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The Mainspring of a rifle that broke due to heavy dieseling.
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From the Bench
Dieseling Air Rifles
Editor's Note: This is the one in a series of columns coming directly from gun technicians who work at Umarex USA. Please check back to see the monthly column, or subscribe to our eNewsletter to get a link to the column every month as a part of the newsletter.
Have you noticed smoke coming out of the barrel or breech of an air rifle or an unusually loud shot? Dieseling is the ignition of a fuel resulting from the heat generated by the compression of air in a cylinder. When the air within a spring-piston airgun’s receiver tube is compressed, the temperature of the air rises to a very high level, igniting the tiny oil droplets that lubricate the piston seal and walls of the compression chamber. Thus, a combustion and sometimes detonation can result.
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A carbon mainspring with heavy buildup and damage caused by dieseling.
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Dieseling in an air rifle is natural due to the lubrication required for smooth operation, but too much lubrication can be damaging to your airgun, and may even result in injury to you or others. This is why we stress to follow the RWS recommended air rifle maintenance schedules and specified amount of lubrication for all of your air rifles.
The accompanying picture of a broken spring is an example of what may happen if you over-lubricate your air rifle. The excessive amounts of oil can detonate, creating a powerful force within the receiver tube that violently slams the piston into the spring. When conditions are right, or rather wrong in this case, the force can cause the internal spring to break, rendering the rifle unusable.
The same thing can happen if you use the wrong type of lubricant. You should avoid using petroleum-based lubricants in your air rifle. These lubes are more prone to combustion and some formulas are known to deteriorate the piston’s seal.
While a broken spring due to over-lubricating is one of the worst things you can do to your spring-piston rifle, excessive dieseling can also lead to tears in the piston seal, which will cause a decrease in power and consequently, the velocity.
Many of the air rifles we receive for repair have been over-lubricated. We’ve seen this so often that it’s immediately recognizable, be it the black build-up of carbon on the piston seal, a torn seal, or a broken mainspring. We’ve even seen situations where excess oil has seeped out of the chamber and onto the stock.
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Dieseling can cause heavy damage to the inside of an airgun if it is not controlled for.
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To avoid dieseling, be sure to use non-petroleum based lubricants, like RWS Chamber Lube and Spring Cylinder Oil. Then, only apply the amount as specified in the gun’s manual or in the RWS air rifle maintenance schedule which is available on our website umarexusa.com.
If you have or have acquired an air rifle that has been over-lubed, or lubed with petroleum-based oil, the best and safest thing you can do is to contact us at Umarex USA. Ship the gun to us un-cocked and unloaded with the Return Authorization number we’ve provided. We have the specific decompression equipment necessary to disassemble and clean your air rifle and we’ll send it back to you shooting like new.
"From the Bench" provides information directly from gun technicians who work at Umarex USA. The monthly column is written by gun technicians as a way to provide firsthand knowledge related to gun safety, interesting facts, and general gun knowledge. Always consult an expert before making any gun modifications yourself. Umarex USA takes no responsibility for any gun modifications or enhancements made by individuals.
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