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4 cyl Firing order

D

David G

Well-known Member
Is there a reason one manufacturer would make a firing order 1342, and another 1243? I am thinking it is only a cam grind change.

Is there a difference in vibration or balance?
 
Absolutely, balance is one issue. Making components that can be interchanged is another, yet, from the 4cylinder engine that isn't going to be a big factor. My I ask which engine maker would use a 1243 firing order, an MG Midget is the one that comes to my mind.
 
AC used 1-2-4-3 on the WC, WF, WD, WD45, B, C, CA, D series. etc. I think Farmall used 1-3-4-2, or similar.
 
David, the reason I mentioned the Midget is because some sources list their firing order as 1243 ccw at the distributor while others list it as 1342 cw at the distributor. This is different than what your question asks, however.
 
The 1243 was just brought up on the Ford forum. The pistons would still go up in the same order. I would think it would get less fuel if intake runners where shared.
 
There are differences in harmonics in the crank that do make a difference. 1342 is more evenly spread on the crank length. The vibration at the whole engine level might be the same, but internally 1342 has the advantage. (and that is why it has the preponderance of use) a flat frank, (as these are) is somewhat less problematic than compound plane cranks, or especially offset journal cranks like on a V6 with 90 degree bores. Complex dampeners and external balance are often needed to assure crank durability. Main bearings between each rod journal (or twinned journals on a V engine) are not found on many of our old iron. that fact is even more of a factor when they are hot rodded.
Jim
 
I knew you would come through Jim.

Another issue I thought of was amount of air that has to go through intake runners per revolution with 1243 is twice what will be needed for 1342.
 
JMS, yeah, I think I very poorly communicated what I intended to ask. Something is just sticking out in my mind about the old MG Midget and how it is represented both ways by varying sources.
 
IH has a great explanation of the imbalance forces in a 4 cyl inline engine. I think it is in the C153 service manual, but not sure. Anyway, they go to great lengths to explain why they added the balancer shaft below crankshaft. It has to do with the fact that a piston moves a different distance in a specific degrees of crankshaft rotation at top dead center than that same piston does at bottom dead center. I have put dial indicators on pistons both top and bottom dead centers and turned crank same amount in degrees and you get a different reading. Try it sometime. Interesting.
 
I think I get what you mean. But I think the amount is delivered in pulses either way. In 1342, the front port sucks then the rear port, then front, then rear.
In 1243, the front sucks twice in a row (sequentially) then the rear port sucks twice. It probably makes little difference, Jim
 
I don't think theres a difference in the manifold- if you take 1342 and move the 1 to the back, it's 3421. Either way the front sucks twice then the back sucks twice....

1342134213421342...... And on it goes.

Donovan from Wisconsin
 
Yes the piston travels a farther distance in the first and last quarter of crank rotation as compared to the second and third quarter of crank rotation. This is due to the side movement of the connecting rod.
Picture a ladder leaning against your house. If you pull he bottom of the ladder away from the house the top of the ladder moves down yet the bottom of the ladder is still at ground level.
In the first quarter of Crankshaft rotation it's pulling the piston down plus moving the bottom end of the rod away (from the house sort of speak) so there are two elements causing the piston to come down. In the second quarter of crankshaft rotation the crank is still pulling the piston downward but it's moving the rod (closer to the house) decreasing overall downward piston travel. Third quarter of crank rotation it's pushing the piston up but pulling the rod away from the house again, the fourth quarter of crank rotation the piston is going up and the rod is moved closer to the house.
 
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