[AMC-list] My new engine...

[Frank Swygert <farna@xxxxxxx>]

Got the new motor in the car Tuesday. 0/060" over 1988 4.0L block, standard 4.0L rods and crank. Decided to build something a bit better on gas this time. I am using a 1999 intake and a Mopar Performance cam (P4529229AB for the cam/lifter kit). Cam is supposed to be good for 1100-4800 rpm. 248° advertised duration intake&  exhaust, 32° overlap 108° lobe centers, 0.440 lift. I went with the 1998 injectors which are 23# at 49 psi, should be 21# at 39 psi (vs. stock Renix 19.6# @ 39 psi). Should work well with the added cam and better HO head.

I was just getting ready to crank my engine earlier today. Put water in, and noticed a leak from somewhere. Put it up on the lift and the water is coming out the exhaust manifold! Can't be a cracked head, the water isn't pouring out but it's a good steady trickle. This is one that I pocket ported, a 7120 casting. I didn't do anything but clean up the bowl area and match the ports to the intake and exhaust. I don't think I took enough out anywhere to hit a water jacket, certainly couldn't tell! But maybe I did. Will be able to tell which cylinder once the head is off. I knew everything was going too smoothly!

My brother and I pulled the head and couldn't find anything at first. We then turned it upside down and poured water in the water jacket. Got a trickle out of #3 exhaust port. Turns out to be a casting flaw! There is a rough area right next to the valve guide boss. That's where it's leaking.

This head I spent FOUR HOURS cleaning up real good (pocket port and manifold gasket match). Apparently that's why the Jeep I got it from was junked -- engine run hot and it cracked at the thin spot (flaw), ruined the engine. Just a guess though. The head looked super clean so we pulled it at the local pull-a-part. I visually inspected it good before doing anything to it, no way that area would be suspect, there is a rough looking spot next to the guide boss in ALL the ports. I couldn't get anything in there to clean it up any. At least I know the head isn't so thin that a good pocket porting will go through a water jacket now!

Luckily, I had chanced upon a good deal on some 1998 4.0L parts, the head and everything attached, starter, alternator, AC compressor, etc. A fellow with a Wrangler had threw a rod and bought a wreaked Cherokee for the engine. The shop doing the swap was going to scrap the engine, let me have everything I wanted off of it for $50! I'd have got the wiring harness and computer too if I could have got there before they moved the wreck out. The exhaust manifold was already buried in the body with other junk ready to go to the crusher or I'd have got it too.

The exhaust ports are slightly smaller on the mid 96-mid 99 0630 casting, but not by too much. The best thing is that the ports are so much cleaner on the inside that there is no real cleaning up to do compared to the 7120 casting I'd worked on so much. I did a quick gasket match (couldn't hog the exhaust ports out that much though!) and some slight cleaning. Just need to hand lap the valves and it will be good to go. I know the engine it came from was running well when it threw that rod, so shouldn't be any problems this time! No head damage.

--
Frank Swygert
Publisher, "American Motors Cars"
Magazine (AMC)
For all AMC enthusiasts
http://www.amc-mag.com
(free download available!)

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