Ben's Z Posted January 13, 2013 Share Posted January 13, 2013 My cam spin and head troubles are well documented on this forum. I mentioned in an another thread that my cam wasn't spinning like my old one so I took to a highly recommeneded shop here in Houston. Lead machinist is a former Z owner and has done numerous heads for the local Z club and he said my cam is fine. I did end up having a shop before that clean up the top of the head (.012) at everyones suggestion on here and that helped the cam spin better. Shop number one just did the piston side of the head. I was setting my cold lash on the bench today and for some reason I couldn't get #1 (front) exhaust any more than .007 lash with the pivot all the way down. I tried swapping in some different pads with the same results. I turned the head over to get a look at the combustion chambers and I noticed that the valve is sitting a little deeper in the seat than the rest. I had machinist blue on my rockers and while my wipe pattern has changed from before having .012 taken off I am not running off the end of the rockers with the lobes. Is this ok, or does it need to be centered more? Running my '77 N/A cam if that matters. All other valves intake and exhaust are fine. Knowing this wipe pattern and my problem with what I believe is the exhaust valve seated too deep, should I consider changing all of my lash pads or just exhaust valve #1 pad? Thanks. Quote Link to comment Share on other sites More sharing options...
Ben's Z Posted January 15, 2013 Author Share Posted January 15, 2013 Should I take out that valve and have it cut down? Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted January 15, 2013 Share Posted January 15, 2013 You should have rebuilt the head right first put seats in it and set the valve hight right , but now its cut the valve to make it work Quote Link to comment Share on other sites More sharing options...
ozconnection Posted January 15, 2013 Share Posted January 15, 2013 (edited) I've had this happen to me on one of my N42's. Stock cam, retainers and lash pads. My solution was to grind the contact face on the rocker arm where it rides on the lash pad. You don't need to take off huge amounts, grind it parallel to the long axis of the rocker arm and then polish the surface when you're done. You will need to check that there is no contact between the underside of the rocker and the edge of the retainer after this mod. If it does touch, youll need to notch the rocker arm where it touches. Polish the scar after you've made it or it will become a stress riser. If you get it wrong, grab a spare rocker arm and start over. I got it right the first time, a grind, then check geometry, another grind, check again etc etc etc. till I had the right wipe pattern and correct lash with the same pad as all the other valves. Absolutely no issues whatesoever with this modification. PS, Heaps easier than cutting the valve. That's a big job compared to my simple fix. Edited January 15, 2013 by ozconnection Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 15, 2013 Share Posted January 15, 2013 (edited) Cam tower shims are 0.015" thick, seems that would be the easiest cobble to add to the mix at this point. It gets you back adjuster height wise or near close to it Pre-0.012" top cut. You cut 0.012", plus whatever they cut before on the bottom, adding a head saver shim of 0.015" would get timing chain slack back where it should be somewhat... Edited January 15, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
JCan Posted January 16, 2013 Share Posted January 16, 2013 I just spend 3 weeks with my head trying to determine why I could not (set the lash?) adjust the gap between the cam and the rocker arm. It is my humble opinion you should NOT grind a substantial amount of material off your rocker arm. I had mine re-shaped (which probably removed 0.001 or less of material.) I like the idea of using a cam tower shim, however once you do this, you are going to have to check how the cam rubs against the rocker arm to ensure your geometry is correct. (it is easy, get a sharpie and blacken the rocker arm and check the wear after one revolution) In general, when you change a cam one has to review the cam/valve geometry to ensure it is correct. A shop adjusts this by changing the thickness of the lash caps. The lash caps on my car vary approximately 5mils (from ~0.150 thick to ~0.160 thick). As an alternative to the above, You could chose to grind down your lash pad 0.010 which would give you a max gap of 0.017 and allow you to achieve a 0.008-0.010 gap. Please note that if your lash pads are stock they are probably ~0.120" If you do this, I suggest you do have the rocker arm resurfaced so that they can mate properly. Jim Quote Link to comment Share on other sites More sharing options...
Xnke Posted January 16, 2013 Share Posted January 16, 2013 (edited) As I said in your other thread, you will need to adjust the valves several times in the first few thousand miles...and they will get tighter before they get looser. If you can't get the cold lash on a new head, you're stuck. I think I adjusted mine every thousand miles for the first 12-14K, and they were tight every time. the last two valve adjustments have come out clean, no adjustment needed, so I think I may have reached the "level" spot in the valvetrain life curve. I'll probably be a few thou tight next oil change, since it's been two oil changes now and they haven't moved. Edited January 16, 2013 by Xnke Quote Link to comment Share on other sites More sharing options...
JCan Posted January 17, 2013 Share Posted January 17, 2013 Xnke. Do you know what causes the valves to get tighter? Heat maybe? I am happy to say that the valves are finally behaving in my setup. they are much quieter than my fuel pump, unfortunately the car is a bit loud ( I went overboard with the cam ). regarding valve adjustment period, you are saying as they seat, they get quiet before they open up. When I was a kid, we adjusted the valves 3 times (cold, hot, then after the first 1-10 miles). Then we drove 100miles and varied the RPMs 0-5500, and adjusted the valves, then we drove the next 900 miles being sure we varied the RPM 0 to 7000 RPM being very careful not to stress the engine as we wanted the rings to seat at high RPM. we adjusted the valves, air fuel mixture, timing. At this time we considered the engine broken in. Keeping on topic, Valley head service (the folks that worked on my head) numbered and adjusted the thickness of each lash cap independently as they adjusted each rocker arm / cam geometry. I really like this technique and (in my opinion) applies to Ben'z problem. Quote Link to comment Share on other sites More sharing options...
JCan Posted January 17, 2013 Share Posted January 17, 2013 (edited) . Edited January 17, 2013 by JCan Quote Link to comment Share on other sites More sharing options...
Xnke Posted January 18, 2013 Share Posted January 18, 2013 Valves get tighter because a newly cut valve and seat will recede rapidly at first, then will be "mated" and will wear much more slowly...the cam lobe and rocker will wear together at a much slower rate than the new seat, which is usually a work-hardening material nowadays. The seats are actually soft, and harden by the impact of the valve seating on them, at least in modern seat materials. Basically you will see a period of rapid valve recession and the valve lash closing up, followed by a pretty abrupt change to little lash change on a properly adjusted system, then you'll start to see valve lash open up again, as the cam-to-rocker and rocker-to-lash-pad interfaces start to wear faster than the valve recedes into the seat. Quote Link to comment Share on other sites More sharing options...
JCan Posted January 19, 2013 Share Posted January 19, 2013 Xnke - I hadn't thought about the seat! Thanks for the heads up! I'll be sure to look at the valves more often to ensure they are gapped properlly. Quote Link to comment Share on other sites More sharing options...
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