OS 12TZ
11-19-2006, 01:01 PM
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OS 12TZ
I purchased an OS 12TZ from Tower Hobies a week ago. The motor was carefully run in usin Rocket Science 20%. When run in the fuel was swapped to 30% nitro. At all times a close monitor of the head temperature was taken. During run in the temperature was never higher than 185°C. When run in and at the track the temperature was kept to about 220°C. After 2 runs the supplied plug had blown. This was replaced with a No.7 plug. Again the plug blew. At this point I decided to add a 0.005" head gasket. Getting the button out of the head was hard, however I then noticed that both the insert on piston had severe pitting. I finished the day using another motor. When I got home I removed the back plate and discovered the problem.
The fit of the con rod to crank pin has a terrible amount of slop. Please see the photo.
Thank you for your help,
Nick Marson
The fit of the con rod to crank pin has a terrible amount of slop. Please see the photo.
Thank you for your help,
Nick Marson
11-20-2006, 12:08 PM
#3
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RE: OS 12TZ
The damage to the connecting rod looks like the engine's just not been run properly. What is the oil content of the fuel you're using? What procedure are you using to break in your engine? How is it being run?
If you rely on temperatures to set your engine, then you've found a likely cause. We do not use temps AT ALL to get an engine set. We go by sound and performance. Temps are only good as a reference once you have found the correct setting. Over-reliance on engine temperature for setting your engine is a sure way to guarantee shortened engine life.
If you rely on temperatures to set your engine, then you've found a likely cause. We do not use temps AT ALL to get an engine set. We go by sound and performance. Temps are only good as a reference once you have found the correct setting. Over-reliance on engine temperature for setting your engine is a sure way to guarantee shortened engine life.
11-20-2006, 03:50 PM
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RE: OS 12TZ
Dear Mr. Baxter,
Thank you for your prompt reply!
I have no idea what the oil content of Rocket Science fuel is, I would hasten to add that I use it exclusively, as do most of the people at our track. I am not aware of anyone having a problem with this fuel.
I used six tanks of 20% Rocket Science to run the motor in. It was run-in in the car, the first tank was fairly rich, the motor had smoke coming from the exhaust and was audibly 4 stroking. The mixture was leaned to the point that the glow igniter could be removed. The throttle was gently increased and decreased on the first run. By the forth tank the motor was just breaking into a 2 stroke as the throttle was increased. For the next 2 runs the mixture was leaned, and the temperature monitored. This never exceeded 185°F. No adjustment was made to the idle at this time, the factory setting appeared OK. When the fuel was changed to 30% Rocket Science the main needle was backed off 3/4 a turn. This gave a rich, 4 stroke, run. The main needle was turned in 30° at a time until a reasonable performance was obtained. The temperature was observed at 200°F. Between runs the engine was allowed to cool down for about 20 minutes.
The car was then taken to the car track, this is when the plugs started to blow. As another indication the car was only making a 4.5 minute run. With my Nova Rossi I get in excess of 6 minutes. It should be noted that this was on the same bottle of fuel.
The tone of your reply assumes that you are conversing with someone who is either very young or new to the hobby.
I can assure you that in my case neither is true. I have been aero modeling for 50 years, and racing model cars since the late 70's. In addition to this I have a degree in engineering. I have several OS motor, of note is an OS 40FSR which is in regular use in my wife’s trainer. This motor was purchased in 1984. I also have 2 OS 70 four stokes, that are in regular service, these were bought in 1989.
I have had many car engines and my run in process has always been a success. I am expecting that when you receive the motor you will be able to confirm that the crank pin is under size, or the big-end is oversize, or even the oil hole in the rod is missing.
I trust that there is some point in returning the engine? The tone of your reply would imply the opposite,
Thanks Nick Marson
Thank you for your prompt reply!
I have no idea what the oil content of Rocket Science fuel is, I would hasten to add that I use it exclusively, as do most of the people at our track. I am not aware of anyone having a problem with this fuel.
I used six tanks of 20% Rocket Science to run the motor in. It was run-in in the car, the first tank was fairly rich, the motor had smoke coming from the exhaust and was audibly 4 stroking. The mixture was leaned to the point that the glow igniter could be removed. The throttle was gently increased and decreased on the first run. By the forth tank the motor was just breaking into a 2 stroke as the throttle was increased. For the next 2 runs the mixture was leaned, and the temperature monitored. This never exceeded 185°F. No adjustment was made to the idle at this time, the factory setting appeared OK. When the fuel was changed to 30% Rocket Science the main needle was backed off 3/4 a turn. This gave a rich, 4 stroke, run. The main needle was turned in 30° at a time until a reasonable performance was obtained. The temperature was observed at 200°F. Between runs the engine was allowed to cool down for about 20 minutes.
The car was then taken to the car track, this is when the plugs started to blow. As another indication the car was only making a 4.5 minute run. With my Nova Rossi I get in excess of 6 minutes. It should be noted that this was on the same bottle of fuel.
The tone of your reply assumes that you are conversing with someone who is either very young or new to the hobby.
I can assure you that in my case neither is true. I have been aero modeling for 50 years, and racing model cars since the late 70's. In addition to this I have a degree in engineering. I have several OS motor, of note is an OS 40FSR which is in regular use in my wife’s trainer. This motor was purchased in 1984. I also have 2 OS 70 four stokes, that are in regular service, these were bought in 1989.
I have had many car engines and my run in process has always been a success. I am expecting that when you receive the motor you will be able to confirm that the crank pin is under size, or the big-end is oversize, or even the oil hole in the rod is missing.
I trust that there is some point in returning the engine? The tone of your reply would imply the opposite,
Thanks Nick Marson
