when to re-plate

[scheckaet]

when do you know it's time for a replate?
This came from my 05 cylinder, I did the top end about 2 years ago, and it looks about the same shape as last time.
There was some carbon deposit on top of the piston but it was easy to remove with my fingernail (thanks amsoil)
A bit of blow by on the side and exhaust side.




What concern me are the vertical "scratch" marks on the piston, obviously it scraps the wall some and i dunno if it's normal and how much is acceptable. There is 2-3 deeper scratch on top (the black parts) on the 1st pic







I can't take good pic of the cylinder tonight, I'll try tomorrow and post.
you can see a difference in color of the plating where the rings set compare to the rest of the wall on the lower part of the cylinder. It doesn't look like the plating is gone, the color is not aluminum.

What do you all think? Safe to run another season by just replacing the rings?

thanks

[Indawoods]

I think the blowby is what is causing your scratches... that's debris. Clean and oil your filter more after reringing.

[scheckaet]

so you think the carbon deposit would cause the scratches on the piston?
I replaced and oil the filter every other ride (minimum), maybe sand / dust got through? might get a filter skin and see if it helps.

Here are some pics of the cylinder wall:



you can see the difference in color where the plating is still new.
The plating is smoother where it's worn out / shinny.
I think the plating is very thin there and might be borderline for replate, but again I'm no expert at all...
All comments are much welcome.

[IdahoCharley]

Cylinder bore pretty good from the pictures. I would clean it up with a scotch pad and take a second look - the scotch pad will help even out the reflections and contrast and cylinder it will be easier to identify any problems when you view it or if you chose to post additional pictures.

NOTE - One thing you cylinder does show is the value of running a good synthetic oil - very minimal oil glazing - which is normally the reason you scotch brite a cylinder.

What is your piston to cylinder clearance? Your ring to ring landing clearance? What was your ring end gap clearance (?) ... more of an indication to you on how often you should be opening up the top end than anything else at this point?

FWIW - You can tell somewhat if a piston has worn to the point where it is beginning to rock within the cylinder by looking at the upper crown area and lower skirt areas for wear. Another indication of wear is the horizontal machining lines which run across your piston. (Yours looks good IMHO). The piston oiling holes area planes and the two vertical planes on the opposite side of the piston without the oiling hoes will normally show wear when piston clearance is out of spec.

The amount of blow- by indicated by oil glazing on your piston is nothing to be concerned about. The scratchs look minimal but you should not have any - appear to me to be from dirt making it pass the air filter. Do you also grease the oil filter seal?

Bottom Line IMO is to clean up the piston some - scotch barite pad is fine. Check the relative clearances and if everything is within spec then you could re-ring. If were mine and the cylinder was verified as good after a quick scotch barite session I would be installing a new piston and rings - (verses just rings) the difference is maybe ~$70 but a relatively tight (within specs) piston should last longer and is easier on the cylinder plating. (Loose pistons wear plating, do not transfer heat as effectively, and can lead to a ring hooking a port opening causing $$$ in damage.

[scheckaet]

Thanks IC. I used a scotch brite (the green stuff) to remove whatever was there. Took some shine out of it from what I assume was aluminum deposit from piston slap.
I need to inspect it again in more details tonight, I'll also check the manual to check for the different clearance.

I might be ok just slapping a new piston kit in there, the measurement will tell. This will go on my KDX back up / GF bike and won't see much abuse anyway, but I'd rather spend a little money now than a LOT later...









Note: taking pics showing what I really see is a major PITA! That's the best I could get

[Julien D]

How thick is that ridge at the top of the cylinder where the rings stop? That will give you a quick idea how much plating has worn down. Looks considerable in that last shot. If it's not due for a re-plate now, it will be the next time you tear down.

[scheckaet]

the ridge is actually not that bad, the shot is somewhat deceiving. I'll see if I can guesstimate that tonight. You can feel it by touch.

[IdahoCharley]

If it were mine I would go ahead and run the cylinder. It does not look that bad. The scratches in the last shot are not excessive and not near ports. Don't see any flaking of the plating around the ports.

Bottom Line - Overall cylinder condition looks Very Good for a 5 year old bike.

P.S. Concerning comment related to "ridge." Since the plating is only a couple of mils thick you really can not rely on a ridge to tell you anything within a plated cylinder. If there really was a "ridge" the the plating is total gone and your looking at bear aluminum and really a messed up cylinder. On a cast block or sleeved cylinder then ridge can be useful indicator of wear. I expect the "ridge" being seen in the photo is just "an illusion" due to differences in the cylinder's reflection index.

[scheckaet]

No flacking that I can see; the 2 scratches on the last shot were the same 2 years ago, don't feel any deeper/wider than on the last top end.

About the air filter rim, I do put grease on it and rotate it to get a good seal. I'm using the no toil oil kit and replace / clean the filter every other ride minimum.
However, I think the 3 air filters I've been using are about done (they're about 3 year old); especially the Uni air (the ones with 2 separate foam layers); the outer foam was getting "brittle" so I stopped using it.
I think I'm gonna stick with the twin air now, doesn't seem to degrade the way the uni does.

[Julien D]

P.S. Concerning comment related to "ridge." Since the plating is only a couple of mils thick you really can not rely on a ridge to tell you anything within a plated cylinder.

pffft. Whatever.

presence of a ridge above the rings = plating is wearing down
absence of any ridge = plating is not wearing

I wasn't telling him to try and measure that ridge to get an exact idea of how much the plating has worn, but if you can plainly see a "ridge" at the top of the cylinder, common sense alone will tell you that the plating BELOW that ridge is thinner than it once was. Seeing that should tell you that you probably need to mic the cylinder and get a solid measurement.

For what it's worth, I'd probably run that cylinder as well, so long as it measures out within spec. It seems to me that with some sort of crosshatch visible, and a ridge indicating that the crosshatch should probably have worn off long ago, combined with some of those scrubbed looking spots on the bottom, somebody had at that cylinder with a hone of some sort. I'd want to measure it before making any decisions!

[scheckaet]

somebody had at that cylinder with a hone of some sort. I'd want to measure it before making any decisions!

Not sure i fully understand, but this is the stock cylinder/plating, I got the bike new in 05, so no honing since the bike was assembled at the factory. The only thing I ever did was the scotch brite when I did the top end last time.

Thanks for all the comments, more pics/measurement tonight

PS: I like your avatar Juliend

[Julien D]

lol, me too!

Wow, that's interesting. I was looking at the shiny bits at the edges of the ports and imagining a ball hone or something run through there. Does not seem so.

All in all the cylinder looks pretty good for 5 years on OEM plating. A benefit to aftermarket plating is it's harder than the OEM stuff, and holds up better for longer. I think you'll be fine running it, like I said before. Just make sure you check piston/cylinder clearance and ring end gap.

[Colorado Mike]

On the Air filter issue, Either No Toil or Uni (maybe both) states that they are not compatible with the other. I buy No Toil filters from RM. Pretty cheap.

[scheckaet]

here are some close up of the piston after I clean it up with scotchbrite.