2016 125sx piston life?

Hello. 

Just like title - what is the expected life of a 125s piston when beat at a track?

Manual seem to call for 20hrs and it seems OK, but talking to a engine builder about the jap 125s and he says rebuild every 10hrs and had a friend who fried his org piston at 16hrs in a YZ125. 

Any real life experience who want to chime in? Ive heard some crazy hours but cant take that seriously when ridden on the pipe around a track all time  

 

You'll find the answers are going to vary alot. It depends on terrain and rider. You need to inspect and find your own needs. 

 

 I run "crazy" hours with a rering in the middle. This is off-road with half slow techie stuff. 

When you say crazy hours what do you mean?

Rering at 35 hours.  Piston at 70. On a 150 now and think 40 will be fine. I don't rev it nearly as much. 

 

 I would not try that riding our sand MX tracks or only riding fast open trails. 

 

 Many of the people that fry pistons with low hours have jetting to blame. I sold a fresh  250 to a guy who killed it in 2-3 weekends. I warned him my setup was for off-road not his 5th gear sand track. 

42 minutes ago, GasitandCrash said:

When you say crazy hours what do you mean?

50 hrs at track. 

Im talking about loamy track and ridden on the pipe, above average rider. 

If I could get 30 I would be happy but possibly every 10hrs, damn. 

We have used 125 KTMs for mx racing since 2012. Single ring Vertex in the race bike and twin ring in the practice bike. We always use 53.95s with replate when required. Both bikes' pistons are changed at 15 hours. They are jetted as near perfect as we can get them with a filter change after every moto or 30 minutes in the praccy bike. 99 octane petrol at 40:1 with fully synthetic 2T. We used to run VHM 15 degree top pistons in the race bike but they needed changed every 5 hours and the cost became too high for us to justify. I think if the bike is getting easier use then 25 hours is feasible, but we wouldn't go there. Your piston goes up and down 200 times a second at full tilt with exhaust gases exiting at 1200 degrees F - the piston gets a hard life! Your decision. Bob.

43 minutes ago, 7Tktm said:

We have used 125 KTMs for mx racing since 2012. Single ring Vertex in the race bike and twin ring in the practice bike. We always use 53.95s with replate when required. Both bikes' pistons are changed at 15 hours. They are jetted as near perfect as we can get them with a filter change after every moto or 30 minutes in the praccy bike. 99 octane petrol at 40:1 with fully synthetic 2T. We used to run VHM 15 degree top pistons in the race bike but they needed changed every 5 hours and the cost became too high for us to justify. I think if the bike is getting easier use then 25 hours is feasible, but we wouldn't go there. Your piston goes up and down 200 times a second at full tilt with exhaust gases exiting at 1200 degrees F - the piston gets a hard life! Your decision. Bob.

Thank you. 

How come the twin ring if it doesnt get any extra life?

Ah good question. Just something we have always done. Probably a mind game as the praccy does a lot more hours than the race bike. The pistons are the same price and you can just run the top ring in a twin ring and keep the bottom as a spare. You will have noticed the 16 125s are some way ahead of the pre 16s in terms of performance. To date the race bike (engine has been 'race tuned') has blown a right hand crank seal (which enveloped Hawkstone Park in smoke!) and a new oem left hand main broke up (luckily there is a top hat bush on the crank which prevented any damage so was an easy fix)  For 2 seasons of real hard 125  mx racing on a mix of tracks that is pretty good. Good bikes. Bob.

12 hours ago, seer said:

You'll find the answers are going to vary alot. It depends on terrain and rider. You need to inspect and find your own needs. 

 

 I run "crazy" hours with a rering in the middle. This is off-road with half slow techie stuff. 

 

That's what I ride, so what is crazy hours for this type of riding?

20 hours ago, seer said:

Rering at 35 hours.  Piston at 70. On a 150 now and think 40 will be fine. I don't rev it nearly as much. 

 

 I would not try that riding our sand MX tracks or only riding fast open trails. 

 

 Many of the people that fry pistons with low hours have jetting to blame. I sold a fresh  250 to a guy who killed it in 2-3 weekends. I warned him my setup was for off-road not his 5th gear sand track. 

 

8 hours ago, GasitandCrash said:

That's what I ride, so what is crazy hours for this type of riding?

 

I got 7 years of trail riding and daily street use on my 2000 125 EXC until I dropped it into a river. Compression was still good up until that. Pump fuel, Ipone at 40:1, rarely hit redline, rarely do sand, jetting was a bit rich. Cylinder got scratched up a bit from the muddy water, i used to replace the ring yearly thereafter to keep compression. I also started highway driving (50-60mph, 80mph max only briefly, 50-100miles) about the time and leaned the jetting. I could feel the compression with my foot. When it got under 90psi, I replaced the ring and inspected the piston replacing if needed.

Eventually the crank went, more from 3 dips in muddy water than high speed driving, Rather than replace the crank I replaced the motor with a 2001 SX that ran another 7 years of trail and highway driving on its original piston. The crank went last month on this 2001, at about 70mph. Rod big end bearing failed. Very little heating (bluing) and no bits hit the cylinder. Good stuff these KTMs! 

My son had a YZ125 and he ran it on redline and did the sand bowl circuit. in a couple months when he blew his piston skirt we replated and checked frequently. We were replacing a couple pistons a year with visible cracking. If you are gonna redline, ya gotta at least inspect.

 

A or B level mx replace under 20 or measure ring end gap and replace when out of spec. 
 

Attached is a 95.5 hour 125 piston, with a re-ring at 45 hours.  Oil ratio was 32:1 (yamalube 2R).  Piston is Wiseco (whatever they call their top-of-the-line with coating) and the whole kit (gaskets, etc.) costs $135.  Ring alone is $11 (and you also need a base gasket).  Bike was used for A and B level hare scramble racing and a lot of "race pace" trail riding.  Notice that there is virtually no blow by and the coating on the piston is barely worn off.  The second picture shows another piston from the same bike, also at about 95 hours, but Lucas oil was used.  It still looks good, but much more of the coating is worn off.

I would think even the fastest MX rider could get away with at least 40 hours on a forged piston.  I never run cast pistons (vertex or other OEM) in any bike (KTM or J).  I've seen lots of skirt cracks and other failures over the years, but I don't recall ever seeing a forged piston fail without an obvious cause (rider error stuff like forgetting to mix oil, hole in air filter, etc.).

Enjoy your 125!  I rarely ride my 250 anymore.

piston intake.jpg

piston comp.jpg

Well, I &%$#@!ing did it. I got the 125. Pre owned by a sponsored younger girl and every bigger maintance was made in shop. 

60 hrs and 10hrs on the piston and talked to the shop owner (old champion in Sweden, pretty cool) and he said I could go for 30-35hrs on piston. 

Im not sure about cast vs forged. Race shops have recommended cast but not sure why

KTM cast pistons are pretty good. Like RPT50, I've never had a problem with a KTM cast piston other than eventual wear.

I did have a forged Wiseco seize due to using full throttle after allowing a mile of warm up. I guess that would classify as operator error.

Cast pistons are much more forgiving of warm up. Wossners are forged and are also more forgiving of warm up. 

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