Burning oil w/ decent compression?

[Joe Garfield]

I'm using about a quart of oil for every 3 tanks of gas. I fixed all but maybe 1 of the visible oil leaks, including the starter o-ring and stator gasket that were making a mess out the mystery hole. I was hoping that was the problem but its still using about the same amount of oil. I have one more place to check for a visible leak - the cooling fins under the engine (behind the oil drain plug, but definitely NOT the plug) are a little wet but I don't know if that's from the mystery hole leak or not, and can't really see what's going on w/o a lift or pulling the exhaust.

Anyway, I'm just curious if I could be burning that much oil while still getting decent compression (a little over the Suzuki min spec) and w/o seeing much smoke in the daylight. No drips either, only goes when the bike is running.

Thanks,

 

[geol]

Oil getting by the rings isn't burning. It will come out the crank vent,. If the vent is in the stock airbox, check to see how oil is in there as a first step in tracking down the oil use. If you have a bad oil scraper ring that can cause oil use and not affect compression a whole lot.

 

[tkent02]

Have had a few that do that. No smoke at all.

 

[Joe Garfield]

Oil getting by the rings isn't burning. It will come out the crank vent,. If the vent is in the stock airbox, check to see how oil is in there as a first step in tracking down the oil use. If you have a bad oil scraper ring that can cause oil use and not affect compression a whole lot.

What's an 'oil scraper ring'?

I looked in the air box - it does looks a little oily up at the very top, but the bottom surface doesn't seem wet, and there aren't any traces of oil outside the drain hole.

 

[tkent02]

Fancy name for the oil ring. My 750 uses about that much oil, doesn't leak, doesn't smoke, runs perfectly. No big deal. In fact, BMW's limit for oil burning is 1 liter for every thousand miles, if yours burns less they won't fix it. Won't even consider it a problem. This is for brand new engines.

 

[Joe Garfield]

Thanks. Oil ring = piston ring?

I imagine I'll do new rings and valve seals over (some) winter - I'm not too worried about it, but it's kind of a pain. (FWIW, a tank gets me 135 miles, so we're talking a quart every 400 miles).

 

[tkent02]

Yeah, my math was a little funny. Still I think my 750 might be in that ballpark. Never ridden it far enough to know.

 

[Brendan W]

Get a sheet of paper under it after a run.
What are the plugs like ?
Does it smoke a bit on start up.
Consider using something like MMO to try and free up a possible stuck ring.
When it's cold you could remove the plugs, turn the crank and see if the back of the valve heads are wet.
If the exhaust is coming off you could use that opportunity to inspect the exhaust valve stems for signs of wetness.
I was losing a litre every 400 miles, two tanks, through headgasket, stem seals, tensioner,clutch arm. Pulled like a train, no running issues. The bike dripped on the floor, boots, jeans wet and the odd few drops made it to the back tyre. Consumption now is about a tenth of that after gaskets and seals. The rings stayed.
Get a mirror on the floor under the bike.

 

[alke46]

My 1000 does the same thing. I just throw in a quart after 500 miles and will be replacing the valve stem seals during the winter(I hope).

 

[Buffalo Bill]

I've had oil leaking out the tach cable connection to the head cover, enough to cover the front of the engine. That was just a washer size gasket, fixed it with RTV Form-a-Gasket. The stator gasket was leaking, because a couple bolt seats were stripped. I just fixed those with a Helicoil kit, and carefully hand tightened all the bolts to a firm tightness, maybe 3-4 ft-lb.
My 82 1100G gets 42-46 MPG, no oil consumption.

 

[Joe Garfield]

I had the tach cable leak too - what a mess! That was the first thing I fixed. Cam chain tensioner has been rebuilt, valves adjusted w/ new gasket, stator replaced w/ new grommet and cover gasket, oil drain plug replaced with new gasket, just replaced the breather cover gasket last night.

Last week I liberally sprayed Simple Green all over the engine and hosed it off. I tried to get underneath but didn't do that great of a job. But after using a quart of oil the engine case is still dry, with the exception of the cooling fins on the bottom (as mentioned above). It was hard to spray under there so I don't know how fresh any of that is, but it does seem to be biased toward the mystery hole side. I was losing a quite a bit of oil through the mystery hole due to a split stator grommet, but that's all dried up now. My feeling is the oil underneath is remnant of all the above leaks that are now fixed.

Regarding plugs: I honestly don't know the difference between a rich (fuel) burning plug and an oil covered plug. I need to re-balance and sync my carbs/cylinders after doing some ignition work and believe I'm burning extra fuel because of that. But that's a guess. Anyway, last time I checked the plugs ranged from lean (white) to slightly rich. I posted a pic in another thread and nobody seemed to think there was an issue with the darker plug, and that it actually looked preferred to the others.

So it sounds like oil could be entering the cylinders from the bottom (past the rings) or from the top (past the valve seals). When I did the compression test, the compression went up ~20psi when I added a spoon-full of oil through the plug hole, so obviously it's not a perfect seal. What are some ways to tell if oil is getting past valve seals vs piston rings?

 

[alke46]

From what I know, the oil getting past the stem seals will show up quickly after the engine has been off several hours, then upon start up, it will belch out a bit of smoke then it goes away.

 

[alke46]

[QUOTE=Buffalo Bill;2313970]...........................
My 82 1100G gets 42-46 MPG, no oil consumption.[/QUOTE]

Well now this just sounds like bragging to me.

 

[Steve]

It's not "bragging" if it's actual FACT. :-\\\

.

 

[tkent02]

Walter Brennan is here.

 

[Joe Garfield]

I don't see much smoke when I start - either none, or hardly any.

 

[geol]

Valve stem oil seals are not meant to be 100 percent effective in stopping oil from going down the valve stems but allow a little for lube. When the valve stem oil seals wear they will allow a bit more than enough to lube and the little few extra drops of oil will settle in the combustion chamber to smoke when the bike first starts but generally becomes un-noticeable after the bike is running. If they are really leaky, the bike will puff a bit of oily smoke when you downshift. They will never account for the amount of oil lost by the OP. That prety much can only come about from a large and very noticeable leak or the oil scraping rings are either broken or just worn or the piston to cylinder spec is now much out of space of the pistons have been rocking and the bores oval. Just aren't any other reasons. You don't see a pool of oil? You will likely have to install oversize pistons and rings after having the cylinders bored.

 

[Buffalo Bill]

Walter Brennan is here.

HA! Exactly what I thought, Sons Of Will Sonnet.
But, I was just trying to say, if the damn engine is all good, it should not burn oil, the only oil loss should come from leaks.
Even with the leaks, I only had to top off the oil at the end of summer.

 

[Guest]

I have the infamous secondary drive auto fill on my '82. After about 400 miles I have to drain the secondary drive oil and replace it and my engine is about a quart low. I'll fix it after riding season.
It will leak out the breather tube and down through the mystery hole. But when it does it's obvious.
Have you looked at the secondary drive oil level lately?

 

[Joe Garfield]

That pretty much can only come about from a large and very noticeable leak or the oil scraping rings are either broken or just worn or the piston to cylinder spec is now much out of space of the pistons have been rocking and the bores oval. Just aren't any other reasons. You don't see a pool of oil?

Nope. I park the bike in my garage and would definitely notice. It did leave a few drips from the mystery hole leaks, but that's all gone. Wouldn't all that stuff about bad rings or roundness show up in compression test? Or maybe running just above the min spec is enough to say there's wear?

I wonder if it could be coming out from the oil pan gasket, but only when the bike is running? I'll have to get some pics of the underside of the bike, but for now I'm in and out running errands on the bike, and enjoying it too much to stop

Have you looked at the secondary drive oil level lately?

I changed the secondary drive oil about 500-750 miles ago. I didn't know or think about an 'auto fill' since my secondary and final drives use hypoid oil, so this shouldn't have any influence on motor oil...right?