Oil leak from somewhere under the tank?
 

My wife and I just got done with our first LONG ride (for us noob's :D ), ~340 miles in one day! The bike did great, but our "backsides" were killing us! After we got back we parked the bike and it sat for about a week and a half before I noticed some oil on the ground just behind the side stand. There was a trail of oil from the left underside of the tank down the frame, down the engine cover and then a small wet spot on the ground. What could be leaking from that high up? I haven't had a chance to pull the tank and look around myself yet, so I'm hoping someone can point me in the right direction for things to look for specifically. -Thanks!

I would have to guess the highest point would be the valve cover gasket?Maybe it sprayed up on to the underside of the tank under acceleration> Just a guess hope it helps

That's kind of what I was thinking too... I guess I just need to find the time to get the tank off and take a look around. I had a thought that it might be coming from one of the vents, but they seem to be on the wrong side, unless it's blowing into the filter box somehow. Even then it's a longshot. I rode it around a little the other day and haven't see any new oil leaking yet. I did change the oil and filter before the ride, but I didn't see any leaks from those areas, so I'm thinking it's mostly coincidental that this is happening now.

Check that the breather hose on the front left side under the airbox is still attached. It it comes off, oil mist will collect on the underside of the airbox and drip down. Don't ask me how I know this. :o

I have the exact same leak, but only seems to happen when the bike has been idling on the side stand for awhile...

I really need to get some time to get the tank off and check these things out! Right when my project pile was getting slightly lower my wife's truck A/C went out and my Jeep's transmission just went out (this morning!!).

I figured a couple of you guys might have seen a leak like this before! hehe It's good to have this place as a resource. It's odd that the bike did this after a long ride... I'm thinking it might have had something to do with the sustained high speeds. It was over 100-degrees for about the last 80 or so miles too, but I don't know if that could have been part of it (hot oil + high revs?). I had to get on the throttle pretty hard a couple of times too. I'll see what I can do about getting the tank off soon and let you guys know what I find.

Hard riding = increased blowby. Really sounds like your breather hose is disconnected.

Well, I got the tank off and the breathers are all connected. There wasn't a trace of oil anywhere under there. I was sure that had to be it too. It looks like at least part of the problem is fuel! The sending unit was sealed with some kind of RTV that apparently was not fuel proof. It really looked like oil so I'm still puzzled, but I know I need to find a way to seal that tank better at least. There was some kind of grease on the air box seal, so maybe that was getting heated up and the oil was cooking out. Also, the filter is a K&N and was oiled up pretty liberally. I guess those could have been culprits too.

Wow! Sounds like you found a whole bunch of questionable stuff under there. The sending unit is supposed to have a gasket - probably $3 from your dealer. The petcock has an O-ring. Get that fixed. It's kind of a safety issue, ya?

Well, now I'm looking for a fuel proof RTV-type material I can make a gasket out of. Does anyone know of such a thing? The construction of this tank is such that it doesn't have a nice, smooth sealing surface for the low fuel sender. I'm going to have to at least "help" any gasket I put on there. There was an o-ring, and some non-fuel proof RTV, but obviously that wasn't enough.

Yardstick,

The bike in your avatar looks like one that was posted on this site for sale in arizona. It had a TON of trick carbon fiber bits including a tank. Same bike?

When it gets hot, a simple buildup of chain goo can drip down near the sidestand too.

Is this Jeff's old Carbotex bike from TX? You can try a thicker O-ring. I believe True Value has an assortment.

It's the same bike. It now resides in my garage with the tank off. I've put ~1000 miles on it since I got it a couple of months ago. It just started this leaking trick very recently.

Any remote chance it is a leaky fork seal and the oil blew back on the bike while you were riding?

No... When I took the tank off I had it sitting upside-down for a while and I was watching fuel (probably vapors) come out from between the tank and the sender, pooling up next to the sheetmetal sender. The fork seals are very dry as well, so I have no reason to suspect them.

I finally got a chance to investigate the Honda "Seal" for the sender. It's just an o-ring. Probably the same o-ring I already have on there. I've tried contacting a couple of gasket companies to see if I can get a small sample of some fuel-proof sheet material, but no luck so far. I'm stuck here... What else can I do to seal this thing up? I don't have a metal tank to put on, can't find anything that will seal this thing and stay fuel proof and can't get any help from manufacturers of material that would be fuel proof. I've got a nice, silver, expensive boat anchor holding down my garage floor...

Permatex does make a gas/oil resistant product that I have used with good results:

http://www.permatex.com/products/aut..._2_Sealant.htm

On my old Nighthawk S, the fuel level sending unit began leaking. I took the tank off removed the unit and removed the bad gasket. I cut my own gasket out of cork gasket material bought at Advance Auto. I put the Permatex Product on both metal surfaces and coated the cork with a thin layer (so as to minimize gas weeping through the cork). I then slapped it all back together.
That was about 2 years ago and it hasn't leaked any more.

On a similar problem a few years back, I used the sama Permatex product and cut a gasket out of a bicycle inner tube.
Same results: it sealed quite nicely.

Get a THICKER O-ring, like I suggested before. That'll give it more room to flex and seal.

I've been looking for a thicker o-ring in my travels, but haven't come up with one yet. I'm doing a test of a bicycle inner tube in fuel now because that *might* work. I also came up with an idea of using fuel tank repair epoxy putty to build up a smooth sealing surface for the o-ring I have. Thanks for the suggestions though! I was getting really frustrated yesterday not finding anything.