Keeps blowing pistons

Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez
Edited Date/Time 7/5/2020 5:30pm
Hi I got my son a 2015 kx 85 an now it blew the piston 3 times. Scared up on intake an exhaust sides pretty bad I got cylinder replated an it just did it again today what could be wrong with the spark plug is a brownish color. An it smells like it’s overheating I get a anti freeze smell. Someone please help I put like 1600$ in this bike this yr. mixture is 32:1 not losing coolant
|
Paul_Pitzonka
Profile picture for user Paul_Pitzonka
Posts
693
Joined
5/1/2018
Location
Grand Terrace, CA, USA
Paul_Pitzonka 8/11/2019 6:21pm
8/11/2019 6:21pm
Ryan_Paez wrote:
Hi I got my son a 2015 kx 85 an now it blew the piston 3 times. Scared up on intake an exhaust sides pretty bad...
Hi I got my son a 2015 kx 85 an now it blew the piston 3 times. Scared up on intake an exhaust sides pretty bad I got cylinder replated an it just did it again today what could be wrong with the spark plug is a brownish color. An it smells like it’s overheating I get a anti freeze smell. Someone please help I put like 1600$ in this bike this yr. mixture is 32:1 not losing coolant
Photos would help... are you positive you have no air leaks?
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 6:31pm
8/11/2019 6:31pm
I’m not sure how do I check for that
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 6:32pm
8/11/2019 6:32pm
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 6:34pm
8/11/2019 6:34pm



The Shop

See All »
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 6:36pm
8/11/2019 6:36pm
Any idea what could be going on an the other 1 s looked the same except the top is a little more brown color
Paul_Pitzonka
Profile picture for user Paul_Pitzonka
Posts
693
Joined
5/1/2018
Location
Grand Terrace, CA, USA
Paul_Pitzonka 8/11/2019 6:58pm
8/11/2019 6:58pm Edited Date/Time 8/11/2019 7:17pm
Could be a small coolant leak (cracked head, cylinder) washing the cylinder, and causing a seizure... what does the bore and head look like?
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 7:20pm
8/11/2019 7:20pm
The bore is scracted up to an I just got it done the head don’t look bad but I don’t really know what to look for on the head
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 7:24pm
8/11/2019 7:24pm
The head cylinder is where the spark plug goes?? I don’t know much about dirt bikes my son races an I always take bike to get fixed. The hole bottom end was done by a shop in North Carolina like 20 hrs of riding an he hasn’t really rode it hard yet so I hope it’s not that. I hope it’s a air leak.
c0ncEpT
Profile picture for user c0ncEpT
Posts
1318
Joined
5/13/2015
Location
Harrison Twp., MI, USA
c0ncEpT 8/11/2019 7:32pm
8/11/2019 7:32pm
Not enough piston to wall clearance or lean jetting. To much heat.
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/11/2019 7:49pm
8/11/2019 7:49pm
Would that make it smell like it’s overheating. An how do I make it not run lean. Like I said I don’t know much about dirt bikes
Paw Paw 271
Profile picture for user Paw Paw 271
Posts
3632
Joined
4/3/2013
Location
Benton, LA, USA
Paw Paw 271 8/11/2019 8:22pm
8/11/2019 8:22pm
That shows to be a "cold sieze". This can happen when the engine is not allowed to fully warm up prior to putting it under a hard load. ( You know how most kids are...Crank it up and then take off full blast all in about 10 seconds.)

How many heat cycles did you put the engine through prior to allowing the kid to get wide open?

I would not rull out a leaking head gasket as well.

Paw Paw
2
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 4:03am
8/12/2019 4:03am
Yea he just started it an took off. The gasket could be problem it looked a little funky
danman
Profile picture for user danman
Posts
1204
Joined
4/1/2008
Location
Readstown, WI, USA
danman 8/12/2019 6:19am
8/12/2019 6:19am
Ryan_Paez wrote:
Yea he just started it an took off. The gasket could be problem it looked a little funky
There is part of your problem. Cold seizure. You need to let the bike warm up prior to putting it under load.

For what it's worth, my method of warming up prior to riding is to completely idle the bike until the cylinder itself is warm to the touch, then go ride. No blipping of the throttle or anything. Perhaps that's a bit extreme, but I've never had anything like that happen.
Some people wait until the wide part of the pipe is warm to the touch. I don't like that because the cylinder wall is thicker and will take a bit longer to get to temp.

At this point, you should have the head and cylinder surfaces checked to ensure they aren't warped. If they are, nothing you do will prevent this from happening over and over again.

I'd also check to make sure the airbox is sealed properly each and every time you put it on. Keep the dirt out.

good luck.
1
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 6:59am
8/12/2019 6:59am
Thx. But 1 ? My son rode the bike for a good hr an on way home from the trails is when it happen. Would a cold seizure let it run for a while
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 7:01am
8/12/2019 7:01am
An do u know what the jetting is supposed to be on the kx 85
danman
Profile picture for user danman
Posts
1204
Joined
4/1/2008
Location
Readstown, WI, USA
danman 8/12/2019 7:24am
8/12/2019 7:24am
Ryan_Paez wrote:
Thx. But 1 ? My son rode the bike for a good hr an on way home from the trails is when it happen. Would a...
Thx. But 1 ? My son rode the bike for a good hr an on way home from the trails is when it happen. Would a cold seizure let it run for a while
Yes, it could. Every cold start does a little more damage. Eventually, it weakens a part enough to chip/break, which floats around and does more damage, leading to what you have.
Sorry, I don't know the jetting specs. It's been many years since my boys were on 85's.
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 7:28am
8/12/2019 7:28am
An how do I check if head is warped or cracked
danman
Profile picture for user danman
Posts
1204
Joined
4/1/2008
Location
Readstown, WI, USA
danman 8/12/2019 7:45am
8/12/2019 7:45am
Ryan_Paez wrote:
An how do I check if head is warped or cracked
For the head, put it on a known flat surface. I've heard of people using glass. Use a feeler gauge and go around trying to fit it under the head.
I don't know how to do it for the cylinder.
If I had to check, I'd send it to someone reputable to check for me.

Pit Row

See All »
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 7:49am
8/12/2019 7:49am
I’m going to just get a new head I ordered a new cylinder so hopefully it’s that. If u think of anything else that could help me please send it over an thank u very much
charlie68
Profile picture for user charlie68
Posts
161
Joined
6/28/2019
Location
North Windham, CT, USA
charlie68 8/12/2019 8:40am
8/12/2019 8:40am
I had a similar problem years ago with a brand new CR125 ( in 03 ) cylinders, pistons, heads etc.... come to find out the bike was actually overheating and not spitting the coolant, the radiator cap would not hold pressure. Cooling system needs pressure to cool the engine, luckily for me Honda stood behind their product and sent techs numerous times until they got it right.
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 9:17am
8/12/2019 9:17am
U think that’s y I keep smell burning anti freeze
exbmxmx
Profile picture for user exbmxmx
Posts
159
Joined
2/13/2017
Location
Houston, TX, USA
exbmxmx 8/12/2019 9:20am
8/12/2019 9:20am
Are you running the stock jetting (pilot = 38, main=140)? What fuel and oil are you using? Are you getting any spooge out the exhaust? If this is the third piston problem, are you measuring the piston to cylinder clearance as outlined by the piston manufacturer? Vertex includes very specific info for piston installation.

If it has a significant air leak, the bike will not idle correctly. Typically, they will idle high or require some throttle input to keep the bike running.

As far as warming up the bike, I always crank it up and ride it around the pits for a few minutes making sure the cylinder is hot before I give it to my lil ripper. Doing this allows me to check the front and rear brakes, clutch and shifting, making sure its steering straight and verify nothing is vibrating or wobbling before he goes and hits the track. From a safety standpoint, I think everyone should be doing at least this before letting their kiddo out for a moto.
exbmxmx
Profile picture for user exbmxmx
Posts
159
Joined
2/13/2017
Location
Houston, TX, USA
exbmxmx 8/12/2019 9:22am
8/12/2019 9:22am
Have you removed the radiator cap when you first start the engine to verify the coolant is actually being pumped around the system?

Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 9:33am
8/12/2019 9:33am
Yes getting little spooge out of pipe running 93 32:1 Koltz mix. Not sure about the jets. What should I do for the jets size wise
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 9:39am
8/12/2019 9:39am
No never took cap off rad while running but the radiator has a big bend in it but nothing leaking out u think that’s the problem
charlie68
Profile picture for user charlie68
Posts
161
Joined
6/28/2019
Location
North Windham, CT, USA
charlie68 8/12/2019 9:43am
8/12/2019 9:43am
Ryan_Paez wrote:
U think that’s y I keep smell burning anti freeze
There is a very good chance of it, in my case the steam was leaching by but not the liquid. I would be interested in seeing a pic of the radiator neck as soon as you remove cap and the inside of the cap as well.
exbmxmx
Profile picture for user exbmxmx
Posts
159
Joined
2/13/2017
Location
Houston, TX, USA
exbmxmx 8/12/2019 9:50am
8/12/2019 9:50am
Ryan_Paez wrote:
Yes getting little spooge out of pipe running 93 32:1 Koltz mix. Not sure about the jets. What should I do for the jets size wise
I would start with the stock jetting. With the stock jetting you should not have a problem like this.

1
exbmxmx
Profile picture for user exbmxmx
Posts
159
Joined
2/13/2017
Location
Houston, TX, USA
exbmxmx 8/12/2019 9:54am
8/12/2019 9:54am
Ryan_Paez wrote:
No never took cap off rad while running but the radiator has a big bend in it but nothing leaking out u think that’s the problem
What do you mean by a big bend? You need to verify you are moving coolant through the system.

An overheating and/or oil starved engine will score the piston on the exhaust side because its sees the highest temps.
Ryan_Paez
Profile picture for user Ryan_Paez
Posts
42
Joined
8/11/2019
Location
Downingtown, PA, USA
Ryan_Paez 8/12/2019 9:57am
8/12/2019 9:57am
It has moon shape bend from top to bottom . Oil starved what do I do about that
exbmxmx
Profile picture for user exbmxmx
Posts
159
Joined
2/13/2017
Location
Houston, TX, USA
exbmxmx 8/12/2019 10:02am
8/12/2019 10:02am
Ryan_Paez wrote:
It has moon shape bend from top to bottom . Oil starved what do I do about that
The radiator is bent in a moon shape from top to bottom? Obviously, you can't check the radiator flow now but you can take it off the bike and place your house water hose in the fill neck and make sure you get a good flow out of the radiator outlets.

Oil starvation would be from too lean of jetting.

Post a reply to: Keeps blowing pistons