[Supras] "mystery" bent valves

[berniek at technicaldevelop.com]

Hi list.

    I could not help but read with some head-scratching the subject of mysteriously bent valves.  Certainly the 7M is a non-interference engine.  However, iif it does jump time or if the belt shreds, the intake and exhausts come relatively close to each other if both are full open at the same time with the stock cams.  The effect would probably be more pronounced with longer duration and/or higher lift cams.  

    There could be a valve float condition in addition to the jumping of time, although it would be difficult to understand how the engine could run under such conditions.  Float will occur with fatigued springs, which are not replaced or shimmed after a valve job is done.  The redline for 88 and prior years was about 500 RPM higher than for 89 and later engines which used a fully counterweighted crankshaft, so valve float is a possibility in earlier engines.  From examination of two heads I have on the bench, it does not take much for the intake and exhaust valves to contact heads if valve timing is far off.  

    BernieK