If you bought your CRX or Civic used, it is quite likely that the head has been reworked at some time in its life, as overheating is common in these cars. The metal of the head bolts expands at a different rate than that of the aluminum parts they hold together and leakage occurs. If enough coolant leaks out, or if the combustion chamber gases leak into the coolant passages, the car will overheat. This usually warps the head. The fix that most shops employ is to simply machine it flat, but there is a service limit on this thickness. Often, it requires more than the limit to cure the warp and many shops will just cut enough to make it flat regardless of that limit. Cheaper for the customer that way. You may have inherited such a head.
BTW, there is a technique whereby the head is bent back into shape and then a minimal surface cut taken to finish it off. Very few shops can do this effectively, though.
To measure the head thickness while still on the car, remove the distributor (plug the hole with a shop rag to minimize the oil drip) and valve cover. Next, position a caliper across the span from the valve cover mounting surface down to the bottom of the head at the area just abiove the "D16A6" designation. Rock the caliper around to get the smallest reading you can and that will be your thickness. A better measurement requires removal of the head.
In addition to warpage, a high mileage head will likely need exhaust valves and guides, as the high temps tend to wear these quickly. Be careful on each of these to service them per the shop manual. Many shops will take short cuts on the guides. Do it per the FSM.
Same with the valve job...specs are clear. Do not exceed.
Replacements valves and springs should come from Honda to be certain they are correct. Most parts store springs are not exactly the same length or rate as OE. And the exhaust valves tend to be of the wrong material to improve performance (chromed or sodium-filled). In addition, the head thickness may not be correct which affects compression.
While a standard service procedure for many marques, shimming of worn valves springs or to correct valvetrain geometry when cutting new seats is not allowed on a D16A6, per the service manual. Make certain your head guy understands this. This one cost us a couple of championships.
If you have an 88 and your cam needs replacing, you are in a tough spot. Honda has discontinued this part and the 89-91 cam does not supercede. 14.11 would provide alternate-sourcing relief, but only for a cam that delivers the same cam event specs. There is nothing like this in the aftermarket at the moment.
And finally a note on cleaning. Many shops will bead-blast a head to clean the combustion chambers and ports. This is not allowed as it alters the surface texture of these surfaces. Instead, request only that chemicals and/or high-pressure washing be used. A dishwasher-style parts washer is also quite effective. A bead-blasted head will stick out like a sore thumb and at least one national championship has been lost to this point.
Once your head is done, it's time to bolt it back onto the block and for that we'll need a gasket. Honda responded to the overheating issue with an improved design head gasket (MLS) and spiral-shanked head bolts. The spiral bolts expand at a rate more similar to the aluminum they secure. The steel gasket has similar properties and is also less likely to blow through under pressure. There is no actual performance advantage to using this gasket other than reliability as its compressed dimensions are the same as the standard composite piece. Note: These are not supercedes but are instead legal to use per the TSB.
There has been some debate on whether the TSB applies only to Civic models or whether the CRX is considered to be a trim level of the Civic for the purposes of TSBs. Honda is inconsistent in their offifical documentation in this regard but evidence suggests that for the purposes of TSBs that a CRX *is* a trim level. Examples of this can be found in the following TSBs: 88-026, 88-031, 89-007, 89-027, 91-016 & 91-031. Each of these specifies "Civic - All" at the top, and then spells out specific affected trim levels (e.g. 3DR DX, 4DR, DX & LX, CRX, etc.). Each time, CRX is called out specifically as a trim level. Since 97-047 applies to all non-VTEC Civics regardless of trim level, it follows that the CRX is included. The confusion among competitors seems to lie in the inconsistency of responses given to inquiries made to various folks at Honda. A service manager gives a different answer from the call center operator at Honda Customer Service which is again different from what HPD reps have said. We are attempting to get official confirmation on our conclusions but the evidence seems pretty clear.
Here's a link to the TSB:
http://hondaworkshop.com/misc/97-047TSB.jpgSpeaking of head gaskets, the TSB gasket is commonly referred to as a 5-layer, and may well have been at one time. But now it is composed of four layers. Three are .010" and the fourth is .018", for a total of .048". There is another D-series MLS head gasket introduced on the 92+ VTEC-equipped cars, that is thinner with only three layers. This gasket is commonly supplied mistakenly by Honda service departments if you ask for the "MLS head gasket for D series", or used by race shops looking to "do you a favor". Fortunately, it looks different and can easily be detected visually with no disassembly. Furthermore, the compressed thickness can be checked with a feeler gauge near the back of the motor between the head and block. In fact, this was checked at an impound inspection at Nationals in 2009. All cars passed. One final detail on the TSB gasket, note that the bolt tightening pattern and procedure is different than is used for the standard gasket. Also, make sure that the rockers are all loose when installing the head, and also that all of the pistons are halfway down the cylinder so you don't get piston-to-valve contact.
Once the head is bolted on you'll need to time the engine and install the timing belt. Carefully reposition first the head to TDC #1 and then the block. You dont want to ruin everything when you are this close to being done. Note that the Si has a different procedure from the DX and HF motors, with the cam pulley marks aligning differently. This is something not correct in the online Euro/JDM CRX manual many folks use.
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