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Need Help Diagnosing Blown Head Gasket?

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Jul 12, 2005
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#1
Hey Fellas,

My son was running his KX85 this past Saturday without issues. Suddenly, it simply died coming around a corner and it would not start again. We tried in vain to get it going in the pits but finally had to pack up and go home.

The coolant level had been down the week prior and when I checked, it was down again. At first I thought that he had lost his coolant and the cylinder had overheated but that didn't make sense since it was kicking over fine even after it stopped running? I tested the compression and it is down to 60psi.

A friend thought it might just be a blown head gasket so I pulled the head off last night. Difficult to say if it is just the head gasket though?

Here is what I found:
Pulled the plug - It was white and had a crystalized look to the tip.
Drained the coolant - there was a LOT more coolant coming out of the bike then what I added on Saturday so it wasn't as low as I thought.
The gasket looks questionable. It has areas that look like the coating has dissolved away from the metal.
Head may be slightly warped - I placed a straight-edge across it and can see a little light.
The cylinder walls appear to be fine (no visual gouges)
The piston has some deformation around the front at the top. It looks like a little lip has formed but I have absolutely no clue as to why that would be there?

One more thing, if the headgasket blows to the inside of the cylinder and coolant gets in the cylinder, will it leak past the rings and get in with the tranny oil? I ask because the tranny oil looks thin. I haven't drained it yet but will today. I can slosh it back and forth if I rock the bike and look through the glass. Doesn't seem right for oil?

Hope this info will help me get a concise answer.
 
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#2
Well first off 60psi is way to low , but I'm assuming you realized that.


I would spend a bit more time checking the head. Get a good straight edge and check it over real well. If it comes out straight your good, but if it has warped even slightly I would toss it out.



From what you've said either the head gasket failed on its own or the head somehow became warped and caused the gasket to fail.

What type of coolant do you run?

How often do you top it off / check the levels?

Ever had the bike overheat before?



While it would be a good idea to determine the cause of the failure sometimes thats not always possible.

It would take a fairly large leak for the coolant to bypass the rings and pump down into the crankcase. In fact I'm not really sure that is possible, assuming the rings are sealing.

More than likely you had a smaller leak that just boiled / vaporized as it made its way into the combustion chamber.


My guess (emphasis on guess) for the piston deformation is that coolant was coming directly in contact with it at certain points. This was causing the piston to run through rapid heat up / cool down cycles.

I would do a top end job (replacing the head if necessary) and giving the jug a very thorough inspection. While thats off check crankshaft end-play. If everything feels good on the bottom, bolt it back up and take off.

The oil sloshing will depend on it's current temperature and how long it has been in use. It is pretty easy to tell if water has contaminated the oil, it will look like coffee with creamer.

Once you get it back together, watch the cooling system very carefully. It wouldn't be a bad idea to inspect the water pump as well, make sure thats working 100% correctly.
 

IndyMX

Crash Test Dummy
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#3
Also, if the crank seals are working, there shouldn't be any way that coolant from leaking into the cylinder can get into the trans.

You failed to mention how many hours were on this topend, how often you change the trans oil and how often you clean the air filter.

What's the condition of the carb? Did it stop running due to a lack of fuel or a blockage in the carb?
 
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#4
Hey Guys,

Thanx for posting.
Mystery is solved as the cylinder, piston and rings all got destroyed!
I didn't notice the large gouge on the backend (intake side) of the cylinder. Seems to be a classic case of overheating. The rings seized at the front, pushed the end gaps out at the rear and the bottom ring end gap hooked on the bottom of the intake. This cracked the piston and folded the ring under causing the destruction of the cylinder.
Since its nikisil, I have to buy a new top end including cylinder. Really sucks but at least I have 2 weeks before my kid starts the winter series so it will be ready.

The bike has about 20 hours on it from a fresh rebuild. According to my racing buddies, this is too long for a race bike to go between services. That was my mistake I guess.
There were 4 race nights and the rest practice.

I personally don't think it was servicing that killed it. I think it had to do with losing coolant somewhere? Since I had topped it off the week before (Zerex pre-mixed) and then discovered it had dropped in level again when it blew up.

The other drag is that the piece of piston that came out must have gone into the crankcase. I am going to pull the motor and flush it out but I may have to split the cases to be certain there are no bits floating around in there.

Thanx Guys
Bernie
 

IndyMX

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#5
I'd send it to Eric Gorr..

And for future reference, it's always a good idea to check coolant levels before each ride.

Takes just a second, but can save you from serious trouble.
 
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#6
Well,

I have already ordered and paid for a new cylinder but it definately wouldn't hurt to have someone of Eric's talent look this one over. Maybe he could do something with it and provide me with a spare which would be great to have.

Yes, much more serious checks moving forward.

Bernie
 

IndyMX

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#7
Hate to have to learn all of the crap you have to do to make this sport go smooth, due to a major catastrophe, but hey, it happens.