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Carlos Luiz

Kx125 head gasket issue.

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I have 91 kx125. I've had it since last may, out about 85 hours on it so far. Had a rebuild about 15 hours before I got it. 

So my issue is I think the head gasket is bad, But I'm not sure. Since I've had the bike it always seems to loose coolant during rides, it has never overheated but I always check before each ride. I've checked for leaks, no luck. The tranny oil and spark plugs and look good. So it must be coming out of overflow. I replaced the cap, no change. Bike runs great so I keep riding. Through some research I saw head gasket could over pressurize the radiators and spit out fluid. I checked for bubbles and there are some when I give it throttle.

So is my headgasket bad? I have no overheating or other signs. Just little bubbles in the coolant. Anything else it could be before a pull the top end? Like I said it's done this for at least the last 80 hrs and hasn't gotten better or worse.

 

Thanks for the help

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How much coolant are you adding after each ride and,

at what level are you filling the radiator?

 

Most bikes without a recovery tank require the cold level to be about 1/4" above the tubes.

Any more and the excess coolant will be expelled when the engine is up to operating temp.

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46 minutes ago, mlatour said:

How much coolant are you adding after each ride and,

at what level are you filling the radiator?

 

Most bikes without a recovery tank require the cold level to be about 1/4" above the tubes.

Any more and the excess coolant will be expelled when the engine is up to operating temp.

I fill to the base of the neck, per the manual. And I'd say maybe like 6-7 oz after a 3-4 hour ride. I only ride trails so it's slower. I just put a recovery tank on. I'll test ride it this weekend and see how much it spits out. Hard to judge when filling. But doesn't seem to excessive. I know some is going to come out the overflow.

And as far as top end life I compression tested it at 130. Still within spec and still has power, so I'm gonna run it a little longer.

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At 130psi and nearing 100 hours, IMO you are way overdue for a top end refurb.

The longer you wait, the more the worn piston 'rocks' and risks wearing out the plating/bore.

 

You hadn't mentioned trail riding but yes in that usage if the going gets slow and the engine temps increase, 

you are going to loose more coolant than typical faster pace MX riding with constant airflow thru the radiators.

 

A coolant recovery tank will help prevent running low after the engine has cooled down but still monitor the level

until you've confirmed you're not leaking coolant internally.

Make sure to have the appropriate radiator cap (if applicable) for a recovery system.

 

Edited by mlatour

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30 minutes ago, mlatour said:

At 130psi and nearing 100 hours, IMO you are way overdue for a top end refurb.

The longer you wait, the more the worn piston 'rocks' and wear out the plating.

 

You hadn't mentioned trail riding but yes in that usage if the going gets slow and the engine temps increase, 

you are going to loose more coolant than typical faster pace MX riding with constant airflow thru the radiators.

 

A coolant recovery tank will help prevent running low after the engine has cooled down but still monitor the level

until you've confirmed you're not leaking coolant internally.

Make sure to have the appropriate radiator cap (if applicable) for a recovery system.

 

Alright I'll keep an eye on it. And I do plan to rebuild soon. Just don't have the funds quite yet, so I'm still riding.

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That bore is the electrfusion bore no plating. I would say the head surface is warped. 80 hours is alot but if compression is still above 100 keep riding it. If your concerned then do a top end and have the head and deck of the cylinder machined flat. Then the issue will be gone. My 2nd CR500 had a warped head and was doing the same thing. I bought a new head and no more issues. I don't think you will find a new NOS head for a 91 KX.

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1 minute ago, FPMXer said:

That bore is the electrfusion bore no plating. I would say the head surface is warped. 80 hours is alot but if compression is still above 100 keep riding it. If your concerned then do a top end and have the head and deck of the cylinder machined flat. Then the issue will be gone. My 2nd CR500 had a warped head and was doing the same thing. I bought a new head and no more issues. I don't think you will find a new NOS head for a 91 KX.

This was what I was thinking and figure I will check the head when I rebuild. But I still feel like I should have some other signs if its a warped head or even just a blown gasket. But I guess I'll see once it's apart.

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Just now, Carlos Luiz said:

This was what I was thinking and figure I will check the head when I rebuild. But I still feel like I should have some other signs if its a warped head or even just a blown gasket. But I guess I'll see once it's apart.

If the head was real bad the head gasket would have blown along time ago. It's warped just enough to cause minute air pockets and weep coolant into the combustion chamber. When you remove the head lay it face down on a sheet of glass and place a light on the other side and look you will see what I'm talking about. You can even get a big sheet of sand paper and lay it on the glass with the edges taped down and rub the head in a figure 8 on the sand paper and you will also see what I'm talking about.

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Sorry to be blunt in today's PC culture, but you not having money does not mean the engine is great to keep running. It is a high performance, high maintenance motorcycle. Physics does not care. Good luck on the cylinder's condition.

 

Coated or plated, the same principles apply.

 

Do you know that the head is torqued to the proper specs and in the proper sequence by the previous owner?

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34 minutes ago, KDXGarage said:

Sorry to be blunt in today's PC culture, but you not having money does not mean the engine is great to keep running. It is a high performance, high maintenance motorcycle. Physics does not care. Good luck on the cylinder's condition.

 

Coated or plated, the same principles apply.

 

Do you know that the head is torqued to the proper specs and in the proper sequence by the previous owner?

I get that. That's why I checked compression. Book says change below 116psi. Cylinder looks good when looking through exhaust port. That's the only reason I'm still running it. It's not on track, it's spends most of it's time in low-mid rpm. So 100hrs isn't that bad.

And I did retorque all the bolts. All seem good, but I can't guarantee who to PO did it during rebuild 

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Compression can be fine right up until the skirt cracks off of the piston.  I've purchased bikes that start first kick and run great with two cracks running halfway through the intake skirt.

Just by time, unknown from the previous owner and 80 more since you got it, it's due. 

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16 hours ago, FPMXer said:

That bore is the electrfusion bore no plating.

:lol: Really? I'm guessing you don't know what an 'electrofusion' bore is. It does have plating, and once it's worn off it's had it. No honing on those, too thin.

Which is exactly why the op needs to keep the piston and rings in top condition, to help it last.

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5 hours ago, DEATH_INC. said:

:lol: Really? I'm guessing you don't know what an 'electrofusion' bore is. It does have plating, and once it's worn off it's had it. No honing on those, too thin.

Which is exactly why the op needs to keep the piston and rings in top condition, to help it last.

Ya those are shit if ask me cant even deglaze hone with worry.  

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17 hours ago, DEATH_INC. said:

:lol: Really? I'm guessing you don't know what an 'electrofusion' bore is. It does have plating, and once it's worn off it's had it. No honing on those, too thin.

Which is exactly why the op needs to keep the piston and rings in top condition, to help it last.

https://www.ridersdiscount.com/wiseco-piston-56mm-electrofusion-for-kawasaki-kx-125-91-651778

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