Hi there!

Last week i bought a 86 k100rt, but only today i could ride it a bit, first 25kms while i wait for a optional low seat to arrive.
The good: engine wise all seems fine.
The bad: front suspension seems a bit bouncy and i saw these oil leak after the ride:


Am i already in trouble?

"Am I already in trouble?"

Not really, you have just been presented with a sterling opportunity to show a 37 year old classic motorbike how much you want to be it's friend.  Many here have been confronted by worse with a new Brick.

A bit confused a out where the leak comes from, still dont know much about K bike.

I like to do my wrenching and have some experience with other bikes

Looking at the photo you posted, my first guess would be the cam chain cover, or possibly the joint between the cam chain cover and the valve cover.  There are several covers that come together at that front corner and several of my bikes had some unequal surfaces that create a hard area to seal.  A bead of silicone sealant fixes it.

The other possibility, is that there is a leaky oil pump, but I am not sure the oil from that leak would spread as far as it is shown in your photo. 

I would suggest doing a good detailing of the bike with S100 motorcycle cleaner.  Take as much apart as you can and take your time getting into every nook and cranny.  Take a nice afternoon.  The way the bike will look when you are done will make it worth the time.  You will not only have a bike that will be a LOT more pleasant to work on, but you'll have a much better idea of what kind of condition it is really in and what kind of work it needs.

After you have cleaned it, dust the front of the engine with talcum powder and go for a long ride.  After the ride you will have a good indication of where the oil is coming from.  That will determine what needs to be done to fix it.

Rose scented spray on talc sticks better and smells nice. But any fragrance will do, your choice.
Regards Martin.

A common area to leak. Point seven five mentions uneven mating surfaces at the front LH bottom corner - where the timing cover meets the cylinder head meets the cam cover. I suspect BM's quality control because I've had this problem after swapping and changing parts - I ended up rooting around for the original parts to match up, which they do perfectly, so maybe BM machined the timing cover and head as a matched pair? I would if I were making an engine, but I work in a shed on a slightly lower budget 
Anyway, I've used various sealants with various success, but Loctite 518 gave a solid cure where others failed.

These bolts where very loose...

They're just the hall sensor/timing cover. No oil inside there (or shouldn't be!). They might feel a bit loose because A: they shouldn't be that tight anyway & B: the squishy cork gasket compresses and hardens after all these years (last century tech!)

Oh, i thought i had found the culprit! I cleaned everything UP, Will try to source the leak point after a ride.

35 kms later, it looks quite dry...

On a different subject: what hides behind this box? I am missing one Bolt...

The coils. The socket screw ('allen bolt', if you prefer) that is missing is an M4 x 10mm. The OEM ones (the other three) are called 'half height' bolts because the socket head is half the height of the ISO definition for a socket screw of that size. I have replaced all of mine on both bikes with standard height stainless steel ones.

Dai wrote:The coils. The socket screw ('allen bolt', if you prefer) that is missing is an M4 x 10mm. The OEM ones (the other three) are called 'half height' bolts because the socket head is half the height of the ISO definition for a socket screw of that size. I have replaced all of mine on both bikes with standard height stainless steel ones.

I might Just do the same, might BE very difficult to find similar here... Thanks!