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How to Remove a Stuck or Stripped Crankcase Plug

Updated: Feb 10, 2021

You're ready to check your valves clearances.

You start to remove the crankcase plug, but the large one is stuck! After a few tries, you realized you've just stripped the hex/allen hole.

Now what? Here are several tricks to get it off.

Flywheel bolt access plug properly "stripped" on the left case of a DR650

The stripped engine plug will be a problem to remove (not the sloppy red silicone job), but the plug.

A stripped hex or allen hole on the engine plug (also known as magneto cover, flywheel bolt access cover or crankcase cover) is a common occurrence on our beloved bushpigs. But fear not, we've got you covered.

The issue

The flywheel bolt cover plug is made of extremely soft aluminum alloy and is easily stuck in the case

To check your valve clearances, you need to remove both plugs on the left crankcase cover shown in the picture below.

The small one on the side, the timing plug, is made of steel. It's never an issue to remove this from the aluminum case.

But the large plug tends to get stuck, not so much because of the threads seizing on the case (it's somewhat oily) but because of the large o-ring sticking to it.

The soft aluminum cover doesn't provide a snug fit for your 10mm hex key, which means you're likely to strip it trying to remove it. We've all done it.

DR650 left case showing the timing and flywheel bolt access plugs

The solution

Many ways to get that plug out with a hammer and some standard tools!

You may not need them all, this is only the list for all the techniques described below.

  • Allen key size 10 and 11mm

  • Hammer

  • Drill & drill bits

  • Punch set or one like 3/16"

  • Wood chisel

  • Grinder lock nut wrench

Let's back up a little before going into the various ways to get it out and see how to avoid stripping it in the first place: Break the plug loose when the engine is warm.

But remember, you have to wait until it has cooled down to do the valves.

If you've stripped the plug, don't worry, it helps to warm up the engine if it's cold and spray some penetrating oil like WD40 around the plug.

You need all the help you can get.

Option 1: Try to use that hole anyway

The goal here is to find a tool that could be forced into the hole so you can still apply torque. The original being 10mm, you can try the 11mm, but it pretty tough.

Hammer the tool in gently, as you can break the plug itself!

The key here (pun intended) is not to apply torque progressively but to give it a quick tap to break the seal's friction.

Note: Unfortunately, we can't use imperial hex keys to help here.

The 3/8" is smaller than 10mm, the next size up, 7/16" is already larger than 11mm, and the 13/32" isn't available in hex keys.

Option 2: Chisel it out!

Forget about the hex hole and try another tack.

Meaning, use more leverage by stabbing the chisel toward the outer edge of the plug. The goal is to plant it at a roughly 45-degree angle so you can hit it counter-clockwise to unscrew it.

This method seems to be the favourite among our DR community for its effectiveness.

Because you are hitting the plug directly, it helps break the seal created by the o-ring.

Option 3: Punch it nicely

If that didn't work, you could use the same technique with a hole and a punch.

Choose your drill bit and punch size accordingly. Drill a blind hole, again, on the outer edge for maximum leverage.

Be careful not to go through as you want to avoid dropping aluminum chips into the engine. When you drill right by the bevel edge like in the picture below, the o-ring is right behind it.

Using a 3/16" punch to unscrew a stuck plug

A few good thumps with the hammer will do wonders and might make that plug spin again like the chisel technique. You'll have more grip and less risk of slippage that might leave a big ugly scratch in your case.

Option 4: The grinder spanner move

By drilling two holes on the outer edge, you could also use a grinder/polisher lock nut spanner to break it loose.

You only have to drill the two holes large enough for the pins and measure the correct distance between them.

The holes can be a bit larger than the diameter of the pins to accommodate for drilling error.

The spanner method shown with a bicycle tool: an adjustable pin wrench

Option 5: The drill

If the first few steps have failed, this is the last resort and one you must do carefully to minimize bits of the plug going into the engine. If you are working on a barn find or a rusty pig, the engine plug may be seized in place.

To do this safely, take the whole left crankcase cover off the bike, place it on a stable surface and start drilling through along the diameter line, being extra careful toward the edge so you don't damage the case thread.

You will remove the two halves of the plug with a little tape of a punch and hammer at some point.


You will need a new plug (shown below), and not the OEM one again! Be sure to pick up a pair of valve cover o-ring as well, as they need to be replaced each time you check your valves (approx. every 12,000 km or 7,500 miles).

Both available in the store: Engine Plug and Valve Cover O-ring Kit

Note: If you need to check your valves now but don't want to remove the stuck plug or don't have the time right now, you can still check them using the following technique.

Remove the back sparkplug and slide down a straight piece of rigid plastic like a straw.

It will contact the piston head and move up and down as you are rotating the engine by moving the rear wheel in fifth gear. Use a stand or lift to get the rear wheel off the ground.

You can then use it to determine the Top Dead Center of the compression cycle to adjust your valves.

#stucktimingplug #flywheelaccesscover #valveadjustment #coverplug #engineplug

#magnetocover #crankcasecover #flywheelcover

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