Melted piston after 4 hrs

[beefking]

Melted piston after 4 hrs-updated w/pics

*Pics at end of thread*

I just finished rebuilding the 89 KDX200 with +2mm wiseco kit, replated, all that kinda stuff, about 2 weeks ago. We took it out last Saturday to break it in, started to run like crapola. So after some inspection, we found that the intake carb. boot ripped. After some duct tape, all was well again.

So we went off into the woods, and found a nice long straight away. Of course, my dad (on the KDX) just had to open it up! At this point we rode about 4 hours, so the bike was pretty much broken in.
As he was rippin down the straight it just bogged and died. I tried to kick it over again, noticing the lack of compression. As it turns out, the vibration from high RPM's ripped the boot even more, making it WAY lean.

Took it apart today to see what the hell went wrong, and the piston melted right over the rings on the intake side of the piston! Not even 4 or 5 hours on the brand new top end, shifter forks, power valves etc. and the piston is melted up. :(

Anyhow, thank god the plating on the cylinder isn't too bad. You can just barely feel the attaced aluminum from the piston on the wall. But still, I don't think it will run for very long with a new piston and rings.

I guess what I'll do is just replace the piston/rings and sell the damn thing. I swear its cursed! I'm pretty bummed out too, that thing was running like a champ-lots of snappy power everywhere in the powerband. :(



Also, do y'all think I would be better off plunkin down $100 for a new piston kit and selling it as is, or should I sell the bike for parts? Other than the piston, its in great shape-whole list of aftermarket and new OEM parts. I think it may be worth more in parts on ebay vs selling it outright, bike market seems to be rather low.


Moral of the story: replace old, dry-cracked air boots or else!!! ;)

 

[E_Langen]

But still, I don't think it will run for very long with a new piston and rings.

Why do you think it will not run very long?

 

[beefking]

Well it depends, on how I can clean up the plated cylinder. All of the scuffing on it IS melted aluminum from what I can tell. Tommorrow in the daylight I'll get a better look at it.

I just can't decide if I want to sell, part out with it, or just fix it and keep, we did get the bike for free... :think:

 

[David Trustrum]

The problem is removing the ally & not just smearing it all around.

Caustic soda (drain cleaner).

Apply to a rag with some water to dampen & lay in the affected area. Leave for some while. This attacks the aluminium but not the plating. Should come off onto the rag. Keep it off unplated areas of course.

Clean area with scotchbrite pad & inspect that plating is still intact under bright light.

Warning: Caustic soda is the most lethal stuff you can buy at the super market.
Wear gloves & eye protection.


Any bike with a ripped inlet is likely to seize solid. Clue, gas dissolves the glue in duct tape, or most glue in general so this fix was doomed to fail.
Will be much easier to sell in a going condition, but if you do it properly should still be a nice bike to rip around on.

 

[MX175]

Let me be a bit cruel here...

What did you expect with duct tape on your inlet boot? I'd use that to get me back home, but I wouldn't be taking any WFO uphills or drag races. When I got home, the next point of business is buying a new boot. Isn't it embarassing to be riding a bike with duct tape on the inlet boot? It looks tacky. I'll bet it was running great...There is great power when the mixture is lean, but not much longevity for the engine. With a torn boot, you not only have a lean mixture, but you are sucking in unfiltered air that will wreak havoc on your new cylinder. What were you thinking???

If you decide to sell it, let me know...unless you have other problems like worn swingarm bearings, ungreased steering head, or maybe you don't always tighten the spark plug??

Sorry for my lack of tact. Hey a picture of that melted piston would be cool.

 

[rethnal]

Hey... we ALL live and learn! :)

 

[NYkdxer]

The best stuff to use to get rid of the aluminum in your cylinder is Murcuric (sp?) acid. Your local bike shop or swimming pool store should have some. This is very dangerous stuff, do not get it on your skin. Pour some in a little glass cup, dip a zip tie in the cup and apply it to only the aluminum. Let it sit for a couple minutes and wipe it off with a rag. Repeat until the aluminum is gone. Then LIGHTLY hone the cylinder. We blew a top end on one of our sleds this winter and had to do this, it works great. Its not hard, but be careful. Keep the bike :)

 

[canyncarvr]

1. Re: MX175's '..lack of tact.'

Maybe. I wouldn't say so. You're right on the money. It's a simple fact. Note it wasn't HIM doing the riding. (Look at the '12 miles per tank' thread)

2. Re: Get rid of it.

Nah! Besides caustic soda (haven't used that before), doesn't muriatic acid do the same thing? I may recall that incorrectly......

My kdx is missing plating in two spots due to the wonders of belray (it's crap!). I've been running it that way for over two years. My riding buddy's '01 ktm200 b-a-r-e-l-y pulls it on a straight. It can't be that bad!

In any case, sorry to hear about it. I was curious about the 2mm overbore (wondered about static compression for one..) and how it would work out.

Next time it will work much better!

 

[Smit-Dog]

Regarding Muratic acid... be very careful with this stuff, as it is ACID! Be careful not to inhale the fumes either. Creates a fine mist in the air when mixed with water.

 

[canyncarvr]

oh oh...THAT must be my problem. Excessive muriatic (spelled that way AND 'muratic'...although neither one of them is in my dictionary. Can we agree on HCL?) fume inhalation!! I kinda liked the smell! Makes my eyes water, though.....

Will it remove the aluminum and leave the harder coating intact...with a reasonable amount of time in application?

 

[Canadian Dave]

If I'm not mistaken Eric Gorr covers the use of muratic acid to remove smeared aluminum from cylinders on his web page. If it’s not there I know I've seen it in his book.

Assuming the plating isn't damaged I don't see any reason why you couldn't clean up the cylinder, install a new piston and rings, replace the air boot and be right back where you started again. Be sure to check out the connecting rod etc for play as well just to be sure.

LOL I wouldn't say the bike is cursed. Running the bike with a known air leak could have resulted in MUCH worse damage than you experienced. I'd count myself very lucky if I were you.

The lesson here . . . If you expect your bike has an airleak don't ride it until it’s fixed properly!

David

 

[MX175]

For cleaning the aluminum from inside the cylinder, I recommend mechanical methods first. Avoid the chemicals if you can. Scotchbrite should be fine. If that isn't sufficient, I might try a little sand paper, but it depends on what you have for "plating" on the cylinder and how thick it is. You don't want to sand through the plating and it could be very very thin. If you had a steel liner in there, instead of the plating, honing would be the method of choice. Honing is too coarse and will remove your plating.

If you have to go to a chemical corrodant to remove the remants of the aluminum, I would not recommend Muriatic acid (aka hydrochloric acid-HCl). Muriatic acid is probably more aggressive to the "plating" and it is definitely more aggressive to humans. Sodium hydroxide (drain cleaner or caustic soda) would be preferred. It should attack the aluminum more than the muriatic acid, it should be gentler on the cylinder plating and it is kinder to humans. If you decide to use the sodium hydroxide, wear goggles and rubber gloves and be sure to protect the outside of the cylinder because it does not have the protective plating and will be heavily attacked. Have big buckets of plain water around for rinsing/diluting.

Good luck

 

[beefking]

I guess i was kinda over-reacting about the bike being cursed part hehe... :laugh:

I cleaned the cylinder bore up today with just a rag, and it turned out to be somewhat clean. There is only one spot, right above the intake port where the plating could be messed up. The rest is just marked, can't feel any difference when riding your finger along it.

Now that I think about it more, I guess I'll just get new piston and rings and clean up the bore. After all, it does have new rod/bearings, crank seals/bearings, powervalves....
And we got the bike for free to begin with, so even after this extra episode I think we'll be ahead of the game. ;)

Thanks for all the reccomendations, I think i'll try "mechanically" taking the alum. off first though. I also have some Drano, maybe I'll use that once all the big stuff is off....?

 

[aphid200]

BTW, when using muriatic acid (which is 28% HCl) to remove gauled aluminum from your cylinder, it liberates a fair amount of hydrogen which is very flammable. You won't want to be couped up with HCl vapors anyway but having a little Zeppelin replay could really ruin your day.

 

[mulerider]

IMO stick to the Mechanical methods if you are not comfortable handling chemicals. Some 500/600 grit sand paper will work fine when you get down to the little stuff. start of with some 200 grit. Remember you need to polish with the sandpaper not grind, Light even strokes work the best!

The chemical methods work well, I have used both Naoh (caustic) and HCL@ 28% on cylinders. If you don't know how or do not feel comfortable using these methods please don't! Chemicals don't forgive they just keep going and going till properly neutralized. I work with both of these bueaty's and some even better stuff everyday!

 

[beefking]

OK I got my digital camera back so I took some pics of the damage. The plating IS in fact chipped in one spot above the main intake port. Looks like it will need to be replated, but what do I know. :think:

Photos of seized piston/cylinder damage! (fixed link)


Canyncarvr, where is your plating chipped? Mine happens to be about 20mm above the bottom of the piston's stroke, so the rings would pass over it. :ugg:

 

[Smit-Dog]

BeefKing - The link you provided only works if you are logged in as the owner of the album.

Log out of Webshots, then navigate to your public album (may have to search for your user ID to find your public albums).

Once you've found your public album when not logged into Webshots, copy that link here.

 

[MX175]

beefking, Nice pictures.
Another question though. If this damage is from a lean condition, why is there damage on the intake side? Wouldn't that side be relatively cool (from incoming fuel-air) and would not cause interference because of heating expansion of the piston?

Now that I am thinking, let me know if this sounds right. The lean mixture fires completely and burns well, but there is not enough cool fuel coming in to absorb the excess heat. This causes the piston to absorb more heat and its temperature get to be higher than 'normal'. Because the piston is hotter it has expanded a little bit more (all the way around) and it essentially becomes too big to fit in the cylinder. It can't just stick on the exhaust side because it needs to push against something and that is the intake side. This is also aggravated by the lean mixture which has less oil in it to lubricate the piston and cylinder.....Or does heating occur because there is less lubrication (more friction) between the cylinder and piston? So I guess there are three possible mechanisms here:
1) overheating because of a higher burn temperature of the lean mixture
2) overheating because of less cooling effect from the lean mixture
3) overheating because of less oil, more fricitonal heating, from the lean mixture.

Now I will bet someone comes and says all three are right, but which is the most important? I need someone who KNOWS. Maybe I need to address this to Eric Gorr.

Thanks for your patience with my rambling,

 

[canyncarvr]

I recall someone of knowledge (either EG or RR?) saying that intake seizures come from one thing.....oil/lubrication failure. I haven't verified that. Take it only for what it's worth (zip with no doc.!)

I believe that to be a reference to intake ONLY failures, though. That's not so in this case.

BK:
My rings hit the spots on my cylinder also. I didn't take pics, but I recall the rubs being just under the transfer ports. Still, a small fraction of the damage you show in your pics.

 

[beefking]

I honestly don't think it had anything to do with lack of lubrication. I was running 32:1 ratio with Spectro SX. All the bearings and rod had a nice coat of the oil on it, and you could physically feel the oil on the cylinder walls and piston. Granted, some of this could have been from kicking it over after it seized, but I don't think this much could have come from kicking it a few (5 or 6) times.
Also, the heaviest of the damage was on the intake side, but the piston was also melted on the exhaust side of the engine, at 2 spots.

A friend of mine suggested I just try to slap a new piston/rings in there and try to ride it....but I'm not sure it would be worth the money.

CC, is your plating chipped or just brazed? I would like to think I could ride it for a little bit anyhow with new piston/rings. I REALLY don't want to sell this bike, I have alot of money into it, but if it needs to be replated before being able to run at all, I'll have to sell it. Too many bills need to be payed as it is. :whiner:

PS about the Wiseco 2mm kit, I didn't have any detonation problems with 94 octane. I checked the plug with a magnifier glass to see if there was any small filings on it from detonation, but I didn't see any. The power is great, the powerband is just like stock...but theres a little more of it.

 

[MX175]

My first reaction is that you have a pretty severe condition inside that cylinder. I don't have enough experience with plated cylinders to be sure. If you decide to just replace piston and rings be sure to do 2 things.
1) sand the chipped areas so that they do not 'snag' a ring. It will be difficult to sand the hard plating and it will be easy to sand the softer aluminum where the plating is gone. Try to remove as little aluminum as possible.
2) In your first thread, you mentioned that you had a +2mm Wiseco piston. Be sure that you have the right dimensions - everywhere up and down and all around - on that cylinder. If that cylinder was a little tight you may want a +1.5mm piston. Measure everything and be positive. Who knows, maybe they machined the cylinder correctly but put a little too much plating on it

 

[canyncarvr]

re: chipped or something else.

Something else, I'd say. I could see the same pattern on the piston as on the cylinder.....like a plating 'piece' had come off the cylinder wall and welded or melted into/onto the piston. In my case each 'piece' (two of them) was about the size in area of a pencil eraser tip.

I didn't mean to imply that your seizure was due to lubrication. In that case, the only thing you'd see was damage on the intake side.

Your cylinder is pretty goobered. Considering what you've got into the bike already it would certainly be a judgement call as to whether it's 'worth it' or not. Certainly a positive thing to consider is that you know how it came about.

Good luck!