Re: Damaged Valves & Pistons: Yes, no, maybe?

- S
- Scott
  
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posted
20 years ago

Wed, Aug 13, 2003 1:12 AM

My '94 T-Bird started running rough. The diagnostic scan pointed to a #6
> misfire. Sure enough, the #6 plug wire was shorting to another cylinder > plug wire. Easy fix. > > Unfortunately, the engine ran better, but was less than normal. Also, > saw lots of black smoke coming from the twice-pipes. Put the scanner > back on which showed the timing to be 20 degrees BTDC. Ten degrees BTDC > is much more preferable. One of those misfires cause a slipped timing > chain. > > Now, I wouldn't have a big problem having the two timing chains replaced > (and guides and sprockets) if it fer sure fixed the engine. However, > since it is an interference engine, I'm wondering if that ten degree > change caused any valves to have indiscreet, clandestine meetings with > pistons.

Your valves don't have indiscreet, clandestine meetings with pistons, if they come into contact you will know it.

- G
- getupand
  
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posted
20 years ago

Wed, Aug 13, 2003 3:19 AM

Thanks to you and Scott for replying.

Fairly much what Scott implied. While I am not mechanically challenged,

I don't get under hoods unless necessity dictates. I do not have the

empiricism to know if a slight timing change would allow a valve to make an only slight contact with a piston where it would still run but would cause performance damage (e.g. bent valve stem). I never heard any sounds of damage.

I had stopped but after some rudimentary investigation. While it was running with ample exuded black smoke (both exhausts), I heard at the tailpipes the "phhht, phhht, phhht" sound of open valve(s), seemingly only at the right bank. That with the OBD-II scanner timing readout led me to believe the timing was changed. Until the misfire (#6 wire to #3 wire), the engine was running just fine (66K miles). No diagnostic codes registered after I cleared the misfire code.

- T
- Thomas Moats
  
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posted
20 years ago

Wed, Aug 13, 2003 10:40 AM

You can advance the timing to 30 degrees, the pistons will not hit the valves. The mechanical timing between the crank and cam does not change.

Black smoke is an indication of a very rich mixture. A bent valve will not cause that. The sound you hear is because of poor cylinder contribution ( you even indicate the engine is not fully correct in running only better ) most likely caused by an over rich condition. The fuel pressure may be way too high. When changing wires you may have knocked off or left loose a connector. Also I hope you did not just replace #6 wire, but all the wires and plugs. The problem is most likely going to be where you have been ( replaced wire ), look there.

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