OS 33GT Gasoline Engine for Pattern
07-04-2015, 03:25 AM
#476
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What would you change with my baffling? Was only in the upper 70's.
This is weird. The more I think about it the more confused I become. This plane has prob close to 350 flights on it. If its a heating problem, I would think it would of showed up long ago.
What about the pipe and header. Could that change things? I'm running a little longer header than Matt which has retarded the power output by a couple hundred rpm.
This is weird. The more I think about it the more confused I become. This plane has prob close to 350 flights on it. If its a heating problem, I would think it would of showed up long ago.
What about the pipe and header. Could that change things? I'm running a little longer header than Matt which has retarded the power output by a couple hundred rpm.
Last edited by rm; 07-04-2015 at 03:52 AM.
07-04-2015, 03:47 AM
#477
Hey rm,
I wasn't suggesting that your baffling is inadequate. That temp. should be OK as well.
I would say that the metal came from around the plug thread.
Thinking about it some more, it looks to me like a result of detonation or too high compression ratio. Could be a result of incorrect pipe length??
Most likely your set up as you have had 2 that ended the same way.
Cheers
I wasn't suggesting that your baffling is inadequate. That temp. should be OK as well.
I would say that the metal came from around the plug thread.
Thinking about it some more, it looks to me like a result of detonation or too high compression ratio. Could be a result of incorrect pipe length??
Most likely your set up as you have had 2 that ended the same way.
Cheers
07-04-2015, 04:11 AM
#479
do
The common denominator here is the unusual erosion around the plug thread. I'm guessing if the C clip hadn't let go in the first engine, then the same thing would have happened. Just a matter of timing.
Still looks to me like detonation, which would be strange on the first engine when using the Hatori muffler. Detonation will destroy an engine.
The only other thing that I can think of, is too high compression, which could affect a tuned pipe and muffler set up.
Maybe fit a head shim and pull the head say, every 70 flights and inspect.
I maybe barking up the wrong tree, but that's what I would do if it were mine. Matt has more experience, so may be able to provide some advice.
Still looks to me like detonation, which would be strange on the first engine when using the Hatori muffler. Detonation will destroy an engine.
The only other thing that I can think of, is too high compression, which could affect a tuned pipe and muffler set up.
Maybe fit a head shim and pull the head say, every 70 flights and inspect.
I maybe barking up the wrong tree, but that's what I would do if it were mine. Matt has more experience, so may be able to provide some advice.
Last edited by drac1; 07-04-2015 at 04:39 AM.
07-04-2015, 05:28 AM
#480
Senior Member
Thread Starter
The KM unit was intended for the YS but works fine on all IC engines. I notice no performance loss but then again I haven't actually measured if a difference in rpm exists. Just from feel in the air, no difference except ever so slightly mellower exhaust note. My little gizmo produces similar results.
BTW can anyone open the attachments in my posts? I can't for whatever reason. These originally posted properly and then RCU put in attachment links which don't open for me. Weird
BTW can anyone open the attachments in my posts? I can't for whatever reason. These originally posted properly and then RCU put in attachment links which don't open for me. Weird
07-04-2015, 05:39 AM
#481
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Thread Starter
What would you change with my baffling? Was only in the upper 70's.
This is weird. The more I think about it the more confused I become. This plane has prob close to 350 flights on it. If its a heating problem, I would think it would of showed up long ago.
What about the pipe and header. Could that change things? I'm running a little longer header than Matt which has retarded the power output by a couple hundred rpm.
This is weird. The more I think about it the more confused I become. This plane has prob close to 350 flights on it. If its a heating problem, I would think it would of showed up long ago.
What about the pipe and header. Could that change things? I'm running a little longer header than Matt which has retarded the power output by a couple hundred rpm.
I've played with header length some and doubt there's anything wrong there.
The needles are plenty fat especially the LS. I've run 2 of these engines so far and both sets of needles were set-up just about the same.
For what its worth, the heads on mine look the same. It doesn't look to me that anything came off the head. Threads look as they do due to the angle of the cut.
It probably would not hurt to send it in to Hobby Services and see what they can do for you. As meticulous as we are with our Pattern engines I believe there was something wrong with the engine. I agree its very strange to have 100+ runs and now it decides to take a dump.
07-04-2015, 05:53 AM
#482
RM the baffling looks fine. It's similar to mine. The best you can do is to bring it as close to the fins without hitting them as you can. In weedwackers, the baffle is touching the fins in some models. Nothing wrong there.
I've played with header length some and doubt there's anything wrong there.
The needles are plenty fat especially the LS. I've run 2 of these engines so far and both sets of needles were set-up just about the same.
For what its worth, the heads on mine look the same. It doesn't look to me that anything came off the head. Threads look as they do due to the angle of the cut.
It probably would not hurt to send it in to Hobby Services and see what they can do for you. As meticulous as we are with our Pattern engines I believe there was something wrong with the engine. I agree its very strange to have 100+ runs and now it decides to take a dump.
I've played with header length some and doubt there's anything wrong there.
The needles are plenty fat especially the LS. I've run 2 of these engines so far and both sets of needles were set-up just about the same.
For what its worth, the heads on mine look the same. It doesn't look to me that anything came off the head. Threads look as they do due to the angle of the cut.
It probably would not hurt to send it in to Hobby Services and see what they can do for you. As meticulous as we are with our Pattern engines I believe there was something wrong with the engine. I agree its very strange to have 100+ runs and now it decides to take a dump.
I wouldn't expect to see that kind of pitting in the head and piston if all was OK.
Hopefully it won't be too long before I get mine set up.
07-04-2015, 06:32 AM
#483
Senior Member
Thread Starter
Scott you may want to take the heads off yours to see. The appearance of the plug threads is normal.
I reloaded the photos and this time it seems okay
I reloaded the photos and this time it seems okay
Last edited by MTK; 07-04-2015 at 06:44 AM.
07-04-2015, 08:36 AM
#484
Looks like classic detonation. On automobiles, too much timing or too low fuel octane will cause molten fragments to depart the piston and score the cylinder wall. If the ring was seized that was because of extreme heat. Look closely at the spark plug for silver deposits. That would confirm detonation. Maybe 100LL avgas or 93 octane auto fuel would have helped prevent this. If no avgas is available, mix auto fuel with 25% 110LL octane gas from a speed shop or 1/4 mile race track. That should raise the octane enough to prevent detonation. Perhaps the factory set ignition timing is off?...
07-04-2015, 04:50 PM
#487
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Spent some time going over the different parts. The cylinder heads look strange, but I think Matts right. The threads are all in tact and it doesn't look like metal has actually broken away from it.
Bearings are smooth, they're not the problem, plus there's no debree at all in the crankcase area. All the carnage is on the side and top of the piston.
Using a magnifying glass I can see where small pieces of metal are missing off the top corners of the piston. That's where it had to come from.
Back when I was running the new OS glow plug on this motor I did remove the sensor from the motor. Reinstalled it when I went back to the iginition and played with it's postion when I was running the motor on my test stand setting up the tuned pipe. That was 28 flights ago. So, I must have screwed it up by throwing the timing off, but in my defense it ran so good on the test stand and showed no signs of detonating. It was actually running really well the last couple days and also right before it failed.
I've been running 90 octane ethanol free gas in it since new.
Bearings are smooth, they're not the problem, plus there's no debree at all in the crankcase area. All the carnage is on the side and top of the piston.
Using a magnifying glass I can see where small pieces of metal are missing off the top corners of the piston. That's where it had to come from.
Back when I was running the new OS glow plug on this motor I did remove the sensor from the motor. Reinstalled it when I went back to the iginition and played with it's postion when I was running the motor on my test stand setting up the tuned pipe. That was 28 flights ago. So, I must have screwed it up by throwing the timing off, but in my defense it ran so good on the test stand and showed no signs of detonating. It was actually running really well the last couple days and also right before it failed.
I've been running 90 octane ethanol free gas in it since new.
07-04-2015, 04:50 PM
#488
Looks like classic detonation. On automobiles, too much timing or too low fuel octane will cause molten fragments to depart the piston and score the cylinder wall. If the ring was seized that was because of extreme heat. Look closely at the spark plug for silver deposits. That would confirm detonation. Maybe 100LL avgas or 93 octane auto fuel would have helped prevent this. If no avgas is available, mix auto fuel with 25% 110LL octane gas from a speed shop or 1/4 mile race track. That should raise the octane enough to prevent detonation. Perhaps the factory set ignition timing is off?...
07-04-2015, 04:56 PM
#490
Spent some time going over the different parts. The cylinder heads look strange, but I think Matts right. The threads are all in tact and it doesn't look like metal has actually broken away from it.
Bearings are smooth, they're not the problem, plus there's no debree at all in the crankcase area. All the carnage is on the side and top of the piston.
Using a magnifying glass I can see where small pieces of metal are missing off the top corners of the piston. That's where it had to come from.
Back when I was running the new OS glow plug on this motor I did remove the sensor from the motor. Reinstalled it when I went back to the iginition and played with it's postion when I was running the motor on my test stand setting up the tuned pipe. That was 28 flights ago. So, I must have screwed it up by throwing the timing off, but in my defense it ran so good on the test stand and showed no signs of detonating. It was actually running really well the last couple days and also right before it failed.
I've been running 90 octane ethanol free gas in it since new.
Bearings are smooth, they're not the problem, plus there's no debree at all in the crankcase area. All the carnage is on the side and top of the piston.
Using a magnifying glass I can see where small pieces of metal are missing off the top corners of the piston. That's where it had to come from.
Back when I was running the new OS glow plug on this motor I did remove the sensor from the motor. Reinstalled it when I went back to the iginition and played with it's postion when I was running the motor on my test stand setting up the tuned pipe. That was 28 flights ago. So, I must have screwed it up by throwing the timing off, but in my defense it ran so good on the test stand and showed no signs of detonating. It was actually running really well the last couple days and also right before it failed.
I've been running 90 octane ethanol free gas in it since new.
That would cause detonation. Sometimes detonation can be hard to pick.
07-04-2015, 05:29 PM
#491
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I AGREE that the damage looks very similar to a failed bearing. I had a few bearing cages fail and most or all of the damage is found in the piston, sleeve and head. Seems like a fair amount of metal bits were distributed in the top of the engine. Finding the source will definitely help determine the cause. Can anybody provide some photos of the same areas of a new, unrun engine for comparison. What does the plug look like? It seems inconsistent that the timing could be off enough to cause that kind of damage and still have the engine run as well as you indicate. Please keep us informed of further discoveries.
07-04-2015, 05:41 PM
#492
The bad thing about detonation is that it is aggravated by high temperature and high loads. On a cool day, you may be fine. Second, you may never hear it. Even 2 to 3 degrees too much timing advance can cause detonation (pre-ignition) damage. I'll put money on the timing was too advanced when the OP re-installed the pick-up.
Last edited by big_G; 07-04-2015 at 05:43 PM.
07-04-2015, 06:54 PM
#496
The bad thing about detonation is that it is aggravated by high temperature and high loads. On a cool day, you may be fine. Second, you may never hear it. Even 2 to 3 degrees too much timing advance can cause detonation (pre-ignition) damage. I'll put money on the timing was too advanced when the OP re-installed the pick-up.
07-04-2015, 07:54 PM
#498
Senior Member
Thread Starter
If the bearings feel smooth and shaft runs free, I find it hard to believe that the bearings lost a cage. But stranger things happen. HP Ultra is excellent oil so I doubt it was a lack of oil that caused dry running and destruction. The oil is designed for 50:1 mix and fatter so the mix was probably fine.
I also don't think there is enough room available on the sensor mount to drive ignition so far advanced that it caused detonation. I haven't played with ignition timing much personally so I can't speak from experience. I've read stuff from a couple long timers that timing can vary between 25 and 30 degrees and still work fine. After all we are running these engines at 7-8K not 14-15K ( don't think it could get there regardless).
Perplexing problem. Could something have let go on the intake side?
07-04-2015, 09:17 PM
#500
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The plug looks good. Actually it's prob the best looking plug I've had in a while. I tend to run somewhat rich and end up carboning the plug. This one has nice color, no carbon, very clean.
Carb looks good and intact. Nothing missing that pops out at me. Haven't found any missing bolts or anything yet.
Carb looks good and intact. Nothing missing that pops out at me. Haven't found any missing bolts or anything yet.
