High temps during break-in
08-01-2016, 06:05 AM
#1
High temps during break-in
I'm getting back into the hobby after being out of the loop for about 7 years. I have a first generation Revo with a OS .18TM and a Trinity Pipe. The engine is brand new which I purchased several years ago. I believe I tried to break the engine in a few years back but never finished the process.
After spending some time and money getting the Revo fixed up with new bearings, battery, slipper clutch, clutch shoes etc I started to break the engine in yesterday. Before break-in I was unable to rotate the engine over so I took the back plate off and inside it looked good - no rust and even still had after run oil in it. I got a wrench and turned the engine over using the fly wheel. Now it rotates nicely and has a good pinch TDC. I'm guessing the engine was just sized up after sitting for so many years.
I pre-heated the engine with my heat gun to about 180 - 200 and it fired up first shot. The idle was high so I adjusted that down. I let it idle with the wheels off the ground for a bit then put it down and tired to slowly rev the engine up. The engine reved but the car did not move much. The temps were also getting high in the 270s. I shut the engine down and took a look. I tightened my slipper up and went ahead and reset all my carb adjustments back to stock. It was too lean I must have fiddled with the carb a few years back.
I fire it back up and it's moving much better now but the temps are still high. I used the HSN to richen up the mixture and this helped but my temps are still high. If I richen up my mixture anymore it's really hard to keep the engine from stalling. I'm getting a lot of smoke and fuel coming out of the exhaust. After 2 tanks of light running I've already burned up a glow plug. When it's sitting idle I'm getting temps in the 220 - 240s. If I do a few passes and take a measurement it jumps up to the 270s.
When giving it gas the engine does not hesitate and it appears to be making more and more power with each tank (I've done 4 tanks so far). If I let the engine idle it will shut off after about 15 seconds. I can keep the engine going by giving it a small blip.
What can I do to get my temps down or are my temps good? It was in the mid 80s here yesterday with medium humidity. I notice when I first start giving it gas maybe 18 / 1/4 throttle the car does not really move much. I'm not sure if I should tighten up my slipper some more or what - it seems pretty tight now. I'm lost as to why it's running kind of hot even being as rich as it is.
After each tank I've been setting the piston back to BDC and letting the engine cool down before going through another tank. I heat the block back up with a heat gun each time I fire it up after a cool down. During each tank I'm just doing figure 8's with a little more throttle each tank. I'd do a few 8's then stop and let it cool off a bit and take a temp reading them repeat.
Any suggestions would be greatly appreciated. Forgot how much I missed the smell and sound of Nitro.
After spending some time and money getting the Revo fixed up with new bearings, battery, slipper clutch, clutch shoes etc I started to break the engine in yesterday. Before break-in I was unable to rotate the engine over so I took the back plate off and inside it looked good - no rust and even still had after run oil in it. I got a wrench and turned the engine over using the fly wheel. Now it rotates nicely and has a good pinch TDC. I'm guessing the engine was just sized up after sitting for so many years.
I pre-heated the engine with my heat gun to about 180 - 200 and it fired up first shot. The idle was high so I adjusted that down. I let it idle with the wheels off the ground for a bit then put it down and tired to slowly rev the engine up. The engine reved but the car did not move much. The temps were also getting high in the 270s. I shut the engine down and took a look. I tightened my slipper up and went ahead and reset all my carb adjustments back to stock. It was too lean I must have fiddled with the carb a few years back.
I fire it back up and it's moving much better now but the temps are still high. I used the HSN to richen up the mixture and this helped but my temps are still high. If I richen up my mixture anymore it's really hard to keep the engine from stalling. I'm getting a lot of smoke and fuel coming out of the exhaust. After 2 tanks of light running I've already burned up a glow plug. When it's sitting idle I'm getting temps in the 220 - 240s. If I do a few passes and take a measurement it jumps up to the 270s.
When giving it gas the engine does not hesitate and it appears to be making more and more power with each tank (I've done 4 tanks so far). If I let the engine idle it will shut off after about 15 seconds. I can keep the engine going by giving it a small blip.
What can I do to get my temps down or are my temps good? It was in the mid 80s here yesterday with medium humidity. I notice when I first start giving it gas maybe 18 / 1/4 throttle the car does not really move much. I'm not sure if I should tighten up my slipper some more or what - it seems pretty tight now. I'm lost as to why it's running kind of hot even being as rich as it is.
After each tank I've been setting the piston back to BDC and letting the engine cool down before going through another tank. I heat the block back up with a heat gun each time I fire it up after a cool down. During each tank I'm just doing figure 8's with a little more throttle each tank. I'd do a few 8's then stop and let it cool off a bit and take a temp reading them repeat.
Any suggestions would be greatly appreciated. Forgot how much I missed the smell and sound of Nitro.
08-01-2016, 06:27 AM
#2
Join Date: Dec 2001
Location: Upplands Vasby, SWEDEN
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Hi!
All glow engines run at the temperarture they are supposed to run at as long as you set the high speed needle at a setting the engine likes!
And how do you know that the engines likes that setting?? Well, it runs and throttle well! Simple as that!
Temp meters is not used (necessary) when setting glow engines, at least not when we talk airplane engines (Both sport and competition). Whats important is that you learn to listen how your engine sounds when setting your engine.
All glow engines run at the temperarture they are supposed to run at as long as you set the high speed needle at a setting the engine likes!
And how do you know that the engines likes that setting?? Well, it runs and throttle well! Simple as that!
Temp meters is not used (necessary) when setting glow engines, at least not when we talk airplane engines (Both sport and competition). Whats important is that you learn to listen how your engine sounds when setting your engine.
08-01-2016, 06:27 AM
#3
For starters, you posted in the aircraft engine forum. Not a problem, but you'll get more advice from the car engine forum.
BUT, I will throw in my two cents. I've run cars for 18 years. Ideally you want your head temp to stay below 250-260F. If the engine temp rises when sitting at idle, your idle mixture is too lean. Richen it up 1/16-1/8 turn. If your temp goes down 1-2 degrees every couple seconds when at idle, your idle mix should be close to where you want it. If after a few WOT runs the temp spikes in the 260-270F range, your high speed is a big lean. Again, Richen it up a little bit. When the engine is still new and tight, it will run a bit warmer. Just run it a bit richer and all will be well. When the engine "drops its nuts" (considered "broken in") around the 1/2-1gal mark, it should run a bit cooler. I recommend using 20% nitro and 10-12% oil for best power and longevity. Higher oil fuel tends to make the engines run warmer and usually require a cooler plug. In general, the cylinder head temp should be used as a reference only and it's generally not a good idea to tune the engine to a specific temperature, however high temperatures generally indicate a lean mixture condition. If no amount of tuning will cool the engine off when running hard, check the driveline to ensure there is no binding.
BUT, I will throw in my two cents. I've run cars for 18 years. Ideally you want your head temp to stay below 250-260F. If the engine temp rises when sitting at idle, your idle mixture is too lean. Richen it up 1/16-1/8 turn. If your temp goes down 1-2 degrees every couple seconds when at idle, your idle mix should be close to where you want it. If after a few WOT runs the temp spikes in the 260-270F range, your high speed is a big lean. Again, Richen it up a little bit. When the engine is still new and tight, it will run a bit warmer. Just run it a bit richer and all will be well. When the engine "drops its nuts" (considered "broken in") around the 1/2-1gal mark, it should run a bit cooler. I recommend using 20% nitro and 10-12% oil for best power and longevity. Higher oil fuel tends to make the engines run warmer and usually require a cooler plug. In general, the cylinder head temp should be used as a reference only and it's generally not a good idea to tune the engine to a specific temperature, however high temperatures generally indicate a lean mixture condition. If no amount of tuning will cool the engine off when running hard, check the driveline to ensure there is no binding.
08-01-2016, 06:38 AM
#4
For starters, you posted in the aircraft engine forum. Not a problem, but you'll get more advice from the car engine forum.
BUT, I will throw in my two cents. I've run cars for 18 years. Ideally you want your head temp to stay below 250-260F. If the engine temp rises when sitting at idle, your idle mixture is too lean. Richen it up 1/16-1/8 turn. If your temp goes down 1-2 degrees every couple seconds when at idle, your idle mix should be close to where you want it. If after a few WOT runs the temp spikes in the 260-270F range, your high speed is a big lean. Again, Richen it up a little bit. When the engine is still new and tight, it will run a bit warmer. Just run it a bit richer and all will be well. When the engine "drops its nuts" (considered "broken in") around the 1/2-1gal mark, it should run a bit cooler. I recommend using 20% nitro and 10-12% oil for best power and longevity. Higher oil fuel tends to make the engines run warmer and usually require a cooler plug. In general, the cylinder head temp should be used as a reference only and it's generally not a good idea to tune the engine to a specific temperature, however high temperatures generally indicate a lean mixture condition. If no amount of tuning will cool the engine off when running hard, check the driveline to ensure there is no binding.
BUT, I will throw in my two cents. I've run cars for 18 years. Ideally you want your head temp to stay below 250-260F. If the engine temp rises when sitting at idle, your idle mixture is too lean. Richen it up 1/16-1/8 turn. If your temp goes down 1-2 degrees every couple seconds when at idle, your idle mix should be close to where you want it. If after a few WOT runs the temp spikes in the 260-270F range, your high speed is a big lean. Again, Richen it up a little bit. When the engine is still new and tight, it will run a bit warmer. Just run it a bit richer and all will be well. When the engine "drops its nuts" (considered "broken in") around the 1/2-1gal mark, it should run a bit cooler. I recommend using 20% nitro and 10-12% oil for best power and longevity. Higher oil fuel tends to make the engines run warmer and usually require a cooler plug. In general, the cylinder head temp should be used as a reference only and it's generally not a good idea to tune the engine to a specific temperature, however high temperatures generally indicate a lean mixture condition. If no amount of tuning will cool the engine off when running hard, check the driveline to ensure there is no binding.
So it sounds like I may just need to richen up my HSN. What about when the engine is sitting idle and it dies? Is this just something you need to deal with during break in since you need to run the engine a bit rich? It sounds like my temps are probably ok maybe a touch on the high side. Maybe another 1/8 turn is all I need.
Do you have any tips on checking the drive line for binding? Right now my gear mesh when you rotate the spur gear - rotates smoothly with no binding. What else should I check? This is the video I checked on to set my gear mesh. https://www.youtube.com/watch?v=ig-PNVIdePQ My mesh sounds pretty much the same as his.
08-01-2016, 07:07 AM
#5
Hi!
All glow engines run at the temperarture they are supposed to run at as long as you set the high speed needle at a setting the engine likes!
And how do you know that the engines likes that setting?? Well, it runs and throttle well! Simple as that!
Temp meters is not used (necessary) when setting glow engines, at least not when we talk airplane engines (Both sport and competition). Whats important is that you learn to listen how your engine sounds when setting your engine.
All glow engines run at the temperarture they are supposed to run at as long as you set the high speed needle at a setting the engine likes!
And how do you know that the engines likes that setting?? Well, it runs and throttle well! Simple as that!
Temp meters is not used (necessary) when setting glow engines, at least not when we talk airplane engines (Both sport and competition). Whats important is that you learn to listen how your engine sounds when setting your engine.
08-01-2016, 07:14 AM
#6
Just noticed the Nitro Engine forum under RC Car Engines - my bad. I can repost there.
So it sounds like I may just need to richen up my HSN. What about when the engine is sitting idle and it dies? Is this just something you need to deal with during break in since you need to run the engine a bit rich? It sounds like my temps are probably ok maybe a touch on the high side. Maybe another 1/8 turn is all I need.
Do you have any tips on checking the drive line for binding? Right now my gear mesh when you rotate the spur gear - rotates smoothly with no binding. What else should I check? This is the video I checked on to set my gear mesh. https://www.youtube.com/watch?v=ig-PNVIdePQ My mesh sounds pretty much the same as his.
So it sounds like I may just need to richen up my HSN. What about when the engine is sitting idle and it dies? Is this just something you need to deal with during break in since you need to run the engine a bit rich? It sounds like my temps are probably ok maybe a touch on the high side. Maybe another 1/8 turn is all I need.
Do you have any tips on checking the drive line for binding? Right now my gear mesh when you rotate the spur gear - rotates smoothly with no binding. What else should I check? This is the video I checked on to set my gear mesh. https://www.youtube.com/watch?v=ig-PNVIdePQ My mesh sounds pretty much the same as his.
Remember ers what I said - if the engine temperature rises at idle, the idle mixture is too lean. It should cool off when idling - roughly 1 degree every 1-2 seconds. If it doesn't cool down, Richen a little bit. Run a WOT pass and check it again. Keep going until it starts to cool off at idle. Run the top end rich enough that it doesn't get super hot after a few hard runs by doesn't run rough and rev slow and smokey. Some engines do just run hot, but 270 is too hot. Not hurting the engine (or at least it shouldn't), but it's not helping it either. My best running engines run about 220-230F after a long hard WOT pass on pavement. Running in grass will make the engine run hotter, so if you run in the grass a lot, set it a little richer.
08-01-2016, 07:23 AM
#7
Binding in the driveline can be bad bearings, bad clutchbell bearings, too tight of sour gear mesh, etc. If the truck can be given a push and it rolls for quite a distance on its own, there are probably no issues to deal with. Setting the spur gear mesh is easy to do - I use a piece of notebook paper between the clutch and spur gears. Slide the engine towards the spur until it's tight against the spur with the paper still between the gears. Tighten the engine mount screws back down and remove the paper. This should be nearly a perfect mesh setting.
Remember ers what I said - if the engine temperature rises at idle, the idle mixture is too lean. It should cool off when idling - roughly 1 degree every 1-2 seconds. If it doesn't cool down, Richen a little bit. Run a WOT pass and check it again. Keep going until it starts to cool off at idle. Run the top end rich enough that it doesn't get super hot after a few hard runs by doesn't run rough and rev slow and smokey. Some engines do just run hot, but 270 is too hot. Not hurting the engine (or at least it shouldn't), but it's not helping it either. My best running engines run about 220-230F after a long hard WOT pass on pavement. Running in grass will make the engine run hotter, so if you run in the grass a lot, set it a little richer.
Remember ers what I said - if the engine temperature rises at idle, the idle mixture is too lean. It should cool off when idling - roughly 1 degree every 1-2 seconds. If it doesn't cool down, Richen a little bit. Run a WOT pass and check it again. Keep going until it starts to cool off at idle. Run the top end rich enough that it doesn't get super hot after a few hard runs by doesn't run rough and rev slow and smokey. Some engines do just run hot, but 270 is too hot. Not hurting the engine (or at least it shouldn't), but it's not helping it either. My best running engines run about 220-230F after a long hard WOT pass on pavement. Running in grass will make the engine run hotter, so if you run in the grass a lot, set it a little richer.
08-01-2016, 08:10 AM
#8
If it cools quickly at idle, you're in good shape there. Probably a bit rich if it's quitting. Lean that out a little bit until it stops quitting at idle. You may want to get a spare glow plug or two - sometimes engines that have sat awhile may want a new plug. Use a long reach medium or medium/hot glow plug. I wouldn't worry much about the driveline right now - make some mixture adjustments and see how it runs before doing anything else. Most likely the mixture settings are just not quite right.
08-01-2016, 09:24 AM
#9
So if it cools down quickly on idle but quits on idle it needs to be leaned out but my temps are already high right now. Should I try leaning my low speed or medium speed needles instead? I want to try setting the HSN to be a tad more rich to see if I can get the temps down under load.
Should the temps be between 220 and 240? Or do I need to add the ambient air temperature to this number as well?
Should the temps be between 220 and 240? Or do I need to add the ambient air temperature to this number as well?
08-01-2016, 10:09 AM
#10
I would do this. Run the engine - get it good and warmed up. Drive it around for half a tank. Note the temperature after a couple WOT runs. If it's in the 260-270F range, Richen the high speed, repeat Wot Runs - do 2-3. Note temp. If still hot, Richen it up some more. The high speed needle controls fuel flow overall, but mainly from 3/4-WOT. The idle/low speed needle controls fuel mixture from idle to about 3/4 throttle. If it cools off quickly and loads up at idle quickly, the idle is too rich. Good settings are a compromise of the two settings. Ideally the idle will slightly load up (but not quit) after 15-20 seconds. The high speed should be set for clean and smooth revving at WOT. The temp should not spike quickly hot and it shouldn't overly cool off either. If the top end is too rich, it will cool the engine off too much.
If you're using telemetry sensors to get your readings, I'd use an infrared thermometer as well to compare. Telemetry works well but often misrepresents the real temp. My telemetry reads about 30 degrees hotter than what it really is. 220-250F is a good range to be working with regardless of ambient air temp. When the ambient is really hot, the tuning becomes a bit more tricky to get a good setting. Depending on the glow plug you're using, a richer mixture may do the trick, but a colder plug may also be required. It takes some time to nail it down sometimes. If the engine is still pretty new (less than a gallon of fuel), get the top end richer and burn some fuel through it. Keep it cool and just run it some. Once you get some fuel through it and it breaks in more, then you can get a better performance tune on it.
If you're using telemetry sensors to get your readings, I'd use an infrared thermometer as well to compare. Telemetry works well but often misrepresents the real temp. My telemetry reads about 30 degrees hotter than what it really is. 220-250F is a good range to be working with regardless of ambient air temp. When the ambient is really hot, the tuning becomes a bit more tricky to get a good setting. Depending on the glow plug you're using, a richer mixture may do the trick, but a colder plug may also be required. It takes some time to nail it down sometimes. If the engine is still pretty new (less than a gallon of fuel), get the top end richer and burn some fuel through it. Keep it cool and just run it some. Once you get some fuel through it and it breaks in more, then you can get a better performance tune on it.
08-02-2016, 04:13 AM
#12
Thanks for the advice guys this was very helpful. I got some more things to try out today when I get home. I didn't have a chance yesterday to run it again - plus it was pretty hot and humid out here yesterday.
08-02-2016, 08:46 AM
#13
Join Date: Dec 2001
Location: Upplands Vasby, SWEDEN
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Hi!
Being in this hobby for more than 40 years I would say that all glow engines are set up the same way ...by listening to how they sound...and there is no exception to this when it comes to car engines.
Soo...have you ever tried to set the needles by ear?
You set the high speed needle first. a litle rich! Then set the low speed needle so the engine runs steady and rews up as soon you give full throttle. It's easy!
Being in this hobby for more than 40 years I would say that all glow engines are set up the same way ...by listening to how they sound...and there is no exception to this when it comes to car engines.
Soo...have you ever tried to set the needles by ear?
You set the high speed needle first. a litle rich! Then set the low speed needle so the engine runs steady and rews up as soon you give full throttle. It's easy!
08-02-2016, 12:57 PM
#15
Its easy for airplane guys to say you tune an RC car engine the same way you tune an airplane engine. Overall they tune similar, but the car engine doesn't have a fan blowing on it. 95% of the time the engine will sound great when running when in reality it's too lean. So many times I hear about guys having problems with their car engines... Almost every time they're too lean despite the smoke trail, sound, or how the car drives. I found the header manifold has a huge impact (did I say HUGE) on how an engine runs. So much so, depending on the engine, the operating temperature can vary 20-50F from one manifold to the next. My Picco .28 ran 270F with a long manifold, but after swapping for a shorter manifold the engine temp dropped 50 degrees and power went up considerably.
Jan - let me ask you this. If after you run WOT with a car and let off the throttle and the rpm hangs for a bit before dropping to normal idle. What needle would you adjust to fix that? How far should the throttle valve (not a rotary carb but a slice valve variable Venturi carburetor) be open for proper idle speed?
Jan - let me ask you this. If after you run WOT with a car and let off the throttle and the rpm hangs for a bit before dropping to normal idle. What needle would you adjust to fix that? How far should the throttle valve (not a rotary carb but a slice valve variable Venturi carburetor) be open for proper idle speed?
Last edited by 1QwkSport2.5r; 08-02-2016 at 01:00 PM.
08-03-2016, 01:20 PM
#17
Yes, returning to idle. RC car radios (pistol grip) are setup so when you let off the throttle the throttle valve closes against the idle stop because the throttle trigger is spring loaded and returns to "neutral" which is idle. So yes, "letting off the throttle" means idle.
08-03-2016, 02:54 PM
#18
Its easy for airplane guys to say you tune an RC car engine the same way you tune an airplane engine. Overall they tune similar, but the car engine doesn't have a fan blowing on it. 95% of the time the engine will sound great when running when in reality it's too lean. So many times I hear about guys having problems with their car engines... Almost every time they're too lean despite the smoke trail, sound, or how the car drives. I found the header manifold has a huge impact (did I say HUGE) on how an engine runs. So much so, depending on the engine, the operating temperature can vary 20-50F from one manifold to the next. My Picco .28 ran 270F with a long manifold, but after swapping for a shorter manifold the engine temp dropped 50 degrees and power went up considerably.
Jan - let me ask you this. If after you run WOT with a car and let off the throttle and the rpm hangs for a bit before dropping to normal idle. What needle would you adjust to fix that? How far should the throttle valve (not a rotary carb but a slice valve variable Venturi carburetor) be open for proper idle speed?
Jan - let me ask you this. If after you run WOT with a car and let off the throttle and the rpm hangs for a bit before dropping to normal idle. What needle would you adjust to fix that? How far should the throttle valve (not a rotary carb but a slice valve variable Venturi carburetor) be open for proper idle speed?
I agree with you. I learned to not argue with or advice a car guy too much due to the differences. They are just too different to mix the glow engine forums together. We almost always guide a car guy over to the car forums for those reasons and not because we are uppity or unfriendly.
Jan, the car environment really is different than what we deal with in flying models. I'm sure the boat guys would say the same thing.
08-03-2016, 04:44 PM
#19
Tim,
I agree with you. I learned to not argue with or advice a car guy too much due to the differences. They are just too different to mix the glow engine forums together. We almost always guide a car guy over to the car forums for those reasons and not because we are uppity or unfriendly.
Jan, the car environment really is different than what we deal with in flying models. I'm sure the boat guys would say the same thing.
I agree with you. I learned to not argue with or advice a car guy too much due to the differences. They are just too different to mix the glow engine forums together. We almost always guide a car guy over to the car forums for those reasons and not because we are uppity or unfriendly.
Jan, the car environment really is different than what we deal with in flying models. I'm sure the boat guys would say the same thing.
One problem with the car forum is that the guys posting there for the most part really don't entirely know what they're talking about. So for new guys or inexperienced guys returning to the hobby get poor advice and end up worse off than they were in the beginning half the time. I will admit that I learned to be a better car tuner from running airplane engines, but they're is a different process to get to the sweet spot. Boats are quite similar to cars except the water cooling allows more exotic fuel (think 50% nitro!).
Engine temperature is more important to be mindful of because it's a LOT easier to cook a car engine from a lean run than it is an aircraft engine. Sport aircraft engine running lean at 14,000rpm is one thing. Try that at 40,000rpm and on fuel with half the oil in it and see where it gets you.
And FWIW, the tuning question I asked Jan - what needle do I adjust if the idle hangs when dropping from a hard WOT run to idle question - on a car engine, you would richen the main needle. On an aircraft engine you would richen the idle needle. This is a good way to find the sweet spot - if the idle hangs, back it off 1/8-1/4 turn rich and you're set for the most part.
08-04-2016, 06:38 AM
#20
I managed to put another tank through my engine on Tuesday. It was hell to get the engine started this time. I had to give it a good amount of throttle after pulling on the pull start. The engine would keep cutting out, even changed the glow plug - same problem. I did finally get it to run for a bit once I pre-heated the engine with a heat gun a little longer. I then had to lean out my HSN almost a full turn. Then the engine came to life. I'm still having good smoke. My engine temps dropped all the way down to 220 - 240 WOT. Things appear to be running a lot better now.
Can someone explain why the engine was running so hot when my mixture was so rich? Probably too rich? Also the temps and humidity were pretty similar between Sunday when I first started break in and Tuesday. Why such the huge change in the HSN just to get the engine to run one day from the next?
Can someone explain why the engine was running so hot when my mixture was so rich? Probably too rich? Also the temps and humidity were pretty similar between Sunday when I first started break in and Tuesday. Why such the huge change in the HSN just to get the engine to run one day from the next?
08-04-2016, 07:09 AM
#21
Did you change the low speed mixture at all? The low speed/idle mixture needle controls fuel mixture from idle to about 3/4 throttle.
When an engine exhibits the same problem with two different glow plugs, that tells me something else is amiss - usually the needle setting.
New tight engines almost always run hotter until they loosen up. The cylinder pinch is much tighter when new and as that loosens up from running the friction goes down. The fuel mixture will need to be adjusted when the climate differs one day to the next, but rarely if ever will it require a full turn of the needle to get it "right". I think your high temp reading initially may have been a fluke because an engine running overly rich will struggle to get above 200F. However being the carb has two needle valves that control fuel mixture at different (and respective) throttle settings, one needle can be too lean and the other too rich and still get a decent running engine because there can be some compensation between the settings depending on the fuel used and also the idle gap. You can get a good quality idle with a narrow idle gap and leaner mixture as you can with a wider idle gap and richer idle needle setting. The difference is the side idle gap and rich idle mix will cause the engine to load up more at idle and consequently cause more flame outs. So it's very important to have the idle gap correct and to also ensure the throttle linkage is moving freely so when the throttle is returned to neutral on the transmitter the slide valve on the carb can snap shut without hanging up or sticking. The idle gap should be .5-.6mm. Any wider than that and you'll likely chase a tune all the time and probably have some tractability issues with running part throttle.
How are you measuring the engine temperature??
When an engine exhibits the same problem with two different glow plugs, that tells me something else is amiss - usually the needle setting.
New tight engines almost always run hotter until they loosen up. The cylinder pinch is much tighter when new and as that loosens up from running the friction goes down. The fuel mixture will need to be adjusted when the climate differs one day to the next, but rarely if ever will it require a full turn of the needle to get it "right". I think your high temp reading initially may have been a fluke because an engine running overly rich will struggle to get above 200F. However being the carb has two needle valves that control fuel mixture at different (and respective) throttle settings, one needle can be too lean and the other too rich and still get a decent running engine because there can be some compensation between the settings depending on the fuel used and also the idle gap. You can get a good quality idle with a narrow idle gap and leaner mixture as you can with a wider idle gap and richer idle needle setting. The difference is the side idle gap and rich idle mix will cause the engine to load up more at idle and consequently cause more flame outs. So it's very important to have the idle gap correct and to also ensure the throttle linkage is moving freely so when the throttle is returned to neutral on the transmitter the slide valve on the carb can snap shut without hanging up or sticking. The idle gap should be .5-.6mm. Any wider than that and you'll likely chase a tune all the time and probably have some tractability issues with running part throttle.
How are you measuring the engine temperature??
08-04-2016, 07:19 AM
#22
Did you change the low speed mixture at all? The low speed/idle mixture needle controls fuel mixture from idle to about 3/4 throttle.
When an engine exhibits the same problem with two different glow plugs, that tells me something else is amiss - usually the needle setting.
New tight engines almost always run hotter until they loosen up. The cylinder pinch is much tighter when new and as that loosens up from running the friction goes down. The fuel mixture will need to be adjusted when the climate differs one day to the next, but rarely if ever will it require a full turn of the needle to get it "right". I think your high temp reading initially may have been a fluke because an engine running overly rich will struggle to get above 200F. However being the carb has two needle valves that control fuel mixture at different (and respective) throttle settings, one needle can be too lean and the other too rich and still get a decent running engine because there can be some compensation between the settings depending on the fuel used and also the idle gap. You can get a good quality idle with a narrow idle gap and leaner mixture as you can with a wider idle gap and richer idle needle setting. The difference is the side idle gap and rich idle mix will cause the engine to load up more at idle and consequently cause more flame outs. So it's very important to have the idle gap correct and to also ensure the throttle linkage is moving freely so when the throttle is returned to neutral on the transmitter the slide valve on the carb can snap shut without hanging up or sticking. The idle gap should be .5-.6mm. Any wider than that and you'll likely chase a tune all the time and probably have some tractability issues with running part throttle.
How are you measuring the engine temperature??
When an engine exhibits the same problem with two different glow plugs, that tells me something else is amiss - usually the needle setting.
New tight engines almost always run hotter until they loosen up. The cylinder pinch is much tighter when new and as that loosens up from running the friction goes down. The fuel mixture will need to be adjusted when the climate differs one day to the next, but rarely if ever will it require a full turn of the needle to get it "right". I think your high temp reading initially may have been a fluke because an engine running overly rich will struggle to get above 200F. However being the carb has two needle valves that control fuel mixture at different (and respective) throttle settings, one needle can be too lean and the other too rich and still get a decent running engine because there can be some compensation between the settings depending on the fuel used and also the idle gap. You can get a good quality idle with a narrow idle gap and leaner mixture as you can with a wider idle gap and richer idle needle setting. The difference is the side idle gap and rich idle mix will cause the engine to load up more at idle and consequently cause more flame outs. So it's very important to have the idle gap correct and to also ensure the throttle linkage is moving freely so when the throttle is returned to neutral on the transmitter the slide valve on the carb can snap shut without hanging up or sticking. The idle gap should be .5-.6mm. Any wider than that and you'll likely chase a tune all the time and probably have some tractability issues with running part throttle.
How are you measuring the engine temperature??
It's possible my gun has the emissivity already set to aluminum. I don't see how it would be that large of a temperate difference but maybe it's possible. When I first tired the gun out I compared the two temps and the fuke was a tad hotter by about 2 - 3 degrees so I didn't think much of it.
I'm taking readings by placing the gun on top of the cooling head and taking a reading at the glow plug.
08-04-2016, 07:40 AM
#23
Join Date: Dec 2001
Location: Upplands Vasby, SWEDEN
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Hi!
It was 35 years since I last drove an R/C car so I forgot (and I used my airplane radio).
But returning to your question...
Since the engine rpm doesn't go back instantly when you let go of the throttle I would assume the idle needle is set to lean. But first of all the full speed needle should be adjusted so the engine runs slightly rich at full speed. And this is done by setting it by ear.
Most R/C carbs for airplane engines are set up so the throttle drum opening is around 1,5-2mm at idle. I would assume a car engine would have the same or a little more (more rpm) as it doesn't have a propeller that contributes to the flywheel effect for reliable idle speed.
It was 35 years since I last drove an R/C car so I forgot (and I used my airplane radio).
But returning to your question...
Since the engine rpm doesn't go back instantly when you let go of the throttle I would assume the idle needle is set to lean. But first of all the full speed needle should be adjusted so the engine runs slightly rich at full speed. And this is done by setting it by ear.
Most R/C carbs for airplane engines are set up so the throttle drum opening is around 1,5-2mm at idle. I would assume a car engine would have the same or a little more (more rpm) as it doesn't have a propeller that contributes to the flywheel effect for reliable idle speed.
08-04-2016, 07:46 AM
#24
By only changing the high speed setting and having to use the throttle to get the engine started tells me you still need to adjust the idle mixture. If you have to open the throttle in order to get the engine started and keep it running, your idle mixture is too rich.
Taking the readings at the glow plug is good, but if the gun you end up finally using has an adjustment for the surface being tested, it may give funky results set for aluminum as you're likely to get a reading off the glow plug itself. This is neither here nor there as most infrared temp guns should read relatively close to one another. I use a radio shack temp gun and when I take readings, I put the end of the gun right on top of the head aimed at the plug as it sounds like you were doing too. The accuracy improves greatly when you're closer to the object being tested.
I would lean lean your low speed so you can start the engine without adding throttle and have the car keep running. Sometimes when cold they may quit, so once the engine starts, drive it around to get some heat in the engine. Once it warms up some, then you can start tuning it. Have the engine completely warmed up before making final adjustments. When you tune the engine, set the high speed for good throttling - smooth power and smooth revving to WOT. Note the temp - if it gets real hot (above 250F), richen the main needle. Once it's stabilized on top, set the idle mixture so it will idle nice and low and throttle cleanly. You want it to be slightly loaded up after 15-20 seconds. It should burble a little bit, but not flame out. If it flames out, lean the idle 1/16th turn and run a WOT pass and test the idle again. Once you get close, make your final needle adjustments when at 1/2-1/3 tank of fuel so when the tank is full it's rich and tank empty is pretty much at the peak setting. This will give you good performance and not run the engine too lean and hot.
Taking the readings at the glow plug is good, but if the gun you end up finally using has an adjustment for the surface being tested, it may give funky results set for aluminum as you're likely to get a reading off the glow plug itself. This is neither here nor there as most infrared temp guns should read relatively close to one another. I use a radio shack temp gun and when I take readings, I put the end of the gun right on top of the head aimed at the plug as it sounds like you were doing too. The accuracy improves greatly when you're closer to the object being tested.
I would lean lean your low speed so you can start the engine without adding throttle and have the car keep running. Sometimes when cold they may quit, so once the engine starts, drive it around to get some heat in the engine. Once it warms up some, then you can start tuning it. Have the engine completely warmed up before making final adjustments. When you tune the engine, set the high speed for good throttling - smooth power and smooth revving to WOT. Note the temp - if it gets real hot (above 250F), richen the main needle. Once it's stabilized on top, set the idle mixture so it will idle nice and low and throttle cleanly. You want it to be slightly loaded up after 15-20 seconds. It should burble a little bit, but not flame out. If it flames out, lean the idle 1/16th turn and run a WOT pass and test the idle again. Once you get close, make your final needle adjustments when at 1/2-1/3 tank of fuel so when the tank is full it's rich and tank empty is pretty much at the peak setting. This will give you good performance and not run the engine too lean and hot.
08-04-2016, 07:51 AM
#25
Hi!
It was 35 years since I last drove an R/C car so I forgot (and I used my airplane radio).
But returning to your question...
Since the engine rpm doesn't go back instantly when you let go of the throttle I would assume the idle needle is set to lean. But first of all the full speed needle should be adjusted so the engine runs slightly rich at full speed. And this is done by setting it by ear.
Most R/C carbs for airplane engines are set up so the throttle drum opening is around 1,5-2mm at idle. I would assume a car engine would have the same or a little more (more rpm) as it doesn't have a propeller that contributes to the flywheel effect for reliable idle speed.
It was 35 years since I last drove an R/C car so I forgot (and I used my airplane radio).
But returning to your question...
Since the engine rpm doesn't go back instantly when you let go of the throttle I would assume the idle needle is set to lean. But first of all the full speed needle should be adjusted so the engine runs slightly rich at full speed. And this is done by setting it by ear.
Most R/C carbs for airplane engines are set up so the throttle drum opening is around 1,5-2mm at idle. I would assume a car engine would have the same or a little more (more rpm) as it doesn't have a propeller that contributes to the flywheel effect for reliable idle speed.
Most car engines are setup to run 15-30% nitro with 20% being fairly typical. At that nitro content, there can be a half turn between rich and lean. You can be 1/8 turn too lean and the engine will run hot and there will be little change in sound from the engine between those settings. If a car engine could be loaded to run at a sustained rpm for a time, it would be easier to set the needle valve properly, but in a car that isn't feasible.