dapiper Posted March 24, 2006 Share Posted March 24, 2006 Just determined my P90 destined for stroker build is humped 0.010" (concave up) and machinist wants to heat to 300F and clamp to straighten to avoid removal of 0.010" off both cam and block surfaces. I am doubtful it will straighten and worried about loosing temper and loosening seats. Anyone have experience with this? Quote Link to comment Share on other sites More sharing options...
Guest Evil280ZX Posted March 24, 2006 Share Posted March 24, 2006 I don't know about heating the head to straighten it out. I have never done it before. But what is wrong with shaving? I have shaved .080 from my P79 head and have had no problems. It's the same as the P90 except for the exhaust ports. And only shaving .010 you will not even need to shim the cam towers up. hth Quote Link to comment Share on other sites More sharing options...
technicalninja Posted March 25, 2006 Share Posted March 25, 2006 Machinist probably doesn't know that cam tower shims are available for the L-series. Machining .010 off of both sides is totally acceptable and the cheapest way to go. You will need 1 set of shims. On the other hand- Heating an aluminum head for straightening is also a normal process and it usually does not disturb the valve seats. They only heat it to 325-375 degrees and the hot head is usually placed in a press and "reverse bent" approx the same amount it is warped and allowed to cool in the press. A really good machinist can get one very close to straight. It will still need to be milled after this process is complete. Unless it is milled a very shallow amount it will need to be milled on the upper surface as well to ensure that the cam towers are in the same plane with each other. So either way you will most likely end up needing a set of cam shims. A large precentage of aluminum OHC heads run the cams directly in the head and this straightening process can be mandatory to fix warped heads. It keeps the cam bores in line and it reduces the amount that must be milled off the head which keeps the cam centerline the proper height (as a head is milled the cam drops in regard to the crank and cam timing retards as a result). The L-series is one of the "unique" heads that has the ability to manipulate the cam height with shims. Your machinist is giving you good information generally. He may not be familure with the L-series and its quirks. One other reason for limiting the amount of milling is if it is already at a high compression ratio and you don't want to go any higher. Quote Link to comment Share on other sites More sharing options...
dapiper Posted March 25, 2006 Author Share Posted March 25, 2006 I have a spare set of shims, but still worried about hardness temper of head. Another machine shop "straightened" a head for my old '88 Mazda 626 Turbo which was warped 0.022 after my wife ran it out of coolant. They overheated it or something and the head went dead soft.....would not hold torque....the head bolt washers would sink 0.030" in the head and the bolts would go from 55 to 10 ft-lb and blow the gasket. Had the head tested and it went from Rockwell C60 to B45. Finally had to visit bone yard for another head. Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted March 25, 2006 Share Posted March 25, 2006 300F is only 150 celsius. That's is pretty close to the temperature(110 celsius?) a head sees when running on an engine. Unless you are talking about 3000F. No...can't be 3000F, aluminum melts before that. Quote Link to comment Share on other sites More sharing options...
dapiper Posted March 26, 2006 Author Share Posted March 26, 2006 I think they cooked my 626 Turbo head to over 500F. Quote Link to comment Share on other sites More sharing options...
speeder Posted March 29, 2006 Share Posted March 29, 2006 Heating an aluminum head for straightening is also a normal process and it usually does not disturb the valve seats. I concur with this. If done propely the valve seats will not be affected. I've had several L heads straightened by this process. It really does minimise the amount you have to cut off the head surfaces. When you have to true both top and bottom the total thickness removed can become excessive otherwise. Just make sure your machinist knows the correct temperature to use. ( Don't go back to the 500 degree guy) Quote Link to comment Share on other sites More sharing options...
zbuild Posted March 29, 2006 Share Posted March 29, 2006 It is a very common head straightening process. One of the reasons they do it is that if you machine it in its present state (bent) you combustion chamber volumes will vary quite considerably from the edges to the middle. It would be the reverse of cc'ing your head is that de-cc cheers - Simon Quote Link to comment Share on other sites More sharing options...
dapiper Posted March 29, 2006 Author Share Posted March 29, 2006 Yeah, I estimated I'd gain 0.15 CR in middle cyl, if they milled 0.010", since I would loose 1.5cc Quote Link to comment Share on other sites More sharing options...
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