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 Post subject: Rotax pistons melting
PostPosted: Sat Feb 03, 2018 4:02 pm 
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Anyone having problems with pistons melting?

I bought the FL400 with the 617 rotax conversion in it. Ran great, had only 2 hours on it when i bought it. noticed bubbles in the fuel line and found that a fuel filter was partially plugged. It was dying on me and bogging down. there were 2 fuel filters. removed the plugged one and it worked great after that. went riding after a couple hours it just died. Turns out it melted the piston in cylinder 2.

Repair time: replaced cylinder 2, piston 2 and the rave valve with parts from FARR-OFFROAD. Parts looked great. rebuilt the carbs and set them to be richer. No more bubbles in the fuel line. Checked compression. New cylinder 2 had 150psi, old cylinder 1 had 180psi. didn't know it was way too high. Ran great for at least another 2 hours or so. Kept checking the spark plugs and they were always black. fuel was mixed 40:1 with royal purple 2 stroke oil and gas was 91 octane. with only 2 hours or so on the new cylinder 2, the older cylinder 1 melted. damn. Pulled the head and noticed that my new cylinder 2 had scoring on the cylinder wall. on the back you can barely feel it with your finger nail. The front had scoring but couldn't be felt.

Any idea what is causing this? I assume the 180PSI cylinder 1 was extra hot because of the high pressure but don't know why it was so high. It looked great when I took the Engine apart to replace cylinder 2. And why would my new cylinder 2 have scoring on it?

Just don't want to replace another cylinder and piston to have it die on me again.

any help would be greatly appreciated. Anyone else have issues like this? I am using the recommended spark plugs BR9ES. The first time i was using BR7ES plugs.

This is piston from Cylinder 2 (first one that failed)
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This is cylinder 2
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This is the piston from cylinder 1
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This is cylinder 1
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This is the new cylinder and piston (cylinder 2) that only has about 1 or 2 hours on it. It was the replacement for the melted piston of cylinder 2
Noticing the scoring. Has it on front and back of the cylinder.
(SEE POST NUMBER 2)

There are the spark plugs. they were black every time i checked them and the Engine temp never got above 187.
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Rotax valve from cylinder 1 had oil in it
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PostPosted: Sat Feb 03, 2018 4:04 pm 
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This is the cylinder with only 2 hours on it. It replaced the cylinder 2 that melted.
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PostPosted: Sat Feb 03, 2018 4:09 pm 
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Location: Hope, B.C Canada
Well that's all I need to see.
That's a clear sign of detonation. Your fuel is crap and its detonating. Your compression is to high for pump gas.


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PostPosted: Sat Feb 03, 2018 4:13 pm 
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Location: Hope, B.C Canada
When you get this thing together again the first thing you will do is run Avgas.
The next thing you will do is make sure you are getting enough fuel flow through your pump. I do not know what the fuel flow rate is for a rotax but I would find that out if I were you and test the pump flow. Replace all your filters as well. It could also have been caused by a lean condition if the pump did not flow enough fuel.
That Engine destruction you are showing there is detonation to me. SHYTE FUEL !!!!


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PostPosted: Sat Feb 03, 2018 4:19 pm 
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Location: Hope, B.C Canada
I am a little bit of a hack n whack guy. I wouldn't re-bore that cylinder. I would just clean it up the best I could and give it a light hone. Then slam in another piston/rings. If the compression is down a bit who cares. First you have to make this thing run longer than a couple hours. Then when it runs you can rebuild it next year. Just my opinion.
Check fuel flow rate and run Avgas ---------- Amen.


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PostPosted: Sat Feb 03, 2018 4:25 pm 
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canadian oddy wrote:
Well that's all I need to see.
That's a clear sign of detonation. Your fuel is crap and its detonating. Your compression is to high for pump gas.


This is a farr-offroad Engine. It is supposed to run on 91 octane gas. I didn't do anything "special" to it. drop it in and go.


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PostPosted: Sat Feb 03, 2018 4:27 pm 
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canadian oddy wrote:
I am a little bit of a hack n whack guy. I wouldn't re-bore that cylinder. I would just clean it up the best I could and give it a light hone. Then slam in another piston/rings. If the compression is down a bit who cares. First you have to make this thing run longer than a couple hours. Then when it runs you can rebuild it next year. Just my opinion.
Check fuel flow rate and run Avgas ---------- Amen.


i forgot to mention I did put a new higher flow fuel filter on it. I think the cylinder with the melted piston is too far gone but I will hone that other cylinder.

So would detonation cause the scoring in the non-melted cylinder?


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PostPosted: Sat Feb 03, 2018 4:28 pm 
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canadian oddy wrote:
Well that's all I need to see.
That's a clear sign of detonation. Your fuel is crap and its detonating. Your compression is to high for pump gas.


so what about the scoring in the other cylinder? detonation?


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PostPosted: Sat Feb 03, 2018 4:38 pm 
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The scoring was caused by the piston getting real hot and then melting. The liquid aluminum just balls up. There was a serious lean condition there or the fuel detonated. I have blown 9 pistons in a row on my oddy and many times it did not run more that 100 yrds -- no FN lie. Those pistons looked just like yours. Some even had a large hole in the center but most had the edge of the piston "smashed" away at the exhaust side just like yours. I realize that's a twin rotax and not an oddy but the concepts are the same.

Edit: I see the ring is broken as well so those metal pieces would cause real damage.


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PostPosted: Sat Feb 03, 2018 4:40 pm 
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Location: Hope, B.C Canada
Here is the cost of my college education


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PostPosted: Sat Feb 03, 2018 4:41 pm 
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canadian oddy wrote:
The scoring was caused by the piston getting real hot and then melting. The liquid aluminum just balls up. There was a serious lean condition there or the fuel detonated. I have blown 9 pistons in a row on my oddy and many times it did not run more that 100 yrds -- no FN lie. Those pistons looked just like yours. Some even had a large hole in the center but most had the edge of the piston "smashed" away at the exhaust side just like yours. I realize that's a twin rotax and not an oddy but the concepts are the same.


wow, that sucks. sorry to hear you had so many problems too.

What about the other cylinder? the piston looks great, it just has light scoring in the cylinder.


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PostPosted: Sat Feb 03, 2018 4:42 pm 
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canadian oddy wrote:
The scoring was caused by the piston getting real hot and then melting. The liquid aluminum just balls up. There was a serious lean condition there or the fuel detonated. I have blown 9 pistons in a row on my oddy and many times it did not run more that 100 yrds -- no FN lie. Those pistons looked just like yours. Some even had a large hole in the center but most had the edge of the piston "smashed" away at the exhaust side just like yours. I realize that's a twin rotax and not an oddy but the concepts are the same.



AHA, that picture answered my question. piston doesn't have to look melted for scoring to happen. thanks for the pic.


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PostPosted: Sat Feb 03, 2018 4:45 pm 
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When the ring broke it would really scare things up in my opinion.


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PostPosted: Sat Feb 03, 2018 4:47 pm 
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Farr builds really good quality stuff. If he said it could run on pump gas then I have to give it the ok, but it would be reluctantly because of my experiences.
So my money is on lack of fuel flow then. Something wrong with your pump flow or line flow.

Avgas


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PostPosted: Sat Feb 03, 2018 4:53 pm 
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canadian oddy wrote:
Farr builds really good quality stuff. If he said it could run on pump gas then I have to give it the ok, but it would be reluctantly because of my experiences.
So my money is on lack of fuel flow then. Something wrong with your pump flow or line flow.

Avgas


i did rebuild the fuel pump and put a new larger fuel filter on after the first meltdown. maybe the timing is too advanced on it?

I have no doubt FARR-OFFROAD makes good stuff. the piston was a perfect fit for the cylinder, and the hone job looked great.

just don't want to melt another one.


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PostPosted: Sat Feb 03, 2018 4:56 pm 
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Location: Hope, B.C Canada
Specter wrote:
canadian oddy wrote:
Farr builds really good quality stuff. If he said it could run on pump gas then I have to give it the ok, but it would be reluctantly because of my experiences.
So my money is on lack of fuel flow then. Something wrong with your pump flow or line flow.

Avgas


i did rebuild the fuel pump and put a new larger fuel filter on after the first meltdown. maybe the timing is too advanced on it?

I have no doubt FARR-OFFROAD makes good stuff. the piston was a perfect fit for the cylinder, and the hone job looked great.

just don't want to melt another one.


Well my question on the timing would be ------- the thing ran fine before right ??
So how come all of a sudden you melted it down ??
How could the timing have changed itself ??
It's possible timing is off but how did that happen ??


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PostPosted: Sat Feb 03, 2018 5:00 pm 
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Location: Hope, B.C Canada
Your going to have to do a complete check list I think.
1) timing
2) fuel pump flow
3) jetting
4) float levels
5) air leaks
6) rusty gas tank and pickup lines ??
Avgas


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PostPosted: Sat Feb 03, 2018 5:06 pm 
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canadian oddy wrote:
Your going to have to do a complete check list I think.
1) timing
2) fuel pump flow
3) jetting
4) float levels
5) air leaks
6) rusty gas tank and pickup lines ??
Avgas



well it only had about 4 hours on it before the meltdown the first time. Then only about 2 hours again before the second piston melted. maybe riding style? I really don't know.

1. I will definitely check the timing first.
2. will then fuel pump.
3. jetting is good, i can set it to run rich (which i did).
4. no floats (it has marine carbs on it).
5. checked for air leaks with carb cleaner.
6. gas tank look really good inside. but i will replace all the fuel lines.

I was checking around and at 150 is should be able to run on pump gas. it has to be either number 1 or 2, or both.


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PostPosted: Sat Feb 03, 2018 5:10 pm 
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Specter wrote:
canadian oddy wrote:
Your going to have to do a complete check list I think.
1) timing
2) fuel pump flow
3) jetting
4) float levels
5) air leaks
6) rusty gas tank and pickup lines ??
Avgas



well it only had about 4 hours on it before the meltdown the first time. Then only about 2 hours again before the second piston melted. maybe riding style? I really don't know.

1. I will definitely check the timing first.
2. will then fuel pump.
3. jetting is good, i can set it to run rich (which i did).
4. no floats (it has marine carbs on it).
5. checked for air leaks with carb cleaner.
6. gas tank look really good inside. but i will replace all the fuel lines.

I was checking around and at 150 is should be able to run on pump gas. it has to be either number 1 or 2, or both.


Not so fast.
You said you checked for leaks with carb cleaner ---- give it up. I got no faith in that.
You need a test rig.


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PostPosted: Sat Feb 03, 2018 5:11 pm 
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Location: Hope, B.C Canada
viewtopic.php?f=1&t=13570&hilit=max+compression+on+pump+gas


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PostPosted: Sat Feb 03, 2018 5:36 pm 
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canadian oddy wrote:
http://www.pilotodyssey.com/PO/viewtopic.php?f=1&t=13570&hilit=max+compression+on+pump+gas



very good info. 165psi and below on pump gas. that 180 was going to be a problem, advanced timing or not.


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PostPosted: Sat Feb 03, 2018 5:37 pm 
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Location: cleveland oh
Got a couple questions

1. You bought the buggy with the Engine already installed and running? Did you change elevations from the previous owner?

If so, jetting changes may be required


2. You saw bubbles in your fuel line?

That's a major problem you need to resolve. You have a poor connection somewhere and are sucking air into the fuel.


3. You're running marine carbs? What carbs are you you using? Do they have internal fuel pumps? Or do they use an external pump?

Some carbs use an internal filter that may be clogged as well.

4. Have you checked the pop off pressure of the carb and.or carbs? Are they equal if using 2 carb set up?

5. Why do you say your jetting is good? Not trying to be a dick, but 2 melted pistons in a matter of 6 hours tells me differently.

Not sure if you're aware, but fuel actually helps to cool the piston crown. When you have a lack of fuel, it creates more heat that the piston can handle and it starts to melt


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PostPosted: Sat Feb 03, 2018 5:45 pm 
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xlint89 wrote:
Got a couple questions

1. You bought the buggy with the Engine already installed and running? Did you change elevations from the previous owner?

If so, jetting changes may be required


2. You saw bubbles in your fuel line?

That's a major problem you need to resolve. You have a poor connection somewhere and are sucking air into the fuel.


3. You're running marine carbs? What carbs are you you using? Do they have internal fuel pumps? Or do they use an external pump?

Some carbs use an internal filter that may be clogged as well.

4. Have you checked the pop off pressure of the carb and.or carbs? Are they equal if using 2 carb set up?

5. Why do you say your jetting is good? Not trying to be a dick, but 2 melted pistons in a matter of 6 hours tells me differently.

Not sure if you're aware, but fuel actually helps to cool the piston crown. When you have a lack of fuel, it creates more heat that the piston can handle and it starts to melt


1. no change in elevation.
2. checked the fuel pump and there were no leaks. found tons of people with the same issue of bubbles in the fuel line that never had a problem.
3. There is one fuel pump that feeds both carbs. everything in the carbs was rebuilt after the first piston melted. There were no more bubbles.
4. nope
5. plugs were black, tested after idle and wide open. before i adjusted the high and low mixture settings they were light brown. Kind of being a dick (i know they melted, obviously). there is more than one way to melt a piston.


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PostPosted: Sat Feb 03, 2018 5:47 pm 
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Specter wrote:
well it only had about 4 hours on it before the meltdown the first time. Then only about 2 hours again before the second piston melted. maybe riding style? I really don't know.

1. I will definitely check the timing first.
2. will then fuel pump.
3. jetting is good, i can set it to run rich (which i did).
4. no floats (it has marine carbs on it).
5. checked for air leaks with carb cleaner.
6. gas tank look really good inside. but i will replace all the fuel lines.

I was checking around and at 150 is should be able to run on pump gas. it has to be either number 1 or 2, or both.


You were checking around and at 150 should be able to run pump gas ------ well your not getting 150. You said one cylinder was showing 180 psi. Not good for pump gas.
I am a great fan of Avgas as you probably have already noticed. The hotter your Engine runs the more dangerous it is for running pump fuel. There are endless threads on this site about melted engines -- endless. The problem with an oddy is that the Engine is behind the seat and it is air cooled. That's why almost everyone melts an oddy air cooled Engine. An oddy Engine must be in perfect condition, jetting must be perfect, fuel flow must be perfect and the weather must be perfect or poofkaboom. Way to many things that have to be perfect for a ride to be successful. You are running a rotax which is liquid cooled so that would not be an issue here, but the high compression is (180). The other issue that has happened several times on this site is that guys find out that their compression tester is crap. Are you sure your unit is good ?? It MUST be checked against another compression tester for accuracy. Trust me. I have two compression testers. One Chinese and one American. The Chinese unit is out by ten pounds. I also checked both against my compressor gauge.


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PostPosted: Sat Feb 03, 2018 5:55 pm 
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canadian oddy wrote:
Specter wrote:
well it only had about 4 hours on it before the meltdown the first time. Then only about 2 hours again before the second piston melted. maybe riding style? I really don't know.

1. I will definitely check the timing first.
2. will then fuel pump.
3. jetting is good, i can set it to run rich (which i did).
4. no floats (it has marine carbs on it).
5. checked for air leaks with carb cleaner.
6. gas tank look really good inside. but i will replace all the fuel lines.

I was checking around and at 150 is should be able to run on pump gas. it has to be either number 1 or 2, or both.


You were checking around and at 150 should be able to run pump gas ------ well your not getting 150. You said one cylinder was showing 180 psi. Not good for pump gas.
I am a great fan of Avgas as you probably have already noticed. The hotter your Engine runs the more dangerous it is for running pump fuel. There are endless threads on this site about melted engines -- endless. The problem with an oddy is that the Engine is behind the seat and it is air cooled. That's why almost everyone melts an oddy air cooled Engine. An oddy Engine must be in perfect condition, jetting must be perfect, fuel flow must be perfect and the weather must be perfect or poofkaboom. Way to many things that have to be perfect for a ride to be successful. You are running a rotax which is liquid cooled so that would not be an issue here, but the high compression is (180). The other issue that has happened several times on this site is that guys find out that their compression tester is crap. Are you sure your unit is good ?? It MUST be checked against another compression tester for accuracy. Trust me. I have two compression testers. One Chinese and one American. The Chinese unit is out by ten pounds. I also checked both against my compressor gauge.


I did test the compression gauge against the gauge on my compressor. it was spot on. I figured it would be way off since it was a cheap Chinese gauge.

I don't think the Engine was supposed to be at 180. no idea why it was so high. maybe it was a wrong piston. I have no idea. I assumed that the Engine was ready to go since it was a drop in.

It's simple. i have a farr-offroad Engine and carburetors. it is a drop in kit that is designed to run on pump gas. I ran pump gas and melted a piston. Had no idea why it happened. I assumed it was from running too lean. now it seems the timing was too advanced as well.

I just want to ride my pilot that has a new Engine in it. is that so much to ask.


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