SDgoods Posted March 19, 2014 Share Posted March 19, 2014 (edited) I just got my p90 back from the machine shop, who apparently took off .012 off the bottom and .010 off the top for a total of .022. I bought .030 shims as I figured after .012 was taken off the bottom, about the same was off the top. Now, in measuring the head height, im getting as low as 4.235" and as high as 4.240". According to a couple sources on this site, stock head height is 4.248. I'm using a matco outside mic that was calibrated in 2011, and measured my .030 shims at .034 (not sure if the mic is slightly off or the shims). 4.248- 4.235 = .013" (????) I was careless and didn't measure it before it went to the machine shop SO, in order to shim the cam correctly, do I go off what the machine shop told me, and stretch the chain .008" with the .030 shim, or closer to what my head thickness is telling me and shim a lot less? The numbers don't add up to the actual thickness of the head according to my mic. The machine shop measured is at 4.2345" (so it is accurate to my lowest reading) Any speculation would be great, as i'm lost at what to do! Edited March 19, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 20, 2014 Share Posted March 20, 2014 Now, in measuring the head height, im getting as low as 4.235" and as high as 4.240". Don't have an answer but curious if you mean that .005" is the range that you get measuring the same spot (your measurement error range), or if you mean that the head thickness varies by .005", from side-to-side, end-to-end. They're both bad, one means you're not sure what your measurements really are, the other means the shop didn't keep things very parallel and/or flat. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted March 20, 2014 Author Share Posted March 20, 2014 (edited) Don't have an answer but curious if you mean that .005" is the range that you get measuring the same spot (your measurement error range), or if you mean that the head thickness varies by .005", from side-to-side, end-to-end. They're both bad, one means you're not sure what your measurements really are, the other means the shop didn't keep things very parallel and/or flat. It must be my outside mic, it is probably not ideal for measuring the head. it's difficult to get a perfect, flat reading the same everytime. They are an experienced shop, and I do trust that they machined it flat, however, i'm very confused as to how shaving ".022" from a head thats originally 4.248" ends up at anything more than 4.226". If it were less, it would mean the head was previous shaved, or they shaved more than they thought they did. In this case, either both of our tools are inaccurate or they didn't shave as much as they said. Edited March 20, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 20, 2014 Share Posted March 20, 2014 I would doubt they cut the top of the head, then. I would imagine they decked the bottom and didn't cut the top, and just told you what you wanted to hear to get you out and not have to fix the mistake of forgetting to cut the top. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted March 20, 2014 Author Share Posted March 20, 2014 I would doubt they cut the top of the head, then. I would imagine they decked the bottom and didn't cut the top, and just told you what you wanted to hear to get you out and not have to fix the mistake of forgetting to cut the top. What??? They cut the top. They removed the remaining studs (?) on the head that were able to stay on ffor the bottom to be surfaced Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 20, 2014 Share Posted March 20, 2014 Back to your original dilemma, to trust the shop, or to trust your faulty measurements: probably best to get the right measurements before you do anything. You can't make a good decision until you know what you're dealing with. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted March 20, 2014 Author Share Posted March 20, 2014 Back to your original dilemma, to trust the shop, or to trust your faulty measurements: probably best to get the right measurements before you do anything. You can't make a good decision until you know what you're dealing with. I agree, my mic is not cutting it, I'm going to use a friends navy spec/calibrated tool. Ill post results when i get them Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 20, 2014 Share Posted March 20, 2014 Head usually measured on granite or other surface plate with height vernier/height gauge. Quote Link to comment Share on other sites More sharing options...
Gollum Posted March 21, 2014 Share Posted March 21, 2014 Are you sure the mic is perfectly aligned with the y axis? If not it's incredibly hard to get consistent and accurate readings. Also, not having a TRUE before reading means that this is ALL just conjecture anyways. I would never trust documentation 100%. Unless it was in a nissan FSM as part of a rebuild spec blueprint then it wouldn't really be even close to "gospel" and even THAT documentation can leave something to be desired at times. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted March 21, 2014 Author Share Posted March 21, 2014 (edited) The shop measured 4.2345" with whatever they used. Edited March 21, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
SDgoods Posted March 24, 2014 Author Share Posted March 24, 2014 Head usually measured on granite or other surface plate with height vernier/height gauge. Measured today on a granite surface with a height gauge, came in at 4.2380, so .010 variance from "stock". Should I even shim for .010?? Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 25, 2014 Share Posted March 25, 2014 How much do you value accurate valve timing? Quote Link to comment Share on other sites More sharing options...
SDgoods Posted March 26, 2014 Author Share Posted March 26, 2014 I managed to get a free set of .015 shims from silverseal because of how long it took them to ship my other ones! With .015, I'll be .005 raised from stock, which I think (hope) is marginal enough to be acceptable, compared to .010 below stock with out shimming. Thoughts? Quote Link to comment Share on other sites More sharing options...
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