I have a brand new 2008 Mazda3 that has already had the engine replaced because the valves bent and now the replacement engine has the same condition (bent valves). Only 762 miles on the car (410 on the first engine) and now the manufacturer tells me they wont fix it. They claim I have over-revved the engine or missed a shift and caused the damage.

 

Chances of you getting the exact same quality condition on 2 separate engines is pretty slim.

About the only way to bend a valve is to over-rev it (beyond redline) and cause the valve to "float" (speed of opening valve exceeds the spring force available in the valve spring.) If you float a valve, the piston can contact it and bend the valve. (This is true of any engine.) High revving performance engines have dual or triple valve springs to create sufficient spring load to prevent valve float at high engine speeds.

 

I have absolutely baby'd this thing since the replacement engine. I think there is something else wrong with the timing or control computer.How can I prove to the manufacturer that I havent damaged it. Better yet how can they proove that I have?

 

They can read the ECU log which should tell them whether the engine has been over-revved.
I think you would have a very hard time trying to prove you didn't damage it, but they should have to prove that you did, imo.

 

What kind of codes would it show? Honestly, how can you over-rev these things, don't they have systems in place to prevent this? I can't believe if you miss a shift or accidentally over rev your engine it causes catastrophic engine failure and requires the engine to be replaced.

 

Ihave read that the ECU logs the max rpm reached. Also, the redline is 6500 on these engines, but the rev limiter does not activate until 72~73k, so it's possible to run the engine past redline, andit's possible to run the engine in a lower gear for extended periods of time which may (ormay not) cause excessive damage. Certainly excessive wear.