Flash point of 2 cycle oils?

[racin4ds]

I'm sure this has been discussed on here before but I can't seem to find it... how important are the flash point numbers of a given 2 cycle Premix oil? My son and I ride hare scrambles on 2 stroke MX bikes, he has a little KTM 50 (all fresh with many go fast goodies) and I have a relatively stock 96 RM250. I love Klotz oils just because its all we used when I was younger and they've never let me down, plus you can't beat the smell!!

Anyway I see the R50 which is there top of the line oil has a 550* flash point and the Benol is 555*. We run these oils now but I've been reading with concern about the little guys bike not generating enough heat to properly burn these higher flash point race oils. Is that true? I really don't ride mine hard either (too old and less brave now )...

 

[Srt20]

If your in cylinder temps aren't over 600* at WOT the engine will not be running very good. Also you have to remember there is pressure in the cylinder as well. The oil may not ignite at the cylinder temps at idle, but add in the cylinder psi plus the cylinder temp and the oil easily ignites. Also the gas lowers the flash point of the oil further.

 

[mlatour]

I have a Yamaha YZ125 motocross, recreational MX track riding / not racing but still some spirited riding.
This engine is always under a load / upper RPM's, never any slow trail/off-roading.

This bike sees max rpm (11K) on occasion but I don't push it to it's limits.

Premixed at 32:1 as per the Yamaha indications,
I carefuly fine tuned the jetting and using Amsoil Interceptor (low flash point, better suited for recreational usage).
Crisp jetting as close to perfect as you will ever see, no un-burnt oil leaks anywhere on the exhaust.

On a whim one day (since my skill/speed had increased) I decided to try out Amsoil Dominator (racing, high flash point).

Without changing anything, after 30 minutes of riding the exhaust showed signs of un-burnt oil leaking out.

My conclusion of this simple test, despite riding somewhat aggressively and some wide open throttle moments,
'Racing' premix oils are simply better suited in constant WOT / high combustion temp conditions.

 

[Cujet]

Originally Posted By: mlatour
I have a Yamaha YZ125 motocross, recreational MX track riding / not racing but still some spirited riding.
This engine is always under a load / upper RPM's, never any slow trail/off-roading.

This bike sees max rpm (11K) on occasion but I don't push it to it's limits.

Premixed at 32:1 as per the Yamaha indications,
I carefuly fine tuned the jetting and using Amsoil Interceptor (low flash point, better suited for recreational usage).
Crisp jetting as close to perfect as you will ever see, no un-burnt oil leaks anywhere on the exhaust.

On a whim one day (since my skill/speed had increased) I decided to try out Amsoil Dominator (racing, high flash point).

Without changing anything, after 30 minutes of riding the exhaust showed signs of un-burnt oil leaking out.

My conclusion of this simple test, despite riding somewhat aggressively and some wide open throttle moments,
'Racing' premix oils are simply better suited in constant WOT / high combustion temp conditions.



After all these years of running 2 strokes, I'm not at all sure one can tell anything about the lubrication properties of a particular oil choice by how clean the exhaust is. But I will agree that many "racing" two stroke oils do leave the muffler as oil and not smoke.

Outboard TCW-III oil typically does not leave much "exhaust spooge" when used on 125cc dirt bikes. It burns fairly cleanly. And, for many, it lubricates just fine, without resulting in premature engine wear or excess carbon.

Switch to Motul 800 and watch the oil accumulate on the end of the muffler. It's clearly not burning completely. And, I'm not at all sure a "playbike" engine will last longer with this particular choice.

A bit farther off topic, but crummy old TCW-III at 25 to 1, will lubricate far better than any synthetic at 100 to 1. The additional oil will also produce more power, by promoting better piston ring sealing.

 

[Mackelroy]

The more protective oils, will tend to spooge more .

Yamaha R2 is about the best compromise. Honda HP2 has a super film strength, but does have a higher spooge rate.

Cheaping out on race bike 2 stroke oil, or using biodegradable tcwII oil, I wouldn't recommend for piston/cylinder longevity wise in a race bike motor.

about 2 decades ago, I used a 2 stroke oil in one bike that worked fine, but in another bike the design was hard on the intake side of the piston skirts, that oil I was using didn't have the film strength to prevent in take side piston wear. Had to switch to heavy racing film base oil, after replacing cyl and piston.

Lesson from The school of Hard knocks, but I would never base a race bike exhaust to be smoogeless as a number one goal.

 

[CT8]

Unburned oil means there is enough oil.

 

[mlatour]

I can probably attribute my 'spoogeless' exhaust to extensive fine tuning
of the jetting according to ambiant temps more than that oil's ability to burn cleanly.
Add to that 25% race fuel plus a corrected combustion squish height also makes for a very crisp running engine.

Preventative engine teardowns every 20 or so hours have shown the piston, ring and cylinder to be in great condition.
Compression drops less than 10% in between teardowns, but since I'm already in there a fresh piston/ring goes in during re-assembly.