Lycoming FB-FC firing order

  • balinwire
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29 Jun 2004 03:54 #1881 by balinwire
balinwire created the topic: Lycoming FB-FC firing order
In the Tech Talk section of the no.4 current newsletter there is a mention of the unusual firing order of the FB. There were quotes of astonishment that Lycoming would use an arrangement such as this. The article also states that is unknown why the designers used this rear to front firing order.

Well this set off bells and whistles that there is a mystery like this, also many questions. Wasn?t this ever discussed by anyone in the sales department or mechanics and mentioned to prospective customers?

When this order is said to be ?strange? that is not what Lycoming is known for. They had the finest engineers on staff and would produce the finest engines of their day and had reasons for doing things a certain way. The whole project could collapse over simple things.

Both the FB and the FC have the 90-degree throw. Again the only difference is the firing order. Has anyone ever had an FB EE-15 carburetor and intake on an FC engine and compared the idling cars characteristics to an FB?

What there would be is two engines running next to each other, the only difference would be the cam and order. There might be a much more perceptible vibration in the FC due to the pistons firing in a right to left motion verses a forward to back motion.

Smooth idling may have been of importance to a potential buyer of a luxury automobile. With the supercharged version vibration may not have been an issue. Just for fun take a pencil and start at piston 1L in the diagram of the article. Follow the firing order lines and notice how much more your hand will shake.

One of the first things I noticed when my FB fired up for the first time after many years of sleep was the unusually smooth idle for a flathead.

Go to the local drag strip and watch a radically cammed engine rock and roll in its chassis.

Wasting time speculating on reasons why, <!-- s:shock: --><img src="{SMILIES_PATH}/icon_eek.gif" alt=":shock:" title="Shocked" /><!-- s:shock: --> balin?

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  • balinwire
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01 Jul 2004 04:29 #1894 by balinwire
balinwire replied the topic: cam grind differences
The two engines shared cams on the FC engine <blown, large carb jets, different firing order>. They may have different lobe placement % for timing but was angle of cam lift the same as the FB cam?

Did the FB use a dual point distributor?

If the FC had the dual point setup that would allow a higher cam angle cut and shorter dwell. It would then have an advantage in top rpm generated.

I can?t tell thru the Bakelite distributor caps. I could not find mention in service manual; it may say ?point?s? but that could also be a single set of points.

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  • Josh Malks
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01 Jul 2004 15:46 #1895 by Josh Malks
Josh Malks replied the topic: FB vs FC
Cams on the FB and FC engines were different, with the FC considerably hotter. And note that Lycoming went to the "normal" V-8 firing order on the new FC. (The only reason they didn't do the same for the '37 FB was probably lack of funds.)

FCs use a dual point distributor.

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