firing order/cylinder number

[19_again]

Thanks!

 

[tony barnhill]

MG is 1-3-4-2

 

[dklawson]

To elaborate a little on TDC, as mentioned, it stands for Top Dead Center. (I apologize if the following is information you already know). TDC is a reference to the highest point the piston travels in its up/down motion. The reason Tony and I mentioned checking either for pressure or loose rockers is as follows. The engine turns over two times for every time the spark plug fires. (Intake stroke = piston moving down, Compression Stroke = piston moving down, (Ignition/Spark somewhere in here), Power Stroke = Piston moving down after the mixture is ignited, and Exhaust Stroke = piston moving up and exhaust moving out. You're looking for TDC at the end of the compression stroke (NOT the end of the exhaust stroke) to determine your spark timing. Typically LBCs run a nominal static ignition timing somewhere close to 8 degrees BTDC (Before Top Dead Center). That means the spark happens when the piston is not at the top but 8 degrees of crank rotation before the piston reaches the top on the compression stroke.

Don't you guys flame me for being too general.

 

[DrEntropy]

Doug, that was an appropriate post: No flame from this direction!

Only thing you didn't mention is that this is the reason these four "cycles" make this the type of engine referred to as a "four-stroke" one.

 

[dklawson]

Thanks Dr.

I didn't have the link below bookmarked when I posted last time. It has neat animated graphics that may clarify my last post.
https://www.howstuffworks.com/ignition-system.htm

 

[motorbill66]

Just a quick not to confuse what should have been a dirt simple thread a bit more. English Fords us a 1-2-4-3 firing order instead of the more common 1-3-4-2. These are the only two possible firing orders for an inline four cylinder engine. Look at a straight four crankshaft some time. It is what you call a single plane crank. In other words, all the throws are in the same plane with respect to the centerline. Therefore, Since it can only be practically manufactured with the end throws(1+4) at one extreme and the middle throws (2+3) at the other, The only firing orders that make sense beginning with number 1 must be as follows: end cyl., middle cyl., end cyl., middle cyl. This keeps things nicely balanced. Depending on how you then cut the camshaft, you can have either a 1342 or a 1243. This works out fine on engines where each valve has its own port. MGs have what we call 5 port engines because of the siamesing. BTW, it sounds to me like the original poster has more than firing order problems...

 

[tony barnhill]

But, to the point of this thread: MG's are 1-3-4-2....we don't want to confuse anybody.

 

[DrEntropy]

motorbill66: my earlier post...

The middle two can be "either-or" depending on head/cam/valve design. "Balance" is the consideration with in-line fours. The "flat fours" (air cooled Vee-Dubs) are alternating banks. Weird! /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

but as Tony says: So as NOT to confuse anyone, the MG firing order is 1-3-4-2. We'll hash out apples-and-apples in another thread, if ya want. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif