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How difficult is an engine swap - O320 C/S replacing F/P?

Saville

Saville

Well Known Member
Hi all,

I'm in the market for a solid RV-4. Up until this point my irreducible minimum was an O-360 with a C/S prop. But in PM discussions with forum members, that 360 might not be ideal - lots of weight up front. And of all the RV-4's I see for sale over time, usually less than half have 360 C/S.

I can't recall ever seeing one with an O-320 C/S.

So I've considered buying an O-320 powered -4 and modifying it later by dropping in a new engine that has a C/A prop. But I have questions about that:


1) Were I to get a -4 built with a 320 F/P, how difficult is it to replace it with a 320 C/S assuming the same mount? Obviously I have to add a manifold pressure gauge and the prop control in the cockpit. But I'm wondering about airframe/cowl/mount rebuilding and/or replacing.

2) How hard is it to find a used 320 C/S engine? Are they scarce? I've done a cursory search on the web and I get the impression that O-360-A1A types (and their derivatives) are far more numerous than O-320-A1A and derivatives.

Any insight would be appreciated.

thanks
 
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Most later model O-320s will accept a C/S prop. Not all, so check the model.

RV-4s and early -6s used a different cowling for C/S. The C/S cowling was shorter as a 4" prop extension was used on F/P. Engine mount is the same unless you go with an IO-320-B1A which uses a Dynafocal II mount.
 
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Mel said:
Most later model O-320s will accept a C/S prop. Not all, so check the model.

RV-4s and early -6s used a different cowling for C/S. The C/S cowling was shorter as a 4" prop extension was used on F/P. Engine mount is the same unless you go with an O-320-B1A which uses a Dynafocal II mount.
Click to expand...

Thanks for the quick response Mel!

So if I understand you, dropping in an O-320 C/S requires that I order and fit a new cowl, yes?

thanks
 
Chris Watson -

in San Antonio has a sweetheart of a -4 with a fuel injected (I believe) O-320 CS prop and it is a horse. Maybe he'll join in.

I'd LOVE to have an O-360 in my -4 too; but don't think they won't perform well on an O-320. Just saying, don't short yourself just because....

It surely "ain't the end of the world" if one only has a RV-4 with an O-320!! ;) I'm not wearing a frown when I get out of mine. :D

Cheers,
 
Hi Deal,

Well that's why I'm considering an O-320.

However it's the C/S part that I'm really stuck on. I fly acro and I would prefer to not have to hawk the RPM on the backside of a loop. I can and have on a Citabria. But I've done most of my acro in a Super Decathlon and the C/S prop is nice to have.

I would also prefer the performance increase of a C/S prop in some non-acro regimes.
 
Ooops..

Just saw Mel's post and he do know his stuff. I think the answer to your question is yes you would have to change the cowl, UNLESS, you were to purchase a -4 that used a 360 cowl. I say that because I have a friend who built 2 -4s using 360 cowls while putting O-320s in the planes. He did that so someone could change to O-360 CS without too much hassle.

Perhaps you could take some photos of your intended plane & post. There are so many variants around, need to focus on your target.

Cheers and best,
 
More than one cowl

The note you got regarding the early cowl being different for the fixed and CS cowls is accurate. That said, my four had the later cowl so no modification was required. Take a look at both and you will see the differences are obvious so you can easily see when looking at different examples you may have an interest in purchasing. Don't forget, there are also the original short and later longer gear. Nothing wrong with the original but the longer gear gives more prop clearance.
 
Saville said:
Thanks for the quick response Mel!

So if I understand you, dropping in an O-320 C/S requires that I order and fit a new cowl, yes?

thanks
Click to expand...

Maybe, but a quick look under the cowl will soon determine if you have a 2.25 inch or a 4 inch spacer between the prop. and the flywheel.
 
Engine

The first question is why a new engine just to accommodate a C/C prop??
Major considerations for engine model:
Wide deck or narrow deck. Most will not want a narrow deck-pre 1964 give or take-pretty old.
Conical or dynafocal mount. Conical is fine with a lightweight wood prop, sometimes a vibrator with metal prop.
Type I or II mount. The type II was used on the Twin Commanches, IO 320 B or C series.
The most popular E series engines use the 0 235 front main bearing and will not support a C/S prop. These include E2D,E3D,E3G,E2H and E3H. The first two are the most popular.
My list shows the 0 320B1A as a high compression A1A. The A1A is the base engine on the current list, even though there was an earlier 320.
I think what Mel meant is the IO 320B1A which is the Twin Commanche engine mentioned above.
There are also sump consideration issues with both the carb and fuel injected engines. Also some accessory cases are not machined for fuel pump and governor.
There are also some very rare 320's that have a front mounted governor.
 
Things to consider C/S to fixed, etc.

I have over 2,000 hours in RV-4s, both fixed-pitch and constant speed. I currently fly a C/S with an 0-360. It depends on whether you are into a lot of aerobatics or just the occasional roll or loop. I think the initial acceleration and climb with a constant speed are great, and can't be beat with a fixed. Also, on downwind and landing the C/S is great for deceleration, speed control and short landings. Fuel economy with a C/S is better. Fixed pitch 320 may be a little more nimble with the lighter upfront weight, but other than that, I'd go for 360. There is no substitute for a little more horsepower and reserve power, which does not cost you a measurable amount in fuel difference between a 320 or 360.

Last year I made a 3,000 mile flight together with an RV-3 with a fixed pitch 320. Throughout the flight the RV-3 set the pace. Each and every fuel stop and fill-up our fuel burn was nearly the same, if any difference the 360 used less fuel. My only other possible advantage was that I converted my 1992-built from a standard canopy RV-4 to a fastback conversion that I completed in 2010. The fastback conversion is not a big deal using a few of John Harmon's parts and a Harmon Rocket canopy from Todd's canopies. The conversion can be done in 60 days.

If I was to do it again, I'd be looking for a 360.

Jake Thiessen
Independence, OR
 
I converted a new, 2008 C/S IO-320 to F/P, and still have the governor and stainless steel oil tube from the conversion. Items were never used after delivery from Lycoming. If anyone is interested....
 
Having bought a couple of planes with intention to modify them, my suggestion would be to buy the plane that has what you want on it already!

Modifications will be more difficult and take longer than you think.

OTOH, you may really enjoy modding a plane!

JOMO, and YMMV.
 
firewall recess

A f/p rv4 may also require modifying the firewall with a firewall recess kit to allow room for the governor.

SAM_0477_zps19fabceb.jpg
 
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jrs14855 said:
The first question is why a new engine just to accommodate a C/C prop??
Click to expand...

Because I want a C/S prop, and I was unaware that one could modify some FP 320's to be CS.

More importantly, I'm trying to find out how much work it is to convert from a FP to CS RV-4. Whether it's an engine mod or engine replacement.
 
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Jaknjoan said:
I have over 2,000 hours in RV-4s, both fixed-pitch and constant speed. I currently fly a C/S with an 0-360. It depends on whether you are into a lot of aerobatics or just the occasional roll or loop.
Jake Thiessen
Independence, OR
Click to expand...

Jake,

My mission works out to be:

60% acro flying
10% Formation flying
30% Cross Country
 
I would not dissuade you from the 180/CS on the RV4 but a picture is worth a thousand words. The video's under "cumulusgrandus" are with a 160hp/fp. Some of those maneuvers are at over 11,500 and she just keeps on tickin' :)
 
PCHunt said:
Having bought a couple of planes with intention to modify them, my suggestion would be to buy the plane that has what you want on it already!

Modifications will be more difficult and take longer than you think.

OTOH, you may really enjoy modding a plane!

JOMO, and YMMV.
Click to expand...

Hi Pete,

Thanks for yoru reply. I take your point and in fact that's why I started the thread. I know what sorts of projects/down time I'm willing to take on. Which is why I'm trying to ask what FP -> CS takes.

For example, I'm willing to buy a -4 with limited instrumentation and then, after flying it for a good while, upgrade. That's a project I know I'm willing to take on both from the standpoint of skills, willingness to learn, and estimated aircraft down time.

So I'm trying to do a similar analysis with regard to FP -> CS conversions.

What does it take?

Are there any structural modifications required?

Initially my question was an upgrade for a 320 FP to a 360 CS. Figuring I would pay less for the aircraft up front and later do the upgrade. Subsequent replies here have got me thinking that an O-320 might suffice. So then my question is:

What's involved with a 320 FP -> 320 CS conversion?

Are there lots of 320 used engines out there? Or would I have to buy a new one?

Thanks
 
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Regarding your question about what mods are required to an O-320 to enable the attachment of a C?S prop.

Some O-320's can not be switched over to a C/S prop easily, meaning you need a new crankshaft. An earlier reply in this thread detailed the dash numbers that are and are not easily converted. If an O-320 has the proper crankshaft, and the proper oil port fitting in the front bearing, the switch over is relatively easy.

You need to find out exactly which engine is in the plane you are looking at, and then you can find out if it can be easily modified to accept a C/S prop.

There are others on this forum that are expert in engines, and props, and who can go into great detail. But the above are the basics.

Hope this helps.
 
Saville said:
...

2) How hard is it to find a used 320 C/S engine? Are they scarce? I've done a cursory search on the web and I get the impression that O-360-A1A types (and their derivatives) are far more numerous than O-320-A1A and derivatives.

Any insight would be appreciated.

thanks
Click to expand...

FYI - The IO-360-A1A is the 200 HP angle valve engine (Heavy!) To confuse things, the O-360-A1A is a 180 HP parallel valve engine.

I think you want a parallel valve IO-360-B something which should be the family of 180 HP parallel valve engines. Check Wikipedia for more details.
 
Another alternative is the 180 hp Titan 340 same weight and physical size as a 320.It uses the same exhaust, baffling, engine mount and cowling. There is a constant speed version available. This engine has been ASTM certified and is used extensively by Cub Crafters. It?s lighter than a 360 by the same amount that a 320 is. It has the same power same reliability as the 360. It takes less money and time to convert than a 360, because it uses most of the stock airframe 320 pieces to fit. There are many flying in RV-4s, 7s & 9s now.
 
Crank

PCHunt said:
Regarding your question about what mods are required to an O-320 to enable the attachment of a C?S prop.

Some O-320's can not be switched over to a C/S prop easily, meaning you need a new crankshaft. An earlier reply in this thread detailed the dash numbers that are and are not easily converted. If an O-320 has the proper crankshaft, and the proper oil port fitting in the front bearing, the switch over is relatively easy.

You need to find out exactly which engine is in the plane you are looking at, and then you can find out if it can be easily modified to accept a C/S prop.

There are others on this forum that are expert in engines, and props, and who can go into great detail. But the above are the basics.

Hope this helps.
Click to expand...

O 320 with solid crank is quite rare. The issue with the 0 320 is the 0 235 main front main bearing. These can only be converted by dissembling the engine and sending the case out for modification. The solid shaft is much more common in the 0 360's. Many Pitts' have the 0 360A4A 0r IO360B4A which are solid shaft engines. Solid shaft means that the front main bearing area is solid, there is no passage for the oil to reach the prop.
 
Engine

N941WR said:
FYI - The IO-360-A1A is the 200 HP angle valve engine (Heavy!) To confuse things, the O-360-A1A is a 180 HP parallel valve engine.

I think you want a parallel valve IO-360-B something which should be the family of 180 HP parallel valve engines. Check Wikipedia for more details.
Click to expand...

The definitive document is Lycoming SSP-108, Certificated Aircraft Engines.
The flaw in this document is that it does a very poor job of designating
type of engine mount. For example the engines used on Piper Tri Pacers and Apaches, SSP 108 does not clearly state that these are conical mount engines. ALL Tri Pacers and Apaches left the factory with conical mount engines.

I find no correlation between the dash numbers/letters from O to IO engines. In each case you have to start with the base engine and work down the list.
 
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