inline6 Posted December 19, 2015 Share Posted December 19, 2015 Wondering if anyone has any experience with what I can expect (approximate head warpage) when welding either an N42 or P90. Quote Link to comment Share on other sites More sharing options...
Lurcher Posted December 20, 2015 Share Posted December 20, 2015 (edited) Depends on where you are welding...? For example, welding up the injector notches can pull the manifold face 40thou. Whatever part of the head you weld up, expect it to require straightening, THEN milled flat. Edited December 20, 2015 by Lurcher Quote Link to comment Share on other sites More sharing options...
inline6 Posted December 20, 2015 Author Share Posted December 20, 2015 Reason I am asking is we are thinking of pre-bending... before welding, so less straightening, or no straightening, if we get really lucky, will be necessary. Quote Link to comment Share on other sites More sharing options...
zbloke Posted December 20, 2015 Share Posted December 20, 2015 Reason I am asking is we are thinking of pre-bending... before welding, so less straightening, or no straightening, if we get really lucky, will be necessary. Isn't there some information in the Honsowetz book regarding amounts of pre-bending before welding the head? Quote Link to comment Share on other sites More sharing options...
CRAracer05 Posted December 20, 2015 Share Posted December 20, 2015 Isn't there some information in the Honsowetz book regarding amounts of pre-bending before welding the head? Yes, the Honsowetz book gives the exact methods of pre-bending the head when re-shaping the chambers for a better quench area. Off hand, I believe you torque the head on upside down with a piece of 1/4" bar stock in between the middle of the block and cylinder head. I would have to re-read the book to know for sure. Quote Link to comment Share on other sites More sharing options...
inline6 Posted December 20, 2015 Author Share Posted December 20, 2015 Isn't there some information in the Honsowetz book regarding amounts of pre-bending before welding the head? Yes, the Honsowetz book gives the exact methods of pre-bending the head when re-shaping the chambers for a better quench area. Off hand, I believe you torque the head on upside down with a piece of 1/4" bar stock in between the middle of the block and cylinder head. I would have to re-read the book to know for sure. Awesome. Evidently, I haven't memorized everything from that book as I thought I had. Thanks for the info. Quote Link to comment Share on other sites More sharing options...
Xnke Posted December 24, 2015 Share Posted December 24, 2015 (edited) 1/4" is a LOT... When I weld up the chambers in the L-series 6-cylinder head, I use a 0.040" flat washer in the middle two headbolt holes, and tighten the two ends till they just barely touch the jigging block, so pre-bending the head that 0.040". Occasionally this isn't enough. For the 4-cylinder heads a 0.020" shim is enough. I'm talking about adding a few CC's of metal here or there to get your chamber volume down, not repairing a broken cylinder...For more drastic modifications, you'll need to prepare for more warpage. The more metal you add, the more shrinkage you get-regardless of how hot you work the casting, this will always be true. Also watch for the manifold face going banana-shaped too, although I've never had a head move from just welding up the injector notches. Also, this is going to depend heavily on your welder, his technique, how he jigs the head, what school of heat control he subscribes to, etc. Plan on doing two heads if you're doing the work yourself and you've never done it before. There is a lot more to it than just plop the filler in, skim it flat, and calling it job done... Edited December 24, 2015 by Xnke Quote Link to comment Share on other sites More sharing options...
inline6 Posted December 24, 2015 Author Share Posted December 24, 2015 I typed this up for my engine builder via email, so I'll share it here also: There is a section of the Honsowetz book about bending heads: If a significant amount of welding is to be done or if only a little amount of material can be milled to straighten the head after welding, it is best to bend the head backward-up at the ends. After bending, the head gasket surface will be convex. This pre-bend will compensate for warpage that bends the head in the opposite direction (concave) that occurs when the combustion chambers are welded. The amount of preload or bend depends on the location and amount of heating or welding. Bolt the head upside down to the deck of the stripped block. Support the head off the block with a spacer block at its center. The spacer should span the width of the block, be approximately 1-in. wide, and at least 0.100-in. thick. Secure each end of the head to the block with two short head blots. Gradually tighten the bolts and check the bow in the head with a precision straightedge and feeler gauges. You'll need a 36-in. long straightedge for checking a six-cylinder head; 24-in. will do for a four cylinder head. With the straightedge flat against one end of the head, check the gap at the other end using your feeler gauges. How much prebend you should put in a head is subjective. It depends on how much welding will be done. This is something you and your welder must judge. Use the following as a guide: For small to significant amounts of welding, pre-bend 0.020-0.040 in. for a four cylinder head and 0.020-0.060 in. for a six cylinder head, respectively; 0.020 in. if there's a minimal amount of welding to be done and 0.040-0.060 in. if you're going to do a lot of welding. If you guessed right, your weld-repaired head will only show 0.005 - 0.008-in. warpage after it has cooled. Use your straightedge and feeler gauges to check. Whatever is required to clean up the head, the same amount must be milled from both sides. Welding Combustion Chambers to Increase Compression: As mentioned previously, the head must be absolutely clean before you can weld the combustion chambers. This applies to both old and new heads. Polish the chambers with cartridge rolls, then with a rotary brush. Bend the head backward the maximum amount because welding all combustion chambers is a significant amount of welding. Therefore, using my recommendations, a four cylinder head should be bent backward about 0.040 in and a six cylinder head about 0.060 in. Instruct the welder to "jump around," or weld a small amount in one area at a time. This will keep welding heat from being concentrated in one place, thus helping to reduce warpage and prevent cracking. Honsowetz also has a section on straightening heads. Basically, it consists of bolting the head upside down on an engine block and using a spacer and bolts as above. He says to tighten the bolts until the head is bent backward about 1.5 times the amount that it is warped. He again uses a straightedge and feeler gauges to set it up. Then he describes using a acetylene torch with a rosebud tip to evenly heat the entire head to 350F. He describes using temperature indicating crayon or paint and marking the head in many locations. It can take up to 30 minutes to heat the head to 350F this way. Quote Link to comment Share on other sites More sharing options...
bradyzq Posted December 24, 2015 Share Posted December 24, 2015 Very interesting stuff! A question I don't see answered is when to unbolt the prebent head from the block after welding. Right away? After a certain specific cooling period? It seems counterintuitive to wait until the head has cooled fully. Quote Link to comment Share on other sites More sharing options...
Xnke Posted December 24, 2015 Share Posted December 24, 2015 You must wait for the head to cool completely. If you unbolt it hot, why did you bother to bolt it up at all? You are trying to constrain the movement of the head to certain directions only, so you have to keep it constrained until it stops moving. When I do an L6, I usually leave it bolted up to the block until completely cold (24hrs) then unbolt it, check the un-welded surface for flat, and peen the welds if I am using 4043/4047 welding rod, or I do nothing if I use 4943 rod. Either way the head sits for a minimum of a week before machining. This "rest period" makes it significantly nicer to machine flat later, much less tearing/pulling/gouging of the welded material. Don't let your welder use 5356 filler rod. It's great for castings, but only castings with a working temperature below 200*F...above that temperature it tends to stress crack. 4043, 4047, and 4943 do not have that limitation. Of those three alloys, I use 4047 for the majority of my head welding, and I am really digging the 4943 for the same purpose. 4943 is quite spendy though but it doesn't need peening because the weld deposit is hard enough to hold a headgasket without any further work. You don't warp the head from the *heat* of welding, you warp the head from the weld deposit shrinking as it cools. Hot straightening a head is not really desirable. Straighten the head cold, pre-bend it in a screw-type press until it's "flat" and then heat the spot opposite the bend with a rosebud until you're 600-800F in that one small section, then let cool. You can't use a hydraulic press with this method because the heat will cause it to increase pressure, and it will bleed down over the long cooling period. By doing the straightening cold, you don't cause nearly the same level of damage to the heat treatment of the casting. Quote Link to comment Share on other sites More sharing options...
Enzo250gto Posted December 25, 2015 Share Posted December 25, 2015 Hello Guys, Merry Christmas from Australia. I am getting a head heavily modified at the moment with Argon welded chambers, etc to go with a bottom end with all Datsun spirit parts. The original head was warped so I purchased a replacement head. When I was discussing the modification with the engineer he mentioned about pre-bending the head prior to commencing the work. I asked him if the head being warped was an issue. He replied that if it hadn't been cooked beyond repair and softening the alloy it would be ok for the modifications. As it worked out the warped head was ok to use with the benefit of being pre-bent and I got to keep a spare good head. Have a safe Christmas and new Year. David (Enzo) Quote Link to comment Share on other sites More sharing options...
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