TRX250R.ORG
Workshop => Engine and Bottom End => Topic started by: Tbone07 on April 27, 2015, 10:36:56 AM
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I'd like to point out that this is not out of my 250r lol. This is a piston out of my buddies KTM 125 that blew up this weekend
What do you guys think is the root cause? The only change he made recently is that he didn't run race gas, I believe his compression was well over 200
(http://forums.trx250r.org/vbulletin_imports/483_5209_2017-04-18_3126.jpg)(http://forums.trx250r.org/vbulletin_imports/483_5210_2017-04-18_1883.jpg)(http://forums.trx250r.org/vbulletin_imports/483_5211_2017-04-18_8568.jpg)(http://forums.trx250r.org/vbulletin_imports/483_5212_2017-04-18_8382.jpg)
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The transparent discoloration and absence of carbon on the piston crown surrounding the crater in the center, is a sign of severe piston crown over heating. Detonation causes severe piston crown overheating.
The crater forming in the center of the piston is from pre-ignition. The pre-ignition is the result of detonation. The carbon/discoloration over this crater is evidence that the crater was formed during one of his prior engine abuse sessions
The piston shows severe detonation damage around the whole circumference of the piston. The sand blasted looking band that is about 1/8" wide around the whole circumference is the result of detonation.
The missing piece of piston is the result of force the ring is placing on the weakened area at high RPM of a severely overheated piston. I do not think that the piece was burned away because the top of the piston shows damage from the pieces. If this area was burned away there would not be debris damage on other areas of the piston crown.
Typical causes of detonation:
1. Low octane rating can cause detonation.
2. Advanced ignition timing can cause detonation .
3. A lean air/fuel ratio can cause detonation.
4. High coolant temperature/engine temperature can cause detonation.
5. An exhaust system that is over-restricted can cause detonation. A carboned up stinger ID or carboned up spark arrestor are common causes of an over-restricted exhaust system.
Is you buddy deaf??
This engine was announcing it was having problems loud and clear right up to the moment of death. I have seen hundreds of engines with copycat damage as pictured.
Why is your buddy trying to save money by running pump gas on such an expensive engine like a KTM?
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The only change he made recently is that he didn't run race gas, I believe his compression was well over 200
^^ This statement, has answered your question.
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^^ This statement, has answered your question.
That's exactly what i expected too, just wanted to hear it from Jerry lol
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The transparent discoloration and absence of carbon on the piston crown surrounding the crater in the center, is a sign of severe piston crown over heating. Detonation causes severe piston crown overheating.
The crater forming in the center of the piston is from pre-ignition. The pre-ignition is the result of detonation. The carbon/discoloration over this crater is evidence that the crater was formed during one of his prior engine abuse sessions
The piston shows severe detonation damage around the whole circumference of the piston. The sand blasted looking band that is about 1/8" wide around the whole circumference is the result of detonation.
The missing piece of piston is the result of force the ring is placing on the weakened area at high RPM of a severely overheated piston. I do not think that the piece was burned away because the top of the piston shows damage from the pieces. If this area was burned away there would not be debris damage on other areas of the piston crown.
Typical causes of detonation:
1. Low octane rating can cause detonation.
2. Advanced ignition timing can cause detonation .
3. A lean air/fuel ratio can cause detonation.
4. High coolant temperature/engine temperature can cause detonation.
5. An exhaust system that is over-restricted can cause detonation. A carboned up stinger ID or carboned up spark arrestor are common causes of an over-restricted exhaust system.
Is you buddy deaf??
This engine was announcing it was having problems loud and clear right up to the moment of death. I have seen hundreds of engines with copycat damage as pictured.
Why is your buddy trying to save money by running pump gas on such an expensive engine like a KTM?
That's a very good question, i've told him multiple times not to take shortcuts or explosions will happen.
He's one of those MX racers that really needs his own mechanic to work on his bikes and tell him what to use and run.
Apparently he also advanced the timing to gain throttle response......I didn't even know KTM came with that adjust-ability
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same thing happened to my buddies KTM 250 last weekend. ouch!
John
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all the ktms ive been around have a fair amount of adjustability at the stator plate. i would take a guess at 6 or 7 degrees judging by the slotted holes http://www.ebay.com/itm/03-Ktm-125sx-Stator-Magneto-98-05-125-105-144-150-200-250-300-Exc-Sx-Mxc-Sxf-/221752521284?hash=item33a17af244&vxp=mtr
the 200 kicking pressure doesnt tell you much. the exh valve may sit very low when its in the closed position. your gauge might not of even been correct. its hard to say. sounds like your friend might be better off to let someone else do the tuning next time