1980 XT500 burning MASSES of oil

[Ryan Rambo]

I have had a 1980 Yamaha XT500 for almost a year now, with little problems. The problem I am running into now is the machine burning mass amounts of oil - more than it used to. I changed the oil about 2 weeks ago and within this 2 week period of moderate amounts of street riding (about 200-300 miles), the oil was nearly empty! (dip stick was not registering any oil). The oil disappearing problem has never been this severe. There are no leaks that I have noticed. There has not been a noticeable performance difference since I really started to notice this problem. Any suggestions as to why this is happening? THANKS!

Ryan Rambo

[peterj]

Just a couple of thoughts. I've always found it difficult to get a reliable reading on dry sump engines. It's very easy to read it two times in a row and get a higher reading the second time. Also, a 500 single will almost certainly burn some oil. From full to just off the dipstick in the distance you mention doesn't sound unusual. I had a BMW R100 (two 500 singles?) that never burnt any oil, until you gave it a really good work out when the level would drop alarmingly. I've since found out that this is caused by the level being maintained by blow by contamination until you get it really hot and then the contaminants evaporate.

I'd just keep topping it up until you are really sure how much it actually using. If its going more than 500 miles per pint I wouldn't worry. If it really is burning too much to live with, it's probably time for a strip down.

[cloggy]

It's either the rings. If the compression is ok the oil ring may still be worn, broken or stuck in the piston ringlands
And/Or it's the valve seals and maybe worn guides and valves
I've got exactly the same problem on my 2 valve DR?GN?SP400 engine. Good compression  and no scratches on the bore so I just got the valves lapped in and replaced the valve seals. It still smokes so I'll have to take the barrel off and investigate

[guest27]

AS Peter J says - the XT being a dry sump can be a pig to get a stable reading on - particulay if there is any possibility of the residual oil in the engine having been drained at the last oil change - when filling the tank and starting the engine will cause the level to drop real quick.

To avoid seizing etc need to keep an eye on the oil - but it may be an idea to check it each day and see if it consistently drops or not.

Do not know if the XT can leak down from the tank to the engine like Triumph twins do sometimes - when the contents of the oil tank end up in the engine - this can cause no end of problem - too much oil in the engine, hydrolic locks etc.  Is there any way of seeing how much is in the engine rather than the tank - ie is there a drain screw for  getting water out of the crank if it is dropped in water etc?

Just a few thoughts.  Friend used to have a R100 beemer, it used more oil than my RD500 two stroke did...

R

[bullet350]

check the oil pump.
on some brit bikes as the pump wears it can stop scavenging properly from the bottom end. the crank cases run with a higher oil level in the bottom than they were ment to, and on a big single it can pressurise the oil, pushing it past the rings which may be fine.
Also check it returns to the oil tank at a reasonable rate, could have a clogged return leading to blow-by.
Check any breathers aswell, a clogged breather can cause blow-by.

350bullet

[squirrelciv]

You say the bike is 'burning' oil, but are you sure?? What I mean is you only refer to the oil level dropping, and that could be for lots of reasons. (burning, leaks, blow out). Take a look in the air box and see if it's filled with oil (I'm assuming the engine breather feeds into the airbox) If it is you could have a ring problem. Oh and you do burn the oil this way too as it can get sucked in through the airways. If its fine, and your sure your burning the oil, it might be valve guides/oil seals. Check for smoke on start up that clears after the bikes been run for a while.

Hope thats a help (though I doubt it :-( )

[Ryan Rambo]

Wow! Thanks for all the replies. I've never joined a forum before and I was not expecting so many replies. I am not a mechanic, I get horribly frustrated when working on anything mechanical, but I will do my best to investigage these issues. Your help is really appreciated.  I am really glad to hear there are other people working with similar issues. Thanks a lot!

[Ryan Rambo]

To answer Rog,

My bike has 2 drain plugs. One underneath where the skid plate is, and the other higher up on the frame as you move closer to the handlebars (but only about halfway to handlebars). I don't know why it has 2 plugs, but possibly for the reason you mentioned with the water.

In addition, what does "blow-by" mean? I am an extreme novice here. Thanks!

Ryan Rambo

[bullet350]

blow-by is when oil goes past the piston rings into the combustion area above the piston. As the piston goes up and down the air and oil below the piston can get pressurised. too much pressure and it all tries to take the easiest way out, usually a breather (designed to allow this) or by pushing past the rings, or even by bursting through a weak gasket.

350bullet

[Steve H]

Must admit my understanding of blow-by was combustion pressure leaking past worn rings, thereby pressurising the cases and blowing oil out of the breather (and into airboxes etc)
Pressure below the piston is sometimes used to force oil control rings onto the bore surface. Look at an XT SRX psiton and there are loads of holes going from behind/below the oil rings to the underside of the piston.

[mini-thumper]

So remember it has to be: SUCK, SQUEEZE, BANG, BLOW

Not: SUCK, SQUEEZE, BLOW, STICKY MESS

Or:  BLOW, BLOW, QUICK, QUICK, BLOW

Or:  SLOW, SLOW, KICK, KICK, BO**OCKS (for those without electric start!)


I'll get my coat.....................

BB

[bullet350]

blow-by can work both ways. hence oil being burnt after wet-sumping.
Or in the case of my norton, bits of piston moving past the rings ;-)

350bullet

[guest27]

Ryan

When you are changing the oil - which of the plugs do you have to remove - I am guessing here - but the upper one would be the oil tank drain and the lower one a sump - crankcase drain.  Again guessing here - when you change the oil you are probably only meant to take the tank one out and drain the tank - possibly leaving some small amount in the engine. If so the recommended refill volume will be for the tank not the whole shooting match.  If the lower one has been removed then the refill volume will be greater.  I have to admit to guessing here - just going on bikes I have known, not based on any knowledge of the XT or its lump.

R

[Ryan Rambo]

The Clymer manual says that both plugs should be drained. I dont know why there are two plugs, but I always drain every drop I can.

So about this "blow-by" - most older, single cylinder bikes have this problem pretty often?? How does it affect the performance of the bike? Ideally, if money and time were not an issue, this problem could be potentially fixed by replacing just the rings?

Im one of those guys that is so terrible mechanically that I cant usually take anything apart - only enough to break something. I can't afford to lose my bike - hence the reluctance to attempt to do any of the work alone. How do you fix THAT problem???

Ryan

[002]

Crankcase and oil tank got to be drained.

You dont know what really needs doing till you strip it.
If I'm going to strip the motor then the valves come out as a matter of course.
Lap check the guides,lap them in and new seals.
As far as piston,rings and bore.Dont know until its looked at.
But there again you do need to know what you are looking for.
If you dont take it to someone who does and ask their oppinion.

Jethro