Greetings, new guy here (don't shoot!) A year ago I bought a 1995 4 Runner for my daughter for her first car, it's got the 3VZE with the 5 speed. It was running but poorly when we got it and the plan was to fix it up and have it ready for her to drive on her 16th birthday last month. According to the receipts in the glove box a reman short block was installed about 11K miles ago along with a swath of new parts including rebuild heads from LC Engineering, studs, water pump, timing belt etc. After diagnosing the primary issue (I thought) to be a bad exhaust valve in cylinder 6 I had a spare set of heads completely rebuilt by a local reputable shop and got those installed about 2 months ago. The exhaust valve on that cylinder was missing a chunk out of it, everything else looked great. While it was apart I did notice that cylinder 3 had one vertical score mark in it that didn't make me too happy, but other than that the block and lower end seemed to be in good shape with good cross-hatch in the cylinders. Prior to pulling the heads I did compression and leak-down tests and all cylinders had good compression, except for #6 due to the missing piece of valve.
Long story short, I got the thing back together and it still smokes like crazy on cold starts and seems to be going through a ton of oil, as in a quart every few hundred miles roughly. It idles smooth, seems to have good power for what it is, runs and sounds much better than before but the oil consumption is concerning me. I did put some Seafoam in the oil, and on start-up after that it wasn't smoking and blew a bunch of black carbon crud out the exhaust, but now the smoke is returning more and more. I need to do compression and leak-down tests again, I'm assuming I have a ring issue on one cylinder or more. My question is, can I drop the oil pan and crank and pull the piston/rod out and reassemble from underneath, or am I looking at pulling the motor and completely pulling it apart again?

 

Valve guide seals?
what oil are you using?

 

New valve guide seals were installed by the shop who performed the head work. I suppose it's possible one was damaged or just a bad seal, but probably unlikely?

 

I've never seen a Toyota oem valve with "chunks" missing, even ones that had nuts or bolts dropped down the carb while running. Ball peened the hell out of the top of the piston and valve surfaces, but nothing broke off.
Given that, and the vertical scoring I think your best best is to pull the heads and pan for a fairly complete inspection, being prepared to pull the whole engine. Once you have the heads off and all the pistons removed you can get a pretty good idea of the scope of what needs to be done.

 

I have no way of knowing if the valves were OEM or not, as stated the rig had rebuilt heads with a receipt from LC Engineering in the glovebox so my assumption is that is where the heads came from, but that's anyone's guess.

 

That’s kinda runs to my point. With so many visible issues/concerns, combined with so many unknowns, I don’t see any path other than pulling heads and removing pistons.

 

Usually, a problem with a cylinder wall so bad it will cause excess oil consumption should show up as low compression.

Valve guides, though, are different. If the engine primarily smokes on cold starts (and then clears up), I would still suspect the valve guides. They won't affect compression that much. When the vehicle sits over night, oil leaks down from the valve train space into the cylinder. On start-up, that oil burns.

Removing the heads will make it easy to do a thorough visual inspection, but it's a big (expensive) step. As a first step, I'd remove the valve covers and visually inspect the valve seals, at least.

 

A leak down test should be able to determine if there’s a ring or valve issue.