Z32Dreamer Posted May 23, 2008 Share Posted May 23, 2008 Well I believe this is my first real post on here so If I botch it up to bad take it easy on me. When I bought the car (77 280z) it had a blown head gasket but still had compression. I took the head off to find that it was pretty warped and deffinatly could use a valve job. I sent it off to the machine shop where they put all new valves in and shaved the head. So now I have the head back and decided to put a new timing chain in while im in their. I put the new head on, set the number one cyl to tdc on the compression stroke. Then sat the head on it torqued it down to spec installed the cam sproket on the number 1 dowl hole. Then put the lighter colored chain link on the number one mark of the cam sprocket and the other light chain link on the crank sprocket that is maked. Now when I bring the no.1 cyl to tdc the valves are closed just as they shold be so I put the entire thing back together and go to crank it over and have absolutly 0 compression accross all cylinders. How is that possible? I have redone the same procedure as the book describes 4 times now with the same end result 0 compression. Any ideas guys or should I just part the car out? Quote Link to comment Share on other sites More sharing options...
woldson Posted May 23, 2008 Share Posted May 23, 2008 Did you hand rotate the engine before useing the starter? Is the valve clearence bigger now then when you set it? Quote Link to comment Share on other sites More sharing options...
katman Posted May 23, 2008 Share Posted May 23, 2008 I that an aftermarket timing set? I've seen them with mismarked crank sprockets. When you're at TDC on #1 according to your distributor and timing marks on the harmonic balancer, where's the cam sprocket notch relative to the tick mark on the cam retainer plate? And where are the cam lobes for #1 pointed? Quote Link to comment Share on other sites More sharing options...
JSM Posted May 23, 2008 Share Posted May 23, 2008 Just because the shop put the head togther doesn't mean they set the valve clearence correctly. Did you check this? Quote Link to comment Share on other sites More sharing options...
Z32Dreamer Posted May 23, 2008 Author Share Posted May 23, 2008 I that an aftermarket timing set? I've seen them with mismarked crank sprockets. When you're at TDC on #1 according to your distributor and timing marks on the harmonic balancer, where's the cam sprocket notch relative to the tick mark on the cam retainer plate? And where are the cam lobes for #1 pointed? The tic mark lines up dead on when the crank is at tdc and their is exactly 20 links between the two. The cam lobes for number one are set exactly opposite of eachother with the valves closed. Quote Link to comment Share on other sites More sharing options...
Z32Dreamer Posted May 23, 2008 Author Share Posted May 23, 2008 Just because the shop put the head togther doesn't mean they set the valve clearence correctly. Did you check this? Is their a sticky anywhere that tells how to chec and set the valve clearence. Quote Link to comment Share on other sites More sharing options...
Z32Dreamer Posted May 23, 2008 Author Share Posted May 23, 2008 I just ran accross another thread which brought something to my attention I had not thought about. When I was putting it back together I noticed their were some shims that went under the cam assembly. Could it be possible that I need to shim the cam up some more so that the valves can completly close. Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted May 23, 2008 Share Posted May 23, 2008 STOP! You really need to have a much greater understanding of what you are doing before you finish this job. Valve geometry is critical if you want the engine to not just run, but also to last an appreciable amount of time. You definitely need to get the How to Rebuild book and should probably get the How to Modify book. You can get them both together for $30.04 at Amazon. http://www.amazon.com/Rebuilt-Your-Nissan-Datsun-Engine/dp/1931128030/ref=pd_bxgy_b_img_b http://www.amazon.com/Modify-Your-Nissan-Datsun-Engine/dp/1931128049/ref=sr_1_2?ie=UTF8&s=books&qid=1211566578&sr=8-2 The shims are required to move the cam back to its original location relative to the crank if you shave the head. But this can move the cam away from the valves (similar to a regrind). When you move the cam away from the valves, you affect the wipe pattern on the rocker arms. This needs to be centered and is adjusted by using different thickness lash pads in the top of the valve keeper. The valve adjustment is done on the other side of the rocker arm with an adjusting nut and locknut. Hope this helps, Sam Quote Link to comment Share on other sites More sharing options...
Z32Dreamer Posted May 23, 2008 Author Share Posted May 23, 2008 So essentially if the machine shop decked or shaved the head and then did not adjust the valves by shimming the cam Up to adjust for the lower head hight... This would cause the valves to not close all the way hence why I am getting 0 compression. Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted May 24, 2008 Share Posted May 24, 2008 I don't know what the machine shop did. I have seen shops take a bent head and only machine the bottom. This leaves a curve in the top surface that binds the cam. In the case I saw, the camshaft snapped in half after a few seconds of running. Machining the L6 (or any OHC head) is not at all like machining a chevy V8 pushrod head (what most shops are familiar with). Quote Link to comment Share on other sites More sharing options...
katman Posted May 24, 2008 Share Posted May 24, 2008 Most shops don't bother adjusting the valves, they'll leave the rocker pivots low so the head can be transported without worry about bending the valves. You probably have no valve lift. Setting the valve lash is a post build, pre startup operation usually. You need a factory service manual before you go any further. Quote Link to comment Share on other sites More sharing options...
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