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100hp Cylinders on a 912 UL

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Posted

I found a set of low time cylinders and piston assemblies from a 100hp ULS. Cheaper than a big bore kit. They have to be machined to fit the 80hp heads, very easy task. Maybe 1 hour total for set up and cutting all four.

912cylinder.jpg

912cylinder2.jpg

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Posted

That's an enviable lathe you have there! 

 

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Posted

Thanks Chris. I have a machine shop at home, that i should really use more often. My full time job is almost 7 days a week between vacations. Pretty common to work 40 plus days straight. Work and home life don't leave much for hobbies.  Next project is to split a 912 and machine the case to the newer heavy duty specs. Here is a better pic of the lathe 

jet.jpg

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Posted

Wow, nice.  I won't post a picture of my lathe....;)  JImChuk

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Posted

Yeah, your lathe makes my Old South Bend Heavy10 look like a toy! 

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Posted

I also have a heavy 10 SB.  I love it.  But I love the big ones at work too. 

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Posted


Then do you use the uls pistons as well?

 

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Posted

Yes, i used the pistons that come with the cylinders. First run was yesterday and i flew it today. More power for sure but not as smooth as the lower compression 80hp. I will work some more on the carb sync tomorrow, it was really good at 5k but not as close at 3 to 4k. I suspect the cable its self. Looking at a Propeller Balance Master , just want everything as good as i can get it first. 

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Posted

If you don't have a slipper clutch in your new high compression 912 you are going to need one. I chased rough starts and broken motor mount bolts for a long time. The engine was powerful but so rough. Bought a low inertia prop. Nothing. Soft start module. Nothing. Slipper clutch and it starts like butter. It's the only thing it needed. I wasted a lot of money and effort all to find the real reason rotax ended up putting the slipper clutch on all their high compression engines. it wasn't in case of prop strike.

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Posted

I have a balance master. It does some good. I think the 912 s is just a angrier engine than the 80 hp version.

 

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Posted

Yes, i used the pistons that come with the cylinders. First run was yesterday and i flew it today. More power for sure but not as smooth as the lower compression 80hp. I will work some more on the carb sync tomorrow, it was really good at 5k but not as close at 3 to 4k. I suspect the cable its self. Looking at a Propeller Balance Master , just want everything as good as i can get it first. 

I have the same setup...ul modified into uls including a high performance camshaft. I did install the balancemaster and it's great. another thing which made a world of difference is the modification of the crossover tube...I have increased it's size to 1in diameter and the engine can idle smooth at 1200rpm, shuts down nice without sudden jolt and the bonus is that it can run on one carb (if one of my cables were to break..). Also the cylinders seem to have a more even mixture when running at lower rpm. Before I alway had the front cylinders running too rich..

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Posted

 

I have the same setup...ul modified into uls including a high performance camshaft. I did install the balancemaster and it's great. another thing which made a world of difference is the modification of the crossover tube...I have increased it's size to 1in diameter and the engine can idle smooth at 1200rpm, shuts down nice without sudden jolt and the bonus is that it can run on one carb (if one of my cables were to break..). Also the cylinders seem to have a more even mixture when running at lower rpm. Before I alway had the front cylinders running too rich..

Do you have the larger fittings in the intake manifolds as well as the 1" crossover tube?  JImChuk

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Posted (edited)

Did you build your own crossover setup or buy the one from HAL? Can you take a picture for inquiring minds?

Edited by aschlem
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Posted (edited)

I too am interested in how anyone has implemented the larger crossover tube.

Edited by ChrisBolkan

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Posted

I ordered some 90deg fittings. I will take picture of my efforts. 

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Posted (edited)

Did you build your own crossover setup or buy the one from HAL? Can you take a picture for inquiring minds?

Hello, I had to get the pictures for you guys..I did my modification the DIY way. As I didn't have a welder welding aluminum I found a pipe, cut out the hole in the intake so that the pipe fits super snug and then used JB weld at the same time pressing the tube into place. Super strong and has held up 2 years now. 

My 2 dollar crossover mod :)

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P1120878.JPG

Edited by flywise

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Posted

Is that 1'' outside diameter pipe?

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Posted

I did buy a 1/2" and 3/4" pipe tap, but if I just enlarge the hole it gets closer to the carb then I like.  I suppose I could enlarge the holes with a die grinder so the carb side of the hole doesn't get any closer to the carb, and finish it up with the right size bit.  I might revisit it.  I have a couple of new manifolds and carbs on the way, maybe I'll address it then.  JImChuk

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Posted

intake1.thumb.jpg.3a5da8b520e529eb36eeed

 Figuring out the setup. I will wait for the 1'' aluminum radiator fittings from Jegs to show up before i start cutting. 

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Posted

balance.thumb.jpg.dedc483e781d002cf9b102Installed the Balance Master today. Ran out of time today, I will run it tomorrow.

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Posted

It helps some. I would not call it the Holy Grail of balance but i believe i could notice a difference. Next is the crossover 1'' mod and a slipper clutch for the gear box. 

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Posted

After re-reading a previous post about my 912 S I feel like I need to explain better. From the beginning I have had two issues with it. First was starts that would sometimes shake the engine so hard I KNEW damage would be done. And it was being done. It manifested itself in the form of motor mount bolts (upper pilot side in my case) This happened multiple times until I finally installed a slipper clutch. Everything else I did up to then did virtually nothing. The things that did nothing to fix the rough starts were rebuilding and finely balancing the carbs, replacing the existing heavy club bladed prop that way exceeded the gearbox rating to a very nice lightweight Whirlwind like those seen on a lot of kitfoxes, and built and installed a soft start module. None of those did any good. The Slipper clutch solved rough starts and stops INSTANTLY. 

The other bothersome but not destructive issue I have is with vibration at some RPMS. It idles like butter, is pretty smooth between 4800 and 5600 RPM but has an annoying vibration from about 3300 to about 4600 that peaks somewhere around 3800-4000. Annoying but doesn't feel destructive. I took the balance master that I had on it off when I installed the slipper clutch just to see what would happen. I will re-install the balance master again and see how much difference it makes. I think I'm down to it's just a harmonic thing like some airplanes just have, or possibly a compression difference in a cylinder or maybe the fancy expensive lightweight prop I bought is out of balance. I've set blade pitch precisely numerous times with no real change.

The reason I just posted this is because in my previous post I think I blurred the two problems into one, and thought that might be confusing to someone else reading that might be chasing down problems. 

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Posted

After re-reading a previous post about my 912 S I feel like I need to explain better. From the beginning I have had two issues with it. First was starts that would sometimes shake the engine so hard I KNEW damage would be done. And it was being done. It manifested itself in the form of motor mount bolts (upper pilot side in my case) This happened multiple times until I finally installed a slipper clutch. Everything else I did up to then did virtually nothing. The things that did nothing to fix the rough starts were rebuilding and finely balancing the carbs, replacing the existing heavy club bladed prop that way exceeded the gearbox rating to a very nice lightweight Whirlwind like those seen on a lot of kitfoxes, and built and installed a soft start module. None of those did any good. The Slipper clutch solved rough starts and stops INSTANTLY. 

The other bothersome but not destructive issue I have is with vibration at some RPMS. It idles like butter, is pretty smooth between 4800 and 5600 RPM but has an annoying vibration from about 3300 to about 4600 that peaks somewhere around 3800-4000. Annoying but doesn't feel destructive. I took the balance master that I had on it off when I installed the slipper clutch just to see what would happen. I will re-install the balance master again and see how much difference it makes. I think I'm down to it's just a harmonic thing like some airplanes just have, or possibly a compression difference in a cylinder or maybe the fancy expensive lightweight prop I bought is out of balance. I've set blade pitch precisely numerous times with no real change.

The reason I just posted this is because in my previous post I think I blurred the two problems into one, and thought that might be confusing to someone else reading that might be chasing down problems. 

Hey Chris, I had the same kind of problem when starting & killing the engine. I took another road and instead of installing a slipper clutch (more weight & money) I did the 1" crossover tube mod. After doing that the engine can idle well down to 1200 rpm and my shut down is perfect, no jolt. Same when starting the engine, its progressive now. for me an added bonus being a float plane on water with no brakes, I can approach a dock at much lower speed making it much safer for the nose of my Catalina...

My 1/2 cent

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Posted

I am considering the crossover mod, but my engine idles so smoothly and down real low too. I believe it is primarily done to reduce sensitivity to carb balance at idle. Did you notice any midrange improvement in smoothness with the X-over mod?

 

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Posted (edited)

I am considering the crossover mod, but my engine idles so smoothly and down real low too. I believe it is primarily done to reduce sensitivity to carb balance at idle. Did you notice any midrange improvement in smoothness with the X-over mod?

 

Hey Chris, I did the mod 2 years ago....my memory is not that good. What I do remember is that before the crossover I always had the rear cylinders overly rich and black and the front cylinders were on the too lean side...that was mostly solved with the crossover. My understanding is that the intakes don't have the same length from carb to front/rear cylinders making it very difficult to even out mixture, especially at lower rpms.

Edited by flywise

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