Losing Gearbox Oil

[TeamDoty]

Hi everyone,

I have a 2002 KDX200 (pretty sure that's the "H" model).

I've owned it a few seasons and I don't have any history for the bike. It appears to have aftermarket reeds, carburetor and an FMF Gold series pipe.

I've only been on two rides this season. After the first ride I noticed the gearbox oil level was low. That was certainly unusual as the bike has never lost oil while I've owned it. Not thinking much of it I topped it off and took it out this past weekend for another ride. After about 4 hours of riding I noticed the oil level was down below the low mark (!)

The bike runs great and is still running great. The engine coolant is perfectly clear blue and remains at the full mark in the reservoir. I have noticed a little more "splooge" than in the past but there has not been excessive smoke (confirmed by 2 of the riders I was with). I didn't notice any leaks, oil puddles, etc. The rear fender wasn't awash in oil vapor as I've seen pictures of on here.

I will drain whats left in the gearbox and try to see if there's particles in it but honestly, I'm not sure where to start. I'm a decent mechanic but don't have a lot of experience with full rebuilds of motorcycle engines (I've done top ends but not gearbox rebuilds). I'm certainly willing to try but being right in riding season has me bummed out.

Any help, ideas, etc. would be greatly appreciated... thanks!!!

Heath

[TwistedRoot]

Do you have excess oil around your counter shaft sprocket? This is a fairly common issue with a leaky shaft seal. This usually occurs when your chain is too tight, and you will see excess oil gather around your shift lever and that area will be a mess.

[TeamDoty]

Do you have excess oil around your counter shaft sprocket? This is a fairly common issue with a leaky shaft seal. This usually occurs when your chain is too tight, and you will see excess oil gather around your shift lever and that area will be a mess.

Don't believe so... I don't recall any oil leak there... we washed the bikes off after our ride (sorta muddy ride) and I'm sure I would have noticed but I'm going to take another look.

I've done some (more) digging around on here and on YouTube and I'm thinking it's the crankshaft seal that keeps the crankcase separated from the gearbox/transmission side. I bet it's letting a lot of the transmission oil into the crankcase and it's burning it all up. There is definitely more splooge than before and more smoke... just not the amounts I've seen on some videos. Maybe at least I've caught it before any major damage has occurred.

I'm hoping to get a couple other thoughts, ideas, suggestions before I tear it down. I'm guessing the case needs to come apart to do this job. Uugh.

[Slick_Nick]

Yes the case needs to come apart, but the KDX engine is simple, and with the right tools, it's actually quite fun and satisfying to rebuild it.

Do all of the bearings and seals while you're in there, as well as a fresh top end. You'll love how it runs afterwards!

[KDXGarage]

Pressure test and vacuum test before any disassembly!

How long are you allowing the engine to cool before checking the oil level?

Are you checking it while the motorcycle is horizontal?

Where is your crankcase vent hose routed?

[TeamDoty]

Pressure test and vacuum test before any disassembly!

How long are you allowing the engine to cool before checking the oil level?

Are you checking it while the motorcycle is horizontal?

Where is your crankcase vent hose routed?

Thanks! I will definitely run those tests and get back with you... it'll be a couple weeks before I can really dig into it though as I have a big trip coming up to prepare for.

I did let the engine cool a long time - approximately 3hrs after the ride before checking and I did make sure the bike was level. I'll double check the vent hose... I can't say for sure where it goes on my bike. I was just working on my son's CRF150F and it was routed up to the airbox. Is that where my KDX should be routed?

[TeamDoty]

Yes the case needs to come apart, but the KDX engine is simple, and with the right tools, it's actually quite fun and satisfying to rebuild it.

Do all of the bearings and seals while you're in there, as well as a fresh top end. You'll love how it runs afterwards!

Thanks! I'm not queasy about buying tools and digging into stuff so yeah... it might be fun. Probably time for a complete rebuild... I'm just bummed that it's happening RIGHT NOW when I should be planning more rides vs. planning an engine rebuild :(

[KDXGarage]

1986+ crankcase vent hoses route up to the air box.

I would rule out all possibilities before opening it up.

[bufftester]

Leak-down test will tell you how your seals are doing pretty quickly, doesn't take much time and is pretty easy (once you get the right bits together).

[TeamDoty]

Leak-down test will tell you how your seals are doing pretty quickly, doesn't take much time and is pretty easy (once you get the right bits together).

I found a video where they hooked up a shop vac to the crankcase, closed off the vent (or maybe used the vent hose) and then had some other hose running from the gearbox into a bottle of fuel/oil/etc. Turned the shop vac on and you could see the fuel being drawn into the hose indicating a leak between the crankcase and the gearbox. Is this a legit test?

[TeamDoty]

I double checked and there's definitely no leaks. No leaks at the sprocket and no leaks anywhere else. I'll have to let this sit for a bit until I get this project/trip done but I'll also take off each side cover and look for oil... I believe that's also an indicator of where the oil loss may be coming from.

[bufftester]

No need to bother with the clutch side cover, pull the flywheel cover off and look for oil in the bottom of it.