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The Miata Project (UPDATED!)
I’ve mentioned “the Miata project” on the podcast, giving updates each day, and I’ve promised to post photos, but I’ve been negligent in doing so. Honestly, when I get into working on the car I don’t think about photographing the progress often, and when I do it’s to send photos to a friend who also owns a Miata and is interested in what I’m working on.
But today I have some photos to share. It turns out that I took a lot more photos than I thought!
After replacing the radiator and refilling the cooling system I made sure the cam position sensor was unplugged and cranked the engine over until oil pressure began to build, then reconnected the sensor and turned the key. After a few seconds of rough idle it settled down and ran smoothly.
The engine temperature gauge, which had been intermittently working before, now works perfectly – I discovered during the project that the sensor wire was broken inside the connector, and also found another spot where the insulation had become brittle and broken. I repaired both problems and that took care of the finicky temperature reading.
But… it still smokes. In fact, if anything, it’s worse than before.
That means the cause of the oil seeping into the combustion chamber(s) wasn’t faulty valve stem seals. It’s something else. It may be a really worn valve guide, but that’s what the seals are supposed to do – seal out oil. From examining the photos I can tell that the rearmost intake and exhaust valves in #4 had a lot of carbon buildup, so I suspect the oil is running down one or both of those valve guides
It also has a new valve tick. It isn’t loud, but it’s there. I traced the sound to the #4 cylinder. One of the lifters may be sticking.
I took a drive to heat the engine up and see if that helped the lifter settle in, and it helped a little. On the drive it ran poorly at low RPM, stumbling and hesitating.
When I got back home I pulled the spark plugs and checked for signs of oil. Plug #4 has black smudge but all the rest are clean. I suspect a lot of oil is getting into #4, and that’s causing it to misfire.
At this point, honestly, I’m at a loss. I’m not an auto mechanic. I’ve just learned how to work on this little car as a hobby, and now I’m beyond my level of expertise. It looks like my options are:
1. Have the head rebuilt.
2. Buy a rebuilt head.
We’ll see what happens next.
After some thinking and tinkering, “Lil Smoky” is no longer smoking, and running better than it has in a long time.
At breakfast Saturday morning I described how the car was smoking to my friend Mike. He’s been working on cars most of his life, and it was because of his encouragement that I started getting deeper into working on my little car instead of taking it to a repair shop. His puzzled expression told me that the way it was smoking didn’t make sense to him – it wasn’t smoking while idling, but was on acceleration. That made me think that maybe oil wasn’t getting into the cylinders through the valve guides, but from below. Maybe there was too much oil in the engine.
So I checked the oil level and it was high. I had put too much oil in. (Stupid me!)
Sunday morning I drained some of the oil, checked the level and it was on the “Full” mark on the dipstick. I took the car out for a short drive, and it smoked like crazy at first but stopped smoking soon afterward.
The excess oil was the problem.
But it still stumbled badly upon acceleration, so there was more work to do. I suspected that the timing was off, so that was my next thing to check. My thrift store timing light score from a few weeks ago turned out to be a dud, so I picked up a cheap one at Harbor Freight Tools (which is going back because it’s a piece of junk) and started tweaking the timing. Since this is a 30 year old car the timing marks on the harmonic balancer are hard to see, plus there are several scratches which can be mistaken for timing marks, but I eventually found the right one and set the timing according to recommendations found online.
After adjusting the timing I made a 40+ mile round trip and the little car runs great! The stumbling is all but completely gone (what’s left I think is a fuel injector problem) and acceleration is much snappier than before.
Since I fiddled with the steering components I’ll need to get the alignment checked, but other than that I think the Miata Project is a success!