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List Of Questions (porting and installation)


NAXJA Forum User
Ok I have a long list of questions about my jeep... I am rebuilding the engine and getting ready to put it back together with the next week...

1) I am porting & polishing a 91 head....So far I have gasket matched the intake ports and also the intake manifold... How important are the other things that are listed such as exhaust work (my ports look very good already no bumps or anything) also the short side and bowl work.... I dont really know what the sort side work would be, but I know my bowls areready look like they have been polished..she are completly smooth... And what about the chamber work?? I dont have an extra set of valves so I am leaning away from that unless it would be worth it...

BTW this is not going on a stroker engine just a modded 4.0

2) Do i need to clean the tops of the pistons before I put the head back on??

3) Can I attach the intake/exhaust maniolds before installing the head to make things easier??

I have a ton more just they wont come to my mind...

OK - In the order asked...

1) Sounds like you picked a good head - 7120 casting, right? Anyhow, smoothing the exhaust ports can be helpful, but not strictly necessary. Having a slight "step" at the exit of the port (relative to the header) is not a bad thing - it helps keep exhaust reversion down. This isn't a step that is cast into the head - rather, it is the relationship between the port exit and the header entry. You don't want to "port-match" on the exhaust side.

2) It's not a bad idea, if there's a lot of carbon buildup. Clean with the piston at TDC, and use either a Scotch-Brite drill pad or a brass wheel brush - GENTLY. Stuff the cylinders you aren't working on with CLEAN rags to keep from having to clean too much - and you can just blow out the cylinder you were working on with carburettor cleaner. If you have the means, having an air clast of some sort across your work area will help keep "crud contamination" down.

3) YES! Do that, and you'll save yourself all sorts of trouble!

Oh - I've covered some helpful ideas elsewhere, but just in case...

A) Use silicon bronze or brass bolts when reattaching, rather than steel. Steel galls on iron when heated, and will gradually get softer. Copper alloys do not, and the process which softens steel will harden copper and copper alloys - it's an incremental process, but should be accounted for. You can get these bolts from Fastenal (I use silicon bronze.)
B) If you don't have the dish-shaped washers, or if they are all nasty and unusable, get new ones. Belleville Spring Washers will work - you can get them from MSC Direct or Small Parts, Inc (MSC has better pricing.)
C) Apply a THIN layer of RTV Copper evenly on both sides of the gasket when you install.
D) Get a bottle of LocTite 272 for the bolts - it's the only one that holds up to exhaust heat.

Unless you plan to get silly later, you really don't need a lot of chamber work. I'd suggest smoothing the sand-cast surface of the chamber and breaking the sharp edge of the bowl slightly, but it's not strictly necessary unless you have bigger plans.

Did you know I wrote a book on this sort of thing - mainly because so many questions come up? Let me know if you're interested...