Engine lifetime

Discussion in 'Technical' started by Pando, May 2, 2009.

  1. 1) Which component(s) usually break first in an engine as a result of regular use, with the service program followed properly, over enough time?

    2) Which component(s) usually break first in an engine that is raced a lot, abused, driven on track days, etc. (however besides that, has had its service program followed properly)?

    3) Which component(s) usually break first in an engine that is brought way over its redline?
     
  2. 1. bearings, rings
    2. valvetrain
    3. valvetrain
     
  3. Interesting, what causes the valvetrain to break? Is it mechanical stress? Does it literally *break* or does it stop functioning as result of something else?
     
  4. well, valvetrain is the most frail part of an engine due to the complicated nature. valves are also directly above the piston so in modern engines the compression ratio is enlarged in whats called an interference engine, the valves travel down past the piston's tdc, this means that if youre revving the engine super high they can hit. valve float is also a sure killer, and happens when youre revving the piss out of something usually without a rev limiter since those ensure the engine cant rev to the point of self destruction. as for your last question, depending on the circumstances, valves can warp, bend or break altogether which means you cant have compression properly maintained. Valves can also be completely ruined so that they drop into the combustion chamber as a result of extreme stress.
     
  5. 1) So piston hitting the valve could happen because the timing is not made to handle RPMs way higher than redline -- when this happens the timing is so much out of sync that they can actually hit?

    2) Valve floating, I think I know what this is -- the springs are not strong enough to force the valves back up as result of too high acceleration? So given that this is true, it results in the same as 1)?
     
  6. valve float mainly occurs when you dont have sufficient spring force from your valve springs to keep the valve seated when lift is completed.

    but yeah, bearings, springs, first things to go I imagine. Areas with the highest loading.
     
  7. yes
     
  8. If valve floating prevents the valves from getting seated again -- then how can it hurt the valves themselves, if they are in the clear of getting struck by the piston that is?
     
  9. burnt valves, gases/fire/whatever coming out your intake, possible secondary effects of valve float.

    EDIT: and with that, if you get carbon build up and no valve rotation, you're gunna end up with a bad seal.
     
  10. As has been hinted at, heat is a huge issue with the failure of objects. Values being part in the combustion chamber will see higher temperatures than say the crank shaft. This is why you will see some hollow value filled with salts to help deal with the high temperatures.
     
  11. Also depends on the car.. Some cars just have certain weak points.. For example, Ive seen many stupid failures, because of people not paying attention.. Such as oil pump failures.. Or people not servicing their engines properly and it goes unnotices..

    2 big things not mentioned here(although not sepcific mechanical parts) has to do with the engines Tune and the oiling...

    Ive also noticed a lot of timing chanin failures, on high performance LSx motors, because people building them are ignoring bad harmonics..
     
  12. sodium filled valves are ace
     
  13. The valves are actually not filled with salt but the metal sodium. Sodium becomes a liquid during operation, and the movement of the liquid together with the higher heat transfer of sodium compared with steel reduce the valve temperature. High performance racing engines rarely used sodium filled valves though as sodium filled valves aren't as strong as normal valves. Instead, valves made from a superalloy, a high temperature resistant titanium alloy or titanium alumnide are used for the exhaust valve together with beryllium copper valve seats and beryllium copper or bronze guides.

    As for over reving an engine, several things can happen. Valve float can obviously result in bent valves and damaged pistons, but often the con rod snaps resulting in total failure of the engine. Too high engine speeds can also starve the big end bearings of oil, resulting in bearing seizure and often also a broken con rod.
     

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