Jump to content

Recommended Posts

I had my bike overheat on me one day and when I was putting fluid in coolant and oil. I noticed that my oil was not touching my dip stick. And I noticed that it was leaking through the vent hose on top of the head. I didn't lose much just wondering why it was low and coming out of that hose?

Share this post


Link to post
Share on other sites

How much was coming out of the vent tube? Kinda sounds like bad rings, bad rings cause blow by, forcing oil out the vents. Oil consumption is because the the oil rings aren't sealing and oil is being burned during combustion or the valve seals are leaking oil. Does oil always come out the vent when it's running or was it a one time thing? Any blue smoke from the exhaust? Also, depending on how hot it got, it could have killed the rings.

Share this post


Link to post
Share on other sites

So the bike is running fine now? Your just wondering why oil was coming out the vent? Probably because the rings lost some seal when everything expanded as it overheated causing blow by. When the piston went up, compressing the air in the cylinder, some of it went past the rings and into the bottom end. When the piston came back down it forced the extra air and the normal air out. There is normally a mist of oil in the crankcase. Some of that mist went out the vent tube, also some was probably burnt when it over heated too. That's my guess of what happened but im not an expert.

Share this post


Link to post
Share on other sites

I have only started tonight since it's sill strapped in the back of my truck. I let it run a little to see if I could find a coolant leak and see if it was going to leak oil or not

Share this post


Link to post
Share on other sites

Yah if it still leaks oil I would say you cooked the rings/cylinder and it needs rebuilt. Mostly likely just a topend. However if it ran low on oil it could have destroyed the cam journals and rod/crank bearings. I would ride it for a couple minutes, not a long time but see if it clears back up before jumping to a new topend.

 

 

 

 

Share this post


Link to post
Share on other sites

That advice is filled with errors.

The oil coming out the breather tube can be a normal occurance.

Long Wheelies, dropped bike still running, over filling the oil, long wide-open throttle runs, etc.

Worn out rings will NOT cause oil to come out the breather hose. There is no passage from the Cylinder to the valve cover.  You would just burn the oil.

It is possible that valve guide seals are passing oil, but that would not be a lot. That is the only entrance into the cylinder to the valve cover area. The bike would be down on power.

The most likely senario for oil loss is that you are just  burning the oil.  Very common with older motors.

It is normal for a bike like yours to consume as much as 2.5cc per hour, stock.  As the motor gets worn out, this can go up 10, even 100 times.

The only way to know, is to do two things:

1. A leakdown test, to see where the blow by is coming from, if any

2. dissassemble the motor and mic the components involved in making combustion, to see what is worn out.

 

You have made no mention of year, model, condition, hours, time between changes, last head work, last top end, etc etc.

 

 

Share this post


Link to post
Share on other sites

So is it safe to still ride the way it is now. I ran it for about 5 minutes tonight and I didn't see any oil drop. And about 30 minutes ago I checked again to see if there was anything on the bed of my truck and I didn't see anything fresh.

Share this post


Link to post
Share on other sites
36 minutes ago, THE KRAN said:

Worn out rings will NOT cause oil to come out the breather hose. There is no passage from the Cylinder to the valve cover.  You would just burn the oil.

If the rings are worn enough to allow significant combustion blow by, there is indeed a passage from the combustion chamber to the valve cover.  Weak rings cause combustion gasses to leak past into the crankcase, and then up the chain tower and out.  This adds to the other listed factors that cause oil to leak from the breather tube.  Apart from that, the quoted post is correct.

  • Like 1

Share this post


Link to post
Share on other sites

If you want it to stop using oil altogether, yes, but if it runs alright and has reasonably good compression, it's probably not immediately necessary. 

Some oil out the breather is always going to be normal.  If you change oil at a reasonable interval (every third ride day or so, 6-8 hours of run time), even a very healthy 426 or YZ450 will use a little bit between changes, but it shouldn't drop off the stick altogether.  Something to remember is that oil will run down out of the frame tank while the bike sits, so you can't accurately check the oil level unless the bike has been run within the last 5 minutes or so.

The two biggest hazards of not replacing the top end soon enough are excessive piston wear, which can allow the piston to tilt too far in the bore, accelerating bore wear, and leading to possible destructive failure, and allowing the engine to run too long on worn valves.  Worn valves will chew up the seats, which may cause enough wear to require their replacement, and the flexing of the valve stems that the condition causes can lead to a broken valve, potentially destroying the entire engine.

If the engine has a lot of time on it, it may be well to tear it down and have a look at it.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×