How To Fix Motorcycle Engine Knock

Your bike can automatically detune its engine, but there’s an easy fix.

_by Eddie Hilgendorfen |May 10, 2023

Many modern motorcycles are designed to compensate for low-octane gasoline in an attempt to prevent motorcycle engine knocking. Unfortunately, the technology involved may also cause reduced performance, rough idle or lack of throttle response, making for a less than stellar ride experience. Fortunately, we can help you understand the root cause of this problem, and offer an inexpensive, quick and easy solution.

What is engine knocking?

Engine knock or pre-detonation is caused by an improper detonation within the engine, which happens when fuel ignites outside of a timed ignition from the spark plug. In the race to improve fuel economy, modern high-performance engines have increased compression ratios, which also inherently increases the chance of pre-ignition detonation.

Octane measures gasoline performance against pre-ignition, detonation and the resulting engine knocking or pinging. The three most common octane ratings are:

Anti-Knock Index (AKI)
The rating typically displayed on North American gas station pumps as the average of the fuel’s RON and MON octane ratings (R+M)/2.
Research Octane Number (RON)
This rating is determined by testing fuel using a variable compression ratio under controlled conditions and is the most common industry rating worldwide. When comparing octane ratings, RON is typically higher than the AKI number, so an 87-octane AKI fuel at a typical gas station typically has a RON of 91-92. AMSOIL uses RON when conducting product validation and performance testing.
Motor Octane Number (MON)
MON differs from RON testing by using a preheated fuel mixture, variable ignition timing and a higher engine speed to increase ignition stresses on the fuel. Though the tests are unrelated, MON results are typically 8 to 12 octane lower than RON.

Causes for loss of power and efficiency

Low-octane gasoline is more susceptible to uncontrolled and early ignition in the combustion chamber, so the higher the octane, the more compression the fuel can withstand before igniting. Pre-ignition robs the engine of power, can cause a noticeable knocking or pinging sound, and if left unchecked, can even cause catastrophic piston or cylinder damage.

This is why I decelerate (turning off the cruise control) when driving up or climbing steep hills and I also sometimes turn off the air conditioning. Also doing this you can see A decent increase in your fuel efficiency

High stress combined with lightweight design caused this dirt bike piston to fail. Dude was in first place so missed out on the cash prize.

Reduced performance.

Many modern motorcycle engines are equipped with a knock sensor. Pre-Detonation causes this sensor to adjust timing to compensating for low-octane gasoline. Unfortunately, adjusting the timing usually results in a noticeable decrease in performance, rough idling and lack of throttle response. When timing changes are done correctly, most riders shouldn’t even be aware that the performance has been reduced, but it’s easy to resolve this performance problem.

Boosting octane To Reduce Knock

The risk of engine knock can be reduced by:

retarding ignition timing
enriching the air-fuel ratio
reducing cylinder pressure or engine load
reducing the throttle or boost especially as you climb a hill
increasing the octane rating of the fuel
Engine work – lower compression

Therefore, the performance degradation caused by reduced engine timing can most easily be eliminated by increasing the fuel’s octane number. AMSOIL Motorcycle Octane Boost increases octane up to three numbers. On a bike that can be significant! This helps to eliminate motorcycle engine knocking and maximize power, performance and fuel efficiency. We get a LOT of feedback on this. Check out the product reviews.

AMSOIL SABER® Professional Synthetic 2-Stroke Oil resisted performance-robbing deposits and maintained power and performance in ECHO string trimmers.

Published September 2016

Overview Government mandates require modern handheld trimmers and other twostroke equipment to produce less exhaust emissions. To comply, some original equipment manufacturers (OEMs) design their equipment to run on leaner fuel/oil mixtures. Burning more air and less fuel/oil, however, also increases heat. To withstand this intense environment and ensure equipment lasts as designed, modern two-stroke oils must demonstrate improved wear protection and detergency. Objective Demonstrate through lab testing that the latest generation** of AMSOIL SABER® Professional Synthetic 2-Stroke Oil exceeds the increased performance needs of ECHO* string trimmers in particular, and modern two-stroke string trimmers in general. Methodology Testing was conducted on eight ECHO trimmers in the AMSOIL mechanical lab and followed a test plan designed to compare two-stroke oils in simulated real-world conditions. Test duration is designed to simulate an extended length of service. The OEM’s recommended 50:1 mix ratio was followed.

SABER Professional was installed in four trimmers and ECHO Power Blend was installed in another four. Computer-controlled actuators operated the trimmer throttle triggers according to an identical protocol for each unit. Images of trimmers arranged on the test stand are included for reference.

Test administrators monitored engine rpm, spark-plug temperature, exhaust emissions and other parameters to ensure consistent, repeatable operation and gauge overall performance of each trimmer. After 300 hours of operation, the trimmers were disassembled and inspected. Note: Test results published in this Technical Study describe and represent properties of oils that were acquired on the dates listed in Table 1 on the facing page. Results do not apply to any subsequent reformulations of such oils or to new oils introduced after completion of testing. All oils were available to consumers at the time of purchase. Testing was completed in July 2016. The differences in effects between AMSOIL SABER Professional and ECHO* Power Blend* are statistically valid at the 95% confidence interval for exhaust port blockage and spark arrestor screen plugging. The carbon buildup on pistons was not numerically quantified as part of the study.

The test was run using two engines for each treatment. The study was then replicated using the same n=2 design. Exhaust- port blockage and spark-arrestor screen plugging were compared using a paired t-test. Equipment was run at factory-set conditions and there was no effort to intervene on any problems developed by the equipment outside of recommended maintenance in the owner’s manual. String trimmers arranged

Piston Rings/Piston Skirts

Deposits in the ring grooves can cause the rings to stick and lose effectiveness. Engine rpm can decrease and the engine cab lose compression. Significant compression loss leads to engine failure. Heavy deposits on the piston skirt increase friction and reduce performance.

Deposits appear heavier on the pistons lubricated with ECHO Power Blend. The pistons lubricated with SABER Professional appear cleaner. SABER Professional provided improved detergency and extreme-heat resistance. Both oils guarded against piston ring sticking well.

Piston Crowns/Undercrowns Heavy piston crown deposits can cause preignition and poor performance. While undercrown deposits are unlikely to impede performance, they are an indicator of the oil’s detergency properties. With modern two-stroke equipment running hotter, oils must demonstrate strong detergency and heat resistance to maintain piston cleanliness and peak performance.

Pistons lubricated with ECHO Power Blend appear to contain heavier crown and undercrown deposits. In contrast, the piston crowns lubricated with SABER Professional look clean, with low levels of deposits. SABER Professional provided improved detergency and extreme-heat resistance.

Wrist Pins & Bearings The wrist pin and bearing are exposed to extreme heat due to their proximity to the combustion event. Ineffective lubrication can result in deposits, polishing and flat spots on the wrist pin restricting rotation. As the engine works to overcome this restriction, the piston can bear increased pressure, leading to scuffing and eventually failure.

All eight wrist pin bearings demonstrated no issues throughout the test, indicating the oils provided good protection. None of the wrist pins contain flat spots. Both of the oils performed well in this area.

Exhaust Ports

For the engine to run properly and produce maximum power, exhaust gasses must flow freely out the exhaust port during operation. Restricted exhaust causes RPM and power loss, starting difficulties and eventually, failure to operate.

SABER Professional demonstrated low exhaust-port deposits. In contrast, all four exhaust ports on the engines using the ECHO product suffered blockage, with two more than half blocked with deposits.

Note: Airflow loss was calculated using a flow bench to measure restriction which was converted to a percentage of flow compared to an unblocked exhaust post.

Spark Arrestor Screens

Exhaust gasses continually flow through the spark arrestor screen located on the muffler which is prone to plugging. Like the exhaust ports excessive deposits on the spark arrestor screen restrict airflow and reduced power.

SABER Professional demonstrated low spark-arrestor screen deposits. In contrast, screens on the trimmers lubricated with the ECHO product contained higher levels of deposits. The screen from engine 5 was nearly completely blocked with deposits after 239 hours of the 300-hour test and required replacement. On average screens from engines using ECHO Power Blend suffering 4X more airflow loss than screens on engines using SABER Professional 2-cycle oil.

Note: Airflow loss was calculated using a flow bench to measure restriction which was converted to a percentage of flow compared to an unblocked spark arrestor screen.

Main Bearings

The main bearings receive little lubrication given their location in the lower end of the engine. Deposits are an indicator of poor oil detergency. Heavy deposits can restrict bearing rotation and eventually lead to failure.

The bearings lubricated with SABER Professional appear to contain fewer deposits.

Crankcases

Oils with ineffective detergency properties can allow deposits to accumulate in the crankcase. During operation, deposits can circulate throughout the engine and reduce performance.

Crankcase deposits look heavier in the engines using ECHO Power Blend. The engines using SABER Professional appear clean and free of harmful deposits.

RPM & Spark-Plug Temperature

Reduced rpm and spark-plug temperatures are indicators the engine is producing sub-optimal power. This can be caused by heavy exhaust port and spark arrestor screen deposits which restrict air flow through the engine and result in reduced power. The following graphs depict the average rpm and spark-plug temperature of engines at wide-open throttle using SABER Professional and ECHO Power Blend.

Engines using SABER Professional maintained consistent power throughout the study, while the average spark-plug temperature declined slightly. In contrast, the engines using ECHO Power Blend slowly lost power as the study progressed. Similarly, the average spark-plug temperature suffered a drop.

Conclusion

As demonstrated in lab testing designed to simulate a full season of real-world use, AMSOIL SABER Professional Synthetic 2-Stroke Oil provides excellent protection for ECHO* brand string trimmers. SABER Professional outperformed ECHO Power Blend* XTended Life* Universal 2-Stroke Oil by providing improved resistance to piston deposits, crankcase deposits and exhaust port blocking. Due to its ability to limit exhaust-port and spark-arrestor-screen deposits, SABER Professional protected against rpm loss 21 percent better, resulting in reliable operation. The latest generation of SABER Professional meets or exceeds the increased performance requirements of ECHO SRM 225 trimmers.

AMSOIL fully supports the use of SABER Professional as a replacement for ECHO Power Blend XTended Life Universal 2-Stroke Oil, and warrants its use according to the AMSOIL Limited Liability Warranty (G1363).

Tag: piston

How To Fix Motorcycle Engine Pre-Detonation