What did I do wrong?

Hello guys,

I rebuilt my 98 YZ250. After two hours ride(have hour meter) my cylinder looks like this from the exhaust port.
The cylinder was replated and I'm using a new Wiseco piston.
No scoring on the piston just on the cylinder wall. The top of the piston is clean(brownish).

When I put everything together I washed out all the intake ports with brake cleaner.
I also used compressed air to clean out all the ports. I installed brand new air filter. I cleaned the carb/rebuilt it.
I washed the airbox. I haven't checked the compression yet. I will do it tomorrow.
Sorry for the low quality pictures. I didn't have my DSLR on me. And it was dark in the garage so I didn't have any chance to make
good quality pictures. I'll make some more tomorrow.

Is my cylinder f...ed? 

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If you can feel the scratches with your fingernail or a long pick u should address it,otherwise I'd run it.

That "looks" normal.

However, did you follow the instructions (if there was any) to wash the entire cylinder with soapy water, and cleaning it out? 

I know you said you used brake cleaner, etc. but it is always a good idea to clean it per instructions. (That is if they told you to.)

Edited by 2 STOKE YZ DOC

Did you use anything for lube during assembly? I've never put in a dry piston for the small chances it'll score the cylinder.

If they are scratches you can feel then dirt probably made it past the filter.

I don't have an explanation, but several replated I've had done shows similar vertical discolorations for the first few hours. By 20, 30, 50 hrs they are gone. I always chalked it up to manufacturing tolerances and the cylinder being polished by the rings with different pressures around the diameter. Never have they been a scratch I could feel.

It's a new bore with new rings and new piston. It's wearing in. Send picks in 5 more hours. Chances are if you take some paper towels and wrap them and tape them on a large screwdriver then poke that in those lines will wipe off. If the piston has the black break in stuff on the skirt....thats what you're seeing and it's wearing in, will clean up soon.

I don't think I've ever seen a sleeve that didn't have some kind of marking, run it, it'll be fine from what I see. If yz doc speaks listen is my best advice! 

Thanks doc, for other post!

I sometimes get them after top end rebuilds. If you cannot feel them (low grooves) with your finger then don't worry about them. 

My guess is that they are some kind of build up coming from either contaminated cylinder spots prior to assembly or some material rubbing off the piston skirt.

For the past couple of years I've been assembling new pistons with ATF as the lube, instead of premix oil or dry.  I was told it's enough lube to prevent any scoring or galling, but not slippery enough to prevent a good ring seal.  I keep the RPMs down on early warm up, then go moderately hard to seat the rings.  I've been getting very good compression using this method, and less of those discolor stripes too.

When you assembled the engine did you check ring end gap prior to just putting it together?

The worst line looks like it lines up with where the ring end gap is located.

When your motor heats up the rings expand and if there isn't enough room for the rings to expand and the ends of the rings come together it can cause this, especially if you didn't check it after a cylinder has had work done to it.

Also I agree it could be some dirt from getting past the air filter or marks from the black coating on the side of the piston.  Not all pistons have the black teflon coating on the skirts.

Its up to you if you want to keep running it, but I'd pull it off and feel for scratches and through a new set of rings in it after you check ring end gap.

checking ring end gap is done by installing the ring in the cylinder without the piston.  Then using the piston to push the ring down into the bore.  Then using a feeler gauge to find the gap from tip of ring to tip of ring.  Most common gap is approx .004 per inch of bore.

good luck

Agree with 400yzturbo's comment,

I'd also add that the ring end gap specs should be of the piston's manufacturer

and not as per the Yamaha service manual, the OEM piston being cast rather than forged.

 

Also, was this piston supplied with the cylinder when sent to be replated?

On 11/4/2017 at 7:48 PM, mudmixer said:

If you can feel the scratches with your fingernail or a long pick u should address it,otherwise I'd run it.

I can't feel the scratches but It has different feel on the surface.

On 11/4/2017 at 10:43 PM, 2 STOKE YZ DOC said:

That "looks" normal.

However, did you follow the instructions (if there was any) to wash the entire cylinder with soapy water, and cleaning it out? 

I know you said you used brake cleaner, etc. but it is always a good idea to clean it per instructions. (That is if they told you to.)

They didn't provide any instruction with the head nor did they tell me anything. I have a little background with nitro RC cars.
What I did I cleaned the cylinder wall with a  clean cloth and WD40. That what we used to do with RC cars when we installed new sleeve.

On 11/5/2017 at 5:18 AM, MaybeMe said:

Did you use anything for lube during assembly? I've never put in a dry piston for the small chances it'll score the cylinder.

Yes, I did use 2 stroke oil.

On 11/5/2017 at 6:10 AM, adam728 said:

If they are scratches you can feel then dirt probably made it past the filter.

I don't have an explanation, but several replated I've had done shows similar vertical discolorations for the first few hours. By 20, 30, 50 hrs they are gone. I always chalked it up to manufacturing tolerances and the cylinder being polished by the rings with different pressures around the diameter. Never have they been a scratch I could feel.

I can't exactly feel the scratches but they did feel different. 

On 11/5/2017 at 6:13 AM, hondaman331 said:

It's a new bore with new rings and new piston. It's wearing in. Send picks in 5 more hours. Chances are if you take some paper towels and wrap them and tape them on a large screwdriver then poke that in those lines will wipe off. If the piston has the black break in stuff on the skirt....thats what you're seeing and it's wearing in, will clean up soon.

I tried to wipe it off and I couldn't. Hopefully nothing serious.

On 11/5/2017 at 0:59 PM, Smoking 2's said:

I don't think I've ever seen a sleeve that didn't have some kind of marking, run it, it'll be fine from what I see. If yz doc speaks listen is my best advice! 

Thanks doc, for other post!

Yes, "Doc" is one of my favorite member here. :)

On 11/5/2017 at 4:45 PM, numroe said:

I sometimes get them after top end rebuilds. If you cannot feel them (low grooves) with your finger then don't worry about them. 

My guess is that they are some kind of build up coming from either contaminated cylinder spots prior to assembly or some material rubbing off the piston skirt.

For the past couple of years I've been assembling new pistons with ATF as the lube, instead of premix oil or dry.  I was told it's enough lube to prevent any scoring or galling, but not slippery enough to prevent a good ring seal.  I keep the RPMs down on early warm up, then go moderately hard to seat the rings.  I've been getting very good compression using this method, and less of those discolor stripes too.

Yes, they exactly feel like some kind of build up rather than deep scratches.

On 11/5/2017 at 5:31 PM, 400yzturbo said:

When you assembled the engine did you check ring end gap prior to just putting it together?

The worst line looks like it lines up with where the ring end gap is located.

When your motor heats up the rings expand and if there isn't enough room for the rings to expand and the ends of the rings come together it can cause this, especially if you didn't check it after a cylinder has had work done to it.

Also I agree it could be some dirt from getting past the air filter or marks from the black coating on the side of the piston.  Not all pistons have the black teflon coating on the skirts.

Its up to you if you want to keep running it, but I'd pull it off and feel for scratches and through a new set of rings in it after you check ring end gap.

checking ring end gap is done by installing the ring in the cylinder without the piston.  Then using the piston to push the ring down into the bore.  Then using a feeler gauge to find the gap from tip of ring to tip of ring.  Most common gap is approx .004 per inch of bore.

good luck

I received a paper with my Wiseco top end kit. It said to set the ring gap with the follow method .004 x bore size. If I remember correctly it was somewhere near to .012 so I didn't touch it. However those scratches do not line up with the ring gaps. I pulled the head and checked it.

I bought the pro-lite Wiseco top end kit. The piston did not have any coating.
Those marks did not feel like scratches. It feels more likely some kind of build up.

On 11/5/2017 at 6:00 PM, mlatour said:

Agree with 400yzturbo's comment,

I'd also add that the ring end gap specs should be of the piston's manufacturer

and not as per the Yamaha service manual, the OEM piston being cast rather than forged.

 

Also, was this piston supplied with the cylinder when sent to be replated?

Yes, I sent the piston along with the head.

 

Thank you guys for the replies and helps. I really appreciate it!
Yesterday I didn't have any time to work on the bike.

Today I pulled the head and took some pictures.

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Edited by badassgamer

A small video of the cylinder wall. Sometimes vimeo doesn't want to play the video in 4k.
Try it in 2k it works most of the time.

 

Edited by badassgamer

How long did you run the motor after rebuild?  What was it doing that caused you to look back into it?  Who did you have replace the cylinder?  What does the skirt of the piston look like?

If you measured .012 on the ring end gap you should be fine, especially for a 68mm bore.

I ask the question about who replated your cylinder because wiseco rings say not to use on chrome bores.  They work fine on nickasil and cast sleeves though.

Now that you're this far in it may pay to pull the jug and make sure the piston ring didn't shift off the locating pin.  This locating pin prevents the piston ring from rotating while running.  It's not too easy to install the piston with the ring out of proper location but it is possible.  Also it is possible to roll a piston ring and not catch it.

It still might not hurt to pull the jug/cylinder and inspect the rings and that will also let you inspect the piston skirt.  With an almost uniform scoring all around the bore kinda looks like a light four corner seize.

If you pull the jug post pics of the rings and skirt of piston.

if you can't catch the marks with a finger nail you might be ok to just put a set of rings in it and run it, after a thorough cleaning though.  If the piston skirt has scoring then it's time for a new piston unfortunately.

Keep us posted.

 

Eh, I think there is more worry than needed to take place.

But since you are this deep, you might as well be balls deep and check the rings.

I would have just ran it, although it does look a little rich in the burn.

At 2 hours the rings would have overlapped or caught an edge already if the gap was wrong, or out of alignment with pins.  

On 11/6/2017 at 9:42 PM, 400yzturbo said:

How long did you run the motor after rebuild?  What was it doing that caused you to look back into it?  Who did you have replace the cylinder?  What does the skirt of the piston look like?

If you measured .012 on the ring end gap you should be fine, especially for a 68mm bore.

I ask the question about who replated your cylinder because wiseco rings say not to use on chrome bores.  They work fine on nickasil and cast sleeves though.

Now that you're this far in it may pay to pull the jug and make sure the piston ring didn't shift off the locating pin.  This locating pin prevents the piston ring from rotating while running.  It's not too easy to install the piston with the ring out of proper location but it is possible.  Also it is possible to roll a piston ring and not catch it.

It still might not hurt to pull the jug/cylinder and inspect the rings and that will also let you inspect the piston skirt.  With an almost uniform scoring all around the bore kinda looks like a light four corner seize.

If you pull the jug post pics of the rings and skirt of piston.

if you can't catch the marks with a finger nail you might be ok to just put a set of rings in it and run it, after a thorough cleaning though.  If the piston skirt has scoring then it's time for a new piston unfortunately.

Keep us posted.

 

I did 3 heat cycles. I haven't rode this bike on the pipe yet. Went for technical wood riding and I did two hours ride there. I got a small hole on the exhaust.
I had to take it off to weld it in. While I was there checked inside the jug and saw those scores.
PowerSeal USA did the replating. They did a great job on the cylinder.

What's the best way to clean the cylinder wall?

On 11/6/2017 at 9:58 PM, 2 STOKE YZ DOC said:

Eh, I think there is more worry than needed to take place.

But since you are this deep, you might as well be balls deep and check the rings.

I would have just ran it, although it does look a little rich in the burn.

At 2 hours the rings would have overlapped or caught an edge already if the gap was wrong, or out of alignment with pins.  

You are probably right. :) It was rich. I'm going to lean it out a little bit.

 

I didn't really have too much time to work on the bike. I pulled the jug and took some pictures. Can I re-use the head gasket or should I use a new one?
I'm going to replace the o-rings on the head I just wondering if I should replace the head gasket too.

Pictures of the piston and rings.

It  doesn't look that bad, does it? I think I'm going to put it back together and ride it for another 40-50hrs(hopefully). :)

Personal bike... 

Me, I would reassemble and ride it the way it is, and use all the original stuff for at least 20-30 hours. That looks way to clean to be way to cautious. 

Go ahead others.. Flame me if you want, but this was a bad case or PME or ERD, you call it what you like. 

Personal bike... 
Me, I would reassemble and ride it the way it is, and use all the original stuff for at least 20-30 hours. That looks way to clean to be way to cautious. 
Go ahead others.. Flame me if you want, but this was a bad case or PME or ERD, you call it what you like. 
No flames. Just agreement.

Its one of those cases in which it's better safe than sorry.

Better to look into a possible problem than ignore it and hope it will go away on its own.

The piston looks fine.  I'd go ahead and run it.  If it were mine though, I'd just change the rings and gaskets and put in back together.  If you have the new orings for the head they will be fine to reuse, but I'd put a new base gasket under the cylinder.  They're cheap and it's piece of mind.

Im glad it doesn't look as bad as we had feared.

put it together and run it, just clean the cylinder really well.  Also be careful putting it together being extra careful to keep it super clean and use plenty of two-cycle oil.

 

I gotta ask,what are the big holes above the wrist pin hole?

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