Zuki-Ron said:
Slight milling to straighten a head should not affect the valve train geometry enough to worry about it. Infact, you can easily make up that distance by using a fatter head gasket if you are worried about it; though you shouldn't be. Most heads are trued sacrificing a small amount of metal. Since you are changing years of head, you may want to at least compare lenght between the 83 and 93 pushrods. Using used pushrods is not an issue unless they are not straight (roll them on a flat table, if they go "thump, thump..." then they are not straight), or the ends are gauled. Hydrolic lifters are forgiving within a range. If you want to examine the valve geometry, you will need to take an old lifter apart and make it solid, then take your readings, both intake and exhaust.
Besure to use assembly lube or a bit of gear oil on the pushrod ends, yes both ends, the rockers and the valve stem to "preoil" them. It makes one hell of a squeeking noise if you don't (don't ask how I aquired this knowledge)
If you decide to have the heads fluffed, just go with a basic 3 angle valve job. Make sure when you get the heads back that all the valve stems sit at the same level. Unleaded seats are much tougher than their leaded counterparts and require less maintance.
Ron
So, how did you acquire that knowledge?:roll:
Just kidding - it's not a good idea to be stingy with assembly lube. My engines would smoke for the first hour or so they were run - due to leftover oil in the cylinders from piston assembly insertion.
As far as the assembly lubricant (and make sure you use engine assembly lube - NOTHING ELSE!) anytime I crack open a bearing, it gets relubed. If I pull the head off, I'll lube the lifter feet (one at a time, so I can't mix them up!) the lifter cups, the pushrod ends, the rocker arm cup, and take an acid brush (checking for loose bristles) and get some lube between the rocker tip and the valve tip.
It's cheap insurance - pretty much anytime you open up the lubrication system, it can't hurt.
You are also correct on the later seats - they're hardened, to allow for the lack of tetraethyl lead (TEL) in modern gasolines. However, there aren't actually "guides"
per se in the 4.0 - they're integral to the cylinder head casting. Of course, they seats can be machined to accept hardened steel guides if necessary or requested (and paid for...)
Anyhow - since you've got the head off, get some assembly lube at the local parts house, and get it all over. I'd also put a couple ounces or so in the crankcase before you put in the oil, since it is oil-soluble, and will help give things that "first oiling" when you start the engine - I've found it helpful.
5-90
