Author Topic: Why did Honda use reverse cylinder firing order comparerd to cars?  (Read 2436 times)

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Offline jonda500

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The firing order (1243) of these motorbikes for over a decade caused me many head scratching moments- japanese in line 4cyl car engines all use 1342 firing order and I assumed my bikes would be the same. Luckily (or unluckily?) since these bike fire every stroke any way, although my ignorance confused the hell out of me, it never stopped me from being able to get my bikes to work.

Hypothetically if (forgetting about the tacho drive section of the camshaft- pretend it's not there) I reversed the camshaft(thus reversing the firing order) periodically, would my engine longevity be increased slightly or decreased slightly?
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Offline dave500

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #1 on: January 10, 2014, 08:25:20 pm »
?

Offline Powderman

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #2 on: January 10, 2014, 08:26:52 pm »
Do you think you are smarter than the Honda engineers in building longevity into their product? Would your engine longevity increase or decrease? I don't know, but I think your riding time would decrease significantly.
« Last Edit: January 10, 2014, 08:29:25 pm by Powderman »

Offline jonda500

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #3 on: January 10, 2014, 08:29:49 pm »
?
Did I give u a head scratching moment?

btw I'm not asking about the cam or rocker sufaces which obviously may wear more...
Remember that an ignoramus is only someone who doesn't know something you just learned yesterday!
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
A starter clutch thread:
http://forums.sohc4.net/index.php/topic,122084.0.html
1972 CB500K1 original 4 owner bike
1972 CB500K1 returned to complete/original condition
1975 CB550F built from parts - project thread:
http://forums.sohc4.net/index.php/topic,149161.msg1711626.html#msg1711626

Offline jonda500

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #4 on: January 10, 2014, 08:33:59 pm »
I don't think reversing the firing order would make any difference, just wondering whether ppl agree
Remember that an ignoramus is only someone who doesn't know something you just learned yesterday!
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
A starter clutch thread:
http://forums.sohc4.net/index.php/topic,122084.0.html
1972 CB500K1 original 4 owner bike
1972 CB500K1 returned to complete/original condition
1975 CB550F built from parts - project thread:
http://forums.sohc4.net/index.php/topic,149161.msg1711626.html#msg1711626

Offline dave500

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #5 on: January 10, 2014, 08:36:08 pm »
if you do that youll have the inlet lobe profile running backwards on the exhaust rockers and the exhaust lobe the same on the inlets,they have different lifts aswell.

Offline bjbuchanan

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #6 on: January 10, 2014, 08:38:56 pm »
Ford had a revised firing order for either the 302 or 351 back when the engines were atleast in cars. It can be for many reasons, I believe ford, along with others (modders were doing it first with custom cams) smoothed out the engine.

They change stuff because tech gets better, they can get better feedback from better machines to detect harmonics and all that stuff. Some of it is to improve scavenging, sometimes harmonics, sometimes ram tuning or could be a bit of all

If you pound a couple energy drinks and really feel inclined you could pore over some SAE tech papers and read why, I'm not gonna  ;)
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Offline jonda500

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #7 on: January 10, 2014, 08:48:30 pm »
 :) thanks bjbuch

Thanks dave, I just learnt something else I've never realised before- the camshaft is not symmetrical - that's why the rockers all slant the same way!(also not symmetrical)
Remember that an ignoramus is only someone who doesn't know something you just learned yesterday!
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
A starter clutch thread:
http://forums.sohc4.net/index.php/topic,122084.0.html
1972 CB500K1 original 4 owner bike
1972 CB500K1 returned to complete/original condition
1975 CB550F built from parts - project thread:
http://forums.sohc4.net/index.php/topic,149161.msg1711626.html#msg1711626

AJK

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #8 on: January 10, 2014, 09:30:40 pm »
For an inline 4 cylinder, there are two combinations that can be run, those being 1,2,4,3 and 1,3,4,2. The reason this is the case has nothing to do with the camshaft but everything to do with balancing the crank as it spins (crank end balance).
 The two outer pistons are weights that fly up and down together. Likewise the two inner pistons do the same. What happens here is that when you look at the crank (picturing all 4 pistons going up and down), you have effectly (lets say almost - but not entirely) cancelled the crank end forces. This way, the crank doesn't want to pull-up or pull-down excessively on the end journals due to having a different crank journal arrangement. So the crank is machined with #1 and #4 journals & #2 and #3 jounals 180 deg to each other, purely for reciprocating weight balance reasons.

So accepting that its all due to crank end balance, the two outer pistons must coincide with each other, just as the two inner pistons must as well. See picture below (top picture is a balanced crank, bottom picture is an example of an unbalanced crank that i whipped up & would never exist in the real world)

Given this, then the camshaft must be machined to match one of the two applicable firing orders. Once the manufacturer has settled on one, then thats what it becomes. You are correct, that its the camshaft that dictates the firing order, but this is still a by product of solving crank end balance.

To animate the firing in your mind:

1243 does this |-->|<--|
1342 does this |<--|-->|

The sohc can be run from a distributer (just like a car) and some have done so in the past. The reason waste spark is employed is simply due to economics. Its more compact and cheaper to just fire on both the power stoke as well as the end of the exhaust stroke in an attempt to do away with a distributer.

It is quite possible that a motor could run in reverse, but your camshaft also needs to be reversed. The motor is just a air pump, so it wouldn't care providing the valve timing and ignition timing is correct in the reverse direction. Of course, then you need to start looking at reversing the pistons as well because they have an arrow pointing to the front for a reason (because the gudeon pin is offsetted). And on some newer motors (more so these days), the actual block is offeted as well to both increase torque and reduce piston slap. Not to mention that your oil pump is now sucking instead of blowing. So you'd be ending up with a case of all sorts.

Interesting question, its been thought of before. The Ford Kent motors are 1243, so its not that cars don't use that firing order. Lots of cars use 1342.

So to sum up, yes, if you machined up a camshaft to fire with 1342 instead of the 1243 that we have, your sohc would run just fine. You wouldn't even need to touch the ignition timing. Let me know how you went  ;D
« Last Edit: January 10, 2014, 11:09:48 pm by AJK »

Offline dave500

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #9 on: January 10, 2014, 09:31:12 pm »
the windsor 351 has the same firing order as the clevelands,you can use say a 289w cam in a 351w if you swap the ignition leads around to suit.

Offline Don R

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Re: Why did Honda use reverse cylinder firing order comparerd to cars?
« Reply #10 on: January 11, 2014, 01:14:22 pm »
My big block chevy has a 4-7 swap cam. It went from 18436572 to 18736542 Smooths things out a little and supposedly cures the problem of 5-7 being in order on the same corner of the intake. It does however, move 4 and 2 into that situation.
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