Motorcycle two-stroke that does not need cylinder oil?

[Owen_N]

My memory may be playing tricks on me, but I seem to remember a comment that an old-time manufacturer such a CZ once made an engine that only used the petrol as a lubricant.
There is no trace on line, so this may not be true.
If it were true, more people would be doing it.

A holdup to this theory is that petrol will vaporize at engine temperatures, and will not adhere to surfaces.

possibly a special petrol blend that does not use heavy mineral oil could be made that will lubricate.
Petrol is normally a blend of highly volatile and less volatile liquids.
You can buy "emergency" petrol that has low volatility, but will extend your existing petrol.

You can run an engine on kerosene if you first start it on petrol, but I suspect that knock resistance is not so good.- maybe 6.5:1 in a 4-stroke engine would be safe, but not
in a more modern carburetted engine.

I will look this up.

You need a lubricant that remains in liquid form at quite high temperatures.

Possibly diesel fuel would mainly remain liquid right up to the flash point in air, and could lubricate the engine.

However, this is mainly injected close to tdc, and not circulated through the engine.

Small, variable compression model airplane engines could run on diesel fuel. ether, and kerosene , instead of using diluted castor oil as a lubricant.
no-one seems to use mineral oil-maybe it doesn't mix well with kerosene?

Mineral oil mixes well with methylated spirits.
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The overall objective is to remove "wet" oil emissions and smoke from the exhaust.

I have heard of "ashless" two-stroke oil, but haven't heard of it lately. I will do a search.
<edit>
Stihl synthetic says 1:50. I have been using 1:28, so maybe I will go to 1:50 once my engine is run in a bit.
1000/50 = 20 ml per litre.

 

[Longboy]

Not true of course....per your own research. Seems like petro chemicals cover both ends. Either as a lubricant or a solvent. Now about those cars that run on water.............

 

[Owen_N]

Maybe a blend of kerosene and petrol would be worth a try.

how about 1/3 kero, 2/3 petrol??
the 1L kero bottles are a bit expensive, but I may be able to get bigger containers.

How volatile is kerosene? It seems to burn fairly well in engine, but leaves chamber deposits.
If it is not fully evaporated as it passes through the engine, then some will adhere to the cylinder walls,

I don't think full dynamic lubrication is needed, though a very fine piston finish would help.
needle rollers and rings would be ok, I think.

Can the piston be made from brass? The very early engines had cast iron pistons, but brass was/is used for steam engines.

Brass takes a fine surface finish, and is harder than standard piston aluminium.
It is also less prone to seizing than aluminium.



However, dynamic bearing loading will be higher, and balance factor would need adjusting.

Maybe I need to try this out on a very cheap engine off Ali Express- one of those 30cc pull-starter units?

Piston temperature may be hot enough to fully evaporate kero , in which case it will not work.
Diesel fuel could be used in a trial as well, in smaller proportion.

- I don't like using the pull starters- the ropes are a bit short. The one on my lawnmower works OK, but my line trimmer was too hard to start-
now deceased due to failed plastic fittings.

Possibly I could get it going with some transplant parts, and remove the trimmer tube.
I could rig an electric dog-cam-out starter, as per my 60cc engine.
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I find even with a 1.5 mm wall stainless tube the starter is too lightly made.

maybe 11 mm bore, 2.5mm wall? I will look though my collection.
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Not that this lube system should be used on my next 49cc engine, but it will be interesting to see if it works on a fairly low-speed utility engine.

 

[Owen_N]

Brass as a piston material for a model engine:
1) density 8.5, vs 4032 al-si of around 2.7,
al-bronze 7.6, steel 7.8
yield 95 vs 315 (al)

If swapped straight on to a bottom end designed for 6500 rpm, top rpms should be dropped a bit by inverse square root of the rpms.
relative weight 8.5/2.7 = 3.15, sqrt = 1.77, so 6500 becomes 3672.
However, these engines can easily run at 8500 rpm, but are limited by cooling, so 8500/1.77 = 4,800 rpm.- a good target rpm.

Wear on the top-end needle-roller and piston pin will be accelerated, but still should survive about 50 hours running.

There doesn't seem to be much data available on relative thermal expansion, corrosion, or dimensional stability at raised temperatures.
Piston temperature seems to range from around 300 (under crown) down to 180 degrees c (skirt)
If the skirt gets hot enough to bake on deposits, it is too hot for good lubrication, and will seize.
I think brass is fairly stable under this temperature range.

Has anyone tried brass as a piston material, or maybe people would not bother trying it?
Sliding interaction of a brass piston against the Nikasil bore should be OK.
Brass on brass is definitely not OK!
<edit>
Brass on aluminium sliding, lubrication, is not often considered.
There seems to be no easily found google information on brass vs aluminium.
I will look at various allows vs brass and lithium grease.- I saw something in passing.
I have heard of other materials sliding against brass, and aluminium vs various bronze, cast iron, and hardened ground steel.
It is best if one material is much harder than the other.
Babbit metal on Cast Iron seems to work quite well.

 

[MRA]

My memory may be playing tricks on me, but I seem to remember a comment that an old-time manufacturer such a CZ once made an engine that only used the petrol as a lubricant...

Stihl synthetic says 1:50. I have been using 1:28, so maybe I will go to 1:50 once my engine is run in a bit.
1000/50 = 20 ml per litre.

I don't know if this will be helpful - but I used to spend a lot of time with Eastern Bloc bikes, and I never heard of such a CZ. MZ (from the DDR) used to specify 33:1 mix on bikes up to the 'ES' series, which were replaced by 'TS' in mid 70s. The latter specified 50:1, despite having a very similar engine and still being premix - we used to assume this was because 2 stroke oil was now 'better' and run everything on 50:1 with no ill-effects. Jawa-CZ were a bit more conservative and (from memory) went from 25:1 to 33:1 in the same kind of time period.

 

[Owen_N]

I don't know if this will be helpful - but I used to spend a lot of time with Eastern Bloc bikes, and I never heard of such a CZ. MZ (from the DDR) used to specify 33:1 mix on bikes up to the 'ES' series, which were replaced by 'TS' in mid 70s. The latter specified 50:1, despite having a very similar engine and still being premix - we used to assume this was because 2 stroke oil was now 'better' and run everything on 50:1 with no ill-effects. Jawa-CZ were a bit more conservative and (from memory) went from 25:1 to 33:1 in the same kind of time period.

This story could have been conflated from possible factory tests using blended fuels with heavier fractions for lubrication.
This could be useful in wartime, say, if there were a shortage of gasoline and refined heavy oils.
I doubt if this ever would reach the stage of an official consumer model.

 

[Longboy]

I don't know if this will be helpful - but I used to spend a lot of time with Eastern Bloc bikes, and I never heard of such a CZ.................

https://en.wikipedia.org/wiki/Česká_zbrojovka_Strakonice

 

[GregNixon]

I used to ride a Suzuki 250 two stroke motorcycle. It ran on premixed fuel and oil. I think it was about 25:1. BP at the time, had a product straight out of the pump called BP Zoom. I don't think it performed very well but it saved the mixing in the tank routine. Then there are two stroke chain saws which had 2 lubricant tanks, one for the crankcase and one for the chain.
As technology moved along the direct oil injected two strokes appeared where the oil was pumped onto the bearings themselves.

 

[Steamchick]

Having run BSA, Raliegh, Villiers, AMC, Jawa, CZ, MZ, Yamaha, etc. all need oil via the crankcase as a total loss system, but in varying amounts. Nothing less than 50:1, or more than 20:1 when pre-mix. Later engines have oil pumps - throttle regulated - that feed oil into the inlet tract to be picked-up and carried through the engine to lubricate crank big-end, small end and bores. Some feed via the crank (I have heard but not experienced?).
A good 2-stroke oil is blended from suitable lubricants that are "lower" in the molecular chain (so relatively more H versus C) so burn easier and produce less free carbon. But Diesel fuel (DERV), is the lightest oil I know with GOOD lubricity, as it must lubricate the fuel pump as it passes through it. Central heating oil does NOT have very good lubricity, and Paraffin/kerosene hardly any.
Without GOOD lubricity, you will have spalling, seizures and/or high wear of the engine.
The only 2-strokes I have heard about without "oil departing via the combustion chamber" are specials where the crankcase is NOT use for charging the cylinder (large ship engines, a Suzuki prototype cross-over engine with "double diameter" pistons, or the Ricardo engine). But All crankcase charged engines must have lubrication which is total loss and vented through the transfer ports to combustion chamber... at least in my experience.
K2

 

[gbritnell]

Engines require oil for lubrication. Stihl the maker of chain saws and small engine powered machines has a new technology for their 4 stroke engines. Here again the fuel is mixed with oil but rather than having oil in the crankcase it operates similar to a 2 stroke engine in that some of the fuel/oil mixture is drawn into the crankcase to lubricate the internal components. As with a 2 stroke engine when the piston is on it's down stroke the pressurized crankcase returns the mixture back into the intake circuit. The 4 stroke engines can be used at all angles unlike conventional oil-in-crankcase designs.

 

[Peter Twissell]

I remember reading about a 2 stroke design which didn't burn oil.
It has a 4 stroke type pumped oil system, with each bearing being sealed and the oil recovered through a second set of oil ways back to the tank.
The piston was relatively tall with oil rings top and bottom, oil being fed into the space between and drained via holes in the cylinder wall.
I think it also used a ceramic coating on either the piston or bore.
It didn't use conventional piston porting, but had a poppet exhaust valve and some kind of valve which I don't remember in the piston crown.

 

[Nerd1000]

Some oil in the exhaust is essentially unavoidable for a 2-stroke, whether it uses the crankcase for scavenging or not. The reason for this is the ports in the cylinder wall, it is inevitable that some oil will be wiped from the rings into the ports after which it mixes with the charge (in the case of inlet ports) or gets blown out the exhaust directly (exhaust ports).

 

[lohring]

All large two strokes run without oil in the fuel. They run pressure lubrication systems just like four strokes. The issues are simplicity and cost. Model airplane four strokes run oil in the fuel for the same reasons. I'm sure some small engine builder has looked at pressure lubrication and decided it wasn't worth the trouble.

Lohring Miller

 

[abby]

The Villiers "wulf" 2 stroke twin had stepped pistons and oil bath bottom end.
Dan.

 

[Peter Twissell]

Some oil in the exhaust is essentially unavoidable for a 2-stroke, whether it uses the crankcase for scavenging or not. The reason for this is the ports in the cylinder wall, it is inevitable that some oil will be wiped from the rings into the ports after which it mixes with the charge (in the case of inlet ports) or gets blown out the exhaust directly (exhaust ports).

The design I remember did not use piston porting, but poppet valves.
This not only avoids oil consumption, but also allows for asymmetric valve timing which makes for a more efficient engine.

 

[Brian Rupnow]

I owned a two cycle engine snowmobile that burned straight gas. Oil was in a seperate container and was injected onto the bearing surfaces. This was about 30 years ago

 

[Steamchick]

Owen, I have just been reading these posts again.
Don't use kerosene as a lubricant. It does not have good lubricity. Diesel road fuel does have good lubricity to lubricate the fuel pump. But it depends on your size of engine. For 2-stroke aero engines, use castor oil in your fuel mix, or proprietary mixed fuel. For motorcycle engines, use what the manufacturer recommends. Same for small 2 strokes for garden tools...
You don't mention what 2-stroke motorcycle you have?
My experience of 1970s CZ was 25:1 mix, for Jawa, 33:1 or fill the engine driven oil pump when fitted (1978 onwards?), for MZ 50:1.
Yamaha and Suzuki around that era used an oil pump driven from the engine. Puch used 33:1.
1960s BSA, Villiers, etc. All used 25:1 in my experience.
In the 1970s before emission laws I used straight 30 motor oil to save cost, but needed very frequent de-coking of the silencer. But when I had decent bikes I used proper 2 stroke oil which left a much cleaner silencer. Just cost 2 or 3 times more!
Using too much oil can give combustion problems of lean mixtures, too little oil can cause siezures... so check manufacturer's instructions as they DO know best! They have Lots of professional Engineers to decide these things, instead of well meaning amateurs.... (I have been both).
K2