oil consumption

[BA80]

Well, you can claim it to be a myth, but when I switched from Mobil 1 Syn to Castrol Dino juice, the oil consumption dropped dramically. Maybe it is something other than viscosity ratings that allows it to slip by the rings(?)

The most prominent of downfalls of synthetics are that if there is anywhere it can leak (including rings) it will. The other is it's VERY slippery, even where it shouldn't be.

[skids]

Maybe the propensity to leak has something to do with the efficiency of the rings at wiping the cylinder walls???

[BA80]

Maybe the propensity to leak has something to do with the efficiency of the rings at wiping the cylinder walls???

No, really? Ha ha ha

[graybird78]

so i see im not alone with oil consumption issues. have been here for few years,not much spoken of this issue compared to other problems.im not complaining at all. bike runs very well,never stranded me,or failed to start. have had some problems but have been easy fixes. so i must be lucky in that respect . of my oil issue ,have never had anything of mechanical nature failure.bike has 45k on original motor and trans .no gear fixes.for abike that runs so good to use oil suprises me .this year will flush engine and use 20-50 to see what happens. as always kudos to eveyones replys. without these forums where would some of us be.thanks to all again

[rdmcguy]

Oil burner

This should make a few of you feel a little better.
My first 11(marie)uses a quart every 100/150 miles.
It had sat for 10 years or more and even though I tried a number of things
atf.ring free,Marvel mystery oil, It still smokes,...and drinks.
What the hell it's over 21.
I'll dig into it sooner or later
Might even try one of those Flea bay cheapo kits.
I haven't read any definitive negative things about them other than to
check total height some are found to be 1mm shorter than oem/wiseco
And to cut the tang off of the wristpin circlips.
If anyone has used these kits I would like to know what you think?????

[natemoen]

Before I changed ring I was burining through oil faster than I could pour it in. After I replaced my rings I really don't burn any oil now. I don't have to add any between oil changes.

[trbig]

Might even try one of those Flea bay cheapo kits.
I haven't read any definitive negative things about them other than to
check total height some are found to be 1mm shorter than oem/wiseco

Hmmm.. Since OEM and Wiseco aren't the same height, which one are they comparing it to? The 78/79 pistons are a low-dome piston, almost flat. The 80/81/82 pistons are a much higher domed piston. The Wiseco pistons are in between the two. Here's the later on the left vs earlier piston on the right.









So, in theory, the Wisco pistons would have slightly reduced compression numbers vs OEM for the later motors and an increase for the earlier models, only... it hasn't seemed to work out that way. Numbers on my '82 motor were right at the top of OEM, and TC's were well above OEM.

This is my long winded version of saying that as long as the dome isn't higher than than the later pistons where you'd be concerned with valve/piston contact and it isn't even flatter than the earlier piston, the piston dome shouldn't concern you as long as all 4 are equal. You'll have a tight fresh engine for many miles of smiles.

[skids]

No, really? Ha ha ha

All I was trying to say is that viscosity, the resistance to shear, may not be the only fluid property involved with oil consumption. Maybe you got that and maybe your point is that you don't care: If it useds oil, it loses oil.

[BA80]

Maybe you got that and maybe your point is that you don't care: If it useds oil, it loses oil.

Yes, I concur with all..............Relax man, take it down a notch or two. Blaringly obvious statements beg for a smartazz like me to yank the chain.

[crazy steve]

I bought my '78 new, and while it didn't usually use enough oil to require any added between changes at first, by 10K miles it did. Extended high-speed use, I've always had to add oil between changes.

The major weak point IMO is the valves stem seals, as mine started 'puffing' a bit of blue smoke on start-up at about 10K if it sat for any extended time between starts, i.e. total cool down.

[XS1100 Newbie]

My 80 has about 40,000 on it now, and considering the age, miles, the need for stem seals, and the fact that i run the hell out of it, the use of a quart or two between changes doesn't concern me. If i ride it easy, then it doesn't seem to use a quart between changes, but that doesn't happen often. Just can't help twisting the throttle.

[BA80]

The major weak point IMO is the valves stem seals, as mine started 'puffing' a bit of blue smoke on start-up at about 10K if it sat for any extended time between starts, i.e. total cool down.

The valve seals are a weak point on most engines however being a cause of excessive oil consumption is not a trait. Very little oil runs down through the valve guides when the engine ISN'T running let alone when it is. Exhaust ports have pressure blowing it back up for obvious reasons and even intakes have positive pressure more than not. ever seen the fuel that gets blown back out of the carbs when the engine is running?

Oil consumption is pretty much totally from bypassing the rings. Some other may be because of vaporization due to friction, i.e. slipping clutch, excessively loose gears and or engine bearings.

[crazy steve]

Greg, I'll have to semi-disagree about the valve seals. Mine never showed any blue smoke until I did a several-hour high-speed run across some high desert in extreme heat (extreme, as when I got to the first place that was 'cooler', the local temp in the shade was 120; 100 mph+ high speed because I couldn't get out of that heat fast enough...). I don't know how hot it was, but 120 seemed like AC when we got there...

The bike did start using markedly more oil after this, although still not enough to be a major concern; it went from about 12-1400 miles per quart down to about 1K, more if running on the freeway for extended periods.

I talked to multiple knowledgeable people about the oil smoke after this incident, and all agreed I cooked the seals on that run. All said that replacing the seals would eliminate the smoke and slightly reduce oil use, but it seemed like more trouble than it was worth (and still does... lol) so I never did anything. I will agree that valve seals won't be major contributing factor in oil use unless you have big-time guide wear, but if that's the case new seals won't help for long....

All this happened while the bike was still relatively new; the 'desert run' was in 1980 IIRC (handily out of warrantee...), oil use never got worse (and was still well within what Yamaha deemed as 'acceptable') until the bike was parked in '85.

[clcorbin]

Exhaust ports have pressure blowing it back up for obvious reasons and even intakes have positive pressure more than not.

Actually, this isn't completely true. While the exhaust port does have a higher total pressure, the exhaust value and guide cause a venturi to be formed right at the exhaust (and intake) valve locations. It pretty much can't be helped without completely jacking up the rest of the port shape. With the VERY high exhaust velocity, I would be very surprised to find the pressure at the valve -> value guide junction wasn't significantly lower than ambient air pressure even with a higher than ambient exhaust pressure.

ever seen the fuel that gets blown back out of the carbs when the engine is running?

That's due to reversion caused caused by too much cam overlap at slower engine speeds. Rev it up to it's design point and that won't happen as the cam timing will be more optimized for the dynamics of the air/fuel at that engine speed.

[BA80]

Actually, this isn't completely true. While the exhaust port does have a higher total pressure, the exhaust value and guide cause a venturi to be formed right at the exhaust (and intake) valve locations. It pretty much can't be helped without completely jacking up the rest of the port shape. With the VERY high exhaust velocity, I would be very surprised to find the pressure at the valve -> value guide junction wasn't significantly lower than ambient air pressure even with a higher than ambient exhaust pressure.

The venturi effect will be negated by the valve stem blocking the flow over the opening of the guide.

That's due to reversion caused caused by too much cam overlap at slower engine speeds. Rev it up to it's design point and that won't happen as the cam timing will be more optimized for the dynamics of the air/fuel at that engine speed.

It will still be a positive pressure just before the valve closes because of the duration of the cam. The fuel blows out even at high RPM's. It's only negative for a fraction of a second.