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Bicycle Motor FAQ

In this section we cover a number of frequently asked questions about every day items that can affect the performance of bicycle engines. We cover the following quick check items that are frequently asked:

1. Recommendations for the best 2 stroke oil.

2. Analysis of the best gas to oil ratio you should use to improve performance.

3. The benefits of using high octane gas.

4. Spark plugs

5. Finally, we cover some key maintenance items that you should check regularly.

Our Testing Facilities

We point out here that our tests are real world trial and error. When testing the properties of oils, fuel or performance parts, we change only the component under test.  We take our bike for a run, make modifications, and test again.

For oil tests, for example, we mix different ratios of various brand oils and test how they perform on road. We don’t take samples to a lab to analyze the lubricating properties under a microscope.

Peter, our chief mechanic, takes an 80 cc motorized bicycle out for a short 5 minute run at least 30 times a day when testing. We take performance notes from our test run, make changes, and set out for the next test run to look for any performance variance.

Our test road provides consistent terrain to test for a range of performance differences. We have a couple of straights to test for speed and acceleration. Following this, a long, slow upward gradient which helps us evaluate torque. Finally, we have a short, 20 yard steep incline which has to be driven slowly to enter our workshop.

Peter is a trained mechanic who has built and raced top level 2 stroke carts for over 40 years. By his own admission, his carts are fast although he lacks the driving edge of top racers.  Pete’s tuning skills have kept him consistently at the top of the sport.

We are powered bicycle enthusiasts so we know (and feel) when the motor is picking up a little power. Rider observation is our major test instrument. We also use speed and acceleration meters fitted to our test bikes and use an infra-red thermometer to check engine temperatures. We have additional instruments to test air oxygen, barometric pressure, etc. however, other than a quick check of conditions, these are not used extensively.

What is the best 2 stroke oil?

We have tested a huge variety of 2 stroke oil and Valvoline Racing 2 Stroke oil is a clear winner.


To be clear, we are not sponsored or connected with Valvoline in any way, we have tested many brands of oil and, in our opinion,  mineral based Valvoline Racing 2-stroke surpasses them all.

Valvoline oil

Why do we like Valvoline Racing 2 Stoke oil? At face value, it seems to be a little odd to use racing 2 stroke oil for a relatively low performance engine.

The first thing we like about Valvoline Racing 2 stroke oil is that it is relatively low cost. It is usually only a few cents more than regular, plain vanilla alternatives such as Castrol 2T.

The outstanding property of this Valvoline oil is that it provides exceptionally good lubrication. We tested many brands of oil at different concentrations. Valvoline provided the best results, providing better lubrication at lower concentrations than other oils.

An additional benefit was that it doesn’t smoke as much as other oils. At a 20:1 Gas:Oil ratio, Valvoline purred out a light blue haze compared to the heavy smoke produced by other 2 stroke oils.

The only negative we could say about Valvoline Racing 2 Stroke oil is that it is relatively difficult to find. Although big retail outlets such as Supercheap Auto have it in their on-line store, it is most often not available off the shelf. Supercheap will order the oil in for you at no cost if you give them a few days notice.

If you can’t get your hands on Valvoline then other mineral based 2 stroke oils are fine. All mineral based 2 stroke oils that we tested fulfilled their purpose. Castrol 2T is the most commonly available at garage forecourts and, other than producing more smoke, we did not observe a huge difference.

Best gas : oil ratio

The best gas:oil ratio was 30:1 using Valvoline racing 2 stroke oil mixed with E10 gasoline.

 

We tested a variety of 2-stroke oils using increasing concentrations of oil : gas. We started with a lean 35:1 gas to oil mixture and increased the oil concentration to 12:1. We found that engine performance varied very slightly for any oil concentration. A greater amount of oil will not significantly slow the engine or provide any speed benefit.

Gasoline pump

As oil concentration reduced beyond 30:1 we found that with most oils tested, engine temperatures began to increase after a short, hard run.

So, what does this mean for bicycle engines? Most bicycle manufacturers recommend 16:1 gas:oil for running in and 20:1 gas:oil after a couple of tanks of fuel. These recommendations stemmed from early tests undertaken over two decades ago and still hold good today.

20:1 gas:oil provides good engine protection with reasonable smoke. This mix ratio works well for all mineral based 2 stroke oils.

If you run a better grade oil such as Valvoline Racing 2 Stroke oil then you can lean the mix down to as far as 35:1. Other than a little cost saving and a little less smoke, there is little point in going this lean. More oil provides improved lubrication for bearings, rings and barrel walls.

As an extreme test, we decided to test an engine with no 2 stroke oil in the gas. The engine ran for an unexpectedly long time (more than 10 miles). The engine power dropped progressively with distance as the engine overheated. After less than a mile, the engine would have stalled if we slowed the bike. With the intention of testing to destruction, we continued at full throttle and the engine slowed more and more and eventually stalled.

Surprisingly, after a 20 minute cool down, the engine started again will little apparent damage. Of course, running an engine without 2 stroke oil will drastically shorten the engine life. The test did, however, surprise us with how robust these low cost engines are.

The most common problem that we see with overheated engines is that the lower end crankcase seals are damaged. Failing oil seals cause a loss of compression in the crankcase which dramatically reduces transfer of fuel:air to the combustion chamber. A small loss in bottom end compression results in a huge loss of power and poor starting.

Running with no oil

As an extreme test, we decided to test an engine with no 2 stroke oil in the gas. The engine ran for an unexpectedly long time (more than 10 miles). The engine power dropped progressively with distance as the engine overheated. After less than a mile, the engine would have stalled if we slowed the bike. With the intention of testing to destruction, we continued at full throttle and the engine slowed more and more and eventually stalled.

Gasoline pump

Surprisingly, after a 20 minute cool down, the engine started again will little apparent damage. Of course, running an engine without 2 stroke oil will drastically shorten the engine life. The test did, however, surprise us with how robust these low cost engines are.

The most common problem that we see with overheated engines is that the lower end crank case seals are damaged. Failing oil seals cause a loss of compression in the crank case which dramatically reduces transfer of fuel:air to the combustion chamber. A small loss in bottom end compression results in a huge loss of power and poor starting.

Using high octane gas

High octane gas was useful for highly tuned engines as it can prevent detonation.  No performance improvements were observed.  For standard engines, regular ULP or E10 provides the same performance as high octane gas.

 

We tested a number of engines with 10% ethanol gasoline, regular unleaded gasoline and high octane fuel. There were no performance benefits to using higher octane gasoline. Engines ran at the same temperature and no gains were found using high octane fuel. We also tested octane booster additives with no perceived performance improvement.

Using high octane fuel was useful for certain tuning scenarios with high compression cylinder heads. We have found that some tuning alterations with high compression cylinder heads can result in engine detonation. In these circumstances, high octane fuel can remove the engine detonation.

Engine detonation sounds more serious than it is. The sound gives the impression that the piston is hitting the cylinder head at the top of every stroke although this is not the case.

Ultimate Guide to Powered Bicycles
Bicycle tuning FAQ
Everything About Power Bicycles
Bicycle tuning FAQ
Quick tuning tips on how to get your bicycle motor performing to its maximum potential
Steve
Power Bicycle
Power Bicycle
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This Post Has 4 Comments

  1. Daftar Gbo007

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    1. Steve

      Thank you for your input Dafter. I have decades of experience in this business so I hoped to share some of the knowledge I have gathered over the years. It is difficult to know what to write that people would find useful (or interesting). I am glad that the article was useful for you.

  2. Zeke

    Wait so my 80cc 2 stroke bicycle engine kit
    Is it 20:1 or 30:1 bc I been using 50:1 and my bike is acting strange

    1. Steve

      Hi Zeke,

      50:1 gas:oil is far too lean. The engine will be overheating and you are highly likely to have damaged your oil seals if you travel any distance. Leaking oil seals will reduce power and make starting more difficult. Look for tell tale signs of oil behind the magneto (LHS) and the main drive bearing (RHS).

      Oil seal replacement is a low cost repair and, it is unlikely that you have any major damage if the engine is still running.

      Minimum recommended oil ratio is 30:1. Using a higher ratio of oil will not reduce performance although the exhaust can get smokey.

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