81 replies to this topic

[meb58]

I was having a conversation with a fellow a few days ago about a fleet of commercial lawn mowers, 20hp single piston type. He said that he had read that 87 octane fuel placed less stress on these motors. While pondering this I thought that perhaps a better oil might be key but what do I know.

Is there any plausible theory that supports this? Seems to me that fuel consumption might change as well...?

[J. Edlund]

No, more or less octane does in itself nothing if the engine isn't knocking.

[cheapracer]

I was having a conversation with a fellow a few days ago about a fleet of commercial lawn mowers, 20hp single piston type. He said that he had read that 87 octane fuel placed less stress on these motors. While pondering this I thought that perhaps a better oil might be key but what do I know.

Is there any plausible theory that supports this? Seems to me that fuel consumption might change as well...?

Most likely has non adjustable ignition so the manufacturers octane rating is going to work out best if you can't change the timing.

On the drill rigs we used Moreys Engine Oil Stabilizer into all the stationary engines and hydraulic motors because they actually did run cooler as per Moreys claims.

[meb58]

I've always viewed these small engines - lawn mower tpye - as somewhat crude when compared with what we find in our cars these days. So I couldn't imagine the octane number changing much except the cost of fuel. But I guess we would have to know more about the particular engine design, CR, timing etc?

But the key here, and this is a question, is if the engine isn't knocking with 87 octane the engine shouldn't run into reliability problems? Meaning, it should also run fine on 93 octane?

[cheapracer]

I've always viewed these small engines - lawn mower tpye - as somewhat crude when compared with what we find in our cars these days. So I couldn't imagine the octane number changing much except the cost of fuel. But I guess we would have to know more about the particular engine design, CR, timing etc?

But the key here, and this is a question, is if the engine isn't knocking with 87 octane the engine shouldn't run into reliability problems? Meaning, it should also run fine on 93 octane?

If you put 93 octane in you could try opening the inlet valve clearance by say 0.002" to increase compression a bit - most of those stationary engines have the inlet valve open very late a few thousandths to act as a decompressor at starting motor windover speed but they can be a pain then to turn over if you have too much clearance as you eliminate the decompressor function.

If you're really keen pull the engine down and clean up the ports and put a thinner headgasket/s on, they respond to tuning the same as any other engine, better in fact as they are so restricted in the first place. There's a stationary engine dirt kart club in Brisbane, Oz and the performance they ring from the 200cc 5hp engine starting base is terrific, they use Briggs and Stratton aftermarket drag pistons and rods, flat slide carbs and dry sump them etc, crazy stuff and money for the origins.

[meb58]

I'm going to lean on you a bit here Cheapracer because I'm just too lazy today to search through the threads.

Octane means what really? I think I know 87, 91 and 93 do not differ in energy content...? So what exactly affects engine perofrmance or timing requirements?

[bigleagueslider]

J.Edlund is correct. With the typical air-cooled, single cylinder gasoline lawn mower engine, using a fuel with higher octane rating than that specified would provide no benefit. Until recently, most of these engines were flat head (side valve) designs, in order to save money. As a result, they used very low CR's to prevent detonation. Usually something like 6.5:1 or so. This low compression ratio also made them easier to pull start. And since these engines also used cantilevered cranks, aluminum rods, and splash lubricated bearings, having a low CR kept combustion pressure forces low.

Being a gearhead myself, I own an 8hp Honda lawnmower, which has a 2-valve overhead cam engine and variable speed transmission. It makes it a joy to mow the vast expanse of beautiful, dark green Kentucky bluegrass in my front yard. That thing starts on the first pull and runs like a Swiss watch.

[Kelpiecross]

I was having a conversation with a fellow a few days ago about a fleet of commercial lawn mowers, 20hp single piston type. He said that he had read that 87 octane fuel placed less stress on these motors. While pondering this I thought that perhaps a better oil might be key but what do I know.

Is there any plausible theory that supports this? Seems to me that fuel consumption might change as well...?

The difference in low and high octane petrol being able to be ignited in an engine is fairly distinct when it is used in low CR (sidevalve or two-stroke) lawn mower-type engines. The low octane fuels are more easily ignited and thus are more suited to low CR engines.

I discovered this when I had a 1937 Austin Seven which had a CR of about 5:1. After about two weeks of having the same high octane fuel in the tank it would refuse to start until it was given fresh fuel. I did not have the same problem with low octane fuel.

I have read that the very low octane petrol of the 1930s was dangerously explosive - far more so than today's petrol which is far less igniteable.

It seems to be a commonly-held belief that "high-octane" means "dangerously explosive" when actually the opposite is true.

[Tony Matthews]

That thing starts on the first pull and runs like a Swiss watch.

That has rather put me off Swiss watches...

[Magoo]

The problem of premature ignition is referred to as pre-ignition and also as engine knock, which is a sound that is made when the fuel ignites too early in the compression stroke.

Pre-ignition and knock (aka detonation) are two different events that are invariably confused.

Knock occurs at some point after spark ignition. When the A/F mixture lights, the combusting gas expands and the pressure in the cylinder rises very rapidly. Naturally, the A/F charge is not perfectly homogeneous, leaving cells or pockets of less combustible mixture. The expanding main combustion charge or flame front squeezes these pockets until they spontaneously detonate. The colliding pressure waves produce what we call knock.

Preignition occurs when some feature in the combustion chamber gets hot enough to ignite the air-fuel mixture before the spark plug fires, effectively serving as a glow plug. Examples: sharp edge on the piston crown, overheated spark plug ground electrode, or carbon buildup heated to incandescent temperature.

[Magoo]

That has rather put me off Swiss watches...

Me too. No more gasoline timepieces for me.

[Catalina Park]

24gerrard will be along in a minute telling us that electric timepieces are the way of the future.

[Tony Matthews]

I'm blowed if I'm walking around plugged into the mains...

[Grumbles]

I'm blowed if I'm walking around plugged into the mains...

Get with the times Tony.
Wind power.

[24gerrard]

The design of these lawn mower engines is very basic.
The engines compare with early car engines as do many (even current) light aviation engines (30s designs).

The less controlled burning of the early petrols (and Benzines) suits the 'bad' combustion areas in these engines.
This bad design coupled with long strokes and low compression ratios results in relatively smooth and reliable running.
Mainly from the restrictive flame paths in the designs that prevent detonation.
I am thinking pre Weslake/Heron head design etc.

If you use a high octane modern fuel with different additives and no lead, the fuel will not work well in these old engines.
It will only be partialy burnt.
The spark plugs will coat with oxides at a much higher level than in a modern engine (which have finely controlled and higher powered ignition) and valves (4 stroke) and piston rings will also work less well because of the excess coating.
It can even negate the effectiveness of the oil through contamination and chemical reaction and burn out exhaust valves.

To sort these problems, you would need to replace the exhaust seats and valves (4 strokes) with a harder and semi self lubing material and replace the piston rings with a modern steel ring set.
Undertake a port and cylinder head re-shape (and volume balance multi cylinders) and increase the compression ratio.
Change the spark plug heat range and increase the spark intensity if needed.
With the higher C/R the ignition should be advanced (usualy about 30 degrees BTDC).
Most vacuum and centrifugal weight ignition advance mechanisms on these old engines (if they have any) are there simply to allow the engine to tick over at a reasonable rpm (500 max?).
To improve the ignition, it is often useful to lock any mechanical advance rigid and to do away with any vacuum advance.
However this usualy means living with a high tick over rpm.
Idealy a modern computer ignition can be cobbled up.
The fuel system is usualy a big problem.
The carbs fitted are to small in intake diameter and fuel flow to the float bowls is to restricted, the bowls are also to small.
The dash pot type often have the wrong oil (use non), wrong needle and or jet sizes.
Fixed jet types are very often cheap, untunable and covered in multi springs and linkage (on mowers mainly, to allow for the idiots using the device).
Change the carb for something bigger, easier to 'jet up' and connect it to basics (throttle cable, choke?).

Edited by 24gerrard, 07 August 2011 - 11:35.

[24gerrard]

I'm blowed if I'm walking around plugged into the mains...

Many people do Tony when they mow the lawn.
Wearing a mechanical time piece today is a bit like hanging a steam engine around your neck.
I suppose it still gives the excuse for weedy 'bling' man to wear girly jewelry though.

[cheapracer]

Get with the times Tony.
Wind power.

Indeed, assists forward thrust.

I recommend beans, the musical fruit.

[cheapracer]

The design of these lawn mower engines is very basic..................

And yet at their peak some 20 years ago Briggs and Stratton were manufacturing 80,000 engines per 24 hour shift from their 3 main factories so someone likes them.

Not a typo, 80 thousand engines per 24 hours or around 20 million a year. I believe they are about half that now with the Japanese and other American competition.

Edited by cheapracer, 07 August 2011 - 13:51.

[Magoo]

The design of these lawn mower engines is very basic.
The engines compare with early car engines as do many (even current) light aviation engines (30s designs).

The less controlled burning of the early petrols (and Benzines) suits the 'bad' combustion areas in these engines.
This bad design coupled with long strokes and low compression ratios results in relatively smooth and reliable running.
Mainly from the restrictive flame paths in the designs that prevent detonation.
I am thinking pre Weslake/Heron head design etc.

If you use a high octane modern fuel with different additives and no lead, the fuel will not work well in these old engines.
It will only be partialy burnt.
The spark plugs will coat with oxides at a much higher level than in a modern engine (which have finely controlled and higher powered ignition) and valves (4 stroke) and piston rings will also work less well because of the excess coating.
It can even negate the effectiveness of the oil through contamination and chemical reaction and burn out exhaust valves.

To sort these problems, you would need to replace the exhaust seats and valves (4 strokes) with a harder and semi self lubing material and replace the piston rings with a modern steel ring set.
Undertake a port and cylinder head re-shape (and volume balance multi cylinders) and increase the compression ratio.
Change the spark plug heat range and increase the spark intensity if needed.
With the higher C/R the ignition should be advanced (usualy about 30 degrees BTDC).
Most vacuum and centrifugal weight ignition advance mechanisms on these old engines (if they have any) are there simply to allow the engine to tick over at a reasonable rpm (500 max?).
To improve the ignition, it is often useful to lock any mechanical advance rigid and to do away with any vacuum advance.
However this usualy means living with a high tick over rpm.
Idealy a modern computer ignition can be cobbled up.
The fuel system is usualy a big problem.
The carbs fitted are to small in intake diameter and fuel flow to the float bowls is to restricted, the bowls are also to small.
The dash pot type often have the wrong oil (use non), wrong needle and or jet sizes.
Fixed jet types are very often cheap, untunable and covered in multi springs and linkage (on mowers mainly, to allow for the idiots using the device).
Change the carb for something bigger, easier to 'jet up' and connect it to basics (throttle cable, choke?).

Oh, yeah, an African swallow maybe, but not a European swallow, that's my point.

[24gerrard]

I can throw in a nice 'shrubbery'.
I wish Apple and Blackberry were still just fruits.

[meb58]

But they are

I can throw in a nice 'shrubbery'.
I wish Apple and Blackberry were still just fruits.

[bigleagueslider]

That has rather put me off Swiss watches...

Tony......Wow.......what a trooper.....Like you could have actually afforded a Rolex to begin with?

...or were you just foreswearing any future potential purchase of a plastic Swatch?........

[Tony Matthews]

Tony......Wow.......what a trooper.....Like you could have actually afforded a Rolex to begin with?

...or were you just foreswearing any future potential purchase of a plastic Swatch?........

Well, that is faintly insulting. I had a Rolex some years ago but sold it as I realised that a) I didn't like the look of it, and had only bought it because it was a Rolex, and b) it felt uncomfortable. Nowadays I rarely wear a watch, wearing one at work is pointless, they get seriously marked, and dust and grit under the strap/bracelet makes you want to hurl them. Having not worn one all day it seems odd to put one on in the evening. How's your Wal-Mart Timex?

[meb58]

Yes, yes, but the Timex uses 87 octane...the Rolex uses 103...unleaded of course.;)

24gerrard, why is wearing a time piece like hanging a steam engine around one's neck?

Edited by meb58, 09 August 2011 - 12:52.

[Tony Matthews]

Yes, yes, but the Timex uses 87 octane...the Rolex uses 103...unleaded of course.;)

The Timex is easier to tune of course, being fairly basic, I've seen one that could do a minute in 58.32 seconds! Bit noisy though...

[24gerrard]

Yes, yes, but the Timex uses 87 octane...the Rolex uses 103...unleaded of course.;)

24gerrard, why is wearing a time piece like hanging a steam engine around one's neck?

Alright you got me.
Its like hanging an internal combustion engine around your neck compared to an EV.

Mechanical time pieces are to unreliable and inconvenient.
Soon we will have mobile phone jewellery and digital time piece bling.
How about a solid gold blackberry?
Would make a cool company for someone.

[saudoso]

Many people do Tony when they mow the lawn.
Wearing a mechanical time piece today is a bit like hanging a steam engine around your neck.
I suppose it still gives the excuse for weedy 'bling' man to wear girly jewelry though.

Of all people, you saying that. What could be wrong with something that works on human power instead of lithium? Or that will need to be recycled sooner than later?

And there are steel and plastic automatic timepeaceas around - no bling at all - just like the one I'm looking at right now.

[meb58]

I imagine!

The Timex is easier to tune of course, being fairly basic, I've seen one that could do a minute in 58.32 seconds! Bit noisy though...

24gerrard,

If suggest the gold blackberry idea someone will no doubt hang one from one's neck...in the name of good taste I am sure.

[Magoo]

Of all people, you saying that. What could be wrong with something that works on human power instead of lithium? Or that will need to be recycled sooner than later?

Exactly right. I've been wearing the same watch since 1988. No filthy batteries to change, either. Self-winding, runs solely on my naturally athletic body movements.

Though why I need a watch when i can just check the time on the Blackberry is unclear...

[Tony Matthews]

... runs solely on my naturally athletic body movements.

I know when someone is being economical with the truth.

[desmo]

Yeah. I just look at my phone if I need to know the time.

[Magoo]

I know when someone is being economical with the truth.

There's nothing wrong with a positive self-image.

[Tony Matthews]

Very much an American trait - I wish we had more of it. Specifically, I wish I had more of it...

Edited by Tony Matthews, 09 August 2011 - 22:22.

[saudoso]

Exactly right. I've been wearing the same watch since 1988. No filthy batteries to change, either. Self-winding, runs solely on my naturally athletic body movements.

Though why I need a watch when i can just check the time on the Blackberry is unclear...

Thanks gos there are still moments (not many, that's true) when the iPhone is switched off and I still have my watch on. There are otherts when hecking the time is not important at all.

[saudoso]

I know when someone is being economical with the truth.

Sloooow to catch...

[saudoso]

24gerrard will be along in a minute telling us that electric timepieces are the way of the future.

I have the impression that he did it already...

Edited by saudoso, 09 August 2011 - 22:29.

[Canuck]

The strangest thing happened when I stopped wearing a watch - what time it happened to be mattered less and less. Still a wage slave with obligations but my time checks limited to the ones that matter.

[Tony Matthews]

The strangest thing happened when I stopped wearing a watch - what time it happened to be mattered less and less. Still a wage slave with obligations but my time checks limited to the ones that matter.

Exactly! I have my phone in my pocket, if I need to know the time I can fish it out, but seeing it every time you move your wrist - so to speak - is tedious. I don't even like a clock on the wall when I'm working.

[24gerrard]

Very much an American trait - I wish we had more of it. Specifically, I wish I had more of it...

American 'self image'?
Is that what the rioters in the UK have been taught from watching American films and computer games?

[mariner]

And yet at their peak some 20 years ago Briggs and Stratton were manufacturing 80,000 engines per 24 hour shift from their 3 main factories so someone likes them.

Not a typo, 80 thousand engines per 24 hours or around 20 million a year. I believe they are about half that now with the Japanese and other American competition.

I had not realised that Briggs and Stratton volumes had dropped so much but I do remember reading that they relied on a lot of manual labour to assemble the engines as this was ( they felt) more flexible than heavy automation.

I havea B and S 150cc mower engine and the main fuel thing is to put new fuel in each Spring and to always keep the tank topped up. I guess the crude carb relies on the fuel level to work.

I think the overall efficiency of these engines must be very low as the fuel consumption ( versus work done) seems horrendous.

BTW ( for 24Gerrard!) based on my wanderings around the USA if every John Deere ride on was replaced by an electric one powered by modern batteries I am sure it would make a significant dent in US oil consumption. Just kidding but in the Mid West there are thousands of JD ride-ons and whilst many car dealers have closed in the last few years the JD dealerships seem to be prospering!!

Edited by mariner, 10 August 2011 - 10:55.

[24gerrard]

I had not realised that Briggs and Stratton volumes had dropped so much but I do remember reading that they relied on a lot of manual labour to assemble the engines as this was ( they felt) more flexible than heavy automation.

I havea B and S 150cc mower engine and the main fuel thing is to put new fuel in each Spring and to always keep the tank topped up. I guess the crude carb relies on the fuel level to work.

I think the overall efficiency of these engines must be very low as the fuel consumption ( versus work done) seems horrendous.

BTW ( for 24Gerrard!) based on my wanderings around the USA if every John Deere ride on was replaced by an electric one powered by modern batteries I am sure it would make a significant dent in US oil consumption. Just kidding but in the Mid West there are thousands of JD ride-ons and whilst many car dealers have closed in the last few years the JD dealerships seem to be prospering!!

Strange as it may seem, I know of a company looking into exactly that Mariner.

[meb58]

Several of my neighbors have JD ride-ons. Our lawns are so small as to make even the visual of a JD ride on sitting in the middle of those lawns ridiculous. ...must be why they're a wee bit over-weight as well.

Mariner, I agree, the fuel consumption is horrid. So why not bump CR, advance the timing, arrange the valves in a more efficient manner? Might require 93 octane? As an aside, I've had a lot of trouble with fuel sitting for more than two months despite using a stabilizer. Carbs and jets get all gummed up. I buy a gallon at a time and use the stabilizer.

...this begs the question, if 87 octane is more combustible than 93, does it also go bad faster?

Edited by meb58, 10 August 2011 - 12:27.

[cheapracer]

As an aside, I've had a lot of trouble with fuel sitting for more than two months despite using a stabilizer.

2 months? That's ridiculous, are you using the same brand fuel, where are you parking them?

One thing I always did with my dirt bikes that went into the shed for months at a time was to leave the fuel tap on and keep everything functioning as it slowly seeped through the carb (leaving a big red fuel dye spot on top of the cases). When a carby dries out is when you get problems from the fuel residuals.

[meb58]

...hmmm, the advice I've recieved is to run them out of gas and fill up for the next mowing cycle...Then they sit for a week or two without fuel...that could be the problem?

2 months? That's ridiculous, are you using the same brand fuel, where are you parking them?

One thing I always did with my dirt bikes that went into the shed for months at a time was to leave the fuel tap on and keep everything functioning as it slowly seeped through the carb (leaving a big red fuel dye spot on top of the cases). When a carby dries out is when you get problems from the fuel residuals.

[mariner]

From my dim memory of petrochemicals I think fuels have "light ends" added in winter to help starting and are produced with a lower vapour ( reid?) pressure in summer so wait until the spring grass is good and long before buying fuel. Good excuse to the wife anyway.

One possible reason why higher octane fuels could be worse for mowers is that the higher octane fuels are, IIRC, much more oxygenated. This helps combustion but maybe it accelerates fuel deterioration in the can as some of the oxygen to consume the fuel is already in the fuel.

Also here in the UK the general advice is to only buy higher octane at a high volume fuel station as otherwise the stuff sits too long in the tnaks and deteriorates.

[Kelpiecross]

From my dim memory of petrochemicals I think fuels have "light ends" added in winter to help starting and are produced with a lower vapour ( reid?) pressure in summer so wait until the spring grass is good and long before buying fuel. Good excuse to the wife anyway.

One possible reason why higher octane fuels could be worse for mowers is that the higher octane fuels are, IIRC, much more oxygenated. This helps combustion but maybe it accelerates fuel deterioration in the can as some of the oxygen to consume the fuel is already in the fuel.

Also here in the UK the general advice is to only buy higher octane at a high volume fuel station as otherwise the stuff sits too long in the tnaks and deteriorates.

I still think the reason lower octane fuels are more suited to lower CR engines (like mowers) is because the lower octane fuel is more easily ignited than higher octane fuel making starting much easier and low speed running steadier.

This means that higher CR engines would also start more easily on low octane fuel but they could have detonation problems at full load.

As I wrote previously, the difference in starting with low and high octane fuels becomes a lot more obvious on very low CR (like 5:1) engines.

[bigleagueslider]

Well, that is faintly insulting. I had a Rolex some years ago but sold it as I realised that a) I didn't like the look of it, and had only bought it because it was a Rolex, and b) it felt uncomfortable. Nowadays I rarely wear a watch, wearing one at work is pointless, they get seriously marked, and dust and grit under the strap/bracelet makes you want to hurl them. Having not worn one all day it seems odd to put one on in the evening. How's your Wal-Mart Timex?

OK...truce....alright?. Just giving you a hard time about the Rolex. And as for my preferred choice of WalMart timepieces, I'm a dedicated Casio man. I wear my watches surfing, and the all-plastic Casio holds up better in saltwater than the more upscale Timex models.

Incidentally, like you, I also briefly owned a Rolex at one time and eventually decided to get rid of it. It was a "solid gold" Submariner model that I bought from a guy on the street in LA for $20 (after haggling him down from his original $500 asking price). Within half an hour of putting it on my wrist, it turned my skin green. A few days later I gave it to my 8 year old nephew, who wore it to school for a few days, until the hands fell off of the dial. I can only imagine what his teachers were thinking about what my brother did for a living if his 8 year old son was wearing a gold Rolex....... In the end, the whole affair was just a sad commentary on the decline in the quality of cheap Chinese knock-offs. I'm glad that your experience with "Rolex" watches was not quite so bad.

Finally, I'm sure Hurley Haywood loves the feel on his arm wearing all five of his Rolex Daytona watches.

Regards,
slider

[bigleagueslider]

Several of my neighbors have JD ride-ons. Our lawns are so small as to make even the visual of a JD ride on sitting in the middle of those lawns ridiculous. ...must be why they're a wee bit over-weight as well.

meb58,

If you'd ever lived in a rural, small farming town in mid-western America, you'd appreciate that the most practical use of a JD riding mower is to provide motorized transportation to & from the local bar, after one "loses" their automotive driving privileges. Riding at even 2.5mph still beats walking.



slider

[Canuck]

I bought a Rolex copy for 20DHs...about $7 at the time. Was a fairly nice copy, complete with second hand sweep and the perpetual motion mechanism visible through a clear back. It kept perfect time for almost 6 years at which point I gave it to my then 4-year old. Remarkable what one can buy for nothing.

[J. Edlund]

The difference in low and high octane petrol being able to be ignited in an engine is fairly distinct when it is used in low CR (sidevalve or two-stroke) lawn mower-type engines. The low octane fuels are more easily ignited and thus are more suited to low CR engines.

I discovered this when I had a 1937 Austin Seven which had a CR of about 5:1. After about two weeks of having the same high octane fuel in the tank it would refuse to start until it was given fresh fuel. I did not have the same problem with low octane fuel.

I have read that the very low octane petrol of the 1930s was dangerously explosive - far more so than today's petrol which is far less igniteable.

It seems to be a commonly-held belief that "high-octane" means "dangerously explosive" when actually the opposite is true.

Lower octane fuels are not easier to ignite. You can't say how easy or hard a fuel is to ignite by looking at the octane rating.

What you're describing here is related to the fuels vapor pressure. For any fuel to ignite there have to be a certain amount of fuel vapor in the air. Each fuel have an upper and lower ignition limit, typically for gasoline 0.6 to 8 vol. % gas in air. So for the engine to start, you need an air fuel mix in between those limits, and to create such a mixture you need the correct amount of gasoline to vaporise. Gasoline contain hydrocarbons having boiling points between 25 and 225 degC. During your start attemt you won't have much luck vaporising those hydrocarbons with boiling points close to 225 degC, but those with a low boiling point easily vaporise and will form a combustable mixture given that enough fuel is injected. Depending on where and when the fuel is intended to be sold adjustments are made to the boiling point curve of the fuel so that it works with the temperatures encountered where sold. So during the winter, more light hydrocarbons are added (low boiling point) and during the summer less light hydrocarbons are used (prevents vapor lock). If left in the fuel tank for a while these lighter hydrocarbons can also boil off, making the engine difficult to start.

Both high and low octane fuels are dangerously explosive under the right conditions. Put a spark plug in a gas tank and trigger it and nothing will happen, the mixture above the fuel level is far too rich to ignite. Cool the fuel tank so the mixture above the fuel level is just right and it will go boom when the spark plug is triggered!