SDgoods Posted February 20, 2014 Share Posted February 20, 2014 So I took my P90 head to get resurfaced, the machine shop took .012 off the bottom. I asked if the top was (presumably) warped because the bottom obviously was. He said yes, So I said well then don't I need to have the top resurfaced as well. He said "I've seen these heads come in with different size cam tower shims to account for the warping on the top" Is it me or is this just sketchy to do? He said its a lot more work to resurface the top because of the need to remove the dowels and such. If its acceptable to use shims to account for this, and there is an accurate and acceptable way to do it, I'd love to save the cash, however, it just seems like a bandaid fix, any input would be greatly appreciated, thanks! Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 20, 2014 Author Share Posted February 20, 2014 (edited) Well, according to a well known engine builder, thats the way to do it. Edited February 20, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
NewZed Posted February 20, 2014 Share Posted February 20, 2014 The shims or the top side resurface? The shims restore the height, but after the top surface is milled. The shims are all the same thickness. Shims plus top side resurface, not either/or. No pro though. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 20, 2014 Author Share Posted February 20, 2014 (edited) The bottom has been resurfaced. I was going to use shims anyway but since the top is warped i need to use different size shims on different towers correct? Per the fsm, as i was told by an experienced professional engine builder, that is the correct way to keep the cam straight and true Edited February 20, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
NewZed Posted February 20, 2014 Share Posted February 20, 2014 I don't know the correct answer. Using different shims under each tower doesn't match anything I've heard of though. I was referring to Tom Monroe's "How to Rebuild" book and Honsowetz's "How to Modify" book. They both describe milling top and bottom, and using shims to restore the camshaft to crankshaft distance. I've never seen a procedure for using different thickness shims, certainly not in the FSM. How would that even be done? The FSM says to replace the head if it's warped. Who is this experienced professional engine builder? Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 20, 2014 Author Share Posted February 20, 2014 Nick hunter, hes a friend of mine. Hes a nissan master/gtr tech and builds engines for moto iq/ turbonetics/ jim wolf/ dai yoshihara etc etc... Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 21, 2014 Share Posted February 21, 2014 I just had a P90 straightened. They heat it, then use a press to straighten it, then let it cool with the press still applying pressure. $130. Then I had my machinist just take a few thousands off the bottom for clean sealing surface. Since you have already taken 12 thousands off the bottom, then you also have to take the same off the top and shim the cam towers of the cam will bind. This is how I knew my head was warped, because I couldn't get the cam to spin freely. You will need either custom shims (there is someone on Hybrid that makes them), or use 2 sets of 0.05 shims. Also realize that your compression ratio will increase as well. Pete Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 21, 2014 Author Share Posted February 21, 2014 (edited) Double post Edited February 21, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 21, 2014 Author Share Posted February 21, 2014 I just had a P90 straightened. They heat it, then use a press to straighten it, then let it cool with the press still applying pressure. $130. Then I had my machinist just take a few thousands off the bottom for clean sealing surface. Since you have already taken 12 thousands off the bottom, then you also have to take the same off the top and shim the cam towers of the cam will bind. This is how I knew my head was warped, because I couldn't get the cam to spin freely. You will need either custom shims (there is someone on Hybrid that makes them), or use 2 sets of 0.05 shims. Also realize that your compression ratio will increase as well. Pete Hasnt my compression ratio already increased? How will resurfacing the top increase it anymore? If the top does get resurfaced, Can't i just shim the cam towers about the same amount as was taken off the metal? So if a total of .024 is taken off, can i shim it .030 ( msa shims)? For an increase of cam distance of .006 (assuming it hasnt been resurfaced before, which im going to find out) I was told again by the engine builder that it is and has been common practice to use different size shims. Im still iffy about that method though. Im a little frustrated with this shop as he didn't even state the pressure straigtening as an option. Quote Link to comment Share on other sites More sharing options...
NewZed Posted February 21, 2014 Share Posted February 21, 2014 (edited) It may be that it's okay for a really good builder to machine individual custom shims for each tower. If the guy you're talking to is the guy doing the work and stands behind it then why not. But if he's giving advice that other builders can't follow, there's a problem. You may also be getting advice about old engines from a guy that has only worked on modern ones. Edited February 21, 2014 by NewZed Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 21, 2014 Author Share Posted February 21, 2014 It may be that it's okay for a really good builder to machine individual custom shims for each tower. If the guy you're talking to is the guy doing the work and stands behind it then why not. But if he's giving advice that other builders can't follow, there's a problem. Hes not, the heads at a machine shop and i went to the builder for advice Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 21, 2014 Share Posted February 21, 2014 No, the CR won't increase any more after shaving the top. If you can get 0.030" shims, then that is the way I would go. Just verify your cam timing once you put it all back together. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 22, 2014 Author Share Posted February 22, 2014 No, the CR won't increase any more after shaving the top. If you can get 0.030" shims, then that is the way I would go. Just verify your cam timing once you put it all back together. The chain is wedged, so ill just put the cam gear on as it came off as I was going to do anyway. Thanks for your help. Quote Link to comment Share on other sites More sharing options...
Xnke Posted February 22, 2014 Share Posted February 22, 2014 Silver Seal makes 0.020" shims, which would be fine in this application. You don't use different thickness shims...you shave the top of the head. I don't know why you would attempt five different thickness shims...that's a LOT of work compared to a 20$ set of shims and a ten minute surfacing. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 22, 2014 Author Share Posted February 22, 2014 (edited) Silver Seal makes 0.020" shims, which would be fine in this application. You don't use different thickness shims...you shave the top of the head. I don't know why you would attempt five different thickness shims...that's a LOT of work compared to a 20$ set of shims and a ten minute surfacing. yeah, that was my concern. The top is getting resurfaced. Now, should I go with the .020 or .030 shims? There will likely be another .012 taken off the top I suppose the .010 will difference will let the cam gear slip on that much easier Edited February 22, 2014 by SDgoods Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 22, 2014 Share Posted February 22, 2014 12+12=24 using 20, you will be slightly slack (0.004") so you will have even less life in the new chain set you are using. using 30 you will be slightly tight, but the chain will stretch as you run it in just giving more life than you would otherwise get. On that kind of shave, I'd go for the 30's. Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 22, 2014 Author Share Posted February 22, 2014 12+12=24 using 20, you will be slightly slack (0.004") so you will have even less life in the new chain set you are using. using 30 you will be slightly tight, but the chain will stretch as you run it in just giving more life than you would otherwise get. On that kind of shave, I'd go for the 30's. Thanks for the input, ill go with the .030 Quote Link to comment Share on other sites More sharing options...
Leon Posted February 23, 2014 Share Posted February 23, 2014 So I took my P90 head to get resurfaced, the machine shop took .012 off the bottom. I asked if the top was (presumably) warped because the bottom obviously was. He said yes, So I said well then don't I need to have the top resurfaced as well. He said "I've seen these heads come in with different size cam tower shims to account for the warping on the top" Is it me or is this just sketchy to do? He said its a lot more work to resurface the top because of the need to remove the dowels and such. He's too lazy to remove a few dowels but wants to straighten the cam towers with different thickness shims? I don't get it... Quote Link to comment Share on other sites More sharing options...
SDgoods Posted February 24, 2014 Author Share Posted February 24, 2014 He's too lazy to remove a few dowels but wants to straighten the cam towers with different thickness shims? I don't get it... Yeah, it was kind of weird. Ended up getting the top surfaced for an additional $60, which I thought was fair. Quote Link to comment Share on other sites More sharing options...
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