced (one power stroke every 360 deg of crank rotation) the machines shake terribly. Standing on hard ground and idling I've seen the entire tractor rock forward and back a good 1/2" with each revolution of the flywheel.

Deere indeed had a "better idea" with their uneven firing but better mechanically balanced engine design!

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55 50

09-05-2007 08:36:04




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 Re: J D engine design in reply to Bob, 09-04-2007 21:16:29  
Right on Bob. For anyone who is skeptical, just take a sheet of paper and a pencil and sit down and draw the whole thing out. It is pretty easy to understand if you draw it out.

Slightly different subject. I have a garden tractor with a twin Kohler engine (4 cycle) where the cylinders face exactly oppposite directions. It sounds like a four cylinder and I've never done what I said above (pencil and paper) to see what differences (if any) there are in that style of engine. Of course the Kohler RPMs are MUCH higher than a 2 cyl JD.

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Gerald J.

09-06-2007 08:12:36




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 Re: J D engine design in reply to 55 50, 09-05-2007 08:36:04  
The opposed cylinder engine is the easiest to balance because all the reciprocating parts are always moving at the same speeds but in the opposite directions. VW Beetles used them, lots of small aircraft have used them for more than half a century now, and lots of Subarus use that design. Makes getting at the crankshaft inconvenient and some like the Corvair had a hard time keeping oil in the crankcase but that arrangement makes an inherently smooth engine compared to a V or inline engine with the same number of cylinders.

Gerald J.

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Bob

09-05-2007 11:25:40




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 Re: J D engine design in reply to 55 50, 09-05-2007 08:36:04  
I agree with you, 55... those little horizontally-opposed twins sound like a 4-cylinder. Only thing, the 4-cylinder would have to be running 1/2 as fast to make the same exhaust sounds. A 4-cylinder will have 2 cylinders firing for each crankshaft revolution, while the opposed twin will have one cylinder firing for each crankshaft revolution. (ASSUMING, of course, that both are standard "four-cycle engines.)

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Kurt_JDB

09-05-2007 07:35:58




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 Re: J D engine design in reply to Bob, 09-04-2007 21:16:29  
Saw an article in two cylinder magazine where a guy had cut the drankshaft on his G and welded it back tegether so that the two rod journals were on the same side. He was able to balance it also. Since a wico mag actualy fires on the exaust stroke as well as the compression stroke, it worked just fine. Apparantly the sound of the engine is a lot different and very cool.

Kurt



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mark

09-05-2007 06:50:52




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 Re: J D engine design in reply to Bob, 09-04-2007 21:16:29  
Strange. I read that they fire only 22 degrees apart...instead of a bang....bang...it's a bang-bang. You ever notice how close the plug wires sit in the distributor cap...side by side. If the thing struck every 180 degrees..they'd be located one on each side of the cap..180 degrees apart.or half way around.



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Bob

09-05-2007 07:21:02




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 Re: J D engine design in reply to mark, 09-05-2007 06:50:52  
Mark,

The information I posted is correct.

Whether YOU like it or not, it's a FACT that they fire 180/540.



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mark

09-05-2007 08:33:44




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 Re: J D engine design in reply to Bob, 09-05-2007 07:21:02  
Bob,

You don't have to get smart about it...I just repeated what I read. Some of us don't know everything as you apparently do.

Thanks for your enlightenment.



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Bob

09-05-2007 11:30:37




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 Mark... in reply to mark, 09-05-2007 08:33:44  
Sorry I came across to you like that!

I'm not trying to be "smart", nor do I claim to "know everything", which should be evident by the number of times I've erred on these boards, and owned up to it and posted a correction.

Admitting to an error and moving on is more productive than persiting in arguing against verifiable facts.



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P Browning

09-05-2007 08:49:57




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 Re: J D engine design in reply to mark, 09-05-2007 08:33:44  
Mark -- that's not the point. If you are saying something here for which you have no basis in fact -- say that too! Opinions ARE ALLOWED!

Your current response is as smart-like as the post to which you are responding. I agree things can often be better said, but my Mother always told me two wrongs do not make a right!

I almost responded to you -- that the "dit-dit" you hear is the No. 1 + No. 2 fire and then a 540-degree coast. Oh Well! Have a better day! (PatB)

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P Browning

09-05-2007 08:49:51




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 Re: J D engine design in reply to mark, 09-05-2007 08:33:44  
Mark -- that's not the point. If you are saying something here for which you have no basis in fact -- say that too! Opinions ARE ALLOWED!

Your current response is as smart-like as the post to which you are responding. I agree things can often be better said, but my Mother always told me two wrongs do not make a right!

I almost responded to you -- that the "dit-dit" you hear is the No. 1 + No. 2 fire and then a 540-degree coast. Oh Well! Have a better day! (PatB)

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buickanddeere

09-05-2007 07:08:15




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 Re: J D engine design in reply to mark, 09-05-2007 06:50:52  
You might be thinking of a V-twin bike engine using a single crankshaft throw.



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CPeter

09-05-2007 08:52:30




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 Re: J D engine design in reply to buickanddeere, 09-05-2007 07:08:15  
The Harleys actually fire 315º-405º and the unique sound is caused by the uneven timing between firings. The JD 180º-540º sound is, many think, caused partially by exhaust valve overlap. As for the plug wire location on the distributor cap being side by side vs. opposite, remember the distributor on those engines is running as 1/2 crankshaft speed so 90º apart on the distributor is 180º of crank rotation.

CPeter

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