Pionjar and Cobra Combi FAQ

This FAQ covers the most frequently asked questions we get about the Cobra and Pionjar series of gasoline-powered drills and breakers. These include:

• Atlas Copco Cobra Combi
• Pionjar 120 (discontinued)
• Pionjar 130/140 (discontinued)
• Chicago Pneumatic Redhawk gas drill (same as the Cobra Combi)

The Pionjar, Cobra and Redhawk series are all made by the Berema Corporation in Sweden. They are distributed by Atlas Copco in North America. Chicago Pneumatic also picked up the Cobra Line at some point and marketed it as the “Redhawk.” The Atlas-Copco TT line of breakers are substantially different and not covered here. There are also some knock-offs made in Asia. Some of the parts are compatible.

Who uses these things?

In our experience, the most popular Pionjär applications are as follows:

• Mudjacking and concrete lifting
• Backcountry trail work
• Small drill/blast jobs
• Remote mining and mineral exploration
• Large tent and awning installation

These drills can be tricky to get running just right. If you change altitude for instance, you may need to re-tune your unit. Check out our comprehensive tuning guide for details.

See our Pionjar Accessories Page for detailed info about the tools that can be fitted to a Pionjar or Cobra Combi gas drill.

The Pionjar 120 is the “classic” backcountry rock drill. It was produced from the late 1970s until the mid 2000s. It was replaced by the Combra Combi series of drills and support for the “Pionjar” labeled models has since been discontinued. Both drills feature the same 185cc 2-stroke engine, the same 7/8 x 4 1/4″ chuck and similar fuel capacity. The main differences are as follows:

Pionjar	Cobra Combi
Needle-type fuel metering	Standard Carburetor made by Walbro
Noise level 112db, no catalytic converter	109db muffler with EPA catalytic converter
Push-button throttle, normally at full power	Hand throttle, normally at idle
Adjustable mixture control	Mixture automatically set by carb
Requires 12:1 or 20:1 fuel/oil mixture	Requires 50:1 fuel/oil mixture

For all practical purposes, they both work and will do the same jobs. Some people prefer the simplicity of the Pionjar and believe it has slightly more power. It has no carburetor and only a couple of o-rings in the fuel system. This makes it mostly immune to ethanol fuel and very simple to service.

The downside is that Pionjars can be fussy to get started and warmed up. The carburetor-based system in the Cobra drills is definitely easier to start and keep running. The downside is that it has carburetor diaphragms and other parts that can be damaged by ethanol fuel or improper storage.

If you have a Cobra Combi drill, be careful cleaning the carburetor. They are not easy to replace and can be easily damaged with compressed air.

These units work as both rock drills and light-duty jackhammer/breakers. We would rate rock drilling ability at around the same as a 30lb class pneumatic rock drill. The basic work envelope is as follows:

• Drilling holes in moderate to hard rock, 1-2″ diameter and up to around 4′ deep
• Breaking thin concrete
• Digging, tamping and cutting hard soils
• Driving ground rods, pins, large stakes
• Breaking up rock that has been previously-blasted or cracked with demolition grout

How big of a hole can I drill?

Field tests have shown that it’s possible to drill up to a 2.5″ hole with a Cobra Combi or Pionjar drill. Doing this requires really babying the drill. The natural cycle of down/up/turn they operate on may not be reliable and you requires a light touch with the throttle use and down-pressure is applied to the drill. But it can be done if you just need a couple of holes. The process is slow – maybe 15-20 minutes for one fence post hole 18″ deep.

A more sensible maximum size is 1 7/8″ or less. The same 18″ hole can probably be drilled in 5-6 minutes. Smaller holes drill easily and and quickly. A 1″ hole will probably drill around 12″ per minute.

Drilling in concrete, a good operator can punch 1 1/2″ holes through a typical slab extremely rapidly. This makes these machines ideal for mudjacking and sign installation, where many holes must be drilled over a large area. The bits and steels are the same type used on pneumatic drills in underground mining and they last much longer than the typical SDS Max or spline drill bits made for electric hammer drills.

Using a progression of steels, it’s possible to reliably drill up to around 48″ deep. ‘5 or even 6’ deep holes are possible, but require good drilling technique. The Pionjar and Cobra drills use hollow drill steels and actually produce their own supply of compressed air to help flush out the drill cuttings. The air flush is weaker than that of a pneumatic drill, so it is possible to get the drill stuck if you are not careful.

We like to use 2-3 steels with carbide cross-bits for most rock drilling. Start with a short steel (18″ or 24″). A typical progression is 2,4,6′ or 18″, 36″, 48 or 60″. The following tips can help with deep hole drilling.

1. Use a shovel or broom to remove any soil, loose rock or other debris that could fall down the hole before you start. These drills only work well on rock and not dirt unless it is extremely hard.
2. Start the drill and warm it up. Position the bit over the hole and use your boot to help stabilize it. Apply downward pressure and hold it steady until the hole is started (collared).
3. Keep the drill positioned straight up and drill at a steady rate. Adjust your downward pressure, use of the hand throttle (Cobra Combi) and mixture (Pionjar) until the drill bit is cutting at a steady rhythm. You may need to pulse the throttle button a bit on the Pionjar series to keep the cutting cycle going.
4. Gently rock the drill around in a circle as you drill to prevent the drill binding up. Also, periodically pull the drill up to clear out any chips that have accumulated around the shoulder of the drill bit.
5. Use a battery-powered leaf blower and an assistant to help clear accumulated rock from the hole if possible.
6. When you are nearly bottomed out, begin withdrawing the drill while still under power if possible. Shut down the drill and change to the next longer steel.
7. Deeper holes are easier to drill if you bring a small 2-4 step ladder to stand on. This makes withdrawing the drill and steel changes much easier.
8. Depending on the rock type, it may be better to collar the hole with a larger drill (i.e. 1 5/8″) and then progress down to 1 1/2″ and 1 3/8″ to have more clearance for chips to leave.
9. Using these techniques, it is possible to drill 48″ deep reliably and even 60 or 72″ with care. In bad ground, you may want to use a drill steel fitted with auger flutes around it.

We recommend keeping a few tools and accessories with your drill. You will need to perform some periodic maintenance and minor repair work if you use a Cobra Combi or Pionjar in the field. Here is our recommend list

• Clean rags, stored in a zip-loc bag. You should wipe down the drill and tool shank every time you change tools and before storing.
• Fuel funnel with a narrow spout
• Measuring cup, approximately 1/2 liter capacity. This is needed for mixing the 2-stroke oil with fuel. (12:1, 20:1 or 50:1 depending on model)
• Small gas can. Our absolute favorite for these drills is the 5-liter NATO style gas can. They hold enough fuel for a typical 1/2 – full day of work.
• Spark plug wrench and gapping tool. Spark plugs only last 10-20 hours on these and they usually do not come pre-gapped.
• 8mm, 10mm and 12mm socket and wrench or nut driver
• Small adjustable wrench for removing the exhaust duct valve on the tool head
• 6″ piece of coat hanger wire for cleaning exhaust duct
• Optional: Drill chuck wear gauge, 7/8″.

The Pionjar and Cobra are powerful tools and create rock dust. We recommend that all persons operating one of these first acquire appropriate personal protective equipment (PPE). This includes

• Boots with safety toe
• A fitted P100 half-face respirator to limit silica exposure
• Safety glasses
• Hearing protection

With proper care, these units can drill several thousand feet of rock before requiring a major overhaul. They can typically be rebuilt at least twice. A minimal overhaul includes:

• Disassembly and cleaning
• Piston Rings (power and drill pistons)
• Drill chuck
• Carburetor rebuild (Cobra Combi)
• Fuel-metering system rebuild (Pionjar 120/130/140)
• Gaskets
• Pull rope
• Spark plug
• Air filter

A Complete rebuild if required adds the following

• Cylinder replacement or chroming/Nikasil treatment
• Bearing replacement
• Piston replacement
• Ignition and other parts as needed

The best way to ship a Cobra or Pionjar drill is in the factory-supplied crate. A Pionjar 120 in the crate weighs 75-80lbs and a Cobra ships at about 90lbs. If you are shipping one, we recommend the following:

• Drain the fuel tank and wipe down the unit. UPS may refuse it if there is a strong fuel odor or visible leakage from the package.
• Place the unit in a trash bag and secure the drill in the crate. Add blocks of closed-cell foam to keep the drill from moving.
• Put your return address on a paper inside the crate to maximize the chances of getting it back if the shipping label is torn off.
• Secure the latches with zip ties.
• Ship via UPS Ground or UPS Freight. You will need to select the option for “irregular package,” as a wooden crate incurs an extra charge.
• “We recommend using Pirate Ship for economical shipping. A UPS store can also do it, but their costs are 50-100% higher.
• If you are shipping units to us for repair, please contact us first.