datzenmike Posted November 2, 2014 Report Share Posted November 2, 2014 PCVs were installed on all N Am vehicles around '62. Chevy owners just drive them. Old chevys had better cams that the late '70s. GM used exotic metals and manufacturing to make them cheaper but it relied on the owners keeping to strict oil changes. GM should have known that people got used to the old cams and rarely changed the oil, so at 50K they were toast. Changed a buddy's '79 MonteCarlo 265? cam. All were worn down some were perfectly round. My '79 Olds 305 same thing and the tappets were cupped and mushroomed. The wear was unbelievable. Easy enough to get a caliper on the lobes and check them. Lobe height on a Z series cam is 1.515" to 1.517" The wear limit is about 0.001" but that is less that the thickness of a piece of paper on the actual valve lift. It would take a lot of wear to notice any difference in performance. 1 Quote Link to comment
720inOlyWa Posted November 4, 2014 Report Share Posted November 4, 2014 Great info, all. Thanks. I didn’t notice any cam wear when I replaced my head gasket, but I didn’t mic the lobes, either. I just cleaned and looked. In fact, when I replaced my head gasket, I didn’t have any head work done at all, which I now regret. I just removed the cam tree and gently shaved the head face on a glass plate with 400 grit wen and dry paper contact cemented to it. It cleaned up flat with about a dozen strokes, so I figured it was not too badly warped. The valves looked okay ad the engine only had 560k, so I (carefully) slapped it back together. The reason I make this embarrassing admission of cheapskatedness is that I know better now. By morning, a little oil has dripped past the guides, making the first crank rotation slow and stiff. Oh it runs great now and I am sure it would continue to do so for a long time, just as it is. But, for the money, having the valves ground, guides replaced, cam checked, etc., is just about the best money you could spend on one of these little trucks. When I do a zero time rebuild on it next summer, you can bet that the head is going straight to the machine shop- whether it needs it or not. Cheap has its limits. Quote Link to comment
trjerm Posted November 4, 2014 Author Report Share Posted November 4, 2014 Well today, I adjusted the valves while engine was warm and loosened (1@a time) the head bolts and retorqued to 61 ft/lbs. Yesterday I lubed the throttle cable and the throttle linkage and went thru the vacuum lines. It runs GREAT, idles @ 950 rpm and the choke and high idle seem to work as designed and it seems to run better through out the rpm range. It's fun driving around a Nissan in a sea of yota's up here in the Sierra's. 1 Quote Link to comment
datzenmike Posted November 5, 2014 Report Share Posted November 5, 2014 The head bolt re-torque is done on a cold engine. The metal will expand when warm and you won't get the correct torque. The valve guide seals can easily be replaced with the head on the engine. A few feet of nylon rope in the cylinder and turn the crank toward TDC on the compression and the rope will prevent the valves dropping into the cylinder. 1 Quote Link to comment
trjerm Posted November 5, 2014 Author Report Share Posted November 5, 2014 I retorqued the headbolts probably 2 hrs after I turned it off, so hopefully it was cool enough, and The machine shop install the valve seals after doing the valve job. Quote Link to comment
pesegu Posted June 8, 2015 Report Share Posted June 8, 2015 Will this work for the Z24? http://www.amazon.com/Alltrade-648831-Nissan-Timing-Holding/dp/B0002Q8TV4 1 Quote Link to comment
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