How bad does blow-by need to be before swapping the engine?

My 88 4.0 has about 220k miles on it and a serious blow-by problem when I head up into the Sierras with the 35s on and loaded for the trail. It runs just fine, maybe a little low on power but I don't have much to compare it too, but the blow-by is just crazy, probably 1/2 quart in a real strenous 600 mile trip. I've replaced all the appropriate lines, cleaned the valve cover and snorkel things, but none of that helped much at all.

I really want to make it through the summer wheelin season (under 2000 miles) before replacing or rebuilding the engine. I am perfectly content to build a good catch-can and be sure to replace oil as needed, but would this actually be bad for the motor in any way? Does this severe blow-by indicate that my motor is on the very verge of going kaput even though it runs fine in every other regard?

Make sure you get a good seal on the valve cover gasket. I clean all the stuff and still had problems. Getting a good seal did the trick. I also changed to a 91-95 valve cover and did the MAD-XJ update with the bigger new style hose. I had to cut it and use fuel line hose since the Renix ones are a longer length.
Tom

Blow-by isn't the determining factor. Do a compression test and a leak-down test, then use the results to decide.

Eagle said:

Blow-by isn't the determining factor. Do a compression test and a leak-down test, then use the results to decide.

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I checked the compression last year (~5000 miles since) and it was very close to within spec: http://www.naxja.org/forum/showthread.php?t=22706

BrettM said:

From front to back, 150, 152, 142, 117, 135, 148

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Eagle said:

120 to 150 psi, max variation 30 psi

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Blowby hasn't increased since then, I'm just pushing the engine harder with the 35s compared to the 33s.