Spark plugs exploded, why?

**Honclfibr** · 03-30-04, 09:33 PM

See the what I'm talking about here...

http://www.nestreetriders.com/forum/...5&pagenumber=3

Any ideas?

I'll post pictures of the plugs within the hour...

**Honclfibr** · 03-30-04, 10:08 PM

The answer was staring me in the face and I never saw it. In a brief flash of clarity, I figured out the (likely?) cause of the problem on the drive home.

When I went to pull the gas tank, I noticed that the vacuum line was already disconnected. On the 250 you have to pull the side covers away to get to the fuel tank, and I dismissed it as the vacuum must have gotten caught then and pulled out. when I moved the side covers.

But now I see what must have happened. Somehow the vacuum line came dislodged at speed, causing fuel to shut off to the engine. At 85 miles per hour, the gradual lean condition as the float bowls emptied generated enough heat to destroy the spark plugs, and probably enough to diesel for a little while once they were no longer sparking. This sound plausible?

As to why your vacuum line came undone, I'm not entirely sure. I'll check it for cuts and cracks tomorrow. Two other things, first is that your fuel tank bolts were barely finger tight. And since there's only two of them, this probably gave your fuel tank a little more room to vibrate and wiggle, and may have helped. Second, I'm absolutely apalled at what kawasaki passes off as spring clips on the EX250. It's nothing more than a piece of bent wire. I thought spring climps were bad enough, I can't believe they'd put that crap on FUEL lines! What if a fuel line came undone at speed and poured raw fuel onto the hot engine below? I think I'm going to replace my zx6r's spring clips with hose clamps, I just don't trust the damn things

Anyway, back to the matter at hand. I'm still going to check your compression tomorrow, if things look good I'd like to replace the spark plugs, change the oil (probably some metal shards in there), and give a shot at getting the engine to turn over, as I'm 99% sure this is the cause of the problem. Elaine, let me know if you want me to give it a shot, or if you'd prefer to have it looked over more thoroughly first. Everyone else, anything else I should do before trying to turn this engine over?

**Honclfibr** · 03-30-04, 10:29 PM

Plugs:

electrode:

**StumpyNB** · 03-31-04, 10:22 AM

Wow.. thats impressive! One thing I can think of that I might do before trying to fire it up, is pull the timing cover, and just turn the engine by hand, make sure it goes smoothly, before trying to start it up. Are you sure you got all the pieces of plug out of the engine? It would be important to get those out before starting as well. They may have just exited the exhaust if they were small peices, but they may not have as well.

**snaggle** · 03-31-04, 12:46 PM

I hate to burst your bubble, but every time I've seen a plug that had a big gob of metal on it like that one, there was an accompanying hole in the piston. But your compression test should show that.

**Honclfibr** · 03-31-04, 01:49 PM

Originally posted by snaggle
I hate to burst your bubble, but every time I've seen a plug that had a big gob of metal on it like that one, there was an accompanying hole in the piston. But your compression test should show that.

Yeah that's definitely a concern, I mean that metal had to come from somewhere, right?

I forgot to bring the compression tester today though, so it'll be tomorrow before I know anything

**Honclfibr** · 03-31-04, 01:51 PM

Originally posted by StumpyNB
Wow.. thats impressive! One thing I can think of that I might do before trying to fire it up, is pull the timing cover, and just turn the engine by hand, make sure it goes smoothly, before trying to start it up. Are you sure you got all the pieces of plug out of the engine? It would be important to get those out before starting as well. They may have just exited the exhaust if they were small peices, but they may not have as well.

I have absolutely no idea what's left in the engine or not. I'm going to stick a small magnet down the spark plug holes in a vain attempt to fish anything out which might have dropped in, but I don't anticipate much success there.

Turning the engine over isn't a bad idea at all, might give me an idea if the valve seats are burned up too...

**Honclfibr** · 03-31-04, 01:52 PM

Originally posted by Mystery Squid
Then based on that theory, wouldn't the same thing have happened to me when I suddenly ran out of fuel doing about 120mph on a straight?

I'm not sure. Certainly, it does seem like your scenario is just as much a case for preignition as this one, if not more. Just, based on what I know, the symptoms described here point to a preignition condition which I figure could be explained well by the lean condition I think may have occured. But I'm open to any other suggestions, I'd really rather not blow up two more spark plugs in the engine, in the case that it did turn out to have decent compression...

**Honclfibr** · 03-31-04, 10:01 PM

Originally posted by kmf
What was the difference between those plugs and the OEM plugs?

With the electrode all smashed up are you sure the pistons aren't hitting the plugs?

The OEM plugs were resistor type, and were one heat range colder. There was very little construction difference, both seemed to have the same thread pitch and length from what I remember. The new plug did run the threads down a bit closer to the tip...

I don't *think* the pistons were hitting the plugs, the electrode wasn't smashed up so much as melted. The tip on one of the plugs wasn't broken or bent, it just had a blob of metal on it.

Do you think plugs one heat range hotter could do this kind of damage? That strikes me as unlikely, but I'm far from an expert mechanic...

**Honclfibr** · 03-31-04, 10:02 PM

Originally posted by kmf
As for the hose clamps, how many people have you heard of that had the fuel line pop off and their bike burst into flames as they were riding it donw the road?

Dead men tell no tales?

Ok, maybe spring clips aren't so bad. But the ones on the 250 suck!

**Collision pro** · 03-31-04, 11:43 PM

I think I would be alittle more worried about where the rest of that plug went then the clamps!!

**Honclfibr** · 04-01-04, 12:37 PM

So far no good. Cylinder 1 has 110 compression, but cylinder 2 (the cylinder where the plug blew up) reads zip zero zilch.

I'm gonna shoot some compressed air down there tonight, see if I can tell where it's going...

**StumpyNB** · 04-01-04, 01:26 PM

Bent/jambed valve? Cylinder siezed?

**Honclfibr** · 04-01-04, 01:47 PM

Originally posted by StumpyNB
Bent/jambed valve? Cylinder siezed?

Place your bets. I've got my money on "hole in top of piston"

**twrayinma** · 04-01-04, 01:52 PM

yo, elaine, you should totally get your money back from the farquaad who screwed up your bike.

**Honclfibr** · 04-01-04, 02:17 PM

Originally posted by elaineo
Glad it's not your bike, eh?

Hey you'll be the only kid on your block with an EX125

Seriously, figure out what you want to do. I can get the EX500 fixed up and you can take that and part out the 250, or we can try and do an engine swap. Engines looks to be pretty cheap for this thing if you look hard enough...

**stoinkythepig** · 04-01-04, 03:10 PM

Bummer.

My money's on a cracked exhaust valve. Can't really say why, just a feeling.

**Honclfibr** · 04-01-04, 04:39 PM

Originally posted by stoinkythepig
Bummer.

My money's on a cracked exhaust valve. Can't really say why, just a feeling.

Damn Dave, I'm impressed. You're good. Put cylinder 2 at TDC and ran a few psi in there, and you can feel it coming straight out the exhaust canisters

Or, at least, that's *one* of the problems

**bemused** · 04-01-04, 04:42 PM

um-m-m... I may be showing my ignorance, here, but:

@ TDC, shouldn't either the intake or exhaust valve(s) be open?

if the latter, wouldn't that explain the flow you were getting?

**Honclfibr** · 04-01-04, 04:48 PM

Originally posted by bemused
um-m-m... I may be showing my ignorance, here, but:

@ TDC, shouldn't either the intake or exhaust valve(s) be open?

if the latter, wouldn't that explain the flow you were getting?

TDC is when the piston is all the way into the head, furthest from the crankshaft. This is the point of highest compression, the point at which the spark sparks and the mixture ignites to push the piston back down. Neither valve should be open at that point, among other bad things you'd lose power as the combustion gasses leaked out around the valve.

The exhaust valve should open after the piston travels back to BDC, then the piston's next travel up is the exhaust cycle, and the movement of the piston back into the head should push the exhaust gasses out around the valve into the exhaust.

At least, I think...I'm still learning about engines...

**bemused** · 04-01-04, 07:40 PM

that's what I get for typing in a hurry... must remember to engage brain before operating keyboard...

lemme try again: the way I see it, every other TDC oughta have the exhaust valve open. then, on the next downstroke-- w/ some overlap-- the exhaust oughta close, intake open... sucking fuel/air mix into the cylinder. then, @ BDC (more or less), intake closes, piston compresses mix on upstroke to approx. TDC... plug fires, throws piston back down to BDC... when exhaust opens to release spent gasses on next upstroke.

so... unless I'm out in la-la land here (always a possibility), you'd have a 50-50 chance of having an exhaust valve open when the piston was @ TDC...

did you crank the crank around to the next TDC and repeat the test?

...or am I way out in left field here, and missing some crucial point?

(or just plain wrong... it does happen

)

**Honclfibr** · 04-01-04, 08:01 PM

Ahhh, I understand what you're saying now. I'm not sure which TDC I'm at based on the marks, the compression stroke or the exhaust stroke. And you're saying that there's a possibility the exhaust valves are still partway open during the TDC of the exhaust cycle...

Now I thought that all the valves had to be closed at TDC always, otherwise the piston would slam into them, but maybe that's not true. Certainly, given that I'm still at work, it's worth rotating the engine an additional 360 degrees and checking it again. Thanks for the tip

**wastedincome420** · 04-01-04, 09:08 PM

Ya Let us know wha you find out on the "retest" caus eI' also believe Bemused is on the right track

**Honclfibr** · 04-01-04, 09:47 PM

Rotated the engine 360 degrees, same deal

Oh well, it was worth a shot

**Collision pro** · 04-02-04, 01:29 AM

Originally posted by elaineo
how bout i just kick him really hard in the 'nads?
<font size=0>.... see you soon darrell... </font>

i'm gonna call around tomorrow and see if i can find a used engine for sale. if i can't, i'll call some dealers and see if i can get an engine rebuild kit or something. if that doesn't work out, then maybe it's time for a new bike

It's almost sad for me to say this..........But if you want to have it rebuilt pm KMF he does stuff like this and is great at it!! I'm sure he will give you a better deal then a dealership.

Damm..........that hurt to say!

Spark plugs exploded, why?

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