Tuesday, June 16, 2015

94 Miata - Engine Rebuild, Part 1

Going back about 3 years on this blog you'll find a long series of posts about how I went through my Miata and refreshed a bunch of stuff. Highlights of the project included installing a '99 cylinder head on my '94 motor and painting the entire car myself in my garage. What I didn't do back then was rebuild the bottom end of the engine. Since then it's been burning oil pretty rapidly and showing some rather poor compression when cold. So, I decided it's time to pull the engine again and do a complete rebuild on the bottom end.

I'm picking this project up sort of in the middle here, because I've already got the engine out and on a stand. When I last had the engine out in 2012, the cylinder bores looked very good, so I think I can get away with a simple hone and re-ring job, with new crank and rod bearings. I plan to use a Flex-Hone rotary brush type honing tool. These are inexpensive, can be done by hand with a drill, and provides a high-quality finish with the proper cross-hatch angle to ensure a good seal by the rings. I've torn down a spare 2002 engine block we had at the Gorilla Garage and I plan to use it to practice my honing technique. I also plan to use the pistons from that engine to take advantage of the 10:1 compression ratio enjoyed by the 2002 Miata engine. This will be a true budget-build, because if the block looks and measures ok, I'm going to get by without doing any machine work. We'll see if that pans out! The head only has maybe 35k miles on it, so I'm hoping to leave it alone at this time.

To sum up part 1 of this series, here are my goals for this project:

  • Rebuild engine bottom end
  • Inspect head and correct any issues (don't expect any)
  • Refresh suspension
  • Install soft top
  • Install Flyin' Miata frame-rail braces
  • Detail engine compartment
  • Repaint hardtop
This list is subject to change and I probably won't get to all of it before I put the car back into service as a daily driver, but it's all the stuff I'd like to get done, so I can drive this car for another three years. Stay tuned for part 2 of the series as I get into the engine over the next few weeks.