converting an 0 290 lycoming to a 320

[Donskr1]

Well here we go again. My plan is to convert an 0 290 Lyc to a 320 using A1A cylinders with 8.5 to 1 pistons and an 18840 cam. From what I can see talking to people here it's a do'er. My question to the readership is, what's involved other than opening up the holes and how durable an engine will this be. I'm also looking for a 360 bottom feed oil pan, I'm hoping Gary Barber has something for me there
Don C

[4 pistons and a Prop]

I'am assuming you have an o-290D2 (hydraulic lifters), If you have mechanical lifters you have to do case work to modify to accept hydraulic, and tap them and provide additional oil. The carb will need to be changed. The bigger holes you are talking about- case boring? yes that will need to be done. As for reliable, its up to you, you are building it. I would have it aligned after boring, and have the rotating assy. balanced. The higher compression pistons I would guess would give you around 140-160 hp. I dont think that will be too hard on the o-290 case, but a web, and new thru bolts ought to help hold her together. Also the weak link in an o-290 is the prop flange/crank... Double check all clearences,Gasket set. But all this work is adding up $$$$, not sure why you dont just buy an o-360, especially right now I have been seeing them from $4500-6000. Good luck.

[Des Moines Boater]

Gary Barber is the man. He will build you a great O-320 from the O-290G case. It does need to be bored and should be aligned. Don't even try to use the O-290 ground power crank. The flange is just so thin and full of holes too. He can get you a good O-320 crankshaft. I had one of his conversions and it was a great engine. Wish I still had it. The cost to do all the work and new crank plus lifters is going to be a bunch. I would go for a regular O-320 or even an O-360 for the price. Sometimes a bargain can cost a lot more than it's worth. You still can't go wrong if it's an Outlaw Aircraft Engine.

[John C]

In the long run you would be better off selling the 0290 and buy a 0320. You can pick up a 160H2Ad for $2500-$3000. Once you start spending money on that 0290 you will be suprized how quick things start to add up. jmo.

[RJ]

I have an 0360 angle valve rebuilt in the classified section for $5,000, just picked up last weekend from the certified aircraft mechanic. Take a look.http://southernairboat.com/classifieds/ ... 2475/cat/7

[Donskr1]

Thanks Guys for the input. That's the good stuff I'm looking for. Time to weigh my options
Don C

[akholland]

I have a 0-290d running engine and a spare set of 320 cylinders with 150hp pistons.

Why couldn't I just take the adjustable rockers off the 290d cylinders and use them in the 320 cylinder for solid tappets? Then converting the case to accept hydraulic tappets isn't an issue. What is the advantages of a hydraulic tappet anyway other than not having to inspect/adjust every 100 hours? Seems to me manual tappets would be less parts to fail if you warm it up properly. My manual tappets sure do seem noisy though when I put my ear to the cylinder with a screwdriver.

I also have a spare complete 0-290d2 laying around with a bent crank and a cracked cylinder that I could use if I really wanted to go hydraulic, but then i have to have the cases inspected for cracks, and pull the 290d apart anyway to rob the good crank, and im also in it for all new crank bearings since their matched/worn to the 0-290d case, that would be an extra 1000 just in bearings.. $$$

I think this would make a sweet motor that weighs in at about 15lb less than a 0-320. Should make a world of difference on the Airboat for less than 1000 bucks invested in the conversion.

[Outlawaircraftengines]

The conversion makes a really good engine. Also conical mounting. Let me know buddy.

[boobidges]

I have an 0-320 that's apart.needs a new can.took apart for spun rod bearing. Has new crank in plastic from jurniigan
Chrome cylinders. Matching Carb and Bendix mags.buy it for$2000 .haveaa camto get cut. Bobby 239-340-2819

[akholland]

I've finally rounded up enough parts to do the build.

Used 0-320 case ($100 bucks)
Like New low time 0-290 Crank (600 Since NEW) inside a 290 motor ($1000 bucks)
MA4-SPA Carb Freshly Overhauled ($250)
0-320 sump ($50 bucks)
high compression 8.5:1 0-320 pistons (free)
0-320 NarrowDeck Mid Time Cylinders ($450)

Total Invested $1850


I would likely have been better off buying bobby's but I'm 4000 miles away, thats a good deal with the new crank... My big question is, how long will the straight bore NarrowDeck 150 cylinders last once I drop a 8.5:1 piston in it. (No Banana Plates and stock ND thru Studs.)

How many people have EVER heard of a ND thin flanged cylinder cracking from the 8.5 piston?