Yz250 piston

Finally got around to rebuilding the top end on the Yz. The last time I posted, you guys thought that I was running lean to the point of being dangerous long term. I have since been playing with carb settings. I wish I still had the old pictures to post up but I cannot seem to locate them. Anyways, the heat sigs on the underside of the piston have shrunk significantly, however I still do not see the piston wash that I expected to see. This piston had exactly 41.7 hrs on it when I pulled it. Cylinder looks like it just returned from a replate and measured well within spec. after a good bath in the parts washer and a good brushing. This piston got the same treatment to rid it of any nonrelevant blemishes.

 

I am aware that I sucked some dirt. I found a few grains of sand in the intake as well when I removed the filter after the ride so I know exactly when it happened. Right about the 28-29 hr mark.

 

My question is, does this piston look decent aside from the dirt I sucked? 

 

Intake:

E6AF31FA-C3EC-4AFD-BC25-6086A170A098_zps

 

Exhaust:

45AB0113-F554-40CC-9F25-3347B9AE5486_zps

 

Dome:

8C8E7241-8CF9-4626-8D28-D17A001158ED_zps

 

Underside:

AF71BBCB-5C47-4B60-952F-75960F3D4513_zps

You will see machining marks all the way down on a reusable piston. That sucker's worn out.

 

And judging by those two side seizure marks on the intake side...at one point, it was ridden a bit too hard before it was warmed up.

 

The crown doesn't look like you're detonating anything seriously, so that's good. No real pitting.

There should be a burn/wash pattern on top. There are a ton of theories on how it should look.

I typically don't jet by piston wash, but here's a pic!

 

pistonwash.gif

Yea... I don't go by wash either. I jet solely on bike feel. Bike runs great so it has never been a concern for me. Never detonated so never thought twice about it. 

what jetting are you running now? and what was you running before?

Current Jetting #8 slide, JD red needle 2nd clip, 175 main, 48 pilot, a/s adjusted as needed. VP U4.4 at 40:1 Amsoil Dominator. 

 

Previous jetting #7 slide, JD red needle 3rd clip, 170 main, 50 pilot. Same fuel.

 

Bike runs super strong with no hesitation from idle to the stop. Starts first kick EVERY time as well. Very little lugging done with this bike. 

Wait...17,000 posts? Is this a trick question?

My question is, does this piston look decent aside from the dirt I sucked? 

 

No, the vertical wear marks are scary.

How does the intake side of the cylinder look that this piston came out of?

No, the vertical wear marks are scary.

As I stated above... I know what those are from. I am asking about the coloring on the piston, not the wear. 

How does the intake side of the cylinder look that this piston came out of?

Also stated above... cylinder is fine. 

Wait...17,000 posts? Is this a trick question?

Why would this be a trick question? 

 

What does my post count have to do with anything? 

Why would this be a trick question?

What does my post count have to do with anything?

Its a lot of TT experience.

Aside from that, dont think we knew u were looking for a coloring opinion. I probably wouldnt have chimed in with piston wash n wear.

I generally dont use underside coloring for any sort of diagnosis, myself, but Im interested in what there may be to learn. Now i have another thing to obsess about. Ha.

Edit: the obsession begins.

Heres a tuner that claims that a dime size is the correct amount.

Complete with someone that disagrees.

http://www.thumpertalk.com/topic/625889-piston-diagnosis/?p=6138306

Diving further and further, the general consensus seems to be that up to 25% is an indicator of proper temps/jetting and 0 is definitely too cool/rich.

Edited by SellYour4Stroke

run more oil, clean filter more often and i looks a bit lean to me

Its a lot of TT experience.

Aside from that, dont think we knew u were looking for a coloring opinion. I probably wouldnt have chimed in with piston wash n wear.

I generally dont use underside coloring for any sort of diagnosis, myself, but Im interested in what there may be to learn. Now i have another thing to obsess about. Ha.

Edit: the obsession begins.

Heres a tuner that claims that a dime size is the correct amount.

Complete with someone that disagrees.

http://www.thumpertalk.com/topic/625889-piston-diagnosis/?p=6138306

Diving further and further, the general consensus seems to be that up to 25% is an indicator of proper temps/jetting and 0 is definitely too cool/rich.

Yes... I have an extensive history in the Yamaha 2 stroke section even though I am not overly active in here anymore. Some of the members that have been around for a while will remember me. I also spend a lot of time in the Suzuki forum but to be honest most of my posts come from Pro. 

 

Anyways... there is always something to learn and I am interested in learning more about heat signature indications.

 

I was not trying to be rude in my responses but it is obvious that I sucked dirt through the intake, and it is obvious that I didn't warm the bike properly once. I am interested in learning about things that are not so obvious if that makes sense. 

run more oil, clean filter more often and i looks a bit lean to me

I don't need more oil. Crank pool measures perfectly. If anything I need to tweak jetting a little more.

 

However, my bike was never ran with a dirty filter, it was replaced after every ride. It was a bad carb seal. 

Edited by BDubb106

Jetting looks lean IMO, pictures of the top before washing it would be useful,  but the piston wear it's self doesn't look terrible if you are convinced that the vertical marks are from dirt/sand

 

what year bike? 

Edited by subxero

2008

 

I think I have pictures of the top on here somewhere before washing. I just have to see where they saved to. 

Edited by BDubb106

Anyways... there is always something to learn and I am interested in learning more about heat signature indications.

 

I am interested in learning about things that are not so obvious if that makes sense.

Just as a brainstorm, you could try pinging some of the mods or the engineering forum as well.

My sources were a couple road racer/gp guys' quotes here in tt, a few 2 stroke sites and a snowmobile piston reading pdf somewhere out there. Maybe someone will chime in differently, but its pretty standard out there with the 25% or more of the underside of the piston coloring (or carbon buildup) being lean and the 0% coloring being rich.

As far as an opinion:

Underside looks great, crown looks a touch lean.

I don't need more oil. Crank pool measures perfectly. If anything I need to tweak jetting a little more.

 

However, my bike was never ran with a dirty filter, it was replaced after every ride. It was a bad carb seal.

Just to add to the thread here...he may have been talking about those intake scoring marks being due to lack of lubrication...which i also saw out there.

Kind of intrigued me, because it looks like 4 corners, but i also saw in my research that just the two intake corners was a lack of lube type scoring. Personally I find lack of lube scoring to be a bit tougher to swallow than warmup, but its pretty clearly the same type of scoring you have.

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