Notes on dry sump engines

Listener Stuart Watson sent us this email discussing dry sump engines, and their benefits and design details. Stuart pointed us at this link for more information. The majority of road bikes use wet sump lubrication, the ‘sump’ being a pan beneath the crankshaft where the oil is stored. A pump picks it up from here and forces it around the engine into the various bearings, spray jets and so on. After the oil has passed through the high pressure part of the system it drains back down into the sump purely under the influence of gravity. It’s simple and inexpensive, but there are disadvantages. The first is the size of the sump. Usually this will have to hold around 4 litres, maybe more. This is quite large – look at a 5 litre oil can to get an idea – and clearly it has to be at the lowest point, so the engine has to sit higher than might be ideal. Under hard acceleration or braking, or when the going is very bumpy, the oil in the sump can slosh around. In extreme cases this can mean the oil pump’s pick up tube becomes open to the air, and air bubbles are passed around the lubrication system, causing a lot of wear and damage. But it also means the oil can wash up against the crankshaft, which usually spins just above the surface of the sump oil. This causes a lot of drag, reducing engine performance as well as causing the oil to become foamy, which degrades its lubrication abilities.
The alternative is dry sump lubrication. Instead of storing the oil beneath the engine it’s kept in a separate tank somewhere else on the bike – in the frame on the Aprilia RSV Mille for example, or in the swingarm on air-cooled Buells. This means the engine can be positioned lower in the fraSemi_dry_sump_1me (very useful with naturally tall engines such as the V-twins mentioned), and the problems associated with oil sloshing around are eliminated. It’s easier to increase the oil capacity this way too, which means extended service intervals. The penalty is increased complexity (and hence cost), as you now need a separate tank and two oil pumps. One pump scavenges the oil draining down to the bottom of the engine and feeds it up to the oil tank, while a second, more powerful pump takes oil from the tank and feeds it back into the lubrication system under pressure. Some bikes though use a semi-dry sump system, including many off-road machines as well as the BMW. What this really means is that the system is to all intents and purposes a dry sump design, with two oil pumps, but the oil tank is still incorporated inside the engine cases. In the F800’s case it’s still stored beneath the engine, but not directly beneath the crankshaft. It’s a little more complex but by doing it this way the designers have more scope for lowering the engine and making it more compact.

Episode 152: Still prettier than Repsol

Episode 152 - Still prettier than Repsol July 23, 2013

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Not just anyone can own and wear deer skin on their hands. No, wait... that’s not right. Anyone can. All you need to do is buy some Tour Master gloves. And that’s what Chris did. Again. Frustrated with affordable summer gloves that fit is oddly shaped mutant mitts, he went with what he knows and got another pair of Tour Masters. And he likes it that way!

Is Yamaha’s new parallel twin engine too big? Only James knows for sure. But he’s loving the new KTM390, so that should give you an idea. And speaking of right sized... Motus unveils the final production machines, and at almost 1700CCs of torquey monster power, surely that’s the right size to get it done, right? 

The guys wrap up the show by giving props to a very, very cool Ryca conversion on a $500 Craigslist Savage. Check out the pictures, but don’t get too close. It’s a Lycan, after all.

Review:

News:

Links:

Feedback:

  • John Ryder - Which bike for a tall guy?

  • Arno Jansen - What’s high mileage for a bike?

  • Stuart Watson - Chris, get a BMW!

  • Daniel Short - The Lycan, a Ryca conversion.

Episode 132 – “Motard” is just stupid

Episode 132 - “Motard” is just stupid November 18, 2012
News: Links: Feedback:
  • Thomas Hunt
  • Brent Tannehill
  • Russell Hoffman
  • Thomas Hunt - follow up
  • John Hopkins - follow up from last week
  • Christopher Lowe
  • Chris Ashmore
Info:
  • Theme song composed and performed by Raoul Lowe