Engine Diagnosis Question

[G22inSC]

Just a little backstory...out riding the '05 KDX200 with the family a few weeks ago and after an hour or two of riding the KDX just shut off. It kicked over but I couldn't keep it running at low rpm. Thought maybe something plugged the pilot jet (like dirty gas, etc.) since I was able to keep it running as long as I kept the revs up. Told the family to meet back at the track and I hauled tail in that direction. They appeared back at the truck a little while later, we took a break and then decided to try another lap. KDX started up fine and ran great. Near the end of the ride that day I noticed a lot of heat around my knees and thought that was different, but it was getting warmer and haven't ridden in the heat in a while.

While washing the bikes the next day, I noticed the radiator fluid level in the overflow tank was really low. The level has never changed and now the overflow tank was almost empty. Never saw any leaks or spewing of coolant. That got me thinking about me noticing the heat around my knees and got worried it ran really hot. I was hoping all was good due to still having some coolant in the overflow tank and the radiator itself was full. Topped the fluid off and made the note to keep an eye on it.

Rode yesterday with my boys and a few cousins for several hours. Bike ran great, no issues, no power loss, no hot knees, etc. but after getting home and letting the bike cool down, the overflow tank is low again. The level dropped from the just below the "full" line to the "low" line.

I'm currently waiting on a pressure tester cap to arrive so I can pressure test the cooling system. This is what I'm thinking...for whatever reason the bike ran hot, that either blew the head gasket or warped the head and am now the bike is losing coolant internally.

What do you'll think? Are KDX's more prone to blow the gasket or warp the head? If it is the head, what is a suitable item to use to check for "flatness" on the head. And the big question now that I'm thinking over all the events, was there a fuel delivery issue or did the top end blow? Haven't noticed a loss of power or lower compression on kicking. It may be smoking a little more than usual but that may also be my paranoia creeping in. Crossing my fingers and praying that it's just a gasket issue.

[pumpguy]

Can't offer much help with your overheating problem.

How's your transmission oil, clear or milky? If milky looking, it's got coolant in it.

Ideal way to check cylinder head faces is with a machinist's surface plate and some Prussian Blue marking medium. You can get Prussian Blue at most auto parts stores. I've used lipstick as a substitute. Put a VERY LIGHT smear of the Prussian Blue on the surface plate, then lightly rub the cylinder head joint face onto the marked up surface plate. High spots (warpage) will show as blue marked areas on the head's or cylinder's joint face. If the joint face is still flat, you'll see blue marking over most of the joint face area.

A pretty good substitute for a real surface plate is a piece of thick plate glass.

[G22inSC]

Trans oil is clean and does not have coolant in it. Not sure why it ran hot at the moment. Once my tool arrives I'll be able to pressure test the cooling system and verify it's leaking/losing pressure.

Good info on the machinist's plate. I will have to see if I can track one of those down once I verify I have a leak.

[John_S]

Let us know what you find. What tool did you order? I should check mine out. It doesn't run hot or smell like its leaking coolant but every couple rides I have to top off my overflow tank.

[G22inSC]

What tool did you order?

MityVac MV4510 kit. I really only needed the cap adapter (MVA321) but I was in a hurry and could get the kit much quicker. The kit would also give me a backup pressure tool if the one I have now ever failed.

[John_S]

Excellent thank you

[G22inSC]

It's official...I have a coolant leak. I pressurized the system and it slowly looses pressure. Could be a connection at the tool, but I don't believe it is. Absolutely pouring right now and didn't feel like staying out in a metal building so further investigation will have to wait. My trans oil is clean, I have no external leaks so that leaves either a blown head gasket or a warped head. Hopefully I can figure out what made it run hot to begin with or I'm just wasting time and money on parts. The saga continues.

[bufftester]

Well bad news, but at least pulling the head off is easy, can be done with the engine in the bike, and is easily checked for warpage. Don't buy cheap gasket kits if it turns out to be that.

[G22inSC]

I've got a new top end on the way with a Cometic gasket set. I'm going to do a pressure/vacuum test this evening once I can get the exhaust and carb off. Then I'm going to do another pressure test on the cooling system to see if I can detect coolant in the cylinder through the open exhaust. Drain the coolant and pull the water pump cover to examine the water pump fins. If all seems well, guess it will be time to start pulling hoses and looking for blockages (which I don't believe should be an issue). Then it's time to pull the top end and go from there.

One idea I have is these are the first real rides I've had since getting the Rekluse clutch installed. It appears to be working correctly but there aren't any hard set guides for the adjustment on our KDXs. I'm wondering if maybe it's not adjusted completely right and is creating excessive heat which is what caused all this to begin with. May be time to go back to the OE clutch.

[SS109]

Heat from the auto-clutch is a real possibility. When I had one one in my KDX it always ran hot. Had to up the pressure rating on the radiator cap to keep from losing coolant each ride and really wish I would have added a fan. If I were you I would adjust the Rekluse to where it almost stalls at idle. You want it to slip as little as possible. Also, run a full quart of transmission oil to help keep it cool.

[G22inSC]

Passed pressure and vacuum test (leak downiest) flawlessly. Did another cooling system pressure test and it is losing pressure but so slow it’s ridiculous. Factory manual says watch pressure for at least 6 seconds. Tool manual says no change in two minutes is good. Pressure dropped about 3 or 4 psi over an hour. Don’t see any liquid looking through the spark plug or exhaust holes. Then again, top of the piston is clean like it’s been steam washed. Don’t see any carbon buildup on the crown.

Put it back together enough to be able run the engine. According to the tool manual a dynamic test (engine running) will test for major leaks, head damage, blown gasket and cracked block. Immediate and raid pressure spike is indicative of a blown gasket. If no immediate buildup, pressurize the system to normal pressure. If the needle on the gauge vibrates rapidly, this indicates smaller compression or combustion leak into the cooling system possibly caused by damaged block or head. I had the rapidly vibrating needle.

Pulled tool off and restarted the engine with the radiator cap off (wasn’t hot yet). Coolant in the radiator neck was instantly frothy. Never seen that before.

Bought the bike new in '06 and has less than 60 hours on it (it was a backup bike for most of it's life). It's now making a lot of noise. I know the KIPS isn't quiet but I'm thinking piston slap. Really didn't expect that with low hours, no dirt ingestion, etc. Guess it’s time to tear it down.

[G22inSC]

Drained the coolant and oil. All is clean and well. No water intrusion. Found no blockages, signs of corrosion or broken water pump vanes. Everything looked great. Thinking the Rekluse caused the heat problem at this point (no mud riding, sand, etc. as it has just been normal rides) so I swapped back to the OE stock clutch last night. I will tear into the top end hopefully this weekend. The saga continues...

[G22inSC]

Finally got a little time to do some more work. Got the top end off and found a cylinder with no scratches and a very clean head and piston. In my opinion, they are too clean like they have been steam cleaned by coolant. Didn't find any noticeable gasket issues but I don't really know what I'm looking at there. KIPS was all good but dirty. Going to take the cylinder and piston to a machine shop and see if I can get a good measurement on it all. Here is a couple pics of the head and top of the head gasket at time of removal. What do you'll think from the pics?

[G22inSC]

Here's a few pics of the piston. From the bottom pic it doesn't look like the piston was ran too hot or too lean. Ideas?

[kdxsully]

The top rim of the cylinder - around 3 o clock looks chipped? Like detonation damage? And I see little pin marks on the edge head, and the dome doesn’t look smooth. Not sure if that roughness is normal. Maybe someone else knows/can tell for sure.

[G22inSC]

The top rim of the cylinder - around 3 o clock looks chipped? Like detonation damage? And I see little pin marks on the edge head, and the dome doesn’t look smooth.

That is actually wet, oily spots. Not any kind of pitting or damage was discovered. It does look suspect in the pics though as those were taken as is before being wiped down.

[G22inSC]

Pic of the head after being wiped clean...

[KDXGarage]

What's the last thing you changed?

"One idea I have is these are the first real rides I've had since getting the Rekluse clutch installed."


Which brand head gasket is that? Why does it have circles instead of slots for the coolant passage in two areas?

I see you have a "C" piston. Do you have a "C" cylinder?

[G22inSC]

Rekluse was the last thing and for now I have pulled it back out and put the standard clutch back in. As far as gasket, piston and cylinder, everything is original OEM. Piston and cylinder are both marked as “C”. I purchased the bike new years ago and just haven’t put that many hours on it.

[KDXGarage]

Have you ridden it since putting the stock clutch back in?

Thanks for pointing out that you are the original owner. That helps, too.