aewrigh's build

[aewrigh]

What are you guys setting your idle speed at? Also, at what rpm are you keeping it governed to with the prop at WOT?

[aewrigh]

Ok guys, made the maiden voyage. Boat absolutely wouldn't plane with two people, even in shallow water. It planed with just myself in shallow water only and would hold plane in deep water until I turned too sharp and lost momentum. I played with prop pitch several times but didn't try shallow water till the last setting. When I was on plane I seen 19mph at 3400 rpm's @ WOT. I am not sure if less pitch and more rpm's will perform better or less rpm's and more pitch. The jb weld fixed my oil leak near the sending unit but noticed a very small oil seep where the jug meets the block on one cylinder. I have heard on aircraft engines of people putting the engine under too much strain and causing high crank case pressure. Could that cause oil to leak there? Perhaps the bolts could be tightened a bit or do y'all think it will require a new gasket? Any help would be appreciated at this point. Hopefully I can get back out for some more testing/tweaking/tuning in a couple evenings.

[Bart]

i am that you finally got this in the water, not so happy that with all the anticipation, that it is not planing as expected, at the moment.
there are a few like Aerokirk's build, that have posted videos of him and his better half, going at a pretty good clip across a lake, he might have some good suggestions as to what to start looking at. where both of you have the circle S drive.
glad that the JB weld on the sending unit is holding,
a couple of questions about the oil seeping from base of the jug. as to the question about "high crank case pressure"
have you done a compression check on all 4 cylinders? if so was the compression in all 4 cylinders within 10 psi of each other?
are you running with the stock carb?
how is the air vent? is it plugged?
the cylinder head nuts are to be torqued between 22 & 24 ft lbs.
first verify that it isn't coming off one of the push rod tubes above the cylinder. replacing an o-ring is a lot simpler than replacing the seal on the jug.
but if it is leaking around the base gasket, you will need to pull the jug and replace the gasket. while it is off verify that there is no gouges or score marks on the matting surfaces,
i replaced one of the jugs on my 084 last winter, it had a few of the fins broken off, it was a tight fit. ended up using a rubber mallet to work the old jug off. once it was off, i notice a few gouge marks on the mating surface, from a previous jug removal?
but i flattened down the rough edges and used some permatex 515 to fill in the scratches. that is just one of the entertaining things that i have dealt with the motor i picked up.
good luck and when you get everything dialed in, it will be fun seeing it run.

[Corky]

Now comes the adjustment phase of the build..Is the engine sitting in the neutral position{not high or low,front or back}in relation to the hull ?? Was the front end plowing the water ??? Was the bow in the air without breaking free ??? Did you ever weigh the hull and know where you're at on weight ???

[aewrigh]

Bart, I have not done a compression test or checked the breather. The oil is definitely seeping from the bottom of not 1, but 3 jugs now after tonight's run. I originally had an issue with one push rod tube leaking but I siliconed them all up and they don't leak now.

Corky, my first run my engine was sitting 3/4" lower in the front for bow lift because I read somewhere in the early stages of my build that that is where I needed to start out. After some reading today I found that out to be false information. I shimmed the front of the motor to where it sits 3/8" high in the front now. Also talked to chuck today on the phone and he told me to run the engine at 3850 and as parallel to the boat bottom as I could. So at 3/8 high in the front and adjusting pitch to around 3800 at WOT on the water, tonight I saw 25mph top speed but still wouldn't plane in deep water. It did seem to hold plane better in deep water though. That 25mph was with a slight breeze at my back. Going back against that slight breeze took me off plane. I have to stay at WOT all of the time. I feel my prop is where it needs to be as far as pitch goes. With two guys in it it absolutely won't try to get up.....just 5-6 mph pushing water. Also forgot to mention that around 22 mph I started porpoising pretty bad. With just me it doesn't plow, it rides bow high and won't push over the break point it seems unless I am in shallow water. I think I should get the engine completely level and try again but I am afraid my boat hull is too heavy......I didn't exactly keep everything where I could just shift weight around to see if that would help. I do have a heavy battery under my seat and a 13 gallon fuel cell under the engine probably with around 10 gallons of gas in it.

[aewrigh]

Few pics from this evening

[aewrigh]

And yes, I am running the stock carb.

[aewrigh]

Here are some videos

https://youtu.be/qHl1OtYnewI

https://youtu.be/q2O1X3MKNzU

https://youtu.be/6AtzroQTGIo

[aewrigh]

Chuck says I need to spin the motor to 3850, Jerry from Arrowprop says I need to crank the pitch up and only spin the motor at around 3000. I don't know jack really about propellers and thrust and whether not numbers are linear but what is the difference in thrust between a prop pitched at 5 degrees spinning 4000 rpm's vs. the thrust of a prop pitched 10 degrees and only spun to 2000 rpm's? I realize I probably only need to work on one variable at a time so maybe I will pitch the prop back to where the motor runs around 3400 and try the new engine angle....just to see what happens.

[aewrigh]

Bueller?

[Corky]

Sorry I wasn't able to look at this until tonight... Everything I've read points to the engine being too low in the front where you're at now...It's my understanding that you start with engine level {on the same plane as} the hull bottom then keep dropping the front of the engine until you get porpoising then raise it back up until that porpoising goes away{essentially taking the bow back down with a little pressure from the prop pushing against the water in the back}..

Every build is different and nobody really knows what your boat is going to like that's why you're getting suggestions all over the spectrum of adjustments...But they all suggest basically the same two...Engine tilt and prop angle...

Some boats never seem to get rid of the porpoising no matter how you adjust it and have an added trim tab at the transom to help with the problem..

Look in the prop forum at the "homebrew airscrew" for an overview on prop rpms VS size and pitch...http://miniairboatassoc.com/forum/sh...ebrew-Airscrew It's a lot of info in a short paragraph...But in your case the pitch is going to determine just how fast the boat will jump up on the water and break free ...Experiment between those 3000 rpm to chucks recomended 3850 and I'm sure you'll soon see the difference...Engine cylinder/operating temps are going to come into play there spinning it at 3850 for any extended amount of time so keep an eye on those...

I wish I had more precise info for you but I'm not there with my build yet and I'll be going through the same scenario as you I'm sure..

[aewrigh]

Hey corky, I hope to get out and experiment this weekend. My temp stays around 175 until I get to running it hard. Then it creeps up to around 200. It hasn't went any higher and once I slow down to an idle for a few minutes it drops right back down to 175. So I started out at 3/4" low in the front. And I raised it to 3/8" high. I am going to add pitch and try lower rpm's then I will raise the front of the engine some more. I'll report back asap. Thanks

-Aaron

[aewrigh]

Perhaps raising the front of the engine will create lift in the back and get me out of the hole quicker and keep the nose from bouncing. That would be a win win to kill two birds with one stone.

[Corky]

I'm sure Aerokirk will have some pointers for you I know he is experimenting with the prop angle also...If you read towards the end of his build he states about how even small adjustments have a big affect on planing ability...Well at least I can follow you two and know what I'm in for here soon...

[aewrigh]

Hey, 3 heads are always better than 1! We'll get it worked out hopefully. I was also already thinking of the carb change.....I noticed how Papee said he was running around a 200 degree oil temp when running until he swapped the to the solex and now temp stays around 175. That tells me it may be running a little lean anyways. I don't mind running a little fat to aid in cooling and engine longevity.

[Papee]

A Ron, There has to be some up in your setup. Your hull can't be any heavier than my tank and I've run with three people in direct drive. I don't see anything that sticks out but I haven't watched the videos yet. What is your redrive ratio? I haven't seen any specs on that prop but I assume it should be around 2700 for top performance,

OK looked at the videos. You should start first with your engine tilt. You need to push down on the nose, lower the prop end. It looks like you are off quite a bit. When it is set up like that it also pushes down on the stern and slows it down. You're probably about 1/2" off by the looks. Get that fixed before you start with pitch.

[aewrigh]

Hey Papee! So right now I am sitting 3/8 high in the front from level.....so what you are saying is I need to angle my angle of thrust even further towards the water? I will raise it another half inch in the front and try that this evening. As far as my redrive, it is 1.69 to 1 I believe so that would mean I would need to spin my engine to 4,563 rpm's to see 2700 at the prop. What is the max safe RPM for these engines without valve float?

[aewrigh]

One guy on southern airboat says he had similar issues with composite props and went to a wood prop and had night and day difference. I will definitely try re-pitching the thrust angle first.

[Papee]

I'm having a hard time concentrating right now but I'll try to get my point across. As far as the attack angle, yes you would raise the front, the pulley end.

On the rpm, I'm not sure on the rpm aerokirk would be the best to answer that. He's been running a setup like yours for a while. I don't think you should run it over 4000 for any length of time. For testing I'd set the prop up to stall the engine at that. Sounds like you need to take a little out. You need that little bit of extra power you never use to get you out of a jam at some point. That's my theory any way.

I'm no expert on redrive rpms as I've always been direct drive running 3200 tops.
Also my figures are for a longer boat on the engine angle. A shorter boat will need less adjustment.

[aewrigh]

I am now 7/8" high in the front and fixing to head to the water hole to try it out