RC390 Update to leaking oil - Crack in engine case

samroy92

New Member
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Unfortunately my newly bought RC 390 has a bit of an oil leak. Using UV oil and light I was able to see clearly where it came from, right near the rearset through-bolt!

How would you guys proceed from here? Repair the case at a shop/dealership, use JB weld to patch it up, other techniques?

Any help would be greatly appreciated, thanks!
 

cornerslider

New Member
I'm not a fan of dealerships. I just don't think ANY dealer will give my bike the amount care, and attention that I do. That being said, if it's under warranty, I'd say dealer right away. They will probably have to order the part(s). Not sure where you live, or if you can still ride this time of year? If it's still warm enough to ride, I'd put some silicone over it and keep riding while your waiting for the part(s) to arrive. The cases at the back of the motor don't see much heat. I think if you used JB weld over it, you would have a tough time getting warranty to cover it? The silicone should peel off with a little effort, and shouldn't really effect warranty. Just my humble opinion-
 

Diploman

New Member
If your bike is still under warranty, you could take it to a dealership and ask for a warranty repair/replacement. A replacement of the engine case would be a big job, involving total disassembly of the motor and then refitting all the internal components into the new engine case. I think that, at all but the most professional dealerships, the chances are slim that the service department could complete this task successfully and without damage so that the engine runs as before. You might want to think twice before taking this risk. Many dealerships, I believe, would simply try to repair the crack using silicone or JB Weld. You could do this at home equally well, provided the crack and surrounding area were thoroughly degreased prior to application of the sealant/epoxy.

Probably the best and most permanent repair short of replacing the engine case would be to find a welder who can work with aluminum and have the crack welded. You might have to remove the engine from the bike in order to do this, but IMO it would be less risky than having most dealerships completely disassemble/reconstruct the engine.
 

cornerslider

New Member
If your bike is still under warranty, you could take it to a dealership and ask for a warranty repair/replacement. A replacement of the engine case would be a big job, involving total disassembly of the motor and then refitting all the internal components into the new engine case. I think that, at all but the most professional dealerships, the chances are slim that the service department could complete this task successfully and without damage so that the engine runs as before. You might want to think twice before taking this risk. Many dealerships, I believe, would simply try to repair the crack using silicone or JB Weld. You could do this at home equally well, provided the crack and surrounding area were thoroughly degreased prior to application of the sealant/epoxy.

Probably the best and most permanent repair short of replacing the engine case would be to find a welder who can work with aluminum and have the crack welded. You might have to remove the engine from the bike in order to do this, but IMO it would be less risky than having most dealerships completely disassemble/reconstruct the engine.

I tend to agree with Diploman, That would be a HUGE job! Maybe KTM would realized that it would be more cost effective to replace the whole motor? I doubt it, but it's worth a shot? At any rate, I would advise AGAINST having it welded. I am a professional pipefitter/welder, as well as a CWI (certified welding inspector). The cases are made out of cast aluminum, which by nature is very "porous" (which may be the root cause of the leak?) The problem is that the oil weeps into the "pores" in the aluminum. When you weld over it (no matter how clean you get it on the outside), all the heat from welding boils the oil from the "pores", and it can even make more, and sometimes larger "pores". I have firsthand experience doing this with "heavier" automotive transmission cases. On thinner motorcycle cases, it could very easily make things worse by trying to weld it. Also, the oxide (the natural oxide that forms on the outside of an aluminum part) turns to liquid during welding at a temp that's 20 degrees HIGHER than the base metal. You can imagine how difficult it would be to weld on a thin motorcycle case. I know that "Billy-Bob's welding shop" can promise you the world, but they may not know what they're getting into. If you do choose to go this route, you should make sure they have experience on MOTORCYCLE cases. I'm not saying that it can't be done... It just takes a LOT of real talent, and a bit of luck too-
 
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Diploman

New Member
I am strictly a layman when it comes to welding. Since Cornerslider is a professional, I defer to his opinion.
 

Treachery

Moderator
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From the original thread, I understand that the bike has 7K on it, purchased used. Unless @samroy92 has the good fortune of buying it with residual warranty OR a really understanding dealer who's willing to go to bat, repair or replacement's going to be on his own. Sorry to hear.
 

samroy92

New Member
Ok JB-weld gets here today and I have been prepping the area:

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I took a light dremmel to the surface and scuffed it up. I am cleaning it with Kerosene too. I am planning on just applying a bunch of JB-weld to the entire area, and cleaning it up so it looks as good as it can.
 

samroy92

New Member
And after the JB-weld, I will admit it's not pretty but honestly don't care too much. The only thing I was worried about was JB-welding the engine to the frame where the rearsets through-bolt goes through. But oh well!

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simpletty

Member
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Dealer would, or at least should, if under warranty do a cost of repair under warranty vs replacement with new. Obviously if installing a new engine was cheaper it would make sense from a warranty standpoint. As far as welding that it would require low heat since that case is super porous. Jb weld is probably the best case scenario if you have no warranty. Good luck
 

samroy92

New Member
im curious about how long JB weld can withstand the vibration?

From what i've read it handles vibrations fine, just not high heat+vibration (e.g. exhaust manifold). I think the rear engine case has a pretty good chance of being a strong fix. I will ride tomorrow afternoon to see if it lasts a day at least...
 

Diploman

New Member
I agree: Given the problematic aspects of other possible remedies, JB Weld is the most practical option - a pragmatic solution. I think it should work for you. You can tidy up the JB application with some 220-grit sandpaper, and even paint it silver to match the engine cases if aesthetics are very important for you. But I think it should cure the niggling oil leak and restore your bike to full functionality. Good job!
 

Diploman

New Member
Perhaps there is another tiny crack that you have not yet detected - you may have "fixed" one leak (or maybe the first one was not actually leaking) but there could be another one that continues to ooze. Or there could be a leaking seal.
 

samroy92

New Member
Perhaps there is another tiny crack that you have not yet detected - you may have "fixed" one leak (or maybe the first one was not actually leaking) but there could be another one that continues to ooze. Or there could be a leaking seal.

I checked today, basically the JB-weld formed the same exact crack as on the case underneath it. Maybe it's a high stress zone of the engine when it's vibrated and prone to weakness there?

I am going to get a quote for how much it would be to do a proper aluminum weld job at that spot.
 

Muckabucka

Member
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You're wasting your time/money if you don't identify root cause. You have to ask, why did it crack in the first place? Find a set of cases or a new motor and replace. You don't want that weld to fail or something in your transmission to go south while you're at speed. You could end up with a lot worse things than a cracked case.
 

edderz 33

New Member
Problem with this crack is, the crack is happen near to the engine mounting. Don't thing JB weld is strong enough to handle the weight of the engine and its vibration.
Agree to investigate about the root cause of the crack.
 

KTMGene390

New Member
I replied in the other thread you posted about the leak pattern being exactly the same as mine. As soon as I replaced the shift shaft seal and sprocket shaft seal the leak went away. Just saying... could be that crack but I would check to see if it leaks without riding the bike in the same spot.
 
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