Leak down test.

Hi all.. my aimless wandering through the chat and technical threads today had me wondering. Ive read about doing a leak down test to check the health of an engine as its supposed to be more accurate than a compression test. My engine is fine (or so I believe) but it is something I might look into in the near future. My question is what is actually involved in a leak down test? What actually happens? Are these tests expensive?

You can actually make a leak down tester yourself if your that way inclined, but its basically a valve rig with two pressure gauges, and a compressor to supply a constant pressure, I found this pic to illustrate the rig and test.

You supply a fixed pressure and then measure the leakage with the second, the % is important but its really a case of detecting where the main leakage (if any) is coming from, IE valve seats, piston rings etc.

Any garage that any good should be able to conduct the test, but the cost will be determined by how long it takes and their rates, the engine needs to be locked in the correct position for each cylinder as well, so not a short process.

Thats great Ricky. Very informative. Much appreciated. Its actually a little simpler than I thought it would be.

A fresh F3 engine is considered good at 1%. Takes a lot to achieve that! At 5% to 8% one is considered tired out!

A fresh F3 engine is considered good at 1%. Takes a lot to achieve that! At 5% to 8% one is considered tired out!

That's bonkers Chris 1% and how much power loss would there be from that to the 5%! Can't be that much surly

Enough not to win, or to be in with a chance of winning. The things run a restrictor in the air box, and no air filters, so the inhaled grit soon takes a winning engine to a runner up one. This isn't F1, look at how close the lap times ar for say the top ten.... They use every trick in the book to have as much power and torque as the restrictor allows, and maximize its usage from aerodynamics to mechanical losses.

Enough not to win, or to be in with a chance of winning. The things run a restrictor in the air box, and no air filters, so the inhaled grit soon takes a winning engine to a runner up one. This isn't F1, look at how close the lap times ar for say the top ten.... They use every trick in the book to have as much power and torque as the restrictor allows, and maximize its usage from aerodynamics to mechanical losses.

Blimey I can why motorsport is so expensive if the keep changing the engine out, cos they must cost a fare penny for a built engine,