I went in to replace my water pump the other day and since that involves basically disassembling the front of the engine i figured while i was there i would replace the timing belt and the heater bypass hose. when trying to put everything back together i noticed the passenger side valve pulley was about 90 degrees off the timing mark and when i put it back to where it is supposed to be it was hitting on the top of one of the cylinders. Im not sure what happened i didn't turn anything, but anyway i pulled the valve cover off so i could loosen the rocker arms to put everything back in time. I noticed that everything under the valve cover is covered in some black substance. It looks and feels like it was powder coated. I wanted to know if anyone has seen this before. I think the car must have been over heated a few times and that is all burnt oil, but it has only overheated on me once and i replaced the radiator and it fixed it.

Thank you
Michael

 

Looks pretty normal to me... that's what happens as the engine gets old / high mileage. There are some oil additives that can help clean the engine... some are more effective than others.

Are your valve covers no longer the stock red color?

Famous "Never changed my oil" pic on the web:

 

No they are not painted, Where they originally red from the factory? It wouldn't surprise me if the previous owner did something funny. while working on this car i have found a lot of strange things. One of the best, is someone drilled a hole in the front axle bearing cap to pull them off instead of just using a screw driver to pop them off.

 

The original color of the rocker arm covers on the 1986 MY is a silver/grey, not red. The black on the inside is oxidized (aka, burnt) oil residue. It looks like the PO was not very vigilant changing the oil. Using an oil additive that de-carbonizes will reduce this or switching to a synthetic blend or synthetic oil will also clean this up over time.

 

red valve covers? mine are black as well;(1989) i bought a imported engine from Japan for the car and those covers are black as well. i plan on painting mine with a red wrinkle finish. as for the sludge build up, there is a product called RESLONE; it is a liquid detergent in a 10w30 base stock. use a quart of that every old change. it will slowly melt away that sludge. DO NOT use a motor flush! all that crap will drop to the bottom of the pan and screw up your motor. you want to slowly take away the mess, much of that shellac is now keeping your bearings clearances tight, wash it away, you'll have no oil pressure. keep in mind, synthetic oil is just motor oil refined one step further to take the wax out, which happens to be much of what you are seeing there. other than putting expensive oil in your pan, its a complete waste of time and money for what you need to do. BTW, 35 years of automotive experience here, not wanting to step on any ones toes.

 

I don't know Ken but I have had an 85 and two 86 every valve cover has been red. Are you talking about the plenum cover that has 300zx carved into it? the black residue looks pretty normal to me on an engine that old. no overheat needed. seen it on a lot more than a z31

 

All I know about valve cover color is experiential. All A/B series engines I've worked on have had the silver/grey covers (see photo of an early 87 VG30E). The VG30 in my 93 Maxima was a W series motor and it did have red valve covers. Perhaps the turbo engines switched to red covers at some point. I've never seen black on any VG30 that was USDM.