Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: 2STROKEREVOLUTION on February 07, 2011, 08:35:36 AM
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So, here is the story.
I had a 380SX and love the bike. I saw a good deal on a 380exc and decided to jump on it. The guy forgot to mix one ride and it seized. I picked it up for $500.
I asked a couple people what to do and they all said just get it replated(it is all aluminum). Not only was it seized, there was a small crack in a port. Munn racing said no problem about the crack they just weld it up. So I got it fixed, put back together, and took it out riding. I was riding easy, just to break it in. After a few hours it was still working perfect. It was running cool, getting plenty of oil, and then it seized. After taking it apart it looked like it did when I bought it. Completely scraped cylinder and there was a crack in another port.
I don't trust this jug anymore. I think the best thing to do is get a new cylinder or get a steel sleeve.
What are the suggestions? Any places that have good prices?
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At first, i would ask at KTM for the price of a new 380 cylinder..
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If you opt for a steel sleeve - contact these blokes - I think they can provide a few different sizes to bring it up to as much as 434cc. The engine featured in there is based on a 250SX, but the barrel / piston (and crank) are 380 based. The head spigot, exhaust manifold and exhaust boost chamber are modified because the engines going in a late model SX chassis, so not needed with a std 380 chassis.
http://rpmmfg.com (http://rpmmfg.com)
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Have you checked the jetting? What does the plug look like? You describe a symptom very much like a lean seize, that usually does damage like you identified. I know you say it was running cool, but I would seriously look towards the jetting and the cooling system before you trash yet another cylinder.
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Have you checked the jetting? What does the plug look like? You describe a symptom very much like a lean seize, that usually does damage like you identified. I know you say it was running cool, but I would seriously look towards the jetting and the cooling system before you trash yet another cylinder.
It is not jetting. If anything it is running rich. My other 380 has a leaner needle and is still a tad rich in the mid range and I have had no problems with it.
If it isn't running hot I don't see how it could be cooling.
And I was running extra oil for the break in period.
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If you opt for a steel sleeve - contact these blokes - I think they can provide a few different sizes to bring it up to as much as 434cc. The engine featured in there is based on a 250SX, but the barrel / piston (and crank) are 380 based. The head spigot, exhaust manifold and exhaust boost chamber are modified because the engines going in a late model SX chassis, so not needed with a std 380 chassis.
http://rpmmfg.com (http://rpmmfg.com)
I will definitely check them out, thanks. Any word on what reliability and powerband is for the bigger displacement?
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Check your waterpump impellor.I've seen the steel shaft spin in the plastic impellor and it will still circulate some coolant - you'll pop the rad cap and everything looks o.k. but it's not.Only heat will crack that cylinder.
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Running extra oil? how much extra, extra oil could affect your jetting from what I've heard
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True, more oil= leaner air fuel mix. i'd be checking for air leaks too
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I'll buy it off you or get the cylinder replated for you.Sleeves are bad news.
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check that waterpump, the radiators, everything cooling system related, then check the crank, might be a bent rod..
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Yeah all I was saying was, bikes just don't seize for no reason. Something caused that bike to seize twice.
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I had a friend go through the same thing on his 06 KTM 250SX, siezed it twice... turned out to be a bent rod. He replaced the crank, and now all its been two seasons, its been running great.
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If the top end locked up.. twice, more than likely it hurt the bottom as well.
The same oil that wasn't doing its job on the top, I'm sure wasn't doing it on the bottom. :)
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check that waterpump, the radiators, everything cooling system related, then check the crank, might be a bent rod..
Still don't see how it can be cooling issues when it was not running hot. It was perfect.
I will check the rod.
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Running extra oil? how much extra, extra oil could affect your jetting from what I've heard
Normally I run 60:1 fully synthetic. For this break in I was running 40:1. KTM recommends 40:1 to 60:1 for this bike.
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I'll buy it off you or get the cylinder replated for you.Sleeves are bad news.
What is wrong with a sleeve?
My XR250 and YZ125 have steel sleeves and have no problems. High horsepower and high reliability car engines use steel sleeves.
The only downside I know of is a few ounces extra weight and slightly worse cooling. Both unnoticeable.
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What is wrong with a sleeve?
Most people on here will tell you why.
Chief among the problems is cooling. Instead of a nice thin wall for heat to travel through you now have a large heat sink.
Yes they do work and people do use them as a cheap option instead of replating.
If you are going to work your bike hard get it replated.
Hope you get to the bottom of the problem so it doesn't happen again.
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check that waterpump, the radiators, everything cooling system related, then check the crank, might be a bent rod..
Still don't see how it can be cooling issues when it was not running hot. It was perfect.
I will check the rod.
On my buddies bike the rod was bent. It was difficult to see, but once we figured it out, the siezures made sense.
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I'll buy it off you or get the cylinder replated for you.Sleeves are bad news.
What is wrong with a sleeve?
My XR250 and YZ125 have steel sleeves and have no problems. High horsepower and high reliability car engines use steel sleeves.
The only downside I know of is a few ounces extra weight and slightly worse cooling. Both unnoticeable.
XR250's should never be referenced as any sort of a performance yardstick, plus they are infact air cooled. Yes cars have wet liners but they are normaly surrounded by many many litres of water.
Yes heat is the issue they cylinder is not designed to cope with the heat retention of the sleeve(the interface of the sleeve and cylinder is a thermal barrier) causes the engine to ping uncontrolably when hot. A RGV with sleeves I know locks solid if it's ridden in band for longer than 5 mins. When it cools down it goes fine.
Plating is actualy cheaper than a sleeve.
Want any more ?
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I'll buy it off you or get the cylinder replated for you.Sleeves are bad news.
What is wrong with a sleeve?
My XR250 and YZ125 have steel sleeves and have no problems. High horsepower and high reliability car engines use steel sleeves.
The only downside I know of is a few ounces extra weight and slightly worse cooling. Both unnoticeable.
Want any more ?
What about powervalve/piston clearance issues, if steel cylinder is rebored?
Want any more?
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I'd do either.Oddly enough,IC engines went a long time without a plated cylinder.
Plating is probably superior for the above mentioned reasons but the advantages are marginal in the real world.
On the upside,seize a piston on a plated cylinder and it's done,do it on a sleeve and typically a quick hone and you're off to the races.
I've used sleeves with no issues whatever.Given the choice,I'd probably get it plated BUT,if it's cracked anywhere,I'd probably put in a sleeve rather than get it welded-that seems to be 50/50 whether it's going to crack again or not-and sometimes cracks already there aren't detectable-until you ride it after your rebuild.
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60:1 !!!???? dude you might as well be running straight gas. ALWAYS break it in at 32:1!!!! Personally I run 12oz 24:1 then pour in 32:1 and run 3 gallons of that, full tank on my bike. IF it's blowing heavy spooge after that, I'll drop it to 40:1. 50:1 is the lowest I'll go, and that is after the motor is well broken in and there's black spooge pouring out of every available crevice that spooge can run from.
60;1 even with these new synthetics is just asking for trouble.
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I have never had to perform a topend job before 50 hours with this method.
at 50 hours I clean the head dome, powervalve, and piston, and replace the rings and small end bearing.
100 hours sees a new piston,rings, and seb.
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I'd do either.Oddly enough,IC engines went a long time without a plated cylinder.
Plating is probably superior for the above mentioned reasons but the advantages are marginal in the real world.
On the upside,seize a piston on a plated cylinder and it's done,do it on a sleeve and typically a quick hone and you're off to the races.
I've used sleeves with no issues whatever.Given the choice,I'd probably get it plated BUT,if it's cracked anywhere,I'd probably put in a sleeve rather than get it welded-that seems to be 50/50 whether it's going to crack again or not-and sometimes cracks already there aren't detectable-until you ride it after your rebuild.
Myth 298. After seizing a plated cylinder the fix is easier than a liner. Hydrochloric acid on a cotton bud and the aluminium fizzles away. Wash with water a 10 min job.
If a replated cylinder cracks it is the welding that is not up to standard.
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60:1, like Myc said IS asking for failures.
Get your bottom end re-built, fresh top and 32:1.
After that you can have more fun riding not worrying about early failure anymore. :)
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60:1 !!!???? dude you might as well be running straight gas. ALWAYS break it in at 32:1!!!! Personally I run 12oz 24:1 then pour in 32:1 and run 3 gallons of that, full tank on my bike. IF it's blowing heavy spooge after that, I'll drop it to 40:1. 50:1 is the lowest I'll go, and that is after the motor is well broken in and there's black spooge pouring out of every available crevice that spooge can run from.
60;1 even with these new synthetics is just asking for trouble.
exhaust spooge is an air/fuel issue not an oil/fuel mixture problem
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I'd do either.Oddly enough,IC engines went a long time without a plated cylinder.
Plating is probably superior for the above mentioned reasons but the advantages are marginal in the real world.
On the upside,seize a piston on a plated cylinder and it's done,do it on a sleeve and typically a quick hone and you're off to the races.
I've used sleeves with no issues whatever.Given the choice,I'd probably get it plated BUT,if it's cracked anywhere,I'd probably put in a sleeve rather than get it welded-that seems to be 50/50 whether it's going to crack again or not-and sometimes cracks already there aren't detectable-until you ride it after your rebuild.
Myth 298. After seizing a plated cylinder the fix is easier than a liner. Hydrochloric acid on a cotton bud and the aluminium fizzles away. Wash with water a 10 min job.
If a replated cylinder cracks it is the welding that is not up to standard.
Myth 299.Straight hydrochloric is way too harsh-Muriatic is what is commonly used.Even then,a little pick in the plating from the seize and it will eat in to that and under the plating-also be super careful in the port area.Just leave it on for a few seconds and rinse well.It's rare to seize a piston and not damage the cylinder unless you realized what was happening and shut it down before it locked up-despite what it looks like from gawking down in to it.Typically,it's days are numbered at this point.
Many rewelded cylinders crack at the base of the weld-typically they are not the easiest thing to access and any crack,welded or not,creates a stress riser.It's hard to blame the welder for that.
Many also crack elsewhere afterwards.Given the heat and stress when the seizure occurs it's not uncommon to create a hairline crack that isn't visible-even with a boroscope.
Myth 300. You know more than I do. :o ;)
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exhaust spooge is an air/fuel issue not an oil/fuel mixture problem
You beat me to it. If you are getting excessive spooge, fix your jetting, don't mess with the mix.
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That's true but at the same time,even a correctly jetted bike will spooge somewhat if one has a weak right wrist or rides in eastern type off road conditions.
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That's true but at the same time,even a correctly jetted bike will spooge somewhat if one has a weak right wrist or rides in eastern type off road conditions.
Uhm, yeah, that's why I said "excessive" in my post... :P
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I'd do either.Oddly enough,IC engines went a long time without a plated cylinder.
Plating is probably superior for the above mentioned reasons but the advantages are marginal in the real world.
On the upside,seize a piston on a plated cylinder and it's done,do it on a sleeve and typically a quick hone and you're off to the races.
I've used sleeves with no issues whatever.Given the choice,I'd probably get it plated BUT,if it's cracked anywhere,I'd probably put in a sleeve rather than get it welded-that seems to be 50/50 whether it's going to crack again or not-and sometimes cracks already there aren't detectable-until you ride it after your rebuild.
Myth 298. After seizing a plated cylinder the fix is easier than a liner. Hydrochloric acid on a cotton bud and the aluminium fizzles away. Wash with water a 10 min job.
If a replated cylinder cracks it is the welding that is not up to standard.
Myth 299.Straight hydrochloric is way too harsh-Muriatic is what is commonly used.Even then,a little pick in the plating from the seize and it will eat in to that and under the plating-also be super careful in the port area.Just leave it on for a few seconds and rinse well.It's rare to seize a piston and not damage the cylinder unless you realized what was happening and shut it down before it locked up-despite what it looks like from gawking down in to it.Typically,it's days are numbered at this point.
Many rewelded cylinders crack at the base of the weld-typically they are not the easiest thing to access and any crack,welded or not,creates a stress riser.It's hard to blame the welder for that.
Many also crack elsewhere afterwards.Given the heat and stress when the seizure occurs it's not uncommon to create a hairline crack that isn't visible-even with a boroscope.
Myth 300. You know more than I do. :o ;)
The best way of stopping welding induced stress is the slow heat and cool cycle, the welder has control over that. Never had a straight seizure damage a cylinder, only when the piston disintergrates does the damage occur(usually from the rod flapping around). My replater has no problems welding anywhere in a cylinder, ports come back with the timing they went over there with. Cylinders still in use on engines that get a very hard life ie shifterkarts.
The use of a EGT gauge(or detonation counter) tells when seizure is close.
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So what should the EGT be and where would you measure it at? I have access to EGT probes and gauges. What about CHT?
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I don't believe I said excessive spooge,
what I meant was if there is an apearant amount of spooge, it is then safer to lower the oil to fuel ratio.
southeastern woods
3.57 gear ratio
perfect jetting
4 year old bike on it's second spark plug(I only replaced it because I did a topend job, it was in perfect operating condition and now in my fanny pack as a back up to my back up)
very strong right wrist
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very strong right wrist
What do you do for exercise ? ;) :P
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Funny TMKIWI
"Aunt Flo" just came to visit for the week so looks like I'll be training this week.
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;D
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very strong right wrist
What do you do for exercise ? ;) :P
Bwhahahahahahahahahha.Good practice for married life if you're not already anyway :(
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The best way of stopping welding induced stress is the slow heat and cool cycle, the welder has control over that. Never had a straight seizure damage a cylinder, only when the piston disintergrates does the damage occur(usually from the rod flapping around). My replater has no problems welding anywhere in a cylinder, ports come back with the timing they went over there with. Cylinders still in use on engines that get a very hard life ie shifterkarts.
The use of a EGT gauge(or detonation counter) tells when seizure is close.
What?That's it? You're no fun :D
Maybe different quality of work in different place.
I've got EGT's on the snowmobile but probably not real practical for a bike.
McClung-about 1.5" from the exhaust port is good.