Ben's Z Posted October 1, 2012 Share Posted October 1, 2012 Well I finally got lucky and got a good cylinder head back from the shop with a new valve job. The cam checked out to be ok. I did not have them resurface the rockers arms, is this a big deal? I have the "How to Rebuild your OHC Datsun Engine" and plan on freshening up on the cylinder head section this evening. The shop had to take 15 thousandths off the head, which I believe puts you right on the edge of needing shims, but they felt it may have been milled before, they don't know how much. How should I go about ordering cam tower shims? Any and all advice would be great. Quote Link to comment Share on other sites More sharing options...
kaito Posted October 1, 2012 Share Posted October 1, 2012 The machine shop should know how much its been milled. If they dont know the stock thickness then I wouldnt take my stuff to them in the future. You can get shims form ebay, and Im pretty sure you can get them at O'Reilys as well. You can aslo get a head saver shim, which is a big copper headgsket that is 20 thousands thick. I also have some shims in my garage. If you want I can send some to you in an envelope. Just pm me with a price if you want them. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted October 1, 2012 Share Posted October 1, 2012 You can re-use the rockers if you re-install the same cam, keep them on the same cam lobes as before, and you have not shimmed the towers. If you don't have the rockers numbered, consider resurfacing them before re-use. Quote Link to comment Share on other sites More sharing options...
Ben's Z Posted October 1, 2012 Author Share Posted October 1, 2012 The machine shop should know how much its been milled. If they dont know the stock thickness then I wouldnt take my stuff to them in the future. You can get shims form ebay, and Im pretty sure you can get them at O'Reilys as well. You can aslo get a head saver shim, which is a big copper headgsket that is 20 thousands thick. I also have some shims in my garage. If you want I can send some to you in an envelope. Just pm me with a price if you want them. He said they took of 15 thousandths, he thought it was close to 20 overall from new. Quote Link to comment Share on other sites More sharing options...
Ben's Z Posted October 1, 2012 Author Share Posted October 1, 2012 You can re-use the rockers if you re-install the same cam, keep them on the same cam lobes as before, and you have not shimmed the towers. If you don't have the rockers numbered, consider resurfacing them before re-use. Completely different set of rockers that are all mixed up that were not originally with the cam I am using. I am ordering new rockers, so that variable is gone correct? Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted October 1, 2012 Share Posted October 1, 2012 I cant find the spec but I think the oem thickness spec was 4.25" measured from the valve cover gasket to the head surface.Goto your local tool store and get 1 of those digital calipers.If you measure your head and subtract that measurement from the oem spec you will find what has been milled off.There is a mark on the cam retainer plate and a notch on the back of the cam sprocket.The notch on the cam sprocket should be even or slightly farther clockwise than the mark on the cam plate.If that is the case then the cam timing is not retarded .If it fails this check try advancing the cam timing with the extra holes in the cam sprocket.If you shim the head you will need custom lash caps on the valves-and this is a whole new set of problems.Been there done that. Quote Link to comment Share on other sites More sharing options...
madkaw Posted October 1, 2012 Share Posted October 1, 2012 Yes, I believe 4.25" is stock head thickness. I would make sure you find out the thickness incase you need to shim. One of the members here makes .030" shims in one piece(he makes the speaker kick panels). Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted October 2, 2012 Share Posted October 2, 2012 Completely different set of rockers that are all mixed up that were not originally with the cam I am using. I am ordering new rockers, so that variable is gone correct? MSA sells .015" cam tower shims. Given that your head may have had a prior mystery shave, probably a good idea. Somebody in Washington - Delta Camshafts? - sells refurb rockers for ~$4 a piece. Compared to NOS, I'd bet that is a pretty good deal. I purchased them for my top end rebuild and haven't had any issues. Most 'new' Z parts are awfully expensive. The headsaver .020" gasket that someone mentioned will correct your timing chain geometry, but will also sap your static compression. On the other hand, shimming your cam towers might alter your rocker geometry by shifting your cam lobe wipe pattern. 15 thou will not move the lobe pattern much, but it will a bit. Off the top of my head, the lobe pattern should move toward the pivot side since you will need to raise the rocker ends a bit to set your valve lash. Most people prefer to have the cam wipe towards the pivot end, though, so this would be a good thing and you can also reuse the stock shim pads. Quote Link to comment Share on other sites More sharing options...
Ben's Z Posted October 3, 2012 Author Share Posted October 3, 2012 So what should I do then? The headsaver, which I have not found or the shims? If the shop took off .015 and it had been decked before doesn't the head saver take care of all of my problems? MSA sells .015" cam tower shims. Given that your head may have had a prior mystery shave, probably a good idea. Somebody in Washington - Delta Camshafts? - sells refurb rockers for ~$4 a piece. Compared to NOS, I'd bet that is a pretty good deal. I purchased them for my top end rebuild and haven't had any issues. Most 'new' Z parts are awfully expensive. The headsaver .020" gasket that someone mentioned will correct your timing chain geometry, but will also sap your static compression. On the other hand, shimming your cam towers might alter your rocker geometry by shifting your cam lobe wipe pattern. 15 thou will not move the lobe pattern much, but it will a bit. Off the top of my head, the lobe pattern should move toward the pivot side since you will need to raise the rocker ends a bit to set your valve lash. Most people prefer to have the cam wipe towards the pivot end, though, so this would be a good thing and you can also reuse the stock shim pads. Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted October 4, 2012 Share Posted October 4, 2012 I'd do the shims myself, but you might as well go through the exercise with the headsaver. What is your compression ratio now? The Z Engine Calculator can help if you don't have it (search on here I think its pinned in the downloads section). Calculate your current compression ratio and then calculate it with the cc loss caused by subtracting the volume of the headsaver. Also depends on what the engine is for. I.e., if you are building a high performance/track engine you would also want to consider how the headsaver might effect cylinder combustion. If this is a stock rebuild using dished pistons, this probably wouldn't matter as much. Here on HybridZ there are no right or wrong answers, just lots of information available to help people make informed decisions. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 5, 2012 Share Posted October 5, 2012 I just re-used my rockers on a newly ground cam. Checked the wipe pattern and after adjustments and grinding of some of the pads all looked perfect. I guess its a big no-no, but from what I saw at install and a few inspections since - looks just fine. Although the cam I removed was nice and square, and there was no unusual wear on the rockers. Bigger problem was the adjusting pads / shims which are NLA. I had to order huge ones and have them custom ground to get what I needed for best wipe. Quote Link to comment Share on other sites More sharing options...
Ben's Z Posted October 7, 2012 Author Share Posted October 7, 2012 I asked the machine manager about about resurfacing the rocker arms. He said he didn't think it would matter if you kept them in order or not because they don't wear like a lifter on a conventional push rod V8. Anyone else have any input? The cam I am using is used as well and didn't need any work. I just re-used my rockers on a newly ground cam. Checked the wipe pattern and after adjustments and grinding of some of the pads all looked perfect. I guess its a big no-no, but from what I saw at install and a few inspections since - looks just fine. Although the cam I removed was nice and square, and there was no unusual wear on the rockers. Bigger problem was the adjusting pads / shims which are NLA. I had to order huge ones and have them custom ground to get what I needed for best wipe. Quote Link to comment Share on other sites More sharing options...
srgunz Posted October 9, 2012 Share Posted October 9, 2012 I have measured a few heads using the valve cover surface. Front, middle and rear and I get 3 different readings. I have to wonder if the valve cover surface is true front to rear? If not then I do not see how you can get the correct head thickness measurement. Are you guys saying your v/c surface are perfectly true and get the same measurement front to rear? We need a professional Datsun head builder opinion here. Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted October 9, 2012 Share Posted October 9, 2012 Some shops like to shave a head after it is warped instead of straightening. The head will be thinner on the ends and thicker in the middle. The combustion chambers will measure accordingly. Quote Link to comment Share on other sites More sharing options...
Xnke Posted October 10, 2012 Share Posted October 10, 2012 Ok, your machinist is not well versed in this kind of valvetrain...those rockers absolutely DO mate to the cam lobes exactly the same way that the conventional lifters in his familiar V8's do. You can take the risk if you want...but see another thread here for the possible outcomes. Quote Link to comment Share on other sites More sharing options...
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