Kennyt Posted September 17, 2015 Report Share Posted September 17, 2015 Z24 engine in 85 720. Replaced engine with an z24 out of my 83 720. Swap went well. Engine idled great and accelerated great. No noises. Engine ran fine for 2 days. The 85 720 had set for a few years with a blown head gasket before engine swap. Out of no where engine started skipping and a horrible rattle when depressing accelerator with no load sitting in park. Changed plugs wires and cap. All vacuum lines connected. Has original carburetor. Changed both fuel filters as well. No avail Pulled valve cover and inspected. No visible issues. Checked noise with stethoscope and seems to be coming from #4 cylinder exhaust valve side in head. Other than adjustimg the valves, does anyone have any suggestions on what the issue may be? All help greatly appreciated. Quote Link to comment
datzenmike Posted September 17, 2015 Report Share Posted September 17, 2015 Turn engine by hand and look at the valve clearances on the #4 intake and exhaust. Is one excessive, like really bad? Possibly you've dropped a valve seat. A compression test would show zero compression. Your '85 head would work for a replacement if this is the case. 1 Quote Link to comment
720inOlyWa Posted September 17, 2015 Report Share Posted September 17, 2015 What kinds of repair did you do to the engine with the blown head gasket before you put it into your truck? Quote Link to comment
paradime Posted September 17, 2015 Report Share Posted September 17, 2015 Could he have dropped a lash pad? Quote Link to comment
datsunaholic Posted September 17, 2015 Report Share Posted September 17, 2015 He put the '83 engine in the '85. The '85 engine has the blown head gasket. Z24s don't have lash pads. At least I never saw any when I had mine apart. Adjuster acts directly on the valve stem. But I second doing a compression test, but it sounds pretty severe if it's making noise AND not firing on that cyl. You might find mechanical damage to one or both spark plugs in #4, which could indicate you dropped a seat or broke a valve. Quote Link to comment
Kennyt Posted September 17, 2015 Author Report Share Posted September 17, 2015 Thanks everyone. I will do the compression test today and check valve clearances. Will post results later tonite. Again great forum with great tech support. Quote Link to comment
Kennyt Posted September 17, 2015 Author Report Share Posted September 17, 2015 25lbs compression on #3 and about and 40psi on #4. Looks like head job time. 1 Quote Link to comment
datzenmike Posted September 18, 2015 Report Share Posted September 18, 2015 Z24s are notorious for blowing the head gasket at about 100K. The fix is to prevent it by re-torqueing the head bolts every tune up. Quote Link to comment
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