Quote:
Originally Posted by ah-kay
I am not a heavy engine guy but this is what I know. BTDT the hard way.
1) It is very unusual not to have bent valves as it is an interference engine. You were driving slow so you may have dodged a bullet.
2) The scratch on the cylinder wall could indicate a broken compression or oil ring. I had the same scratch on an OM603 engine. You cannot tell unless you push the piston out.
3) Need to find out why the chain snapped. Chain fatigue or something in the way and snapped it.
Other may chime in. Hope this help.
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the reason the majority of motors with valve contact result in bent valves is the valve angle is often canted and the valve face contacts the piston at an angle, resulting in a bend.
the 61x design engine (and others I'm sure...) has a nearly perfect flat valve angle to the piston face. so, when valve and pistons collide, they slam full force into the cam... instead of bending the valves. on the turbo motors, the valves nearly always need to be replaced after contact, as the exhaust valves are hollow, filled with sodium. but the NA motors have THICK solid valve stems, and rarely get damaged from contact.
the piston on the other hand, often gets banged pretty bad, and the dent sometimes makes that piston unusable, depending on how many times the contact is made...