Where's the oil leak?

Where's the most common place for oil to leak from on the back side of a Commando? I'm referring to the oil tank / oil lines / oil filter area. I get oil on my lower frame tubes, swing arm pivot, rear iso's. Hoses look OK at the tank and where they attach to the engine. Battery tray is dry, so no cracks in the lower tank boss.

The tank's rear bracket broke (AGAIN) even after I welded it, and it's now been mod'ed by cNw so that issue will go away.

You can't really see the oil filter hose attachments without significant disassembly, but I'm gonna do that just to be sure they're not the source of my problem.

Engine and rockers etc are tight. Leak is definitely in the tank / lines area.

I hate dripping oil on the garage floor. Where have you guys found leaks from?

Bottom tank stud area cracking. Mine left small amounts of oil all over that region.

Edit, read completely.

Cap, breather hoses, chain oiler.
Use Gunk foamy engine brite to degrease (or S100) then look.
Dry spray talcum powder to help pinpoint. Clean, clean, clean

Just went through this process for the same mystery leak, was convinced it was the oil return line to the tank, turned out to be the gasket in the tank cap. I cut a new one out of rubber and leak has disappeared.

Symptoms are same as yours, and there are only a few pressurized sources that high up which would distribute oil to all those areas (eg. an oil filter leak wouldn't toss oil onto the ISOs). Check to see if the oil migrating to the lower frame rails is actually trickling down the underside of the oil lines.

1. Bottom of the oil tank.
2. Through the felt seal at the primary.
Another issue with primary is engine oil seal bad behind stator, passing engine oil into primary causing it to overfill, causing it to seep out felt seal.

Check around the rear chain oiler. Some people block this off in odd ways that don't always work (golf tee?)

I use Concour's method ...... clean, look, clean, etc.

As a last resort, use a florescent oil dye, and a black light.

Slick

Hose clamps loose, but like others have said clean and look, problem with oil leaks is it runs down other places before it lands on the floor and so many little places it could be leaking from, the joys of owning British motorcycles, but I also own a Land Rover lol.

Ashley

Oil tank bottom crack . Remove bolt . Re-weld up. Put a chunk of dense foam to replace it for support.

I have traced my “leak” to filling the tank to the upper limit level line on the dip stick. If I fill only to the lower level line then the leak almost goes away. I then wrap a paper towel around the filler neck and stuff a couple more in and around the area. Fixed it.

No apparent fault with either cap or gasket but that appearance deceives .

I check levels with the cap compressed too; that is as low as possible

My return is quite vigorous and if the cap doesn't seal perfectly it makes for a mess because the tube in the tank hits almost squarely on the fill nozzle blowing oil everywhere except down. Every time I check oil I entertain the thought of bending it downwards a few degrees.
My cap cannot be removed with the motor running until this minor mod is done anyway.
Yours may have a crack near one of the mounting tabs, or perhaps under in a blind spot. Just talking here.

as Concours stated, you need to clean it all up firstly. Brake cleaner on a rag or similar. A booger to get the fat hands in there. Then keep a watchful eye.
I never noticed the weep around the bottom of the tank until I became serious about keeping the old beast clean. Oil appeared to be wicking from the hose/barb and the clamp couldn't be any tighter.
New herringbone hose then new washers as well made no difference. So I needed to get to know the area on a close personal basis. Off with the banjo. Eyeball everything.
I had a phonographic score on one sealing face of the banjo. Rapid return on a deflecting parting tool at the screw house. Too lazy to change the tool I imagine. Close to the end of the shift, whatever.
This must have been a weeper from the moment oil was introduced.
A very slight smear of soft setting Permatex and Robert's my mothers brother. She doesn't leak there anymore , well, at the moment she's in between leaks let's say.
The sun is up, the sky is clear, I'm off today. It's has the makings of the Best day ever. So does tomorrow and the next day too.
All the Best.

I had a spigot come loose in the alloy base of a filter body once. It was a cheapo aftermarket part however.

Blocked breather? If the breather is blocked oil can come out under the Oil cap if hand tight. If more than hand tight it opens up more areas it could leak from.

I stand corrected. My crankcase breather is my culprit up topside. Apologies for misinfo..

The good news is that you usually have gravity help your analysis. Find the highest spot you find

jbruney said:

My return is quite vigorous and if the cap doesn't seal perfectly it makes for a mess because the tube in the tank hits almost squarely on the fill nozzle blowing oil everywhere except down. Every time I check oil I entertain the thought of bending it downwards a few degrees.
My cap cannot be removed with the motor running until this minor mod is done anyway.
Yours may have a crack near one of the mounting tabs, or perhaps under in a blind spot. Just talking here.

Click to expand...

Something might be wrong, the return should go down, right?

Yes it does. Therefore my post above in confusing it with the breather which I may bend slightly down in order to deflect vented gases/air.
If OP doesn't have tight seal at cap oil will leak at this point from splashed oil in tank at high level mark. At least mine is notorious on this matter and ends up eventually covering everything. It gets into battery box, outside, down back & banjo, swingarm, etc. Gets to be quite messy and used to have me cleaning and searching through everything for the source until I dropped my level a little & checked to really ensure tightness of the cap, but it still seeps. His issue could be something else entirely.
My pulses are somewhat stronger than yours.

Does anyone know the reason for the engine & tank breather outlet arrangement? Meaning, why the engine breather is plumbed to the filler neck and the tank breather to the plenum area? I'm assuming it has something to do with minimizing the amount of oil pushed out the tank breather

Offhand I'd say to satisfy EPA. Allow mist to settle out & burn vapors I would imagine done in methodical English fashion. Since I've no longer got a plenum it goes to earth. Remember on a Commando earth is positive...Heh heh.