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newrv-4

Member
I recently purchased a used O-320 for my project. When it arrived I discovered it has a conical mount instead of a dynafocal mount. I intend to tear the engine down and rebuild it. I was wondering if anyone knew what was involved in converting it to a dyna mount. I have tried to call a few shops, but no one seems to be answering the phone.
 
You'll save some money by leaving it conical. since the mounting rubber bushings are much cheaper for the conical mount. And I kind of remember a thread here a while ago that indicated there wasn't much of a perceived vibration difference.

Dave
 
Go fly a Piper Tripacer or Super Cub then an early Cherokee. You will notice a difference. The Dynafocal "lord mounts" got bigger as the engines get newer.
 
Dyna 1 to Dyna 2

I recently had a IO-320-B1A Dynafocal 2 crankcase converted to a Dynafocal 1 by Divco for the quoted $250. Andy is the man there to talk to. In my case the Dyna 2 mount is not available for the RV 9.



Don Broussard
RV 9 Rebuild in Progress.
 
Mounts

I'm not sure what post #4 is trying to say. All Tri Pacers and Super Cubs left the factory with conical mount engines. They were reasonably smooth running engines with fixed pitch pitch metal props, and those built with fixed pitch wood were very smooth.
The 1960-1963 Cherokees of 150-160 hp were all conical mount. The ones that I flew were the worst vibrators of any flat Lycoming I ever flew. Second worst was the Piper Apache. One did not feel the vibration as much because of the engines being on the wing but the vibration was there.
The Citabrias and Decathalons with conical mount engines, both fixed metal and constant speed do not vibrate anywhere as much as the Pipers.

The main factor is the metal prop, fixed pitch is bad, constant speed is worse. Put a fixed pitch wood prop on that same airplane/engine combination and it will be like a sewing machine.
If you are planning a constant speed or there is any possibility of a constant speed in the future, have the engine converted to dynafocal.
Vibration is directly related to engine displacement. The Pipers with 0 235/metal prop run quite smooth, 0 290 a little worse, 0 320 still worse but not bad on the Tri Pacer and Super Cub.
 
Since you are going to major the engine, send the case off for the conversion!

My first engine, O-290-D2, was conical and I couldn't believe how much it sagged.

The second engine, O-360, is a conical and hasn't sagged at all.

Yes the mounts are more expensive but in the end, that little extra is worth it!
 
No worries mate...

newrv-4 said:
I recently purchased a used O-320 for my project. When it arrived I discovered it has a conical mount instead of a dynafocal mount. I intend to tear the engine down and rebuild it. I was wondering if anyone knew what was involved in converting it to a dyna mount. I have tried to call a few shops, but no one seems to be answering the phone.
Click to expand...

Both of my RV's have had Conical mount engines, my current RVX has a rare conical mount 0-360. They are no worries and Van's does sell Conical engine mount/gear leg combinations, trust me. Having flown both designs I recommend sticking with your current engine and putting your mount and gear legs in the classifieds for sale or trade. There are always several guys looking for just that swap. Vibration? As an A&P it all boils down to mount rubbers. They sell two types, regular and aerobatic which have metal sleeves through them. Many Pipers used the aerobatic mounts for some reason and they are significantly more vibration prone. I buy my "standard" mounts from Aircraft Spruce. Sagging is a non-event.

Several advantages/disadvantages to the Narrow Deck 0-320 which were in most of the early Apaches and Tri-Pacers/Pacers/Cherokees.

Advantages: lighter weight, constant speed crank (if you want CS) all accessories on rear case.

Disadvantages: RV-9A builders have to replace the sump/intake tubes on the Narrow Decks as they interfere with the Nose-wheel mount. RV-4? No worries. Most ND's are 150HP. IO-320B1A's (later Apaches) were modded with cylinder beef up plates/large case through bolts and are 160HP. Earlier 0-320A models have lighter/thinner flange cylinders and smaller case through bolts. What does that mean? 8.0:1 compression (160HP) not recommended on those earlier engines. It has been done though...

Don't fear Conical...
V/R
Smokey
 
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Smokey helped guide me through this back in May. With very little piston airplane experience I was concerned about vibration with a conical mount engine. I can now say I was grossly over-concerned! Smokey helped me buy a great little RV-6 that has a conical mount O-320 with a Warnke prop. I took him at his word that it wouldn't be an issue and I'm very glad I did. I've put about 60 hours on the airplane so far and I have NO regrets. I don't know how it would be with a metal prop, but no issue at all with wood up there.

For what it's worth...

Doug

p.s. Thanks again Smokey!!!
 
Lycoming

I have to take issue with one thing that Smokey posted-the 0 320 powered Piper Apaches never used injected engines. I believe the first production Pipers to use injected engines were the Twin Commanches, first deliveries in July 1963.
First production Apaches were in 1954, 1958-1961 they had the 160 hp 0 320B series engines.
The vast majority of injected 0 320's from certified aircraft are from Twin Commanches, a few from Citabrias and other aircraft.
One additional issue with early 320's is that the crankshafts have lightening holes. I would personally not use one of these cranks with a metal prop
 
I fly a 180hp C/S RV-6 with a conical mount engine. It vibrates significantly more than my dynafocal mounted RV-6 did at startup and shutdown. Other than that there's just a slight difference in cruise.
 
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