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Valve gear refers generically to the cams, and upper end (whatever wears or rubs on them).
Looks like the first owner never changed oil or was very lax. While you have it open I would probably replace the oil pump for “piece of mind” insurance. Probably not absolutely required but I wouldn't rebuild without.
 

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"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."

Check the oil pump then. I seem to remember that a crankshaft bearing as bad as yours can cause low oil pressure but I bet I heard that on Car Talk and it referred to multi cylinder car engines. So make sure that oil pump functions when you get it running again.
 

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Discussion Starter #23
95608


The oil pump (not my photo) is mechanical - similar to the photo above. It looks fine to me - still better to replace you reckon?
 

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Hard to see in the photos, is the cylinder good to go? It doesn't look too bad in the photo, the cross hatching looks pretty good as well. Honestly if you taken the engine apart that much, I would have a machine shop make sure the head is decked and that the cylinder is good. Verify all clearances for the crank, rings, and rod and put her together.
 

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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 don't think the light is a 'low engine oil' warning. It's a low oil pressure warning. And usually it's pretty much over pretty fast after that. Especially with that rodbearing being so loose.
Looking at that engine and you mentioning the poor maintenance by the previous owner, could be they didn't use the correct oil too.

Nice to see your a hands on person and just strip it all apart!
 

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It's absolutely a low pressure sensor and not low level. So you need to figure out what caused that, assuming it's not a result of a really, really, really bad bearing. You should be able to plug a pressure tester in where the sensor unit goes. Alternatively, just bolt it up and start it. If the light doesn't go out in a 5-10 seconds shut it down and put in a new pump.
 

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After noting the rugged build of that pump It's probably OK ... pressure loss was almost definitely out of that big end bearing.
 

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If your engine died from oil starvation (regardless of the exact cause), I would replace anything that had to do with the oil system. Rod bearings don't just die without a reason, whether it is low oil volume or low oil pressure something had to START the catastrophic event.

How are the cam journals in the head?
 

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Discussion Starter #29
Thanks for all the tips. I've attached some better photos, maybe you can help me assess any obvious problems?

95811

95812

95813


The minor scratch marks here come from me sanding all the carbon away
95814
 

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Cam journals look to be in good order, there's nothing on them that catches with your nail right? The head over all looks to be pretty good, my only concern is the head seating surface for the head gasket.... What happened and why does it look so scratched up lol. I'd inspect it and make sure you don't have any gashes, if you do I'd get it decked.
 

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Also I would look at replacing your valve stem seals.... You can see in the photo that one valve is actually darker than the rest, even when you look at the head one of the retainers is a bit darker. Have a look at the seating surface for that valve and make sure it looks good. Did you measure valve lash before pulling your cams?
 

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Discussion Starter #32
That's a wrap for today gents ... 6 hours of assembling.

My new crankshaft finally arrived, so it is time to put everything back.

I will share some tips for the people attempting to do this themselves.

95861


I ordered all the special tools the manual says you need ... you don't need that many. For instance the protection cap for installing the balancer shaft no need. Locking screw and flywheel puller you need.

95862


Next, the counter shaft, transmission and shift levers.

Some tips:
  • Do not take your transmission apart if it's not needed - its an absolute pain to puzzle it back together
  • Make your life easier and buy a simple lock ring plier and the clutch holder tool.
  • Do not forget to put back your bearing holders before installing your transmission
  • Grease up your springs inside your shift rails generously. Notice the difference length of shift rails.
95863


I spent hours cleaning the cases before, hence they are so clean. Works fine with a good degreaser and lots of tissue paper, paint brush and q-tips for those hard to reach corners. Got some compressed air to make sure all the debris is out of all the oil channels.

95864


Lets make a gaskets! Needs to cure for 24h. So I didn't install the oil filter and didn't fill the engine with oil - against the manual's advice.

95869


When putting the cases back together even the slightest off-center will make your crankshaft stuck - which is very scary. I couldn't get the cases to fall in place themselves and had to use the engine screws to tighten the engine cases together. After that all was smooth.

Unfortunately, I didn't take a photo after putting the case back together. Continued with installing the gear shifter, oil pump, primary gear and clutch basket.

After installing the shift drum you have to shift through the gears (turn transmission shaft by hand while turning the shift drum to shift up and visa versa to shift down). You need to put it in neutral before continuing! Otherwise your shift shaft isn't positioned right.

I can't reference Jeet's videos (timestamp 34m) enough - even tho I don't understand anything he says. It's fantastic visual reference.

95867


95866
 

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Discussion Starter #33 (Edited)
The sealant worked pretty good. I hope the excess on the inside of the case will just burn/wash away. I will do an oil change after a 100km or something.

96093


Small part alert 🚨 I lost the gear indicator contact spring, which was located under the sensor pin (see below). When you remove the sensor be cautious to remove both the pin AND spring. It's a tiny 2mm spring, I didn't even know it was there... Now I have to order a new one.

Also, the manual does not describe the steps to put back the statur (electricity coil thing) into the engine case. Took me a while to figure out.

96095


Water pump and clutch plates are back in

96096


Piston rings ... just follow the instructions. It's a bit fiddly but very manageable.

96097


96098


A generic piston ring holder worked fine

96099


96100


96101


It was an absolute pain to put the piston lock rings in (connecting the piston to the crankshaft). The manual says that you have to put the open side of the ring at 6 o'clock. But after fiddling with it for almost an hour we finally got it in but it is stuck at 1pm. QUESTION: I can't move it anymore ... is this a big concern? It seems to be doing the job - I plan on keeping it at 1pm. I would really dread taking it out and trying it again.

Starting to look like a real engine again.

96102


The rebuild is almost coming to an end, now I need to finish to top end. Question: does anybody have a good resource on how to measure valve clearances? I have a feeler gauge but I have no clue on how to use it / where to stick it?

Question: I have new valves, but I am deciding if I should change them or not. The old ones look fine, and I don't want to screw around with something that doesn't need replacing. Also, it might screw up my shims (does it?) if I replace my valves.

EDIT: I found this video that explains how to check your valve clearance. And lo and behold, one of my valves is off (max clearance 0.18mm, mine measure 0.25mm ... ) How bad is this?

Another question, after tensioning my timing chain there is no play between the chain and the bridge. Is that supposed to be?
96107


Don't forget to put in your shims ... manual doesn't say to do that ... and I forgot so I had to take everything off again.
 

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Wow man, this is pretty awesome.

If you have questions you are not getting answered here, there is a whole forum specific to the 390 Duke. It's called ktmduke390forum.com

It's much busier than this one too.

Sent from my VOG-L04 using Tapatalk
 

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Discussion Starter #36 (Edited)
I haven’t gotten that far yet :)

We hanged the engine back in the bike the other weekend. I had to wait on some final parts (that gear indicator spring + water pump nut I lost). There were some shipping delays from USA.

Been struggling with the weather here in Hong Kong and the wiring is quite some work because I don’t remember all the electronics. So need to take a good weekend.

96410


The little spring ...
96411
 

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To answer your question on ring gap spacing, it depends on the oil control ring scrapper positions as well. The goal is to get the ring gaps in a position that they aren't near each other so that you could prevent blow by and oil leak by.
As for the valves, if you are already in there and you have new valves I would go ahead and change them out. The reason why your gap in close is due to the valve stem itself stretching. which closes up the gapping.
 

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Discussion Starter #38
Last week I finished the bike - and it's running like a charm! 👏

96685


Took me quite some time to mount all the cables and tubing back. If you are doing this - mark which cables are not connected to anything. Some cables are supposed to be loose/not connected.

When I started it and after the test drive it gave me the damn "Low Oil Pressure" warning again. Long story short, my oil filters were completely clogged again. Changed them out for new ones and put in the Motorex oil, and after that no issues.

So, better to buy two oil filters sets, and since KTM is such a drama queen it's better to use a cheaper oil to rinse the system and then put in the expensive stuff.

It will go to the shop this week for a check-up, will let you know the result.

Let me know if you want to know anything else, I will post a small guide, lessons learned and money spent soon.
 

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Only just saw this post, so my comments are 'after the fact' and you've pretty much worked them all out by experience. Observations:

1. The problems you had unbolting stuff was due to KTM's love of using copious amounts of Loctite. There are 3 grades that I know of; pink (weak), blue (medium) and green or red (grips like a bastard). The only way to successfully free off parts assembled with green or red Loctite is by heat, and lots of it. It is only removable once cured by heating up parts to 450°F (232° C) for about 5 minutes. That's why those parts got mangled...

2. Whatever amount of gasket sealant appears on the outside of the cases will probably also be present on the inside of the cases. There is a danger of this coming loose and clogging up oilways. With luck it won't but it's better to use gasket cement sparingly, and run a thin line as close to the outside edge of the sealing face as possible. That way most of the surplus will get squeezed to the outside, where it can be cleaned off. You only need a very thin film to seal the cases.

But for someone coming to this problem with no experience, you did a brilliant job and kudos to you. You figured it out, didn't give in and you now have a working motorcycle again. Well done you!
 
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