Help with first airboat

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Saul Good
Southern Airboat Member
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Joined: Wed Aug 02, 2017 4:50 pm

Help with first airboat

Post by Saul Good »

Ok guys, I'm back again. Some of you may remember a few years ago I posted about building a small airboat out of a 90hp opposed twin BMW motor. I won't bore you with the details, but a guy 10 minutes from my house was selling a boat and trailer with rigging minus the motor and prop for $1500 with papers. We made the deal and I'm going pick it up this afternoon. The trailer is in decent shape and so is the hull and rigging.

I was thinking if I decided to build my own hull, I could use the trailer and the other parts that would nickel and dime me to death on my new build, but then he said that he had the 0470 from the boat with a broken crankshaft. The motor is listed on this site in the classified and I was thinking about nabbing it when I pick up the boat. I know the hull is too heavy for the BMW engine, but would it be worth trying to find a crank for the 0470 and just run that with the boat I'm getting from him (cause its already set up for this motor) or would I be better off just getting a running 220 GPU?

I'm looking for a project to do with my 16 year old son and my mechanic skills are pretty sharp, so I have no issues with tearing it down and rebuilding it myself, but if I have to get into 6 or 8 grand worth of motor for the current hull, I'll just build my own aluminum hull, scavenge what I need of the current boat and build a little mini-ish boat with the BMW engine. Then I will already have the trailer, and probably find a good home for the hull and whatever I don't use. Are 0470 cranks really that hard to come by?

Motor in question: https://southernairboat.com/southern-ai ... ft-engine/

BobBrack
Southern Airboat Member
Posts: 77
Joined: Thu May 22, 2008 8:12 pm

Re: Help with first airboat

Post by BobBrack »

The cranks are not hard to get. Just pricey. That engine is what we call a conversion engine. That is definitely a plus. In my opinion he is asking a fair price. I think the last time I needed a good crank it cost me about 800.00. But it was a perfect shape standard/standard crank. I see them often here in Florida for sale in the 400.00 to 600.00 range. Bearings, gaskets, rings will run you right around a grand give or take. Then your major hurdle will be finding somebody up there that can do the machine work on the cylinders. But when your done they make great engines. Very reliable and fairly easy to get parts for. If you have any more questions I would be happy to help. My number is 3214031560. My name is Bobby. If i dont answer during work hours I promise to call you back ASAP.

Saul Good
Southern Airboat Member
Posts: 20
Joined: Wed Aug 02, 2017 4:50 pm

Re: Help with first airboat

Post by Saul Good »

Thanks a ton Bobby. I already called the guy back and told him I was going to take the engine. This will be my first airboat and around these parts, It's seldom to see anything that isn't over priced. The plus was that he was literally 10 minutes from my house. With boats in general, most mistakes are probably bigger than $1200 screw ups, so in the grand scheme of things, I guess the risk here isn't that great. I'm sure I'll be back here asking more questions in a week or so when I get around to tearing the thing down.

Are you saying that this engine is a conversion? I don't know much about aircraft engines, but I know it's common to put 470 jugs on the 220 gpu engines as a conversion. This guy is telling me it is a real a/c engine and not a conversion. What should I look for when I go over there this afternoon? I mean, obviously I won't be able to run it or leak check it.

BobBrack
Southern Airboat Member
Posts: 77
Joined: Thu May 22, 2008 8:12 pm

Re: Help with first airboat

Post by BobBrack »

It is 100% a conversion motor. It has the bottom end of a 220 gpu, aka PE150, and the top end of a true O-470. I cant tell from the pics but they should have installed the second magneto in order to run the other set of spark plugs. If your really feeling froggy you could bore the cases out while you have it apart and put O-520 top end on and really make some H.P.

Saul Good
Southern Airboat Member
Posts: 20
Joined: Wed Aug 02, 2017 4:50 pm

Re: Help with first airboat

Post by Saul Good »

okay, so, the million dollar question. Will a true O-470 crank fit the case? I know if the crack is repaired I will have to have the current shaft re-hardened. Is that right?

BobBrack
Southern Airboat Member
Posts: 77
Joined: Thu May 22, 2008 8:12 pm

Re: Help with first airboat

Post by BobBrack »

A true O-470 crank will not fit. I have never heard of anybody ever having any luck welding those cranks. Find a good one and buy it. If you don't have any luck I'm sure can find you one for you. If you find one and have it turned at machine shop make sure they are able to put a radius in the web. Car cranks are typically turned straight all the way across the crank pin. If you don't put a radius in it then it will break again.

Saul Good
Southern Airboat Member
Posts: 20
Joined: Wed Aug 02, 2017 4:50 pm

Re: Help with first airboat

Post by Saul Good »

Well crap. It seems I'm in deeper than I thought.

First off, thank you Bobby for following and commenting cause it seems pretty dead around here (or maybe it's cause I'm stupid enough to try what thousands before me wouldn't touch with a 10' pole.)

Let's just assume here that I have a couple/three grand now to throw around at this motor situation and may be looking to the easiest way out here. Would it be easier to just buy a running 220 gpu and get the boat running while I disassembled the motor I have now and get everything cleaned and freshened up. Then I could do the 0-470 conversion sometime next year because I have all the parts. Seem logical? Or should I just get a 220 crank for the case I have now and let a machine shop take a look at the rest. Really looking foir the quickest and easiest route here.

BobBrack
Southern Airboat Member
Posts: 77
Joined: Thu May 22, 2008 8:12 pm

Re: Help with first airboat

Post by BobBrack »

Quickest route is to buy a 220 engine. However 90 percent of them burn oil in excess. The PE 150 engine is designed to run at 1800 RPM and make 150 hp. They do that very well. We the airboater turn them up to almost 3000 rpm and the top end wears pretty fast in turn causing them to burn a lot of oil. That is why using the much more robust O-470 aircraft top end makes them a much better airboat engine. My personal opinion is that you should spend that money to rebuild what you have. You could do it pretty fast. There are several guys in Florida that you could ship the cylinders to for overhaul and have them back in 2 to 3 weeks with top end gaskets and new rings and ready to install on your pistons. Look up Ducarra aviation or DG supply on the net and order bearings and bottem end gaskets ( wait till you find a crank so you can order the right bearings). Those parts will be at your door in 5 business days. Clean all remaining parts well and begin assembly. There is an overhaul manual on this sight. Download it and read it. My opinion right now is to begin the hunt for a crankshaft. If you find one that needs turned you can send it to the guy I use in Okeechobee. He is the only one I know that cuts them correctly. If you cant find one call me and Ill get you one. Not sure what shipping will run you on all this but you can overhaul yours and have a reliable motor for about what it will cost you to buy somebody elses worn out GPU motor. JMO

Saul Good
Southern Airboat Member
Posts: 20
Joined: Wed Aug 02, 2017 4:50 pm

Re: Help with first airboat

Post by Saul Good »

That sounds like a solid plan and is exactly what I started thinking about 5 minutes after I hit the "submit" button on that last post. I'll crack it open this weekend and see if everything else looks okay and then start looking for a crank. If all goes well, I may take you up on that offer to call you sometime next week.

Two more questions. Best place to search for crank, eBay/local aircraft mechanics/this site? And, overhaul manual for 0-470, right?

BobBrack
Southern Airboat Member
Posts: 77
Joined: Thu May 22, 2008 8:12 pm

Re: Help with first airboat

Post by BobBrack »

Go to forums, then aircraft power only, then manuals, then GPU then the overhaul and service manuals are there. Remember the bottom end is a gpu the top end youll have to look at that manual for the O470. Its in the same place. I would start on this sight and call some of the engine builders. Jurnigan, justin fickin, gary barber, wally moore. Go through facebook airboats. Put out posts on other forums. Make sure you feel comfortable and trust the person you are buying it from. 90 percent of the airboat community will give you the shirt off of their back. The other 10 percent spend every waking moment making the rest of us look unscrupulous. Those people are not above selling you a junk crank.

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Slidin Gator
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Re: Help with first airboat

Post by Slidin Gator »

Saul Good wrote:
Fri Sep 04, 2020 10:29 am
First off, thank you Bobby for following and commenting cause it seems pretty dead around here (or maybe it's cause I'm stupid enough to try what thousands before me wouldn't touch with a 10' pole.)
It's best you wait for the good advice, otherwise you get us Lycoming boys throwing out guesses, half truths and lies. :violent1:
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

Gary S
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Re: Help with first airboat

Post by Gary S »

Can you post a couple pictures of this motor? the crags list motor is gone.

Saul Good
Southern Airboat Member
Posts: 20
Joined: Wed Aug 02, 2017 4:50 pm

Re: Help with first airboat

Post by Saul Good »

Yeah, I can post some pictures. The ad is gone because I bought it and it is currently I'm my garage. 😁

Bobby was correct. It is a gpu conversion with dual mags and 470 top end. I should start tearing it down this weekend. The crank is cracked, but I have one on the way. I have just about everything I need except for a carb. I've read some like the holly, some like the zenith, and some even use a Ford carb for a 300ci 6 cyl. The guy even threw in a 2 blade prop hub with the other accessories. I have starter, alternator, oil cooler, flywheel and other misc parts.

Saul Good
Southern Airboat Member
Posts: 20
Joined: Wed Aug 02, 2017 4:50 pm

Re: Help with first airboat

Post by Saul Good »

A few pics of the motor after I removed the mags and put it on the homemade stand
IMG_20200907_164719.jpg
IMG_20200907_164726.jpg


And the cracked crank
IMG_20200907_164712.jpg

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