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engine running backwards?

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Dave in MN

09-27-2005 20:10:22




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We have a 4 cyl gas motor out of a combine, I have been told that it is the same as a super A tractor motor...

Firing order on block says 1-3-4-2

engine has run for years wired with cyl #1 on the flywheel end

I wired it the "correct way with #1 cyl on the fan end... nothing. Turned the dist 180 degrees... nothing. Put everything back to the "backward" way, engine runs great. What is the deal with it?????

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Gmitch

09-28-2005 07:37:23




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
This is how I do that:

1. Pull the plugs and pop off the dist. cap.

2. Put a thumb or finger over # 1 hole and hand turn the engine until you get air pressure. Turn it a bit and insert a straw or something that won't damage the engine when you get to the top of the stroke.

3.When you have #1 at TDC more or less, crawl underneath and see where the timing mark is. Line the fly-wheel mark with the indicator you will see there.

4. The rotor will now be at or near where it will fire next. Plug in #1 wire on the cap at that spot and the rest of the wires accordingly and re-install the cap.

5. Loosen the dist. and advance the timing a dab and then with #1 plug wire positioned where a spark will jump to ground someplace on the tractor, slowly turn it back until a spark jumps.

6. Lock down the dist. at that point.

Works every time. If it were actually running backward you would have 4 reverses and 1 forward gear. Gary

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Allan in NE

09-28-2005 05:53:03




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
Hi Dave,

Because on a 4 stroke/4 cylinder engine the firing sequence is identical from either end, no matter how you "label" the cylinders. No matter how you "label" that cap.

Bear with me, hope I can do this. :>)

"I wired it the "correct way with #1 cyl on the fan end. Nothing."

Now you've got the wires and plugs on the wrong cycle; valves are hanging open when you're trying to fire the cylinder.

"Turned the dist 180 degrees. Nothing."

Now, in addition to the wiring and plugs being wrong, you've also got the rotor and cap on the wrong cycle as well. You've finished the job; you've got 'er completely and totally 180 degrees out of time because those valves are still hanging open at that particular instant in rotation.

So you say, let's start all over. Let's bring that "fan" cylinder up on the compression stroke and time it from scratch; working from the inside towards the outside.

Hmmmm okay, away we go. Well lookie here, at the end of the day we are right back where we started.

And, the darned cylinders still seem to be "labeled" wrong. :>)

Allan

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Nat

09-28-2005 05:32:49




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
Turn the distributor 90 degrees, not 180.

There's nothing magical about it; a four-cylinder engine with a 1-3-4-2 firing order will run fine if you time the distributor with the front cylinder as #1, or if you time the distributor with the back cylinder as #1.

Simply rewiring the plugs to their "proper" order and/or rotating the cap 180 degrees won't help. The cap only goes around once for every two rotations of the engine, so everything is divided in half at the distributor. The front piston is 180 degrees away from the rear piston on the crankshaft, so you only need to turn the distributor 90 degrees to get it timed properly.

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ebbsspeed

09-28-2005 06:14:40




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 Re: engine running backwards? in reply to Nat, 09-28-2005 05:32:49  
It is 180 degrees off, NOT 90. Your comment that "engine has run for years wired with cyl #1 on the flywheel end" is what tells me this. Notice that cylinders #1 and #4 in the firing order are one crankshaft rotation apart, equating to 180 distributor degrees. If you turned the distributor (body only, not rotor position) 180 degrees, and moved the wires accordingly, then it should have run. How are you determining that cylinder number 1 is on the flywheel end? Is it a number on the wire, or are you tracing it back to a specific terminal on the distributor cap? Since it is running, and the #1 wire is going to the #4 cylinder, you have many choices. You can leave it as is, and just use it. If the distributor is physically installed "wrong" meaning that it isn't in the proper position according to the book, you can pull it out and turn it to the proper location. Where you reposition it determines where the wires go back in. Best bet is as described in a few other replies. Get the #1/Fan/Front cylinder to TDC on the compression stroke (hold finger over spark plug hole and you'll feel compression) and install the distributor so BOTH the rotor in the distributor, and the body of the distributor, are "clocked" correctly. Then install the wires per the book.

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El Toro

09-28-2005 04:47:32




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
You would need to bring No1 piston up to TDC on the compression stroke. You would also need to watch which way the rotor turns. If the rotor turns CW you would install your wires like this:
2-1
4-3 or if it turns CCW you install the plug wires like this:
1-2
3-4 and you set the rotor on No1 on the distributor and install it in the tractor. Hal



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gene bender

09-28-2005 03:59:56




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
Something is screwed up somewhere start with taking out the plugs and getting the front piston on TDC then go from there. What kind of dist is on the engine?



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Ron in Nebr

09-27-2005 20:43:39




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
Pull the distributor out and turn it 180 degrees and reinstall, then it would run with the "normal" wiring if you want.

But, since it runs fine now, I would leave it and just make a mark on the cap where #1 is for future reference.



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Ron in Nebr

09-27-2005 20:47:36




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 Re: engine running backwards? in reply to Ron in Nebr, 09-27-2005 20:43:39  
OOPS- just re-read your post and saw you'd already turned the dist 180deg. I assume you repositioned wires on the cap when you did that.

Guess I can't help ya there.



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Nat

09-28-2005 05:33:33




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 Re: engine running backwards? in reply to Ron in Nebr, 09-27-2005 20:47:36  
You only need to turn the distributor 90 degrees.



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old

09-27-2005 20:28:55




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 Re: engine running backwards? in reply to Dave in MN, 09-27-2005 20:10:22  
some engines are like that but not very many. You may have just got one of the odd balls



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