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Discussion Starter #1 (Edited)
I bought a 2016 390 Duke a while ago (~16k km) and within 1 week of riding the engine broke. Brought it to two shops (even the KTM official one) and nobody could help me assess the problem. Most likely the engine ran without oil and has some internal damage. Happy to share more details if people are interested (I have the computer readout etc). I've decided to open up the engine and try to assess what is the problem. For my fellow KTM lovers - I will keep a bit of a diary here. Let me know if you have any questions - because there is so much more to share.

Printed the repair manual, chapter 16 how to disassemble an engine ... how hard can it be? o_O

P.S. I live in Hong Kong so space and access to tools is a constraint. We've also never worked on a bike before.

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We've stripped all the parts to get easy access to the engine. In the end it is held into the frame with two through bolts. It became apparent nobody ever properly services and maintained the bike.

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Here is the bad boy.

EDIT: When removing the timing chain - note the direction of travel and mark it - you need this later when putting it back.

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Pop the hood and make sure we know dead center for later.

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Hmmm, the bottom right valve has a lot of carbon compared to the other ones.

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Lots of carbon here as well

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Some oil compatible sanding paper later

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Removing the clutch disks.

Well there is a 10 picture limit to post here. Next up is removing the clutch housing (which I broke..) and rotor.

Give it a thumbs up if you want more :)
 

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Great pictures. Since you have access to your frame, from what you can tell is this the same frame as the rc390? Is there a part# that you know of for your frame I can reference for my frame? Will be also rebuilding 390 engine in the future any inside knowledge greatly appreciated!
 

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Discussion Starter #3
The frame is a bit different. But a lot of part in the engine and around are similar between the Duke and RC. I use several parts websites to compare if parts are similar. They have good schematics which show you part numbers. Helpful if you want to buy a similar part on eBay between a Duke and RC.
 

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Please do post more. I'll be interested in whether folk think that one differently colored valve is normal or not.
 

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The frame is a bit different. But a lot of part in the engine and around are similar between the Duke and RC. I use several parts websites to compare if parts are similar. They have good schematics which show you part numbers. Helpful if you want to buy a similar part on eBay between a Duke and RC.
Thank you. will be researching front fork setup. I have seen a build online converting 390 duke to spoke wheel setup. seeing if I can use entire front end from duke 390 on rc 390 frame. if not find a way to use spoke wheels on rc frame/stronger wp forks.
 

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Discussion Starter #6 (Edited)
EDIT: Apparently it is the Loctite that makes the screws inside the engine very hard to undo. Use heat or a really good impact wrench...

This bike has been over-torqued like crazy, it's an absolute pain! I even got an impact wrench up to 250nm and it doesn't do anything. Unfortunately, I didn't get the right clutch holder (Amazon basic one...) and I broke both my inner and outer clutch hub, trying to make an improvised clutch holder. Ordered a second-hand clutch on Ebay to replace the hubs...

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The TUSK clutch holder from works like a charm. I also ordered the KTM clutch holder but it's on backorder, I will cancel that one.

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It was a two-man job and a massive wrench to be hit with a brick to get the clutch off. Be we got it off finally.

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Next up is the gear connected to the countershaft. Same issue. Just impossible to get off. After hours of trying, we gave up. And stripped the bolt. If anybody has suggestions on how to get this out, please let me know. Think I need to bring it somewhere to get it drilled out.

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With everything remove (except the gear above) we tried to open the case. It split up to 1cm, but unable to open the case. It seems that we need to remove that gear. So, no success there. My hope was that we could split the case with the gear still attached.

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Meanwhile, Santa arrived with all the replacement O-rings, some special tools and other parts that will be replaced, once I get it open.

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Edit: The genuine KTM tools that you really need are the two in the middle + the engine lock screw!

Please do post more. I'll be interested in whether folk think that one differently colored valve is normal or not.
Very keen to learn that too - not sure what causes that.
 

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Use heat on any further bolts. A propane torch works well. It sounds like red loctite, or something similar, was used so you need heat to break down the thread lock compound.
 

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Also might be worth investing in an impact wrench. I have a cordless but if you have an air compressor I'd get one for that.
 

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Discussion Starter #10
I did try with a battery impact wrench but to no avail. Just hits the ratchet immediately.

Use heat on any further bolts. A propane torch works well. It sounds like red loctite, or something similar, was used so you need heat to break down the thread lock compound.
But I think this is it ... need to heat up the bolt first. Kinda pissed I didn't know that before. Now that my bolt is practically stripped .... sigh.

Any suggestions on how to get that gear/bolt out? Drill it out or spot welt on top of the bolt and heat it up with a torch?

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Might try a set of vice grip style pliers on this as a last resort.There appears to be a bit of a shoulder on that bolt, very tight grip and then smack the vice grip with a hammer. Do you know the direction of the thread? We all have tried and tried to later find out it’s a reversed thread direction.
 

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Cut flats on the outside of the bolt with a dremel tool. Or a hammer and chisel used properly might work. Again, apply a lot of heat first.
 

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Discussion Starter #13 (Edited)
Cut flats on the outside of the bolt with a dremel tool. Or a hammer and chisel used properly might work. Again, apply a lot of heat first.
We got him 🔥

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After applying a lot of heat, a concrete chisel at a 45 degree angle and 2 hours of swearing.

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Might try a set of vice grip style pliers on this as a last resort.There appears to be a bit of a shoulder on that bolt, very tight grip and then smack the vice grip with a hammer. Do you know the direction of the thread? We all have tried and tried to later find out it’s a reversed thread direction.
Tried this as well @Spartacus - but this one was too stuck

Splitting this beauty (it got quite some abuse trying to open it - so I hope I didn't do any damage)
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All cleaned up
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And I think I found my problem - way too much play on the crankshaft - time for a new one:

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I do wonder what could have happened for this to occur at only 16k km's....
 

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Wow that’s alot of play.... either starved of oil or never changed the oil. What does the valve gear look like cuz it will show wear faster from this type of abuse?
 

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1) Congrats! 2) I've had one con rod big end bearing go in my life (49 yrs riding). On that one (1973 Bultaco 350 Sherpa T) you had to exert lateral pressure to hear the clunk; no movement visible to the naked eye. Now, is the the crank pin or bearing?
 

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Wow that’s alot of play.... either starved of oil or never changed the oil. What does the valve gear look like cuz it will show wear faster from this type of abuse?
+2 Lots of other stuff should be visibly damaged if that's oil starvation. Piston, valve gear, little end bearing and pin. If they don't, it's a bad part. Others will know more but I wonder if you need to change just the bearing, or also the con rod or even the pin.
 

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BTW, when you said the 'engine broke' what were the symptoms?
 

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Def looks like oil related. Make sure you look at the cam journals for damage, as the head is the last bit to get oil. How does the cylinder look?
 

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Discussion Starter #19
The new parts are on the way, to be safe I ordered a new OEM crankshaft. I don't have the proper tools/knowledge to take the current on apart. But the pieces are starting to fall together what happened to the bike. Since I got it I had a "Low Engine Oil" warning - which I ignored as there was enough oil, so I wrote it off as a sensor issue.

I also had a "Faulty Lambda Sensor" warning. Which apparently is responsible for determining the mix of fuel/oxygen. Now with the engine open, there is a tonne of carbon deposits everywhere (piston/valves/spark plug) - probably related the to the faulty lambda sensor. And probably clogged up the flow of oil and starved some parts of of oil ultimately causing the engine to jam/run dry.

I brought it to the shop to check but its hard to find a reliable shop here in Hong Kong. I took the bike back and did an oil change myself to find all these metal shards. It also became apparent that the previous owner didn't do any basic maintenance ever on the bike.

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Initially it wouldn't even run idle - just a metal clink sound and died. But after the oil change it ran idle but with a rattle (sounds like the timing is off)

Video with sound here

This was the read-out the shop gave me:
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@Chip So there you have it :)
@Spartacus What exactly are the valve gears
@OneJzsupra I will make a photo of the head later and post it here - as I don't really know how to look for damage. The cylinder/piston/rings looks fine to me. No visible scratch or wear marks
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Discussion Starter #20
And just for fun - this was the quote (in HKD - so divide by 8 for USD) they gave me for look at the bike. Later I found out they didn't even look at the spark plugs or throttle body ... just were just looking to charge me through the roof. And this is the official KTM shop...

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