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What's a better engine to go with, a small continental aircraft engine or a continental GPU engine? Which one is more reliable, and cheaper to maintain? Thanks for any info.
Without a doubt go with the 6 cylinder gpu. The engine is cheap, parts are plentiful and the unit is easy to work on if you have to ( but if you treat it right all you will have to do is change the oil and spark plugs ).
The GPU that I am looking at is only a 4cyl. At least I was told it's a GPU. The intake comes from the top and it only has one mag on it. If it's not a GPU then what size engine would it be? I already have the small 4cyl aircraft engine but it needs new mags. I am thinking it might be cheaper to buy this engine instead. What do you think? I can get the engine, stand and prop for $600. Thanks again for any more help I am a newby to the airboat world.
I have never owned a 4 cylinder gpu but what you are describing sounds like a gpu unit. It might be cheaper to buy the gpu but it is really hard to beat the aircraft 4 cylinder you have now. If it were me I would spend the money on my existing motor that is already on the boat.
Well the aircraft motor you have now is rated at 90-100hp and a 4 cylinder gpu could either be a 90hp or a 150hp. does the gpu your looking at look like your aircraft motor, are the valve covers the same? Or does it have bigger cylinders and valve covers with a squarish oil sump?

Here is a pic of a 150hp gpu motor.

These are good running motors and use many of the same parts as the 6 cylinder gpu's, same cylinders, etc.

It looks like the engine in the picture It has bigger oil sump and it's square like the one in the picture. The engine that I have now looks like a 0-200 but it's not. I was told that it's an a or c series engine and it's the small one with only around 65 horse power. The gpu unit that I am looking at buying has been sitting in a garage for almost 20 years, I don't know if it runs. Is it possible that there could be some bad sills in the engine from sitting that long or would it be ok? And what size horse power is the engine in the picture? Thanks again for any more help.
Not sure on the seals, but I run a 4 cylinder GPU, like the one in the picture. The cylinders on mine are the same as the cylinders on the 6 cylinder GPU. This is some info that was given to me...."The PE-90 has a 5 inch bore and 4 inch stroke giving it a 314 ci displacement. The military rates this motor at 110 hp @ 2400 rpm. Ungoverned it should produce around 150 hp." My motor has had some motor work, cylinders are .015 over, and I have a good amount of power. I turn a 68" super snapper, pitched at 2700, and will dry in my area: rocks, sand, etc... IMO, it depends on the boat you are putting it on. I run it on a 12' palm beach, 3/4 deck. I wouldnt go any bigger than that though. Some pictures of mine are in my gallery. Hope this helps.
I may be wrong but I think the 65 HP's had a rounded, bladder-shaped oil sump.

Did you buy the engine off eBay? There was one on there a while ago they thought was a 65 but I think it may have been a 90.
no the engine was on my boat when I bought it but the mags are shot and the motor has been sitting out in the weather for a couple of years and am a little bit leary of spending money on mags for an engine that might not be good. And the oil sump on the engine I have is round. From what I was told it only has 65 horse power, but am not sure because there is no tag on the engine, that says what it is. I am just trying to find a light weight engine to replace the one thats on it now. Any other suggestions or info would be great.
Bandkiller, don't be too quick to give up on what you have. Get your hands on a compression tester, squirt a small shot of WD-40 or Marvel into each cylinder, spin it with the starter and see what the compression looks like. If it has good, even compression on all four cylinders it can be made to run.

I tested the compression but I used a car compression tester and was told that was the wrong way to check it on an aircraft engine. But the numbers were: in firing order 90 87 70 and 90. Thanks again for the help , you guys are a lot of help. I have been pulling my hair out for months. :shock: Let me know if the car tester will do the job or was it wrong to check it that way. I was told you need a special gauge and then you pump air into the cylinder and check it that way.
No, the car tester will work just fine.
What you're looking for is what is called 'cranking pressure'. With all the plugs out of the other cylinders so that the engine will spin easy, spin the starter through at least four or five revolutions, and check each cylinder that way.

If the readings come up pretty close to each other then your're good to go. If one is a lot lower than the others then that one cylinder might need some attention, but again, it may not be anything major so don't be too quick to give up on what you have.

The other test (with air pressure) is called a leak-down test. Don't worry about that one right now.

Yeah thats how I tested it and thats the numbers I got so one cylinder is lower then the others. The engine is probably ok but I need a set of mags to run on it and I don't want to spend a small fortune on new ones for a motor I have never heard run. I am not even sure what mags I need, the old ones are old bendix lunch box style mags and nobody around here will touch them on a rebuild. If anybody has any mags for this engine for a good price let me know. I am willing to keep the engine I have if I can find some mags for cheap. But then again airboats are not cheap.
Howard "THE MAG MAN " Libersky

He's the best, and a real nice guy.
He's located in Okeechobee 863-467-6464

Give him a call

I don't care what mag, or mags you have, he can fix them right.
If he knows it's on an airboat, he'll fix it right, but it won't cost you an arm and a leg.

He'll go through them, fix anything he sees wrong, and test the mag for a number of different problems. When you get it back, it will be right.

Removing your mag for shippment will be pretty darned simple.
Just open the inspection port on the side of the mag. This will let you see the rotor gear teeth.

Turn the engine by hand until you see the painted tooth centered in the inspection port. This is the base timing point. At least it will be back to where it was, and this assumes you base timing is correct now.

Pull the mag off, and make sure you don't turn the engine while the mag (s) is away for repair.

When you get it back, just re-install it on it's mounting pad, and make sure your painted tooth is still centered.

You may want to consider making up some new plug wires while the mag(s) are away for repair.

Put it all back together, and a lack of ignition fire should not be a problem for you.
Hay band killer I'm new to the airboat world to man I have a 13'9" pear-shaped cottonmouth with a PE 90 it's a 150 hp it will run dry. Your motors probably a good motor. Bendix Maggs is the best way to go. not too bad they're pretty reasonable.
If you can get a PE 90 get it. The 65 continental is good for a toy but not for your only boat. The difference is 85 HP. You will be pushing the boat less and enjoying it more.
If you turn the motor over by hand do you here the mag click if so I would say points is all you need take some sand paper and run it through the points .
I ran a GPU 6 cyl for 10 years on a 15' river master it would run ground with 4 people in it , but look out for green grass , 6 cly all the way they run for every leak oil and make noise but that was how they were built to run 24/7