was driving my sti7 jap quite hard last week, it seemed to be lacking in power, i thought nothing of it until i started it up about 1 hour after my run, the engine struggled to start and then did'nt run smooth and was making a loud knocking noise i checked the timing and noticed it had jumped 3 teeth, i put it back on the correct timing, the car now ran smooth but there was still a slight knocking!!(not as bad a before) i have now taken the engine out and removed one off the heads, the valves are fine but one piston has damage on it???? is this detonation damage? and what could the knocking be? would i be wright in suspecting main bearing damage??

 

Have you got a picture of the damage to the piston?
If you have an inprint of the piston crown on the relative combustion chamber of the cylinder head, i would suspect a big end failure.

Mick

 

don't have a picture, may be able to get one.
the damage to the piston looks like its been hit with a small chisel a couple of times, wright on the edge of the piston, both on the top and bottom of the face as you look at it, its puzzeling as there is no damage to the valves, i even removed the valves to inspect properly??

 

I've head that damaged valves only need to minutely bent (imperceptable to the eye) and they will continue to bend and relax as they open and close. Eventually, fatigue causes them to snap. I don't know if this is the case with your engine, but if you have the facilities to check them even more thoroughly it may be worth it in the long-term.

 

yeah, i should get the head and valves checked out by an experience engineer. thanks for that info!