Lots of work over the weekend. The new/used replacement engine was in decent shape, but not good enough to just drop in, unfortunately. Initial leakdown numbers, and leakage location, were:
1-13% blow by
2-7% exhaust valve
3-20% exhaust valve
4-12% blow by
After a bit of massaging (nominally letting stuff soak in seafoam overnight) I got:
1-5% blow by
2-8% exhaust valve
3-25% exhaust valve
4-3% blow by
Other clues:
-Oil in plug wells (valve cover gasket clearly never replaced) i.e. ignition severely compromised
-Spark plugs caked black in carbon
-Tons of carbon build-up in exhaust ports
Conclusion: car was running like s***, lots of carbon deposits caked onto everything. Adding seafoam probably freed up the rings a bit, and partly (but not entirely) cleaned off the exhaust valves and seats, causing extra leakage.
Action: disassemble engine head. Clean head, lap valves, reassemble.
Engine on engine stand. The chain fall is making life really not suck right now. With it I can do everything by myself.
Miata drivetrains have exploded across my garage. It's a disaster.
Three blocks, two heads, dressing for two engines, an extra front and rear subframe (I'm welding up a rear subframe for a guy's V8 conversion), and lots of other crap.
Taking the head apart I found several jammed/clogged HLAs. I'll take them apart and clean them.
Everything apart and soaking in ATF to clean off the immense amount of carbon buildup (way worse than the engine that came out). Learned how to use a valve spring compressor, made pretty quick work of it all things said and done.
The bottom end looks good. No scoring, decent hatching, smooth movements with no detectable slop. I poured oil on top of each cylinder to prevent rust and to give the rings even more opportunity to free up.
Hopefully tonight I'll be able to clean out the ports and valves and maybe be able to lap the valves. Any tips or advice on lapping?
I ordered new valve guide seals (because why not?) so reassembly will be a little delayed. I could reassemble the block and transmission (when the parts for that arrives) and drop that into the car if I'm still waiting on the head, but I'd rather do it all at once if possible.