What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

O-320 Narrow Deck

B

Bob Hoffman

Well Known Member
OK! I an confused about the narrow deck 320's and I'm willing to bet that someone here has the answers I'm looking for.
Are there two types of narrow decks, ones with the plates,and ones without plates ? Is the one with the plates stronger than the one without ??
And if yes ,can the narrow deck without the plates be converted by replacing the cylinder bolts to the longer ones and adding the plates ?
AND when looking at the Lycoming eng. list there is an identifier for narrow decks but is there a way of knowing which engines have the plates and which one don't ??
Thanks
Bob
 
Bob,
Thanks for your reply But I'm still confused ,one of my neighbors has a 150hp narrow deck with no plates on the cylinders and another has one converted to 160hp and he has plates on his cylinders.Both are narrow decks(have socket heads instead of nuts). So what am I missing here ?
Bob
 
Hi Bob,

Most of the "plated" engines came later after the straight 320's of 150hp when they started making and/or converted them to 160's. Rhonda or Mahlon will better be able to give more details that I don't have, but I do know for a fact that you can change the through bolts and studs to accept the plates on the earlier engines (it's been done by many people on many engines many times), although it's not a trivial task....been there done that!

Anyway, all the narrow deck cylinders that I'm aware of use the socket type nuts.

Also be aware there are a few other differences to the old straight 320's. The front main nose bearing is different as well.

I'm not a font of knowledge, but I agree it can be confusing!

Cheers,
Stein
 
It could very well be that somebody decided not to use the plates when putting the cylinders on. Check the serial #...
 
According to my old Lycoming O-320 Parts Manual....

SteinAir said:
Hi Bob,

Most of the "plated" engines came later after the straight 320's of 150hp when they started making and/or converted them to 160's. Rhonda or Mahlon will better be able to give more details that I don't have, but I do know for a fact that you can change the through bolts and studs to accept the plates on the earlier engines (it's been done by many people on many engines many times), although it's not a trivial task....been there done that!

Anyway, all the narrow deck cylinders that I'm aware of use the socket type nuts.

Also be aware there are a few other differences to the old straight 320's. The front main nose bearing is different as well.

I'm not a font of knowledge, but I agree it can be confusing!

Cheers,
Stein
Click to expand...

The -A2A, -A2B, -A2C, -A3A, -A3B, -A3C O-320 models were originally shipped as Narrow Deck (STD vs. WCF in lycoming-parts-speak) without the "169531 - PLATE, Cylinder hold down- STD only".
As Stein says, these were 150 HP (or less) versions, and the only plain nuts listed for cylinder hold down are for the WCF (wide deck) versions.

However, these narrow deck crankcases date from the 60's IIRC, so upgrades during subsequent overhauls could change their original configuration...:)
 
Last edited:
N/D cylinders and crankcases for the 150 HP narrow deck 320's are different then the narrow deck 160 HP cylinders and cases. The cases are basically the same except the 160HP version has longer studs to accommodate the plates the 160 hp version uses on the cylinder decks. The cylinders for the 150HP have spot faces for the cylinder base nuts and the 160HP that use the plates don't. The 150HP cylinders were originally plain steel and the 160HP cylinder were nitrided.
Hope this helps!
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Been there

I have a O-320 A2B on my 4. Narrow deck with no plates as per the parts manual. When I got the engine someone had installed the higher compression pistons to up the HP to 160 and had flown it for 300 plus hours.

My research revealed that I could put in the longer studs and install the hold down plates. Not wanting to spend the extra money I went back with the low compression pistons for the peace-of-mind.

One interesting thing to note is that the 150HP and 160HP have the same fuel burn per Lycoming. One thing to concider.

BTW, I like the engine so well I bought another to rebuild for my PA-22.
 
Costs

Bob Hoffman said:
RV4ER
Do you have any info on the cost,part #'s,and who I might go to for the longer bolts and plates ??
Thanks
Bob
Click to expand...

Bob,

If you have to pay anything like retail for the long studs and hold down plates even second-hand retail forget it. If you are good at scrounging, you might be OK. I've been down this path and it is far cheaper to buy a late model engine and start from there.

I have a narrow deck case in an engine shop at the moment. They want to change the main bearing pegs because they think they can't get the early bearing shells. They also wanted to machine the oil pressure relief valve housing to accomodate the later oil pressure relief valve which I managed to talk them out of. Not being so sure of my ground on the bearing pegs, the case just sits there.

Just think hard before spending the money.

Cheers,
Andrew.
 
You must log in or register to reply here.
Back
Top