Cylinder head oil return holes?

So the FJ has always consumed oil. Not a ton at first, maybe 250ml every 1000kms, but now consumption is ridiculously high and I need to fix it. Biggest visible symptom is the occasional big puff of blue smoke when I cold-start the engine, otherwise nothing. I do notice some amount of blowby if I take off the crankcase breather tube or the oil filler cap, but it doesn't seem excessive if I compare to bad examples of blowby on Youtube.

I replaced my valve stem seals earlier this year and that did nothing. Compression test on a cold engine is okay (ranging from 120 to 140 PSI) and very good on a warm engine (150 to 170 PSI), so it's probably not the piston rings?

I just read (on a Harley forum, so may not apply to my inline-4) that the oil return holes in the head could be clogged, which would cause a build-up of oil in the head, which in turn would force-feed the oil into the combustion chamber. That makes sense, although I'm not seeing signs of this on the plugs. Maybe the trickle of oil is not enough to foul the plugs, but regular enough to cause massive oil consumption? I have to put in like 1/3 of a quart every 250 kms or so, which seems insane.

My question is - where are these oil return holes? Do I even have them? Looking at photos of FJ600 cylinder heads on eBay, I can't see anything. Seems to me that the oil comes back down through the middle, where the cam chain is?

Halp.

Just took a look at the FJ head, you're right, the oil most definitely returns down the center only

If you did the valve stem seals properly, you would have had a chance to look at the cylinder walls and the valves, and check for excessive valve guide clearance. It's quite possible to have good compression but poor oil control. Cylinder walls polished smooth with no cross hatch remaining will do that.

Thanks guys. I did not have a look at the cylinder walls. I did the valve seals with the head still on, using a magnetic "hammer" tool to get the valve keepers out.

I would tear into the engine but I have no place to do that.

Maybe time to sign up for Moto Revere.

My YX600 had a very mild oil consumption habit, with one exception - if you used much throttle while it was still cold, it seemed like it would burn oil instead of fuel. It was incredible how fast it would go. Once it was warm - no problem at all.

I would also suspect rings... but it's pretty much either or. Not a complicated motor I do remember replacing the countershaft seal on either that or a VF500F. You would have significant oil spots in your parking space if that were it though.