P79 head mod

[Mark Maras]

  Compression looks good. My theory on advanced ignition timing (detonation) causing oil smoke is the fuel mixture is igniting before the pistons reach top dead center. This would cause excessive pressure on the rings allowing oil to blow by. I'd back off the timing or increase the fuel octane to ELIMINATE all pinging and or detonation and drive it. Detonation will eventually destroy rings.

[Reptoid Overlords]

I have my BCDD plugged at all the vacuum ports. It isn't fully removed and replaced by a block off plate at the throttle body. I'm using a bare bones '77 manifold, again, on a federal model '80 ZX.

This weekend, or most likely today after work, I am going to look into experimenting with how to hook it back up, and see if it's ability to change manifold vacuum changes anything as far as smoke goes.

Driving it to work again, with timing down, it seems to be producing the best results I've had since I got it running. Minimal smoke as far as I can tell. Perhaps I can eliminate it completely.

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[Reptoid Overlords]

I put a vacuum line on the BCDD from one of the larger ports, forward of the throttle plate, to a vacuum port on the intake manifold. All the other ports on the BCDD are plugged.

 

I'm not entirely sure if what I have done is indeed reactivate the BCDD. It may be that I've done absolutely nothing.

 

At any rate, I tooled around town and on the freeway for about an hour, during evening rush hour, and never saw any smoke. I was not hard on it this time. Not sure if something is settling in, or, more likely the case, retarding the timing as advised has created less vacuum during the combustion process.

 

I thought I had lost my vacuum checker, but I remember I loaned it to a friend. He will return it tonight and I will get a good vacuum reading. In the meantime I'm going to change the oil as I'm at 100 miles since I put it all back together.

 

The Z got to irritate some Leaves at the Nissan dealer while I got an oil filter.

 

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[Reptoid Overlords]

I told myself I would just relax and not do any car stuff this Saturday.

 

Another car guy friend stopped by and before you knew it, we were tearing down the old N42.

 

Does the blue stuff on the deck look like some sort of coolant stop leak? It's all over the head gasket too. There is evidence of head gasket failure around a water jacket mid deck.

 

The no1 Piston rod bearing has a big scrape in it, and numbers 5&6 have uneven scoring. Oddly, the Piston rings look barely worn.

Also, there's some weirdness going on in the water pump housing.

 

I'm glad I took it off the road. It might've been bad if I kept running it.

 

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