Jett "sport" ABC engines.
10-14-2004, 02:04 PM
#1
Jett "sport" ABC engines.
Bob,
....I was wondering if the Jett line of ABC sport engines can be damaged by richening
the mixture, until the engine "four-strokes" ? There were some theories about that
awhile back. I have always used the four-stroking method of cool-down for about
10 seconds, when I break-in ABC or ringed engines....right after a full peak run, and
right before I shut the engine down.
FBD.
....I was wondering if the Jett line of ABC sport engines can be damaged by richening
the mixture, until the engine "four-strokes" ? There were some theories about that
awhile back. I have always used the four-stroking method of cool-down for about
10 seconds, when I break-in ABC or ringed engines....right after a full peak run, and
right before I shut the engine down.
FBD.
10-14-2004, 02:53 PM
#2
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RE: Jett "sport" ABC engines.
Hi Dave.....
Thanks for writing.
Actually, this is a common question, and a few folks have different views on it. Here is the way I look at it.
Let me start with this. With the exception of the RO-JETT stunt engines, you do not really want to run the Sport-Jett engines for a substantial amount of time in a 4-cycle, realllllllly rich mode. Infact, they simply will not run that way...so it does not tend to be a problem
Slightly rich (400-1000 rpm down from peak) is where you would prefer to set them for flight. Some more information......
Shutting down by first cooling the engine with a rich mixture...... is not a whole lot different than choking the engine off. We use flood-off using the airvalve on the Q-500 engines. It avoids a temperature spike that tends to occure with a pinch-off system. For a while, a few of us ran the throttlebody airvalve carbs in QM for the same reason.
On the racing engines, when test running, if we find we get the engine over-lean and it gets hot, we typically ritchen the engine up a bit so it just stays running, and after it cools off a bit we can try to find the peak rpm again.
This is not something you typically want to do over and over again with an ABC or AAC engine, but it will not hurt it.
For engine break-in, there are instructions on the jettengineering.com web site that covers the proceedure we recommend.
The engine does have to be run at near operating temperature and RPM for the best possible break-in, without damage to the engine. On a new engine, it helps to get up to that temperature fairly quickly.
Although this is only slightly related to your question, this may help shed some light on the subject...
Break-in - Basically, install a 1" less diameter prop than recommended (or will be used)....... start the engine with the needle about 4 turns out (rich), take the engine to full throttle. It will be rich ... probably a dirty 2 cycle in this case rather than a fat 4 cycle...but still pretty rich. Lean the engine until you can remove the glow battery, then turn the needle in until the engine reaches the RPM we specify for the engine (where it will typically run). The engine will get up to temperature and RPM at the same time, but it will not be over-loaded... and it will be slightly rich. After a few bench runs, when you note the RPM start to climb slightly at that same needle setting, its time to install the flight prop and complete a couple of more runs. It is then ready to confirm the low end setting and transition, and then ready to fly.
For break-in....yes... it is essential to get the engine up to its approximate operating temperature for the majorty of those runs. This helps optimize the fit and seal at high power. Extended break-in cold can cause improper fitting of the pistion and sleeve.....and in some cases can damage the engine. However, its not essential that the engine remain at one temperature thoughout an engine run. That is simply not practicle... we have a throttle varying fuel flow, air, and thus RPM and temperature.
For shut down, on a test run especially where I was approaching peak rpm, I do what you noted. I back the needle out a bit until the engine sounds fat... let it run there for a few seconds, and then pinch off the fuel line to shut it down. This is the proceedure used for the QM engine test runs (on the plane and on the stand). I also do this on occation with the sport engines when I am putting them away for a while. A short period of rich operation will do no harm to the engine.
With the sport-jett engines, you really do not have to go through the "rich" proceedure for a cool shut down as we tend to with the racing engine. Pulling the carb back into low power or idle allows the engine to cool off considerably. If there were going to be any significant ill-effects of running "cool", there would be few ABC engines that would run in midrange or at idle without. A properly design ABC/AAC engine is designed so the piston/sleeve fit follows the temperature of the engine through its normal operating range, and the crankcase and fins help tranfer heat evenly from the internals.
I hope this is helpful
Bob
Thanks for writing.
Actually, this is a common question, and a few folks have different views on it. Here is the way I look at it.
Let me start with this. With the exception of the RO-JETT stunt engines, you do not really want to run the Sport-Jett engines for a substantial amount of time in a 4-cycle, realllllllly rich mode. Infact, they simply will not run that way...so it does not tend to be a problem
Slightly rich (400-1000 rpm down from peak) is where you would prefer to set them for flight. Some more information......Shutting down by first cooling the engine with a rich mixture...... is not a whole lot different than choking the engine off. We use flood-off using the airvalve on the Q-500 engines. It avoids a temperature spike that tends to occure with a pinch-off system. For a while, a few of us ran the throttlebody airvalve carbs in QM for the same reason.
On the racing engines, when test running, if we find we get the engine over-lean and it gets hot, we typically ritchen the engine up a bit so it just stays running, and after it cools off a bit we can try to find the peak rpm again.
This is not something you typically want to do over and over again with an ABC or AAC engine, but it will not hurt it.
For engine break-in, there are instructions on the jettengineering.com web site that covers the proceedure we recommend.
The engine does have to be run at near operating temperature and RPM for the best possible break-in, without damage to the engine. On a new engine, it helps to get up to that temperature fairly quickly.
Although this is only slightly related to your question, this may help shed some light on the subject...
Break-in - Basically, install a 1" less diameter prop than recommended (or will be used)....... start the engine with the needle about 4 turns out (rich), take the engine to full throttle. It will be rich ... probably a dirty 2 cycle in this case rather than a fat 4 cycle...but still pretty rich. Lean the engine until you can remove the glow battery, then turn the needle in until the engine reaches the RPM we specify for the engine (where it will typically run). The engine will get up to temperature and RPM at the same time, but it will not be over-loaded... and it will be slightly rich. After a few bench runs, when you note the RPM start to climb slightly at that same needle setting, its time to install the flight prop and complete a couple of more runs. It is then ready to confirm the low end setting and transition, and then ready to fly.
For break-in....yes... it is essential to get the engine up to its approximate operating temperature for the majorty of those runs. This helps optimize the fit and seal at high power. Extended break-in cold can cause improper fitting of the pistion and sleeve.....and in some cases can damage the engine. However, its not essential that the engine remain at one temperature thoughout an engine run. That is simply not practicle... we have a throttle varying fuel flow, air, and thus RPM and temperature.
For shut down, on a test run especially where I was approaching peak rpm, I do what you noted. I back the needle out a bit until the engine sounds fat... let it run there for a few seconds, and then pinch off the fuel line to shut it down. This is the proceedure used for the QM engine test runs (on the plane and on the stand). I also do this on occation with the sport engines when I am putting them away for a while. A short period of rich operation will do no harm to the engine.
With the sport-jett engines, you really do not have to go through the "rich" proceedure for a cool shut down as we tend to with the racing engine. Pulling the carb back into low power or idle allows the engine to cool off considerably. If there were going to be any significant ill-effects of running "cool", there would be few ABC engines that would run in midrange or at idle without. A properly design ABC/AAC engine is designed so the piston/sleeve fit follows the temperature of the engine through its normal operating range, and the crankcase and fins help tranfer heat evenly from the internals.
I hope this is helpful
Bob
10-17-2004, 07:08 AM
#3
RE: Jett "sport" ABC engines.
Bob....
....thanks for the answer.
What is the difference with the CL engines that
spend their whole lives at a four cycle, without harm? Most of my engines
are ringed, so I really don't have a problem.
I use different care and feeding techniques on my ABC engines, mainly Rossi
and the Tower .75's. I pre-oil with castor, and pre-heat the top ends prior to
initial start-up....to ease the strain on the rods.
I don't recall off-hand....ever richening an ABC engine until it actually four stroked
because you can get a really fat (rich) setting for cool down, without ever
4-stroking the motor. I was wondering however, if you had personally seen
an engine damaged from running it too rich....or is that an Internet "Old Wives
Tale"....in your opinion.
Dave.
....thanks for the answer.
What is the difference with the CL engines thatspend their whole lives at a four cycle, without harm? Most of my engines
are ringed, so I really don't have a problem.
I use different care and feeding techniques on my ABC engines, mainly Rossi
and the Tower .75's. I pre-oil with castor, and pre-heat the top ends prior to
initial start-up....to ease the strain on the rods.
I don't recall off-hand....ever richening an ABC engine until it actually four stroked
because you can get a really fat (rich) setting for cool down, without ever
4-stroking the motor. I was wondering however, if you had personally seen
an engine damaged from running it too rich....or is that an Internet "Old Wives
Tale"....in your opinion.
Dave.
10-18-2004, 08:37 AM
#4
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RE: Jett "sport" ABC engines.
Good questions on the 2-4 cycle control line engines... I will get to that in a moment...
Yes, I have seen an engine damaged. In one case, the rod bushings were damaged. The piston grows faster than the sleeve if the cylinder temperature is not adequate, and this will damage the piston, and can cause the running engine to actually 'force' this piston into position causing excess load on the rod, crankpin and wristpin. Something has to give. On a couple of import engines, the friction and over-tight fit caused cylinder plating to detach from the substrate... and in one of those cases it somewhat burnished the plating onto the piston which absolutely destroyed the engine. But in general, the big 'damage' is...... the engine will try its best to break-in running rich like that... and it may survive...... but it will always have to run like that and will not likely be capable of turning up much higher rpm.
The very first run on a tight engine is the most critical time. That is one reason Jett engines are all run at the shop before you ever receive it. That first start proceedure is somewhat tricky on a high output engine, and if not done properly the engine can and will be damaged. It makes more sense for Dub to take the "chance" of damaging or breaking the engine. Once he has put a couple of runs on the engine, he sets the low end mixture. He also confirms the performance, and every engine meets advertised rpm before it is shipped. So when you receive the engine, it has been pre-run to the point where you are at lower risk of damaging it. Follow his run-in proceedure at your end to complete the process, and the engine will serve you well for a long time to come.
The CL engines are unique beasts. Compression, timing and bore taper are a bit different that the RC engines. These engines live life on that 2-4 cycle break. Again, they are propped/tuned/broken in for a certain RPM and operating temperature... and they will tend to maintain that performance through the life of the engine. For CL stunt, consistant speed and consistant lap times are critical for presentation....so an engine the runs very consistantly is important. The special timing, correct prop choice, and a tuned exhaust all act as 'governors' of sorts achieving the desired results. Proper break-in is critcal to this as well. For some background on the recommended break-in proceedures for the CL stunt engines, [link=http://www.us-aero.com/Images/Descriptions/ROJBSERE065.shtml]take a look here[/link]
The Jett BSE 3-D engines are based off of the CL setups, which is why they perform best with bigger props at lower RPMs. However, they operate on a clean 2-cycle just as most other engines do.
Oddly enough..... the proceedures followed for ABC/AAC engines actually do fairly well for ringed engines too. Yes, you are trying to get proper wear and seating of a ring... but in most cases, you still want the engine up close to operating temperature and you will want the engine up as close to desired operationg RPM as possible during break-in. You would start off that first couple of 3-4 minute break-in runs with a very rich engine. After that, there is more value in keeping it running as a clean 2 cycle. By that 3rd tank of fuel, let the engine sing. Again..... break-in is done with less load (smaller prop) at desired rpm while still slightly rich. Older (1950-1970s engines) needed a longer sloppy break-in to seat cast iron piston/sleeve combinations. Only a few engines are built that way these days.
Yes, I have seen an engine damaged. In one case, the rod bushings were damaged. The piston grows faster than the sleeve if the cylinder temperature is not adequate, and this will damage the piston, and can cause the running engine to actually 'force' this piston into position causing excess load on the rod, crankpin and wristpin. Something has to give. On a couple of import engines, the friction and over-tight fit caused cylinder plating to detach from the substrate... and in one of those cases it somewhat burnished the plating onto the piston which absolutely destroyed the engine. But in general, the big 'damage' is...... the engine will try its best to break-in running rich like that... and it may survive...... but it will always have to run like that and will not likely be capable of turning up much higher rpm.
The very first run on a tight engine is the most critical time. That is one reason Jett engines are all run at the shop before you ever receive it. That first start proceedure is somewhat tricky on a high output engine, and if not done properly the engine can and will be damaged. It makes more sense for Dub to take the "chance" of damaging or breaking the engine. Once he has put a couple of runs on the engine, he sets the low end mixture. He also confirms the performance, and every engine meets advertised rpm before it is shipped. So when you receive the engine, it has been pre-run to the point where you are at lower risk of damaging it. Follow his run-in proceedure at your end to complete the process, and the engine will serve you well for a long time to come.
The CL engines are unique beasts. Compression, timing and bore taper are a bit different that the RC engines. These engines live life on that 2-4 cycle break. Again, they are propped/tuned/broken in for a certain RPM and operating temperature... and they will tend to maintain that performance through the life of the engine. For CL stunt, consistant speed and consistant lap times are critical for presentation....so an engine the runs very consistantly is important. The special timing, correct prop choice, and a tuned exhaust all act as 'governors' of sorts achieving the desired results. Proper break-in is critcal to this as well. For some background on the recommended break-in proceedures for the CL stunt engines, [link=http://www.us-aero.com/Images/Descriptions/ROJBSERE065.shtml]take a look here[/link]
The Jett BSE 3-D engines are based off of the CL setups, which is why they perform best with bigger props at lower RPMs. However, they operate on a clean 2-cycle just as most other engines do.
Oddly enough..... the proceedures followed for ABC/AAC engines actually do fairly well for ringed engines too. Yes, you are trying to get proper wear and seating of a ring... but in most cases, you still want the engine up close to operating temperature and you will want the engine up as close to desired operationg RPM as possible during break-in. You would start off that first couple of 3-4 minute break-in runs with a very rich engine. After that, there is more value in keeping it running as a clean 2 cycle. By that 3rd tank of fuel, let the engine sing. Again..... break-in is done with less load (smaller prop) at desired rpm while still slightly rich. Older (1950-1970s engines) needed a longer sloppy break-in to seat cast iron piston/sleeve combinations. Only a few engines are built that way these days.
