Oil VS Fuel

[Vintage Engine Repairs]

We get too caught up in searching for that holy grail oil, that removes all carbon and keeps pistons shiny. When we overlook the issue, it’s not the oil, it’s the fuel that causes carbon.

This is stihl ultra (a notoriously “dirty” oil) in their motomix at 32:1 after about an hour and a half run time varying rpm’s. This is in an rc engine, but the point is the same, carbon is from the fuel, not the oil. If the gasoline sucks, you’re going to get more carbon..

 

[Dennisthemenace]

98?

 

[bwalker]

We get too caught up in searching for that holy grail oil, that removes all carbon and keeps pistons shiny. When we overlook the issue, it’s not the oil, it’s the fuel that causes carbon.

This is stihl ultra (a notoriously “dirty” oil) in their motomix at 32:1 after about an hour and a half run time varying rpm’s. This is in an rc engine, but the point is the same, carbon is from the fuel, not the oil. If the gasoline sucks, you’re going to get more carbon..

View attachment 1111635

View attachment 1111636

RC engines run very rich air to fuel ratios in many cases. This will wash the piston clean.
If your pistons are bare metal you are not tuned even close to correctly. I've never seen a two cycle oil that was carbon free and I've tried many. The key is where the carbon is located. You don't want carbon in the ring belt and groove area at all and you don't want carbon on the skirt. You also don't want carbon buildup in the exhaust port.
Sulfates ash buildup on the crown and head is likewise undesirable.
And yes poor quality gasoline will lead to more buildup, but carbon on the piston is completely normal. It's also a good, albeit coarse tool to determine tune.

 

[Vintage Engine Repairs]

RC engines run very rich air to fuel ratios in many cases. This will wash the piston clean.
If your pistons are bare metal you are not tuned even close to correctly. I've never seen a two cycle oil that was carbon free and I've tried many. The key is where the carbon is located. You don't want carbon in the ring belt and groove area at all and you don't want carbon on the skirt. You also don't want carbon buildup in the exhaust port.
Sulfates ash buildup on the crown and head is likewise undesirable.
And yes poor quality gasoline will lead to more buildup, but carbon on the piston is completely normal. It's also a good, albeit coarse tool to determine tune.

That’s not actually true - quite the opposite, especially water cooled like in rc boats, they can be run much leaner than air cooled OP3. Same for the buggies and other 1/5 scale, they run on the ragged edge, much more so than OP3. In my case - the tune was spot on. This engine is no different from a saw. Runs loaded at 10k rpm, ignition is set at 28 degrees btdc, idles a bit lower as it’s got a prop. Tune was spot on - not 4 stroking under load, good acceleration, not loading up at idle, returns nicely, settles down to idle well. Motomix and other alkylate fuels are just cleaner burning.

 

[Tomos770]

Had the same observation with Aspen 4T fuel and JASO FD oil in my freshly built chainsaw....clean sparkplug with spotless piston crown after use...

 

[Vintage Engine Repairs]

98?

I think motomix is 95 but I can remember honestly. I get confused with Aussi octane ratings and USA ones lol

 

[huskihl]

Isn’t ultra different outside of the United States? In the states it’s made by Omni Specialties but elsewhere it’s made by someone else and likely a completely different product.

 

[Vintage Engine Repairs]

Isn’t ultra different outside of the United States? In the states it’s made by Omni Specialties but elsewhere it’s made by someone else and likely a completely different product.

I’m not too sure? Possibly!

 

[jellyroll]

Isn’t ultra different outside of the United States? In the states it’s made by Omni Specialties but elsewhere it’s made by someone else and likely a completely different product.

I’m not too sure? Possibly!

Here is the MSDS for stihl hp ultra for the AU & NZ market.
https://www.stihl.com.fj/p/media/download/STIHL_HP_Ultra_2_Stroke_Oil_Rev_1-0_0818.pdf

 

[WI_Hedgehog]

Isn’t ultra different outside of the United States? In the states it’s made by Omni Specialties but elsewhere it’s made by someone else and likely a completely different product.

Yeah, it's pink.


It's probably slightly different outside the US but mainly the same. Like any top saw manufacturer they want to have the best performing products that fall within government regulations, changing to something vastly different like carnuba wax isn't going to make the saw run better, so they probably take availability/regs in their main markets into consideration before spec.ing oils and fuel, then design saws around that.

 

[bwalker]

That’s not actually true - quite the opposite, especially water cooled like in rc boats, they can be run much leaner than air cooled OP3. Same for the buggies and other 1/5 scale, they run on the ragged edge, much more so than OP3. In my case - the tune was spot on. This engine is no different from a saw. Runs loaded at 10k rpm, ignition is set at 28 degrees btdc, idles a bit lower as it’s got a prop. Tune was spot on - not 4 stroking under load, good acceleration, not loading up at idle, returns nicely, settles down to idle well. Motomix and other alkylate fuels are just cleaner burning.

I don't know anything about rc boats, but rc plains is what I based my comment on.
However, if your piston is bare metal you are rich, period.

 

[bwalker]

Had the same observation with Aspen 4T fuel and JASO FD oil in my freshly built chainsaw....clean sparkplug with spotless piston crown after use...

I've not seen that with alkylate fuels at all.

 

[OM617YOTA]

Isn’t ultra different outside of the United States? In the states it’s made by Omni Specialties but elsewhere it’s made by someone else and likely a completely different product.

Stihl has an HP Super outside the USA that's Jaso FD. Might be that.

 

[Vintage Engine Repairs]

I don't know anything about rc boats, but rc plains is what I based my comment on.
However, if your piston is bare metal you are rich, period.

Na it’s not rich, it’s the normal result with alkylate, just like tomos770 said.

 

[Vintage Engine Repairs]

Stihl has an HP Super outside the USA that's Jaso FD. Might be that.

View attachment 1112047

Interesting! We can’t get that here, just the normal ultra

 

[bwalker]

Na it’s not rich, it’s the normal result with alkylate, just like tomos770 said.

That's funny, I've been running alkylate in my 400C for going on 2 years and in two redmax trimmers with Red Armor oil. They all show proper piston wash.
All gasoline burning engines should have carbon on their pistons..

 

[Tomos770]

Stihl has an HP Super outside the USA that's Jaso FD. Might be that.

View attachment 1112047

No....we still get HP Ultra here....HP Super is not (direct) substitute for it....

https://unicommerce.si/motorna-olja-in-olja-za-mazanje-verige
And yes HP Super is semi-syn rated JASO FD (they misslabelled it on page as FB- click on pictures...)

 

[thompsoncustom]

Na it’s not rich, it’s the normal result with alkylate, just like tomos770 said.

Looks like my saws which I also run at 32:1 and there clean as a whistle.

 

[Vintage Engine Repairs]

That's funny, I've been running alkylate in my 400C for going on 2 years and in two redmax trimmers with Red Armor oil. They all show proper piston wash.
All gasoline burning engines should have carbon on their pistons..

Not sure, myself and the 2 others here have clean internals. I have 2 saws, an rc airplane engine and a model hit and miss. All alkylate and all spotless. I’m very comfortable with engine tuning, none are rich. A rich engine will cause excessive carbon, no doubt the issue is with how you are using your equipment. To get a fully washed piston, the engine will literally have to be hardly able to run at all. Spluttering beyond imagine and run for very short periods without any heat. That’s an incredibly rare condition.

 

[bwalker]

Not sure, myself and the 2 others here have clean internals. I have 2 saws, an rc airplane engine and a model hit and miss. All alkylate and all spotless. I’m very comfortable with engine tuning, none are rich. A rich engine will cause excessive carbon, no doubt the issue is with how you are using your equipment. To get a fully washed piston, the engine will literally have to be hardly able to run at all. Spluttering beyond imagine and run for very short periods without any heat. That’s an incredibly rare condition.

Again. If the piston is washed completely clean you are rich...