Top end seize

[Jim B]

Muriatic acid to remove any aluminum streaking.

This.

[Jim B]

Thanks, I've got some MA around for the pool so that should be handy. Application tips?

Well-ventilated area, nitrile gloves, eye protection, no smoking (??), don't get it on any aluminum you don't want to dissolve. It takes a while to work, but it does work well. Nasty stuff, though - really strong fumes.

I would definitely split the cases to clean everything out. New crank bearings, too. I suspect there may be some aluminum schmeared into them.

[KDXGarage]

I got the muriatic acid tip from an old Kawasaki dealer information sheet. K-Tech, I think.

Quick trivia question: How many revolutions per second are the main (possibly crunchy) bearings making at a KDX's top RPM, which is maybe 9,000 RPM? 60 seconds in a minute, so 9,000 divided by 60 seconds = 150 times per second for the main bearings to eat a piece of shrapnel ( or the big end or small end bearing).

Anyone see why we usually recommend the drudgery of new main bearings, etc. when the top end explodes?

That is a tough pill to swallow after just spending a grand on it.

[C George]

Wow ,,, that caused some serious damage !

So what was the cause of coolant loss ?

Maybe a cheap temp gauge would be a good addition.

I'd hate to gamble that the bottom end is fine,,, heat and debris in the crank seals
would be my main concern.

[Friedom]

We'll see how the crank feels when I've flushed it out. I've put way too much money into this bike already(3k+). A 140$ top end set is palatable. Splitting the case I could do myself (purchasing more tools), then new crank bearings, but I'd need to ship it off to someone to install them (unless you're suggesting I replace the main bearings but not the big end bearings?), then a new engine seal kit.. another 6 or 700$ into a bike that won't sell for more than $1000 at best.
Sad thing is that I never rode this bike before the rebuild, so I haven't even figured out if I like it. There are numerous H series bikes for sale locally for a little more than the cost of this repair, so I'm definitely reconsidering my strategy. And I have a 93 that's up and running great, so the motivation isn't there. Trying to avoid parting it out though.

As far as muriatic acid goes, isn't the cylinder made out of aluminum? Won't it pit or corrode it?

Maybe there's a bottom end in good shape around that I can stick my ported lined BDK top end on.

"Good job, guys. "

[Tedh98]

Just a little something to consider about flushing the bottom end. My son got a 125 and we were going to completely rebuild the engine anyway. So I decided to do a little experiment. I put some steel and aluminum "debris" in the bottom end to mimic a piston breaking apart. I then ran the engine for less than a minute to circulate everything.

I kept flushing the bottom end with gas until it finally ran clean (I lost count of how many times that took) and then did a few more. I then split the bottom end and sure enough there was debris caught between the bearing and seals on both sides.

If you flush it, best case is that it may be fine for a few months or a few years. But I do think that it won't last as long as if you clean it out properly.

Worse case is that something will fail quickly and then you will be out another top end plus who knows what else.

One thing that mistakes and dirt bikes have in common is that they usually aren't cheap.

Regarding the MA, you only apply it to the plated part of the cylinder. You wouldn't submerge the cylinder in a container of it.

[Friedom]

Just a little something to consider about flushing the bottom end. My son got a 125 and we were going to completely rebuild the engine anyway. So I decided to do a little experiment. I put some steel and aluminum "debris" in the bottom end to mimic a piston breaking apart. I then ran the engine for less than a minute to circulate everything.

I kept flushing the bottom end with gas until it finally ran clean (I lost count of how many times that took) and then did a few more. I then split the bottom end and sure enough there was debris caught between the bearing and seals on both sides.

If you flush it, best case is that it may be fine for a few months or a few years. But I do think that it won't last as long as if you clean it out properly.

Worse case is that something will fail quickly and then you will be out another top end plus who knows what else.

One thing that mistakes and dirt bikes have in common is that they usually aren't cheap.

Regarding the MA, you only apply it to the plated part of the cylinder. You wouldn't submerge the cylinder in a container of it.

Yeah, we all know you're right. I'm just tired of throwing money and time into it.

There was a chunk of aluminum in there big enough to stop the crank from rotating fully. I almost got it out, but now it's hidden again. I'll get it.

The whole point of getting a kdx, for me, was reliability. If I don't fix this right, then I can forget about reliability.
Anyone need engine parts?



"Good job, guys. "

[Jim B]

There was a chunk of aluminum in there big enough to stop the crank from rotating fully. I almost got it out, but now it's hidden again.

Are you sure the crankcase isn't damaged? A lot of times the piston shrapnel gets in between the rotating crank and the crankcase and bad things happen.

[Jim B]

(unless you're suggesting I replace the main bearings but not the big end bearings?)

Obviously, the big end bearing also may not be in great shape.

[david]

It ran lean, that's what melted the hole in the piston. My STX 1100 did the same thing a couple of summers ago when the inlet needle on one carb stuck shut. The other two cylinders ran it into the ground before I could get back to the dock. Ended up throwing a rod by that point. And it cracked the bottom of the crankcase, but I was able to weld it up.

The others are right, you need to do a full rebuild again. Or cut your losses now and start over with a different bike if you don't want to throw more money at it.

[Friedom]

Given that it has new bearings and seals everywhere else (such as the tranny), maybe I'll split it and get the crank redone. Assembling myself probably won't be that hard, but I'll need to get a case splitter and something to pull it back together. The other seals are so new that they probably won't need replaced (clutch cover, water pump cover, right case cover, magneto cover), and if they do I'll replace them.
Since the rest of the engine was professionally done over, I think it's worth rescuing. Maybe millenium will give me a repeat customer discount :)

As far as running lean, I don't think there's really any way to be sure of it. The whole thing was so hot from being out of coolant, any number of things could have gone wrong.

"Good job, guys. "

[Tedh98]

I may be wrong but I dont think overheating would put a hole in the piston. The only times I have seen that is from running too lean.

Did you adjust your jetting for running in the sand?

[david]

^^This. During the meltdown, you could have boiled out most of the coolant.

[royadams]

I would think the only way a over heat could cause this is by way of detonation. I'm really surprised you did not hear the engine rattling. It takes a while to burn a hole in a piston.

[Friedom]

Hmm
I'm not used to 2 strokes, nor what they're supposed to sound like. I know the whole thing was loud, but it always is. I'm sure I should have been more aware of something, but I had been out for a whopping 15 minutes if that when it died.

I DID find that the spark plug wasn't tight, neither were several head bolts. Could this have been enough to let air in and make it lean, or let coolant sneak past the head gasket? Would coolant in the combustion chamber make it run lean?


"Good job, guys. "

[Jaguar]

probably was a combination of coolant entering the cylinder and running too lean.
Clean out your main jet and float bowl before you go riding again.

[Friedom]

For sure. I'll check over the whole carb, since I've got 100 parts laid out already.

Now that I think about it, I did notice the engine was revving really fast as soon as I started riding. I remember thinking how the porting really did impressive work.
Probably was a partially gunked main making it run lean!

Anyone remember what aftermarket reeds come with an intake boot? My intake boot is looking pretty rough anyways.

"Good job, guys. "

[Jaguar]

It probably had a high idle and took a long time to settle down after you blipped the throttle. That is because of an air leak between carb and cylinder or a leak at the crank seals. The main jet won't do that. But clean it anyway to be sure it's right.

[Friedom]

Hmmmm when I started it, I noticed it was already a little rich (using enrichment circuit would kill it), and it didn't hang high, so that points away from an air leak lean condition, but air leaks aren't renowned for consistency.

"Good job, guys. "

[Jaguar]

maybe you should clarify this statement then: "I did notice the engine was revving really fast as soon as I started riding"