Unleaded Gasoline

[xsrider]

Our engines were designed to run leaded regular gasoline, according to my documentation. Lead used to be added to gasoline to lubricate the very hot/dry moving parts of the engine, in particular, the valve stems and guides.

Do you think we should be adding a lead substitute when using unleaded gasoline?

The valve guides in my old engine [about 65k miles] were really shot. I thought maybe they should last to 100k without lots of wear...

[motoman]

The Jap engineers were way ahead of the game then........plus little did we know at the time was there was no lead in the fuel anyways by the late 70's..................in fact all the American auto manufacturers were using hardened valve seats by 1970 anyway just for this reason.

[xsrider]

Cool, I feel better already. Gas er up.

[xsrider]

1986. Primary phaseout of leaded gas in US completed.

[Crazcnuk]

lead was actually added to gas to help raise the octane rating.

I had always heard that it was a valve lube too, but apparently not.

HOW DOES LEAD AFFECT OCTANE?
Tetraethyl lead raises the octane rating of a fuel not because it adds more "octanes" to the fuel but because it makes the fuel knock at a higher compression ratio in the ASTM-CFR. According to the latest research, octane ratings go down with fuels comprised of long, straight, hydrocarbon chains (paraffinic fuels). Fuels with branching hydrocarbon fuels, and aromatic fuels, have a higher octane ratings.

Oxygenates and alkyl lead affect the pre-flame reaction pathways by retarding branching sequences. Lead was previously believed (by many, including myself) to work by slowing the flame front, thus leading to a slower pressure rise in the cylinder. While general flame-front propagation speed does affect octane ratings, lead does not significantly affect it.

http://www.prime-mover.org/Engines/G...es/octane.html

Here is an article about unleaded gas in leaded vehicles:
http://www.chevron.com/products/prod...etin/unld-gas/

[xsrider]

Great reply! But it leaves the question unanswered for the high performance motorcycle engines, and suggests contacting the manufacturer for recommendations.

I am having fun with this. I really want to know for sure. I will try to get something from Yamaha. And I will come back with whatever they say.

Thanks, guys.

[Crazcnuk]

Well, I have run regular, unleaded gas in all my bikes, as that is all there is. I had over 90,000kms on my Shadow, 84,000kms on a 750 Virago, can't remember on the 750/4K, 20,000miles on a TS250 Suzuki, 40,000kms on the 2nd 750 Virago and 10's of thousands on a handful of other bikes. The newest was the Shadow which was an '85, the rest were all 1976-1982, and I have yet to burn out a valve.

[edgo]

What about my vintage two stroke dirt bikes? Should I use leaded gas?

Ed

[oseaghdha]

What about my vintage two stroke dirt bikes?

I use octane booster. Spark knock is instant death on two strokes. You don't need the lead for lubrication, you only need the points for preventing pre-ignition.

[motoman]

Octane boost not necessary on two-strokes................the oil mix raises the octane level 2-6points.............just my twocents

[oseaghdha]

Hate to be contrary but.......
2 Stroke oil actually reduces the octane rating by 2 points.
link

[Crazcnuk]

The TS250 Suzuki, mentioned above and my A100 and GT750 Suzukis are/were all 2 strokes.

Never had a problem with regular no-lead gas. The bottom link on that post talks directly about 2 stroke engines.

"In general, two-stroke cycle will operate without problems on unleaded gasoline. These engines do not have valves, and most will actually benefit from using unleaded gasoline because of reductions in spark plug and combustion chamber deposits. Lead is not required to provide lubrication for pistons or piston rings, as is sometimes claimed."

[trbig]

2 Stroke oil actually reduces the octane rating by 2 points.

Hmmm... I wonder why it's been said that adding a small amount of oil to your gas RAISES the octane then? Is it a difference between 2-stroke oil and regular oil?

Tod

[oseaghdha]

Not to beat a dead horse

My dirt bike experiences are limited to mid '70s to early 80's MX running flat out in the desert, so YMMV.

With ratios of 10, 11, and 12:1, and being air cooled, it don't take much to grenade these motors. Single ring and short deck pistons at 10 KRPM won't tolerate any pre ignition.

As stated above: There is nothing to require any lead related lube, but the octane rating is important.

As far as oil in the gas is concerned, oil will tend to decompose when combined with high pressure air. That's why you can run cooking oil in your compression ignition vehicle.

[Crazcnuk]

Probably because your diluting the gas with a soluble compound with a much higher octane of it's own.

Oil will combust, Kerosene, Diesel, Bunker Sea are all oils, and all have octane ratings. I imagine if you mixed diesel with gas it would raise the octane too.

Problem is, you don't want high octane, unless you need it. Higher octane burns more slowly and produces less power. High octane fuels are used in gas engines to overcome poor design.

As for the 70's 2 strokes, In my experience, far more pistons were burnt by using the wrong spark plug, than anything attributed to using the wrong gas. However all my 2 strokes were CCI injected.

I would guess lots were burnt by people mixing their gas/oil wrong in non-injected engines.