Random loss of compression?
07-06-2015, 12:57 AM
#1
Random loss of compression?
So I took apart my engine, sealed it. I ran it too lean a few days back and killed a glow plug. I've noticed recently that the engine has good compression when pulling slow on the pull start but if I pull quickly multiple times one out of 3 pulls will feel like it has little compression?
OH also I've noticed my exhaust literally fills up with fuel to the point where I can pour fuel out of the exhaust when I turn it on its side. The truck runs great and starts up right away so ??? I have leaned it as far as I can, anything further hit over 250F
OH also I've noticed my exhaust literally fills up with fuel to the point where I can pour fuel out of the exhaust when I turn it on its side. The truck runs great and starts up right away so ??? I have leaned it as far as I can, anything further hit over 250F
07-06-2015, 01:49 AM
#2
The problem with the pullstart is probably a slipping one-way bearing. Most engines use these: http://www.amazon.com/INA-HF0612-Rol...words=ina+0612. You can press the old OWB out of the housing that holds it, and press the new one in. Just make sure to get the rotational direction the same, or the pullstart won't do anything.
If you're stuck between running the engine so rich that fuel is building up in the exhaust vs. overheating the engine, then the engine's compression ratio is too high. You need to buy a cylinder-head shim kit for it, and start adding shims until you can tune the engine lean enough that it's not pouring fuel out the exhaust without overheating.
I run 30% nitro, and for me the sweet spot is 0.6-0.8mm of shims on .08-.20 engines, with medium-heat glowplugs on the bigger engines and hot plugs on the smaller ones. (unless you're running a <.12 engine, you won't need a hot plug, though). If you run lower-percentage nitro you might need fewer shims, but you really have to tune it based on your exact running conditions.
If you're stuck between running the engine so rich that fuel is building up in the exhaust vs. overheating the engine, then the engine's compression ratio is too high. You need to buy a cylinder-head shim kit for it, and start adding shims until you can tune the engine lean enough that it's not pouring fuel out the exhaust without overheating.
I run 30% nitro, and for me the sweet spot is 0.6-0.8mm of shims on .08-.20 engines, with medium-heat glowplugs on the bigger engines and hot plugs on the smaller ones. (unless you're running a <.12 engine, you won't need a hot plug, though). If you run lower-percentage nitro you might need fewer shims, but you really have to tune it based on your exact running conditions.
07-06-2015, 06:42 AM
#3
Nothing wrong with an engine at 250. If youre hitting 300 then you need to adjust. What fuel and how old is it? Could have an old/bad batch. Unless you got rid of all the head shims, I wouldn't worry about CR ratio right now, its very unlikely that is the cause.
07-06-2015, 03:05 PM
#5
You know what, the fuel is about 2 years old. Maybe more, I ran out of fuel and started using this stuff because I was heading out on vacation. I don't think this engine has any head-shims, I took it apart not too long ago, but I'll buy some new fuel tomorrow and a new one way bearing. Also just finished using WD40 to spray out any gunk from the piston through the header area. Some small black bits came out with 1 silver bit. Not sure what that's about.
By the way, thanks everyone. Still a noob.
By the way, thanks everyone. Still a noob.
07-06-2015, 03:51 PM
#6
Okay, yeah, 2-year-old fuel is probably no good. Even if it was in a cool dark place in a sealed container (to prevent water absorption and methanol evaporation), there's no guarantee the fuel/oil mixture is still homogenous.
The engine must have come with shims from the factory. They all do, so the shims can be removed for people who are unfortunate enough to live in countries where nitromethane is illegal for private citizens to own (because it's basically rocket fuel), so they can still run their engines on methanol. If you took the shims out (or if you got the engine used and the prior owner removed the shims), that would put your compression ratio way too high for fuel that contains any nitromethane at all.
If bits of metal came out, that's a really bad sign. It's possible they were casting defects around the exhaust port, but you need to completely disassemble the engine and confirm nothing is broken.
Also, don't use WD40 or any "normal" petroleum-based oils on a nitro engine. They're not compatible with the alcohol-soluble oil mixed into the nitro fuel, and if they aren't washed out of the engine prior to starting it, they can hang around and turn into goop, especially around the conrod bushings and the crank bearings. Use nitro after-run oil for lubrication, and if you need to soak your engine in solvents to clean it, make sure to wash any remaining petroleum products off before reassembling the engine.
The engine must have come with shims from the factory. They all do, so the shims can be removed for people who are unfortunate enough to live in countries where nitromethane is illegal for private citizens to own (because it's basically rocket fuel), so they can still run their engines on methanol. If you took the shims out (or if you got the engine used and the prior owner removed the shims), that would put your compression ratio way too high for fuel that contains any nitromethane at all.
If bits of metal came out, that's a really bad sign. It's possible they were casting defects around the exhaust port, but you need to completely disassemble the engine and confirm nothing is broken.
Also, don't use WD40 or any "normal" petroleum-based oils on a nitro engine. They're not compatible with the alcohol-soluble oil mixed into the nitro fuel, and if they aren't washed out of the engine prior to starting it, they can hang around and turn into goop, especially around the conrod bushings and the crank bearings. Use nitro after-run oil for lubrication, and if you need to soak your engine in solvents to clean it, make sure to wash any remaining petroleum products off before reassembling the engine.
07-06-2015, 04:52 PM
#7
Okay, yeah, 2-year-old fuel is probably no good. Even if it was in a cool dark place in a sealed container (to prevent water absorption and methanol evaporation), there's no guarantee the fuel/oil mixture is still homogenous.
The engine must have come with shims from the factory. They all do, so the shims can be removed for people who are unfortunate enough to live in countries where nitromethane is illegal for private citizens to own (because it's basically rocket fuel), so they can still run their engines on methanol. If you took the shims out (or if you got the engine used and the prior owner removed the shims), that would put your compression ratio way too high for fuel that contains any nitromethane at all.
If bits of metal came out, that's a really bad sign. It's possible they were casting defects around the exhaust port, but you need to completely disassemble the engine and confirm nothing is broken.
Also, don't use WD40 or any "normal" petroleum-based oils on a nitro engine. They're not compatible with the alcohol-soluble oil mixed into the nitro fuel, and if they aren't washed out of the engine prior to starting it, they can hang around and turn into goop, especially around the conrod bushings and the crank bearings. Use nitro after-run oil for lubrication, and if you need to soak your engine in solvents to clean it, make sure to wash any remaining petroleum products off before reassembling the engine.
The engine must have come with shims from the factory. They all do, so the shims can be removed for people who are unfortunate enough to live in countries where nitromethane is illegal for private citizens to own (because it's basically rocket fuel), so they can still run their engines on methanol. If you took the shims out (or if you got the engine used and the prior owner removed the shims), that would put your compression ratio way too high for fuel that contains any nitromethane at all.
If bits of metal came out, that's a really bad sign. It's possible they were casting defects around the exhaust port, but you need to completely disassemble the engine and confirm nothing is broken.
Also, don't use WD40 or any "normal" petroleum-based oils on a nitro engine. They're not compatible with the alcohol-soluble oil mixed into the nitro fuel, and if they aren't washed out of the engine prior to starting it, they can hang around and turn into goop, especially around the conrod bushings and the crank bearings. Use nitro after-run oil for lubrication, and if you need to soak your engine in solvents to clean it, make sure to wash any remaining petroleum products off before reassembling the engine.
I'm afraid to take the whole engine all apart because I don't want to lose anything or forget how to put it back together. The furthest I've gotten to taking it apart was removing everything except the piston and sleeve.
Sides of the piston are shiny when looking through the exhaust port. I can't feel any grinding or resistance besides the compression.
I've run this engine way too lean once for a few tanks. (It felt alright but after driving it on the field full throttle back in forth is when I noticed I was running too lean.) It got to the point where there was major loss of power and saw a little bit of smoke coming off the engine + micro popping noises then killed a glow plug the same day so I richened it but also noticed my header was stripped and leaking nitro. Haven't really been able to get it tuned properly since I keep running myself into these odd situations haha.
Oh while I'm at it, if I put soapy water over the bearing near my flywheel I can see bubbles. I know nitro is suppose to lube the bearing and seal it? Think I'll be fine with that small air leak near the bearing?
Thanks, hoping to get it tuned right this time since I know roughly where the too lean area is.
07-06-2015, 07:44 PM
#8
WD40 is just a bunch of solvents, it doesn't provide any lubrication, it just softens existing lubricants. The point of after-run oil is to keep the piston and sleeve lubricated between runs, and to ensure a tight seal between the piston and sleeve when you start the engine next time. Unlike most petroleum oils it's compatible with the stuff dissolved in nitro fuel.
Lay a towel on the floor and take the engine apart there. You won't be able to lose any parts because they won't be able to fall and bounce away. You really ought to know what the insides look like when they're not all assembled together and blocking your view of each individual part. You don't need to pull the crankshaft or disassemble the piston and conrod, you can see what's going on easily enough just by looking at them. The piston and sleeve are easy -- slide the sleeve out the top of the crankcase, and then wiggle the bottom of the conrod off the end of the crankshaft. Installation is reverse of removal.
Just so you're aware, with the HPI engines there's a spring-loaded ratchet pin in the end of the crankshaft, which allows the crankshaft to spin faster than the pullstart shaft once the engine is running. That is the only part you need to watch out for, but I've had them jump out of the engine at me several times and I never actually lost one.
I also caused myself a bunch of trouble by overheating an engine. (actually it was the exact same engine as yours on the inside, it was just called the G3.0 because it had a different crankshaft.) Highest temperature I ever saw was 413°F. Needless to say, it never ran right after that; I had to get it up to 300°F before it would run properly, which meant I had to tune it really lean to get it hot and then tune it richer again to avoid continuing to overheat it.
Basically what you did was you broke-in the engine at a temperature so high that the rest of the engine can't function properly at that temperature, even though the piston and sleeve can still achieve decent compression once they're hot enough. Hypothetically, you can break-in an engine at any temperature you want, and the piston will just wear-down until it fits properly in the sleeve -- the real reason you have to keep the engine below 250°F is because for most engines that's the point at which the fuel will start to boil inside the carburetor. Even if it doesn't cause complete vapor-lock, having the fuel flash into vapor the instant it comes out of the spraybar screws up the fuel-air mixture, and it's basically impossible to tune an engine to run properly under those conditions.
If you ran the engine hot enough to see the residual oil on the outside smoking -- and you didn't notice it until several runs later -- then your piston and sleeve are shot. You'll have to replace them to get the engine to run properly again.
For the first ten runs or so, you have to check the temperature of a nitro engine every couple minutes, and you have to give the engine several minutes to heat up or cool down after you tweak the carb settings -- the temperature won't change immediately. That's how I managed to overheat one of my engines so badly; I tuned the carb, then ran it for about ten minutes without checking the temperature, because while the engine was running lean it was making great power and was tons of fun to drive -- and then I noticed the side of the body shell was starting to warp from the heat.
If you don't have an IR thermometer, that needs to be your next purchase. It is an indispensable tool for running nitro engines, even if you tune according to sound instead of temperature, you still need to make sure you're not overheating the engine. A couple minutes at 275°F is fine, several runs above 300°F is lethal.
Lay a towel on the floor and take the engine apart there. You won't be able to lose any parts because they won't be able to fall and bounce away. You really ought to know what the insides look like when they're not all assembled together and blocking your view of each individual part. You don't need to pull the crankshaft or disassemble the piston and conrod, you can see what's going on easily enough just by looking at them. The piston and sleeve are easy -- slide the sleeve out the top of the crankcase, and then wiggle the bottom of the conrod off the end of the crankshaft. Installation is reverse of removal.
Just so you're aware, with the HPI engines there's a spring-loaded ratchet pin in the end of the crankshaft, which allows the crankshaft to spin faster than the pullstart shaft once the engine is running. That is the only part you need to watch out for, but I've had them jump out of the engine at me several times and I never actually lost one.
I also caused myself a bunch of trouble by overheating an engine. (actually it was the exact same engine as yours on the inside, it was just called the G3.0 because it had a different crankshaft.) Highest temperature I ever saw was 413°F. Needless to say, it never ran right after that; I had to get it up to 300°F before it would run properly, which meant I had to tune it really lean to get it hot and then tune it richer again to avoid continuing to overheat it.
Basically what you did was you broke-in the engine at a temperature so high that the rest of the engine can't function properly at that temperature, even though the piston and sleeve can still achieve decent compression once they're hot enough. Hypothetically, you can break-in an engine at any temperature you want, and the piston will just wear-down until it fits properly in the sleeve -- the real reason you have to keep the engine below 250°F is because for most engines that's the point at which the fuel will start to boil inside the carburetor. Even if it doesn't cause complete vapor-lock, having the fuel flash into vapor the instant it comes out of the spraybar screws up the fuel-air mixture, and it's basically impossible to tune an engine to run properly under those conditions.
If you ran the engine hot enough to see the residual oil on the outside smoking -- and you didn't notice it until several runs later -- then your piston and sleeve are shot. You'll have to replace them to get the engine to run properly again.
For the first ten runs or so, you have to check the temperature of a nitro engine every couple minutes, and you have to give the engine several minutes to heat up or cool down after you tweak the carb settings -- the temperature won't change immediately. That's how I managed to overheat one of my engines so badly; I tuned the carb, then ran it for about ten minutes without checking the temperature, because while the engine was running lean it was making great power and was tons of fun to drive -- and then I noticed the side of the body shell was starting to warp from the heat.
If you don't have an IR thermometer, that needs to be your next purchase. It is an indispensable tool for running nitro engines, even if you tune according to sound instead of temperature, you still need to make sure you're not overheating the engine. A couple minutes at 275°F is fine, several runs above 300°F is lethal.
Last edited by fyrstormer; 07-06-2015 at 08:06 PM.
07-06-2015, 08:13 PM
#9
This is the part you need to replace the piston and sleeve: http://www.ebay.com/itm/T3-0-PISTON-...item3aa7bde06f
07-06-2015, 08:56 PM
#10
WD40 is just a bunch of solvents, it doesn't provide any lubrication, it just softens existing lubricants. The point of after-run oil is to keep the piston and sleeve lubricated between runs, and to ensure a tight seal between the piston and sleeve when you start the engine next time. Unlike most petroleum oils it's compatible with the stuff dissolved in nitro fuel.
Lay a towel on the floor and take the engine apart there. You won't be able to lose any parts because they won't be able to fall and bounce away. You really ought to know what the insides look like when they're not all assembled together and blocking your view of each individual part. You don't need to pull the crankshaft or disassemble the piston and conrod, you can see what's going on easily enough just by looking at them. The piston and sleeve are easy -- slide the sleeve out the top of the crankcase, and then wiggle the bottom of the conrod off the end of the crankshaft. Installation is reverse of removal.
Just so you're aware, with the HPI engines there's a spring-loaded ratchet pin in the end of the crankshaft, which allows the crankshaft to spin faster than the pullstart shaft once the engine is running. That is the only part you need to watch out for, but I've had them jump out of the engine at me several times and I never actually lost one.
I also caused myself a bunch of trouble by overheating an engine. (actually it was the exact same engine as yours on the inside, it was just called the G3.0 because it had a different crankshaft.) Highest temperature I ever saw was 413°F. Needless to say, it never ran right after that; I had to get it up to 300°F before it would run properly, which meant I had to tune it really lean to get it hot and then tune it richer again to avoid continuing to overheat it.
Basically what you did was you broke-in the engine at a temperature so high that the rest of the engine can't function properly at that temperature, even though the piston and sleeve can still achieve decent compression once they're hot enough. Hypothetically, you can break-in an engine at any temperature you want, and the piston will just wear-down until it fits properly in the sleeve -- the real reason you have to keep the engine below 250°F is because for most engines that's the point at which the fuel will start to boil inside the carburetor. Even if it doesn't cause complete vapor-lock, having the fuel flash into vapor the instant it comes out of the spraybar screws up the fuel-air mixture, and it's basically impossible to tune an engine to run properly under those conditions.
If you ran the engine hot enough to see the residual oil on the outside smoking -- and you didn't notice it until several runs later -- then your piston and sleeve are shot. You'll have to replace them to get the engine to run properly again.
For the first ten runs or so, you have to check the temperature of a nitro engine every couple minutes, and you have to give the engine several minutes to heat up or cool down after you tweak the carb settings -- the temperature won't change immediately. That's how I managed to overheat one of my engines so badly; I tuned the carb, then ran it for about ten minutes without checking the temperature, because while the engine was running lean it was making great power and was tons of fun to drive -- and then I noticed the side of the body shell was starting to warp from the heat.
If you don't have an IR thermometer, that needs to be your next purchase. It is an indispensable tool for running nitro engines, even if you tune according to sound instead of temperature, you still need to make sure you're not overheating the engine. A couple minutes at 275°F is fine, several runs above 300°F is lethal.
Lay a towel on the floor and take the engine apart there. You won't be able to lose any parts because they won't be able to fall and bounce away. You really ought to know what the insides look like when they're not all assembled together and blocking your view of each individual part. You don't need to pull the crankshaft or disassemble the piston and conrod, you can see what's going on easily enough just by looking at them. The piston and sleeve are easy -- slide the sleeve out the top of the crankcase, and then wiggle the bottom of the conrod off the end of the crankshaft. Installation is reverse of removal.
Just so you're aware, with the HPI engines there's a spring-loaded ratchet pin in the end of the crankshaft, which allows the crankshaft to spin faster than the pullstart shaft once the engine is running. That is the only part you need to watch out for, but I've had them jump out of the engine at me several times and I never actually lost one.
I also caused myself a bunch of trouble by overheating an engine. (actually it was the exact same engine as yours on the inside, it was just called the G3.0 because it had a different crankshaft.) Highest temperature I ever saw was 413°F. Needless to say, it never ran right after that; I had to get it up to 300°F before it would run properly, which meant I had to tune it really lean to get it hot and then tune it richer again to avoid continuing to overheat it.
Basically what you did was you broke-in the engine at a temperature so high that the rest of the engine can't function properly at that temperature, even though the piston and sleeve can still achieve decent compression once they're hot enough. Hypothetically, you can break-in an engine at any temperature you want, and the piston will just wear-down until it fits properly in the sleeve -- the real reason you have to keep the engine below 250°F is because for most engines that's the point at which the fuel will start to boil inside the carburetor. Even if it doesn't cause complete vapor-lock, having the fuel flash into vapor the instant it comes out of the spraybar screws up the fuel-air mixture, and it's basically impossible to tune an engine to run properly under those conditions.
If you ran the engine hot enough to see the residual oil on the outside smoking -- and you didn't notice it until several runs later -- then your piston and sleeve are shot. You'll have to replace them to get the engine to run properly again.
For the first ten runs or so, you have to check the temperature of a nitro engine every couple minutes, and you have to give the engine several minutes to heat up or cool down after you tweak the carb settings -- the temperature won't change immediately. That's how I managed to overheat one of my engines so badly; I tuned the carb, then ran it for about ten minutes without checking the temperature, because while the engine was running lean it was making great power and was tons of fun to drive -- and then I noticed the side of the body shell was starting to warp from the heat.
If you don't have an IR thermometer, that needs to be your next purchase. It is an indispensable tool for running nitro engines, even if you tune according to sound instead of temperature, you still need to make sure you're not overheating the engine. A couple minutes at 275°F is fine, several runs above 300°F is lethal.
I do have a temp gun and when it overheated the temp was 315F. Also good tip, I made that mistake and didn't bring the temp gun with me plus changed the HSN without cooling down and such. Side of my body near the pipe is warped too haha. Last I drove it was 2 days ago with the old fuel and the idle is actually really good, idled for over a minute before I got sick of watching it. I think what i'll do after I pickup a new glow plug, one way bearing and fuel then run it on the rich side and see what temps I get, tune by the glow pluf, sound and make sure the temps are not high.
If I can't tune it and the thing decides to do weird things ill buy a new piston + sleeve. Also is it bad I'm running a T3.0 in a monster truck instead of the G3.0?
07-07-2015, 01:18 AM
#11
Get some 3M aluminum foil tape from the auto parts store. It makes great heat-shielding for nitro bodies.
The T3.0 and G3.0 are identical except for the crankshaft and the outer part of the pullstart assembly. You shouldn't notice any difference in their operation. However, if/when you get the money, you should consider putting a Losi 3.4 in there; I put one in my HPI Bullet, which came with a G3.0, and it really woke the thing up. Overheating stopped being an issue altogether.
Alternately, if you want a cheaper engine to experiment with, the GO .18 (also known as the EG Sport .18) is a good choice. It costs about $50 from HobbyKing, and RC-WillPower sells replacement pistons and sleeves for about $25.
The T3.0 and G3.0 are identical except for the crankshaft and the outer part of the pullstart assembly. You shouldn't notice any difference in their operation. However, if/when you get the money, you should consider putting a Losi 3.4 in there; I put one in my HPI Bullet, which came with a G3.0, and it really woke the thing up. Overheating stopped being an issue altogether.
Alternately, if you want a cheaper engine to experiment with, the GO .18 (also known as the EG Sport .18) is a good choice. It costs about $50 from HobbyKing, and RC-WillPower sells replacement pistons and sleeves for about $25.
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