TRX250R.ORG
Workshop => Engine and Bottom End => Topic started by: dem3500 on May 30, 2015, 09:31:16 PM
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The title sounds a little more dramatic than it really is but none the less, its messed up and a quick google search didn't provide me any info.
This is a fresh build and the problem started when I was working on jetting. What's happening is the center electrode is being pushed out of the metal body of the plug. The first one was just from throttling the engine in my driveway. It was pretty loud and I thought that I blew my head or something. I almost cried lol. I replaced the plug and finished the initial jetting then took it riding in my yard. It started running like crap. I looked at the plug and it had started to back out of the head. I've put in hundreds of plugs but I figured that I messed up and didn't tighten it. I crancked it back down and rode a little more....pop! There goes another one. It separated like the first one. I got on the phone with an ex sled racer and he said he's seen it before. He said he was running 240 + psi on his engines and the plugs he used and had luck with were the eix plugs. I grabbed some and put one in. That was last night. Today I had an xc race. I made one full lap before it started to run like crap and shortly after died. I reached down and the plug backed all the way out! What the hell is going on!?!? Fortunately I planned ahead and brought more plugs and a wrench. I put another plug in. These are the eix plugs and to shorten the rest of this long story I popped two more plugs. Somebody tell me what the heck is going on!(http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/IMG_20150530_205957046_zpscp7ubmhz.jpg) (http://s537.photobucket.com/user/dem3500/media/TRX250R/IMG_20150530_205957046_zpscp7ubmhz.jpg.html)(http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/IMG_20150530_210007123_zpsiwko6lle.jpg) (http://s537.photobucket.com/user/dem3500/media/TRX250R/IMG_20150530_210007123_zpsiwko6lle.jpg.html)(http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/IMG_20150530_210030137_zps00lua2au.jpg) (http://s537.photobucket.com/user/dem3500/media/TRX250R/IMG_20150530_210030137_zps00lua2au.jpg.html)
Notice the black on the porcelain section. Its blow through.(http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/IMG_20150530_210041669_zpsyin0f4y8.jpg) (http://s537.photobucket.com/user/dem3500/media/TRX250R/IMG_20150530_210041669_zpsyin0f4y8.jpg.html)(http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/IMG_20150530_210055673_zpsjxh88pw9.jpg) (http://s537.photobucket.com/user/dem3500/media/TRX250R/IMG_20150530_210055673_zpsjxh88pw9.jpg.html)(http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/IMG_20150530_210108615_zpshbhiglrl.jpg) (http://s537.photobucket.com/user/dem3500/media/TRX250R/IMG_20150530_210108615_zpshbhiglrl.jpg.html)
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This is a vid of the worse one. All the other ones wernt loose like this one. (http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/th_VID_20150530_210100547_zps0d2pl3bn.jpg) (http://i537.photobucket.com/albums/ff335/dem3500/TRX250R/VID_20150530_210100547_zps0d2pl3bn.mp4)
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I saw a post somewhere about fake NGK spark plugs. Just a thought. Otherwise, I have never seen that before. Only other thing I can think of is too much compression for the octane of the fuel?
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Yea I thought about the fake plugs too but the es plugs came from advanced and the eix plugs came from my buddies dad and they have been in his tool box for years. I don't know enough about compression and fuel to know what to run. I know it needs race fuel and I run 110. I'd have to take the head off to measure for the fuel ratio
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Yea I thought about the fake plugs too but the es plugs came from advanced and the eix plugs came from my buddies dad and they have been in his tool box for years. I don't know enough about compression and fuel to know what to run. I know it needs race fuel and I run 110. I'd have to take the head off to measure for the fuel ratio
If you pull the head and look at the outer edges of the piston and head, I think that you will find evidence that the engine has been experiencing detonation. Evidence of detonation will show up as a sand blasted look around the outer edges of the piston and head near the cylinder wall. Severe detonation will erode the edge of the piston and head, eat away at the ID of a rubber o-ring or eat away the steel fire ring of a metal head gasket.
On this engine detonation occurred first rattling the plug loose. A loose spark plug cannot dissipate it's heat to the head. A spark plug dissipates it's heat through the spark plug base washer and threads into the head. The spark plug center wire and ground strap severely overheated and became the ignition source known as pre-ignition. Pre-ignition always occurs before the spark occurs. Pre-ignition ALWAYS ignites the mixture to early and has the same effect as overly advanced ignition timing. Pre-ignition causes the engine to experience more severe detonation as a result of the early initiation of the combustion process from pre-ignition which leads to more detonation that leads to more pre-ignition...to more detonation until the engine is experiencing detonation every engine revolution. (run away detonation) Escalating advancement of the ignition timing from pre-ignition continues until the spark plug fails and shuts the engine down or the engine runs until it burns a hole in the center of the piston if the rider continues to ignore the engine begging and pleading for the rider to stop punishing it with detonation.
The most common cause of death on an engine's death certificate is run away detonation.
The most common cause of detonation are listed below in the order we see the most piston failures
1. Fuel octane is too low for the engine package.
2. Improper throttle control from the rider for the RPM and load on a high performance two-stroke engine.
3. Lean A/F ratio due to the tuners unrealistic expectations of how responsive and smooth a high performance two stroke engine should run at the lower and mid RPM range.
4. Too much restriction in the pipe stinger and or muffler
5. Ignition timing too advanced.
6. Too much compression and or lousy cylinder head design.
7. Coolant/engine temperature is too high.
8. Wrong spark plug heat range of electrode/ground strap configuration for the way the bike is being ridden.
Points 2 and 3 are very difficult to explain to a customer because of their lack of understanding of the phenomena that occurs during one engine revolution of a highly developed two-stroke engine. Two strokes are mechanically simple but much more complicited than four strokes when it comes to an in depth understanding of what happens when they are running and why it is happening. I may attempt to explain some of the phenomena when I have many hours to try and scratch the surface on this complex topic. I can explain it to you guys but I cannot understand it for you.
This engine was experiencing run away detonation. On the onset of run away detonation, intermittent detonation can easily be heard. If corrective throttle control is not immediately executed, the intermittent detonation will escalated to run away detonation condition where the tone of the engine changes and a very slight power loss WILL OCCUR until spark plug and or piston failure occurs or the rider implements immediate corrective throttle control.
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OK well there's definitely a lot going on here. I can confirm and ruLe out some of your comments.
1. Fuel octane is too low for the engine package.
I'm running 110 but I guess I really DONT know if I need a higher octane or not. When I tead it apart I'll figure out the compression ratio.
2. Improper throttle control from the rider for the RPM and load on a high performance two-stroke engine.
I don't know really know how to use proper throttle control but I can tell you I never went past half throttle except for multiple quick blips anywhere between 1/2 and full throttle if I was stuck in the mud or needed to wheelie over some whoops or something.
3. Lean A/F ratio due to the tuners unrealistic expectations of how responsive and smooth a high performance two stroke engine should run at the lower and mid RPM range.
I followed the thread rss396 posted about jetting a carb. Throughout the process all indicators pointed to a rich condition throughout the whole thing. Included to more than normal smoke and a black plug. I didn't have much time to jet it so I figured if it was rich I was safe but I'm not nor do I claim to be an expert. I have jetted engines though so I'm not completly ignorant on the process.
4. Too much restriction in the pipe stinger and or muffler
This one I don't know. All I can tell you is I have a trx5b
5. Ignition timing too advanced.
I dont know this one either. I have a 01 cr125 set at the factory setting.
6. Too much compression and or lousy cylinder head design.
I don't know what too much is. The engine was built by a very very respected person here for his knowledge. I don't think he would have built an engine of a poor design. I can't confirm but I really want to rule out this point.
7. Coolant/engine temperature is too high.
Engine was running around 200 deg every time I stopped to mess with the plugs.
8. Wrong spark plug heat range of electrode/ground strap configuration for the way the bike is being ridden.
I dont know how to determine this.
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Be very careful with that CR 125 CDI box it really puts a lot of advance into your ignition timing I talked to Dave rss396 at Silverlake last year and he told me to try one on my 330 but to really watch the spark plug because it may get loose. I bought one but I have not tried it yet I am a little afraid to. One other thing that I have heard over the years is that being "on the pipe" at half throttle is not a good thing at all
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If you have to much advance in the timing and the flame front is meeting the piston before it starts its downward travel,more octane will not help,I would try the 01 cdi cr250 cdi.
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I just looked up the timing curve for the 2001 cr250 and 2001 cr125cdi boxes and that 125 box puts out A LOT more advance at the lower RPM's than the 250 does. I would bet that is the problem. Check this thread out http://trx250r.org/threads/96-Ign-maps It shows the timing curves of different ignition systems. If you don't have a CR250 CDI box might try putting the stock ignition back on and see if it does it again.
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Could I just retard the timing a little bit?
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From the way you described you ride, It sounds like you don't spend much time at wide open throttle. Looking at the ignition curve charts, you would have to retard the timing like 10 degrees. I don't know if there is that much adjustment. I run my CR250 ignitions at stock setting. But you could try it if you wanted to but what is happening is EXTREMELY hard on the motor. Be happy that the spark plugs are letting loose first and not the piston!!
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There is 10 degrees more advance right off idle,Do you have that much adjustment and would it start if you could back it off that far.
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From the way you described you ride, It sounds like you don't spend much time at wide open throttle. Looking at the ignition curve charts, you would have to retard the timing like 10 degrees. I don't know if there is that much adjustment. I run my CR250 ignitions at stock setting. But you could try it if you wanted to but what is happening is EXTREMELY hard on the motor. Be happy that the spark plugs are letting loose first and not the piston!!
There almost has to be damage to the piston already,My guess is the damage is in the center of piston
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OK well there's definitely a lot going on here. I can confirm and ruLe out some of your comments.
1. Fuel octane is too low for the engine package.
I'm running 110 but I guess I really DONT know if I need a higher octane or not. When I tead it apart I'll figure out the compression ratio.
2. Improper throttle control from the rider for the RPM and load on a high performance two-stroke engine.
I don't know really know how to use proper throttle control but I can tell you I never went past half throttle except for multiple quick blips anywhere between 1/2 and full throttle if I was stuck in the mud or needed to wheelie over some whoops or something.
3. Lean A/F ratio due to the tuners unrealistic expectations of how responsive and smooth a high performance two stroke engine should run at the lower and mid RPM range.
I followed the thread rss396 posted about jetting a carb. Throughout the process all indicators pointed to a rich condition throughout the whole thing. Included to more than normal smoke and a black plug. I didn't have much time to jet it so I figured if it was rich I was safe but I'm not nor do I claim to be an expert. I have jetted engines though so I'm not completly ignorant on the process.
4. Too much restriction in the pipe stinger and or muffler
This one I don't know. All I can tell you is I have a trx5b
5. Ignition timing too advanced.
I dont know this one either. I have a 01 cr125 set at the factory setting.
6. Too much compression and or lousy cylinder head design.
I don't know what too much is. The engine was built by a very very respected person here for his knowledge. I don't think he would have built an engine of a poor design. I can't confirm but I really want to rule out this point.
7. Coolant/engine temperature is too high.
Engine was running around 200 deg every time I stopped to mess with the plugs.
8. Wrong spark plug heat range of electrode/ground strap configuration for the way the bike is being ridden.
I dont know how to determine this.
Your engine builder should have told you what fuel, pipe, type of carburetor, a close starting point on jetting, type of spark plug and heat range to use. If your engine builder assembled the engine the ignition timing should not need ANY adjustment. Your engine builder should have given you some guidelines as far as the optimum coolant temperature as well as the maximum temperature the engine should experience.
Did you selected any of the following: type of porting, head dome, exhaust system, carburetor, ignition and ignition timing, or spark plug based upon your own research or did your engine builder provide a shopping list for ALL INGREDIENTS for his engine package? If you selected the ingredients, you have done the 1st phase of research and development, which is a starting point for your engine package # 1. Now you are starting to go through the expensive development phase of engine package # 1 that all engine designers and good engine builders go through when they develop (debug and test) a powerful and reliable engine package.
If the majority of your riding requires the engine to be operated and 1/2 throttle or less and the engine is on the pipe, you have the wrong engine package for your type of riding. A highly developed properly tuned two-stroke will not usually tolerate more than a few seconds of this type of throttle control without experiencing detonation. A highly developed package that is not properly tuned may experience immediate detonation and may only take seconds to burn a piston or destroy the spark plug.
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I found a 250 cdi for a decent price on eBay. It should be here towards the end of the week. I'll also pop the head to check for damage