your-real-dad

1992, 3VZ-E, 234K. I've searched for a couple hours, sorry if this is already covered. Which compression ring goes in the top groove?

Rebuilding the 3VZ. Pulled one piston to find out why it has 70psi compression and 34% loss on the leak-down tester. Looks like it's been bored to the 0.50mm standard. Piston and bore are to spec, at least with my crappy tools. I pulled the rings, and the end-gaps are fine (.012 and .014). But, I notice that the two compression rings are different. Both at 1.4mm thk, but one is 3.4mm "wide" and the other is 3.9mm. Which one is supposed to go in the top machined groove? The FSM just says to insert with the "code marks facing up." Only one of mine even has markings.

In general, I bought this as a rebuilt engine. I measured compression at 95 to 100 psi on all cylinders. Took it to a local Toyota shop, and they measured 130 to 135psi, so maybe my HF gauge sucks. Also, low manifold vacuum. With EGR and AS valves sealed off, and no apparent leaks, I could never pull more than about 15 inches. Still, it ran pretty well for about 10K miles. Recently showed a big loss of low rpm power, and running rough. Checked compression again, and found the left bank (1-3-5) were all less than 70psi. Leak-down test shows 34% drop on all three cylinders. Tearing it down, I found a loose screw jammed between crank sprocket and the block, grinding the timing belt to hell. Left cam sprocket had skipped three teeth, or about 15% retarded. (Guess that explains the rough running... must have installed those screws after happy hour started). My thinking is that the timing would not affect the compression or leak-down numbers. For the leak-down, I have the valve covers off, and I'm set to TDC and checked the valves with a feeler gauge to make sure they are completely closed. All the air's leaking through the crank case. But the fact that this head bank dropped 30% in compression, uniformly, seems like too big of a coincidence to ignore. Anybody still reading have any ideas?

Melrose 4r

Just a quick comment on the HF compression tester. I checked mine yesterday against the gauge and regulator on my HF compressor and they read exactly the same. I think they are pretty accurate.
The difference measured by the shop at the time could be if you didn't have the engine fully up to temp and they did.
Sorry can't help you with the ring questions.

your-real-dad

Yeah, I built a little adapter and checked the HF compression tester against the regulator gauge on my Porter Cable compressor, and they were identical. So as convenient as it often is, I can't really blame Harbor Freight here. Recently, I ran the compression test with plugs out, throttle body open, and both hot (160F) and cold (50F) and found a 15% increase at higher temps. The 60psi cylinders went to 68, and the 95psi went to 105. I think a rebuilt engine should be 150psi plus, but I can't find anything wrong with this one. Next step will be run some leak-down tests on the short block (soon as I figure out how to stop the crankshaft from moving.

your-real-dad

Also, measured the depth of the slots on the piston and it looks like the wider ring is the bottom of the two, the narrower is the top ring. So nevermind.... (Seems like every time I hit "post" on a new YotaTech thread, the answer becomes immediately obvious).

Melrose 4r

Good input.

I did a comp test on mine yesterday and been thinking about re-ringing it. #1-3 are at ~150psi and #4 is about 120psi. I think I might have a broken ring or scored cylinder wall.

If you are concerned about the crank moving during the leakdown, can you put it in 4rth gear and lock the e-brake?

your-real-dad

Engine is removed from the vehicle, on a stand. It was pretty easy to put a bolt into the fly-wheel end and then cam-strap that to the engine stand. Kind of interesting. Put a head back on, but not torqued down. Leak-down in this state is 70% to 100% loss. The air just whistles through the rings. I guess it's because the engine is completely dry; no oil at all. But that suggests that leak-down test results depend on the last time the engine was running. Like, maybe you wouldn't want to have it sitting for a couple of days before you do the test? (Like I did, I think..)

Melrose 4r