Read my piston and cylinder please

You got a little blow by, because the cylinder and piston are not sealing that good, needs replating
Head looks ok, just sand down that mark

If that's 15hrs then I would say she runs pretty clean. How much time on the plug, maybe a little on the lean side looking at that plug. What kind of oil you running? As for the oil in the bottom end that is pretty normal.

Hard to tell looking at the pictures of the cylinder wall. I will usually try to clean them up in the solvent tank with some fine (600) sand paper in a circular pattern or a fine ball hone provided it isn't wore or scored through the Nikasil. I would use caution if you use a ball hone. How much time on the cylinder?

Pictures of the piston sides/skirts might tell a better story.

If I did send the cylinder in to get it replated I would send the head as well, there are a couple area's both in the combustion area and oring area they can clean up for you as well.

That plug looks like the gap is smashed and the piston looks like it hit the plug??? The rear intake port has chipped nikisil and need a replate for sure.

Can we get a close up of the plug and the head where the plug goes in it looks cracked

EXACTLY what do you mean by "I played with the jetting"?

Was it running like it was loading up before?

What 2 stroke oil are you using?

What ratio?

Did you switch 2 stroke oil or the ratio for the new piston?

Sure looks like a piston seized in that cylinder at some point so that needs to be addressed. f you can feel grooves in the cylinder, you are better off getting it bored, and if it is plated, then get i replated.

that plug suggests you are likely at least 3 sizes too small on the main jet, unless it has fuel injection and that is close to what it should look like.

It also looks like there might be some damage (pitting) on the cylinder head. You should clean off the carbon then look closely at it. It is possible the engine was detonating.
.

It’s does look like the plug was hitting the piston

dkurtd wrote:

If that's 15hrs then I would say she runs pretty clean. How much time on the plug, maybe a little on the lean side looking at that plug. What kind of oil you running? As for the oil in the bottom end that is pretty normal.

Hard to tell looking at the pictures of the cylinder wall. I will usually try to clean them up in the solvent tank with some fine (600) sand paper in a circular pattern or a fine ball hone provided it isn't wore or scored through the Nikasil. I would use caution if you use a ball hone. How much time on the cylinder?

Pictures of the piston sides/skirts might tell a better story.

If I did send the cylinder in to get it replated I would send the head as well, there are a couple area's both in the combustion area and oring area they can clean up for you as well.

I would guess about 4 or 5 hours on the plug.

Running Motul 800 at 40:1 with 92 pump gas.

I've put about 30 hrs on the cylinder (before that I'm not sure since I picked it up second hand after it had been sitting for a few years).

The nikasil does have some scoring plus a place where it is chipped. I will be sending cylinder and head off.

Is that a domed top piston? It should be a flat top. That would explain the piston hitting the plug.

barnett468 wrote:

EXACTLY what do you mean by "I played with the jetting"?

Was it running like it was loading up before?

What 2 stroke oil are you using?

What ratio?

Did you switch 2 stroke oil or the ratio for the new piston?

Sure looks like a piston seized in that cylinder at some point so that needs to be addressed. f you can feel grooves in the cylinder, you are better off getting it bored, and if it is plated, then get i replated.

that plug suggests you are likely at least 3 sizes too small on the main jet, unless it has fuel injection and that is close to what it should look like.

It also looks like there might be some damage (pitting) on the cylinder head. You should clean off the carbon then look closely at it. It is possible the engine was detonating.
.

Well, every couple hours I would do a plug reading and it always seemed sploogy and rich. Needle is in 2nd clip, so I played with the air screw and main jet. I've always ran motul 800 at 40:1 with 92 pump gas with pretty decent results. Earlier last summer I tried castor 927 and it started sputtering on top. Since then I've gone back to motul.

I intend on sending the cylinder and head off. There is some scoring on the walls but no grooves.

You suggest it appears to have been running pretty lean then?

CarlinoJoeVideo wrote:

It’s does look like the plug was hitting the piston

Would a replating and fresh piston solve the issue of the piston hitting the plug?

DynoDan22 wrote:

Is that a domed top piston? It should be a flat top. That would explain the piston hitting the plug.

Not in front of it at the moment, but pretty sure that piston is domed. But then again the head has a domed curvature as well. Would not the domed head accommodate the domed piston? The piston is a stock size Vertex. If what you say is true, I don't know what piston I actually need then. I ran this same brand and style of piston all the way through 2017 with no issues. (The pictured vertex piston is the one I ran in 2018).

dkurtd wrote:

If that's 15hrs then I would say she runs pretty clean. How much time on the plug, maybe a little on the lean side looking at that plug. What kind of oil you running? As for the oil in the bottom end that is pretty normal.

Hard to tell looking at the pictures of the cylinder wall. I will usually try to clean them up in the solvent tank with some fine (600) sand paper in a circular pattern or a fine ball hone provided it isn't wore or scored through the Nikasil. I would use caution if you use a ball hone. How much time on the cylinder?

Pictures of the piston sides/skirts might tell a better story.

If I did send the cylinder in to get it replated I would send the head as well, there are a couple area's both in the combustion area and oring area they can clean up for you as well.

Teej317 wrote:

I would guess about 4 or 5 hours on the plug.

Running Motul 800 at 40:1 with 92 pump gas.

I've put about 30 hrs on the cylinder (before that I'm not sure since I picked it up second hand after it had been sitting for a few years).

The nikasil does have some scoring plus a place where it is chipped. I will be sending cylinder and head off.

If scoring and chips exist then I would definitely get it replated. Not sure who you use but I've had excellent luck with Millennium Technologies, they do awesome work.

Like I also said I would send the head in as well so they can clean up any detonation marks/pitting. Might be best to send a new piston along as well so they can ensure proper clearance, I know piston brand topics will turn this thread into a ten pager so I won't recommend one but will tell you I've always run OEM in my 2005 KX250 and never had problems. One note; regardless of who does the replate, before assembly ensure you wash the bore really well with some soap and water to remove any residual grit left over from the diamond honing as I've seen some just put together and then they end up scoring a piston.

As for jetting, I would definitely richen it back up. I run C12 and run a 165 main on my KX250.

barnett468 wrote:

EXACTLY what do you mean by "I played with the jetting"?

Was it running like it was loading up before?

What 2 stroke oil are you using?

What ratio?

Did you switch 2 stroke oil or the ratio for the new piston?

Sure looks like a piston seized in that cylinder at some point so that needs to be addressed. f you can feel grooves in the cylinder, you are better off getting it bored, and if it is plated, then get i replated.

that plug suggests you are likely at least 3 sizes too small on the main jet, unless it has fuel injection and that is close to what it should look like.

It also looks like there might be some damage (pitting) on the cylinder head. You should clean off the carbon then look closely at it. It is possible the engine was detonating.
.

Teej317 wrote:

Well, every couple hours I would do a plug reading and it always seemed sploogy and rich. Needle is in 2nd clip, so I played with the air screw and main jet. I've always ran motul 800 at 40:1 with 92 pump gas with pretty decent results. Earlier last summer I tried castor 927 and it started sputtering on top. Since then I've gone back to motul.

I intend on sending the cylinder and head off. There is some scoring on the walls but no grooves.

You suggest it appears to have been running pretty lean then?

ok, "playing with the jets" means absolutely zero", so I will try this ONE MORE TIME.

1. WHAT MAIN JET DID YOU START WITH WHEN YOU INSTALLED THE NEW PISTON?

2. WHAT WAS THE LAST MAIN JET YOU INSTALLED?

dkurtd wrote:

If that's 15hrs then I would say she runs pretty clean. How much time on the plug, maybe a little on the lean side looking at that plug. What kind of oil you running? As for the oil in the bottom end that is pretty normal.

Hard to tell looking at the pictures of the cylinder wall. I will usually try to clean them up in the solvent tank with some fine (600) sand paper in a circular pattern or a fine ball hone provided it isn't wore or scored through the Nikasil. I would use caution if you use a ball hone. How much time on the cylinder?

Pictures of the piston sides/skirts might tell a better story.

If I did send the cylinder in to get it replated I would send the head as well, there are a couple area's both in the combustion area and oring area they can clean up for you as well.

Teej317 wrote:

I would guess about 4 or 5 hours on the plug.

Running Motul 800 at 40:1 with 92 pump gas.

I've put about 30 hrs on the cylinder (before that I'm not sure since I picked it up second hand after it had been sitting for a few years).

The nikasil does have some scoring plus a place where it is chipped. I will be sending cylinder and head off.

dkurtd wrote:

If scoring and chips exist then I would definitely get it replated. Not sure who you use but I've had excellent luck with Millennium Technologies, they do awesome work.

Like I also said I would send the head in as well so they can clean up any detonation marks/pitting. Might be best to send a new piston along as well so they can ensure proper clearance, I know piston brand topics will turn this thread into a ten pager so I won't recommend one but will tell you I've always run OEM in my 2005 KX250 and never had problems. One note; regardless of who does the replate, before assembly ensure you wash the bore really well with some soap and water to remove any residual grit left over from the diamond honing as I've seen some just put together and then they end up scoring a piston.

As for jetting, I would definitely richen it back up. I run C12 and run a 165 main on my KX250.

Thanks for the insight. Will definitely be using Millennium, I've only heard good things

Is it just me, or does that plug look way too clean? I'd say definitely on the lean side..

GoggleFiend904 wrote:

Is it just me, or does that plug look way too clean? I'd say definitely on the lean side..

Definitely agree. When doing a plug reading, I think I was paying more attention to the splooge on the threads rather than what the electrode area looked like.

GoggleFiend904 wrote:

Is it just me, or does that plug look way too clean? I'd say definitely on the lean side..

Teej317 wrote:

Definitely agree. When doing a plug reading, I think I was paying more attention to the splooge on the threads rather than what the electrode area looked like.

Did you notice any detonation or pinging? My bike detonates a little while under a load in the higher gears, and my plug is still pretty dark. I'm surprised there are no metal "speckles" on that plug

GoggleFiend904 wrote:

Is it just me, or does that plug look way too clean? I'd say definitely on the lean side..

Teej317 wrote:

Definitely agree. When doing a plug reading, I think I was paying more attention to the splooge on the threads rather than what the electrode area looked like.

GoggleFiend904 wrote:

Did you notice any detonation or pinging? My bike detonates a little while under a load in the higher gears, and my plug is still pretty dark. I'm surprised there are no metal "speckles" on that plug

Yes, I think I did now that you mention it. It wasn't anything too dramatic though.

Teej317 wrote:

Definitely agree. When doing a plug reading, I think I was paying more attention to the splooge on the threads rather than what the electrode area looked like.

GoggleFiend904 wrote:

Did you notice any detonation or pinging? My bike detonates a little while under a load in the higher gears, and my plug is still pretty dark. I'm surprised there are no metal "speckles" on that plug

Teej317 wrote:

Yes, I think I did now that you mention it. It wasn't anything too dramatic though.

If you are running pump gas you could see some detonation. My kx250 has 225lbs of compression on a good broken in piston and if I run pump gas it will detonate really bad, that is why I run C12. One thing you can do if you don't want to pay the race fuel price is get the head recut to reduce the compression. That is something you could discuss with Millennium.

My first concern would be why the piston is hitting the plug, but I'm just one guy talking here...

Check the big end bearing on the rod.

Okay, I will be getting my cylinder back from Millenium here soon with a fresh replate. No changes to the stock head. How do I know whether or not I need to put race fuel in it? Obviously if it's detonating, I know I need higher octane. But is the right process to do a compression test upon getting my cylinder back in order to verify the use of pump gas vs race gas?

Also, what are the pitfalls of running too high of an octane fuel? thanks.

Did Millenium mention any detonation signs, usually they will let you know and repair it if it's bad enough. So did you send the head in with the cylinder? I would say once you start getting north of 200lbs you could start seeing some detonation. Remember to wash the bore really good before you put it back together. Also verify your jetting as was mentioned before, plug looked plenty lean.

If you ride it and you get detonation sounds when you load the motor under heavy acceleration then you will know you need to up the octane with some race gas. The pitfalls of too high of octane is a lighter wallet.

dkurtd wrote:

Did Millenium mention any detonation signs, usually they will let you know and repair it if it's bad enough. So did you send the head in with the cylinder? I would say once you start getting north of 200lbs you could start seeing some detonation. Remember to wash the bore really good before you put it back together. Also verify your jetting as was mentioned before, plug looked plenty lean.

If you ride it and you get detonation sounds when you load the motor under heavy acceleration then you will know you need to up the octane with some race gas. The pitfalls of too high of octane is a lighter wallet.

Thanks for that tip. I did send the head in as well and they told me it looks acceptable. Before I tore it down, I could hear very faint detonation whenever I revved it really high. I definitely will adjust my jetting as well. Thanks

My 06 RM had a detonation issue on pump gas. Jetting was spot on for my area. Evidence of detonation was visible on the old piston and ever slight on the head, however it wasn't really noticeable when riding, at least not as much as my buddy's YZ250. When a fresh OEM piston went in, I decided to run Sunoco 110 leaded with Mutol 800 @ 32/1 and my issue went away. Pulled the head after 25 hours and no signs of detonation, much cleaner piston and head.