Valve Colors

[afbrian13]

76 280z block, supposedly rebuilt head from early 80's maxima (which I didn't know)

 

Engine was running like crap when I pulled it out of the car. I just pulled the head off. 1st off, the 2 and 3 intake valves are white. Everything else looks fine under the head. A couple cam lobes, funny enough the same valves, are scored like they where running dry. I turned the cam with the head removed-this thing isn't going back on like this anyway, and all vlaves opened and closed like they are supposed to.

 

So what would cause just the intake valve to be white but the exhaust in the same cylinder to be black like the rest of the head?

 

Needless to say I'm going to check the entire engine electrical harness with a meter and FSM before hooking it to any other engine

 

Thanks

Brian

Edited December 22, 2010 by afbrian13

[280zjoel]

Usually if they are white or off white, it means that the engine is running too lean.

[KillerBjt]

I am just going to take a guess here, if you read the casting number on the bottom side of the head, it reads N47 right? In that case you most likely have a somewhere in the range of 10:1 compression ratio which would cause the lean condition but its weird that it is only on 2 of the cylinders. If its not a N47 then it probably has to do with oiling of those lobes, check the oil passages.

[roger280zx]

If you have dished pistons and a maxima head, ahem mn47;) you're around 9:1 maybe 9.5:1 compression, especially if the head was shaved during rebuild. Running that compression with dished pistons on crap gas is going to put the rings and valves through some wicked heat. I would suspect the valve discolloration is a result of this heat, as for the cam wiping??????? Maybe it was a result of a poor cleaning or rebuild, not sure. I hope a real engine guy can chime in and steer you better through this problem as I am a meer ammature.

 

Merry Christmas Hybridzers