Engine Autopsy 1–What Happens When a Bike is Starved for Oil?

Recently, several riders have brought oil-starved bikes into the shop–whether they were new riders or simply neglected to check their oil level for too long, the results have been uniformly disastrous. Motorcycle engines tend to rev high and hot, and like other internal combustion machines, an engine’s metal-to-metal contact points need a consistent film of oil lubrication between moving parts, whether those parts are bearings, camshafts, or piston and cylinder. When the oil level drops below a certain level, it spells certain doom for the bike’s motor–possibly with terrible consequences for the rider. In this case, the V-Strom’s owner ignored the low oil light for approximately 2,000 miles before the bike “began to make a terrible rattling noise” and breathed its last. The unmistakable rattling noise and the sparkling bits of metal in the oil confirmed to us that the motor was in bad shape. Turned out that the engine was damaged beyond repair; we found a replacement engine and installed it, and the rider learned an expensive lesson in responsible bike maintenance.

Riders–remember to check your oil level and keep your bike filled to the appropriate level! The engine is the heart of a bike, and oil is its lifeblood.

The engine from a 2007 Suzuki V-Strom 650--the same bike featured in the oil change tutorial This one, however, was ridden by its uninformed owner until it was dry of oil

Another view of the V-Strom engine--note that the front cylinder has already had its valve cap removed in an effort to diagnose the problem.

It’s painful but fascinating to dig into a ruined engine like this and do a sort of autopsy to discover which parts failed. This is the normally very robust vee-twin engine on the lift, ready for disassembly. It’s a messy, dirty job, so I’ve got gloves on and plenty of rags and a pan on hand to catch spills.

Vee-twin top view, with water pump and coolant hoses intact

First I loosened the bolts and eased out the starter motor.

Out comes the starter motor

Next, off came the valve cap on the forward cylinder head, and then I removed the camshaft journal covers. In both cases, the caps should be removed in a star pattern to prevent the aluminum from warping as it is removed.

Removing the camshaft covers

In order to loosen the cam chain and remove the camshafts, the cam chain tensioner needs to come off first.

Removing the cam chain tensioner

At this point, the camshafts are exposed, and the cam chain is loose and can be pulled off, releasing the camshafts. The cam lobes, which rotate and push the valves open and closed, are vulnerable when the bike’s oil runs dry, as are the camshaft journals, which turn inside their bearings in the engine head. Upon inspection, though, the entire surface of both the intake and exhaust camshafts showed no evidence of wear or galling, a testament to the toughness of the V-Strom engine.

Pulling and inspecting camshafts

With the camshafts removed, the valve tappets (or buckets) are exposed, easy to pull with a pair of needlenose pliers or a magnet. Since the V-Strom uses a shim-under-bucket valve design, each shim sits on the underside of each tappet. The small shims require care and a deft hand to avoid dropping into the engine, a bad scene if you’re doing a valve adjustment.

Pulling valve tappets

Generally, as here, the small shim adheres to the underside of its tappet, and comes out with it.

Shim, stuck under under its bucket with a thin film of oil

With the camshafts, tappets and shims gone, the valve ends and the tops of the valve springs can be seen.

The four valve ends and springs

The head bolts came out next–that took a breaker bar.

Using a breaker bar to remove the head bolts

The intake and exhaust valves showed no obvious signs of being bent, a frequent result of oil starvation.

Underside of the head, showing intake and exhaust valves

Now that the head was off, the cylinder and piston face were visible.

Cylinder and piston face

With the head bolts out, I was able to pull and inspect the cylinder.

Jug and cylinder

The interior of the cylinder shows some scoring.

Scored interior of the cylinder

Normally, the piston rides up and down the cylinder in a thin film of oil. But when the oil is gone, there’s direct metal-to-metal contact as the piston begins to scrape and gouge the cylinder–and you can see the results.

Cylinder scoring

The piston skirt had signs of scoring beginning to show as well. If the engine had not been shut off when it was, the gouges would have deepened in both the metal of the cylinder and the piston, eventually breaking one or both, or melting them together and seizing the engine.

Scored piston

More piston damage

I repeated the process with the other cylinder.

Rear cylinder cap removal

Second piston face

Cylinder #2 removed

Rear cylinder looks less damaged than the front cylinder

This piston, too, showed little to no damage, unlike the front cylinder’s piston.

This piston looks relatively ok

Another view of the piston

The two rear cylinder camshafts were in fine shape, as well.

Rear cylinder camshafts, undamaged

After the cylinders were removed, the stator cover was next.

Stator Cover

With a bit of convincing with the deadblow hammer, the stator cover and stator came away, resisting as the flywheel magnets attempted to hold the stator in place.

Stator cover, pulled, showing stator coils on right and flywheel on left

With the stator cover off, I flipped the engine over to take off the clutch cover on the other side.

Clutch cover

The clutch cover came off more easily, showing the clutch basket beneath.

Clutch exposed

And next, I unbolted the clutch basket itself and removed it.

Removing the clutch springs to free the clutch basket

Now with the friction plates and steels out, the basket lay beneath. I pressed down the folded-up tabs of the washer holding the nut and friction bearing, and took them out.

Clutch plates out, and friction bearing exposed

With the clutch basket gone, the deeper parts of the crankcase are exposed (the plastic gear is the oil pump gear).

Beneath the clutch

With the top end of the engine (cylinders, valve head, camshafts and covers) apart, and the side covers, stator and clutch removed, it was time to get into the depths of the crankcases and see what damage had been wrought in the engine’s bottom end–which I’ll cover in the next post.

4 thoughts on “Engine Autopsy 1–What Happens When a Bike is Starved for Oil?

  1. Awesome page was just looking for some help on repairing the top end/ bottom end on a kx 125 that ran with no oil. Found this page very helpful! cheers

  2. Nice blog. To occure damage, how much less oil an engine need to be damaged? I was running my new bike with the oil just a little bit over the minumum mark and i realy got worried. I just added around 300ml almost to full.

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