Q: Regarding Narrow Deck vs. Wide Deck Lycoming O-320 engines: I just read your article on this.
On substituting one engine for the other, wouldn’t the later D series engine have a type 1 Dynofocal versus the early narrow deck engines having a conical mount determine that?
I cannot find a way to determine through the suffix numbers/letters which is wide deck versus narrow deck. Seems that the B through D series are wide deck, but I’m not sure.
Jim Stoops AP/IA
A: Jim this is a great question that has probably caused much confusion over the years, especially with homebuilders, so hopefully I can provide some clarification on the subject.
The main thing to keep in mind is that the type of engine mount configuration each has does not differ between a Narrow Deck or a Wide Deck engine. The difference comes from the specific model of each engine series.
As an example, all of the O-320-A and B series Lycoming engines incorporate the Conical type mounting configuration, whereas the O-320-D and E series engines incorporate the Dynafocal Type 1 mounting.
There are a few IO-320-A, B and C series Lycoming engines that incorporate Dynafocal Type 2 mounting.
Homebuilt Projects
If you are considering an engine for a homebuilt project, I highly recommend reaching out to others who have built the same aircraft and pick their brains to learn exactly what engine they chose and and why they made that engine their choice.
I realize that many homebuilt projects begin because someone runs across what they believe to be a great engine for their future project only to learn later the actual aircraft plans call for a specific type engine mount and their “got this engine for a real steal” doesn’t work.
I’d hate to guess how many homebuilt projects got pushed off into a corner because of this failure to gather all the facts first.
This type of improper planning then invites all kinds of difficult questions to answer when your spouse asks when are you going to finish your airplane? It can get really ugly from there.
That’s why I appreciate you asking the question and hopefully it’ll make people stop and think about this important subject.
How To Tell The Difference
One other thing: You mentioned that you were unable to tell the difference between a Narrow Deck and a Wide Deck by looking at the engine serial number suffix.
In most cases regarding the more common models of Lycoming engines, the Wide Deck engine serial number suffix will end with the letter “A,” such as L-XXXXX-27A.
The Narrow Deck engine serial number would be L-XXXX-27.
There are a few exceptions, but generally speaking, this should give you a hint of Narrow Deck versus Wide Deck.
Yes Cy. You are correct. A quick visual of the cylinder mounting bolts is a dead giveaway as to the engine being narrow deck or not. The narrow decks use the large cylindrical (or as you call them, internal wrenching hold down nuts). The wide decks use a typical plain nut arrangement. I have owned both.
Doesn’t the narrow deck use the internal wrenching hold down nuts?