madkaw Posted July 9, 2013 Share Posted July 9, 2013 I took the rocker and lash pad to my machinist. He kind of scratched his head on this one. As mentioned above- there could be several possibilities here. Guide not perfect Cam lobe not parallel to rocker He took the rocker to a true machined surface and laid it face down- lobe follower down against surface. He then used a dial indicator on the lash pad part of the rocker. Moving the rocker side to side you could see the lash pad area was not even across. You could almost make it out with the naked eye. So maybe I got 2 bad rockers? The lash pads measured square across the face . Possible fixes- replace rocker and worry about wiping a cam lobe on new rocker. Have the lash area grinded evenly across- if I can find where to do that. Tighten up the lash and see if this quiets things down Quote Link to comment Share on other sites More sharing options...
Lazeum Posted July 10, 2013 Share Posted July 10, 2013 (edited) Rockers are soft metal. You can grind them with a small cylindrical stone on Dremel type tool. If you can reproduce or use the method you've used with your machinist to check them, you'll be fine. If you're not perfectly even, it should be ok. They will wear out and become even over time. With mine, I can see the wear making the rocker tip to match lash pad area. Drawback is you have to carefully track valve clearance since it could change a lot in a very short time. I've done it every 100mi. for the first 500mi. Now it does not change, I can drive without any second thought! Mine are now very shinny, almost polished with lash pad contact pattern perfectly centered. Edited July 10, 2013 by Lazeum Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 10, 2013 Share Posted July 10, 2013 Thanks for the assurance. The wear pattern shows me the high spots so I know what to address. I think I can get them close enough, surely closer than they are now. Like you said, I could check them periodically for a while. What I didn't take a pic of was the wear pattern on the back side of the lash pad that sits on the valve stem. The other bad one actually shows uneven wear on the bottom side. Instead of a perfect circle wear mark , it's more of a half moon Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 13, 2013 Share Posted July 13, 2013 I tried addressing the rockers, but I decided to live with it after doing the first one. The more I thought about it, the more I realized I have a problem with this head that can't be fixed in this manner. Chalk this up to having a shop that does NOT have the experience with Z engines to have machined the head wrong. This wear pattern should have been checked during assembly. Though the rocker to cam wear is evenly spaced on the lash pad, the rocker was NOT evenly loaded on the follower surface . You can see the wear less on one side of the rocker. So either the cam lobes are not cut parallel with the head or the valve guides are not perpendicular to the cam. Whatever it is it makes the rocker ride unparallel between the two surfaces . This shows up more on the lash pads. Almost all of them show some extent of side loading . For now I have tightened the valve clearances and it did quiet the motor down. This head will go to Rebello this winter and hope its fixable Quote Link to comment Share on other sites More sharing options...
Lazeum Posted July 14, 2013 Share Posted July 14, 2013 (edited) That's a safe decision. Having experienced engine failure on the road, you're also buying some peace of mind while you would be driving your car in the future. It does make a difference. good luck! Edited July 14, 2013 by Lazeum Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 14, 2013 Share Posted July 14, 2013 Get another head. It's cheaper to start with a good Nissan core with straight valve bores than pay the price to bore oversize make new custom oversized guides....etc... Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 14, 2013 Share Posted July 14, 2013 That's a shame too- because this head has a lot invested, SS valves and some porting, ect... Quote Link to comment Share on other sites More sharing options...
JCan Posted July 14, 2013 Author Share Posted July 14, 2013 I wish you wouldn't give up! The tip of the rocker arm, should have a slight crown on it. The purpose of the crown is to ENSURE the rocker arm is both parallel to the cam shaft and touches the valve lash cap at one place in the center of the cap. This is why the rocker arm is made of soft material. AS you break in your motor, the rocker arm will mate to the lash cap as it self grinds down perfectly parallel to the cam. IT is a very simple job, just get 600 or 800 sand paper on a machine and gently grind the sufrace side to side so that you see a definite crown (think of the surface of a 4" diameter sphere. I guess that if you leave your rockers alone then they might eventually wear in to allow you to gap them properly. Best of luck! Jim Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 15, 2013 Share Posted July 15, 2013 Well I kind of gave up, but my issue is a bit different then yours. You issue was about a rocker that wasn't properly seated because the design of the lash pad. My issue is something in the machining is not true. Something is not parallel and the rocker grinding would be a bandaid fix. Someday when I put together another motor I will have the head re examined to see what the true story is. For now, I tightened the lash by .002 on every valve. It made a world of difference in the valve noise and the engine still runs very well, if not smoother. I appreciate all the help Quote Link to comment Share on other sites More sharing options...
skirkland1980 Posted July 16, 2013 Share Posted July 16, 2013 Well I kind of gave up, but my issue is a bit different then yours. You issue was about a rocker that wasn't properly seated because the design of the lash pad. My issue is something in the machining is not true. Something is not parallel and the rocker grinding would be a bandaid fix. Someday when I put together another motor I will have the head re examined to see what the true story is. For now, I tightened the lash by .002 on every valve. It made a world of difference in the valve noise and the engine still runs very well, if not smoother. I appreciate all the help So what was your final lash setting? Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 16, 2013 Share Posted July 16, 2013 ..006 and .008 cold Quote Link to comment Share on other sites More sharing options...
JCan Posted July 18, 2013 Author Share Posted July 18, 2013 Madklaw. Its really hard to mis-align valves and therefore I still believe your problem is caused by the person who dressed your rocker arms did it crooked. However... with the small gap you stated above, I would suggest you continue to check it every 200-250 miles or so till 1000 miles as your valves will seat and you dont want to burn them prematurely. I also expect that you will be able to gap your valves at stock specifications after 1000 miles due to the fact that I believe your rocker arms will also seat to the valves. Best of luck! Quote Link to comment Share on other sites More sharing options...
Josh280z Posted August 6, 2013 Share Posted August 6, 2013 I have to say I thought I wasn't going to have this problem with my engine build. I was using all stock parts and using the rocker arms exactly as they came off the head, cam lobe matched to rocker arm.... Anyways couldn't for the life of figure out why I had a LOUD tap, then I remembered this thread. So going on a whim I pulled my rockers and sure enough there were some with really bad wear, and were "wonky"(yes that's a technical term) So I replaced those with some good rocker arms, and the noise decreased..... Now if i could only get the valve lash set, and the gap would stay I would be golden. Oh well I guess I'll be looking into some new springs. Sorry to thread jack. Hope all goes well for you. Thanks for your experience. Quote Link to comment Share on other sites More sharing options...
JCan Posted August 6, 2013 Author Share Posted August 6, 2013 (edited) Josh. the reason the rocker arms are made of soft metal is so that it will seat into the lash pad. Remember, the old motors had a manditory 500 mile break in time.! Valve seats will wear in first, as they do, the gap gets smaller, then the rocker arms seat, when they do the gap gets bigger. Regarding gapping your rocker arms. Gap your rockers with the motor hot. be careful to gap only the valves which the cam lobe is pointed up (typically you can gap 4 rocker arms at a time, turning the motor 2 times to get all 12 rockers). if you are gapping at 8mils, bring out the 8 mil and the 9 mil metal spacer. when the 8 fits and the 9 doesnt, you have it right. This is time consuming. Once you have finished, your motor should run quiet. I dont believe you have a spring issue, Big springs are designed to work at high rpm not idle. As you drive, your motor will get louder, regap as requried then once at 1000 miles. Good luck! Edited August 6, 2013 by JCan Quote Link to comment Share on other sites More sharing options...
Josh280z Posted August 6, 2013 Share Posted August 6, 2013 I was just gonna go with new springs with a stock spring rate. Good thing to know about the feeler gauges, never though about doing it that way. I just used the normal method of setting the valve lash, had an old hot rodder show me how. I gapped them first cold ( 8 intake, 10 exhaust), then warmed it up and gapped them hot (10 intake, 12 exhaust), it's the only way to do it. I will put more miles on it and see what happens.... Quote Link to comment Share on other sites More sharing options...
skirkland1980 Posted August 13, 2013 Share Posted August 13, 2013 same thing here Quote Link to comment Share on other sites More sharing options...
JCan Posted August 13, 2013 Author Share Posted August 13, 2013 Skirkland. Your video is a great representation of what we have been talking about! You found problems with rockers that were dressed. At the time of my build i didnt know how important it was to check this. We will be interested to learn how your head sounds after you start and gap your rockers. Thanks again! Quote Link to comment Share on other sites More sharing options...
skirkland1980 Posted August 13, 2013 Share Posted August 13, 2013 Of the 12 I had resurfaced only 2 were noticeably bad. I'm going to have these corrected before assembly. Thanks to this thread I know to check this. I'm glad a found this. Thanks Quote Link to comment Share on other sites More sharing options...
madkaw Posted August 13, 2013 Share Posted August 13, 2013 That's exactly what my machinist did- didn't know if I got that across in my explanation or not. Some of my rockers were off .014 + in that little area , I should say most if them were off some what and 2 were off really badly. You can actually see the wear pattern on the cam lobes too. Great video and thanks for posting Quote Link to comment Share on other sites More sharing options...
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