IncompetentOne Posted May 21, 2013 Share Posted May 21, 2013 (edited) 1977 280z 2+2 non-California model I recently rebuilt my "engine" due to a blown headgasket and decided to replace the head as a whole while I was at it. It came off of a race car (owner claimed). It was straight as an arrow and was obviously shaved a good bit. Now it is on the car with a new Fel-pro Gasket (not sure of thickness). I tried to start it a few times but it would not turn over. It would only try to run on one or two cylinders. I then put a head on my shoulders and "finger checked" the compression of each cylinders. None at all. I then looked at the rocker arms and saw that all of the lash adjustments were as high as they could go. I wound them down until my wrench could not fit anymore. There is still zero wiggle room in the rocker arms though. I plan on buying some thin wrenches and taking them down more. But if that does not work I was going to buy these: http://kameariusa.com/L6_CamHolderSpacer.php They are cam holder spacers. I would buy the largest and just wind the rocker arms up to fill the gap but not so much to kill the wiggle room. Sound like a good idea? Anyone have any experience with these? Edited May 21, 2013 by IncompetentOne Quote Link to comment Share on other sites More sharing options...
Xnke Posted May 21, 2013 Share Posted May 21, 2013 You need a bigger cam! (smaller base circle) Babalouie has a few posts here...mostly on AusZcar or Performanceforums, but he had the same kind of deal. What head casting code is it? In all honesty, "I would buy the largest and just wind the rocker arms up to fill the gap but not so much to kill the wiggle room" is probably the worst idea you could have. It doesn't quite work that way. The cam rubs on the rocker arm across the inserted piece. If the wipe pattern is not centered up by using the correct lash pads, correct valve lash, and the correct valve stem heights, the valvetrain will destroy itself quite quickly...and fill your engine full of metal shavings while it does so. To do this correctly, you need to measure the thickness of the cylinder head, and check not only the deck surface for flatness, but also the cam tower surface. Most shops don't think to skim cut both faces of the head...which is needed if it was ever warped. Once you know the thickness of the cylinder head, add shims to bring the thickness up to ~108MM. The distance from the bottom of the cam towers (where they stack on top the cylinder head) to the top side of the headgasket, should be very close to 108mm. Once you have the camshaft in the proper position, you can measure for lash pads to fit your camshaft. Quote Link to comment Share on other sites More sharing options...
tooquick260 Posted May 21, 2013 Share Posted May 21, 2013 Xnke has told you everthing. Just for an example. I just put a P90 cylinder head on an L26. If I would have just bolted it on the compression would have been below 7.0 to 1. Way to low. So I had a 0.080 fly cut on the cylinder head. When I did this I had to put shims under the cam towers and buy new longer valves and some valve spring shims. This is to get rid of the slop in the cam chain as well as the lash for the rocker arms. There is a member here that sells these, Derek. Lives in Florida. I used the stock size bolts to bolt the cam towers on. My question is why do you not have any compression. Are your springs not tight holding the valves to the seats? Are the seats egg shaped out of round to release compression? How are your rings on your pistons? Was this head on a running motor or did you put a new cam on this motor? I.E. this is a totally new setup on the head and the head on the motor? Quote Link to comment Share on other sites More sharing options...
IncompetentOne Posted May 21, 2013 Author Share Posted May 21, 2013 (edited) The engine has no compression because most of the valves are always open. The new head is a shaved N42 and the old head was an N42 as well. The N42 block is still being used as well. What If I bought a new cam with a smaller base circle? then would it work? there is zero slack in the chain, the only problem is the rocker arms are ALWAYS applying pressure not allowing the valves to fully close. Also: would the link that I posted in the first post be the same as shims? If not then could someone provide a link to some solid shims that would do the trick? Edited May 21, 2013 by IncompetentOne Quote Link to comment Share on other sites More sharing options...
IncompetentOne Posted May 21, 2013 Author Share Posted May 21, 2013 (edited) http://www.thezstore.com/page/TZS/CTGY/PEM01 Which cam should I buy? I was thinking about the stage 3... Grind: 17034. Lift(In/Ex): .460/.460. Duration(In/Ex): 270/280. I still have to research exactly what each of these mean but It sounds about right so far. Edited May 21, 2013 by IncompetentOne Quote Link to comment Share on other sites More sharing options...
Xnke Posted May 21, 2013 Share Posted May 21, 2013 Please realize that if you do not correct the cam location, it won't matter what cam you use...the cam-to-crank distance needs to be correct or you need to do the math to figure out just how far off your cam timing will end up. My comment of the bigger cam relies on a very large camshaft profile....much bigger than you will want to street drive. Regardless of the cam profile, you will still have to correct the cam location in order to keep your engine from self-destructing. Quote Link to comment Share on other sites More sharing options...
IncompetentOne Posted May 22, 2013 Author Share Posted May 22, 2013 ah I understand now, cam has to be an exact height above the head/block so it does not grind itself to pieces. Thanks! Quote Link to comment Share on other sites More sharing options...
Xnke Posted May 23, 2013 Share Posted May 23, 2013 I would pick up the two books every datsun enthusiast that is working on a modified engine should have. they are NOT exhaustive texts, but there is a LOT of info in them. How To Modify Nissan/Datsun L-Series Engines, Frank Honsowetz How To Rebuild Nissan/Datsun L-Series Engines, Tom Monroe Both are available on amazon, both have a LOT of information in them. Quote Link to comment Share on other sites More sharing options...
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