Miata Engine Rebuild Tips

By Miq Millman


I just rebuilt Basher's engine after a crankshaft failure. Engine had 160K+ but _no_ maintenance what so ever (6 oil changes in lifetime from PO in first 154K miles).

As far as engines go, the Miata's is fairly complicated, dual cams, fuel injection, dual ignition, 4 valves per cylinder. As well everything is in pretty cramped quarters.

With that said, having a shop manual and the Enthusiats manual and all the right tools, the task is difficult but not impossible.

It is not a weekend project. More like 6 weekend projects, assuming you have all the right parts.

I did the head work myself, which is something you'll likely want to ship out (unless you have a mill and lathe and know how to use them?), but shipped out the intake plenum to get extrude honed (a performance option, not a necessity).

This was not the first engine I rebuilt, and since I was mostly ploping new parts into recently machined recepticles and not fixing badly mangled stuff (well except for #3 combustion chamber...), it went fairly quickly. It was one of the most complex engines I rebuilt, I grant that. The only thing I'd rank as more complicated would be rebuilding an automatic transmission. This was about on par with rebuilding a manual transmission.

Some of the other engines I've rebuilt to let you knwo where I'm coming from:

So, I guess I already knew what to expect, and had a good idea about what to do next.

So tips should you decide to jump into the fray:

  1. Know exactly what is wrogn with the engine, ie why are you doing this? Can you get away with just replacing some of the parts?
  2. Get all the gaskets and assembly bits in one swell foop. Having them around will help you make value judgements about what is salvagable and what needs to be replaced, you can always return what you don't use.
  3. Unless you've done machine work before, ship out the heads for valve replacement, its a task that can easily destroy a $1500 dollar part if done wrong.
  4. Label everything as you disassemble it. I use 1 1/2" masking tape and a Sharpie permanent marker.
  5. Use sandwich bags to keep like parts together.
  6. Save up those egg crates to keep similar parts sorted according to placement in the engine. (like the oil pan bolts, or the head bolts or the cam bolts or the bearings that you might reuse)
  7. Plan on being without the car for at least 6 full weekends worth of work, unless you take time off to work on the car. If you ship stuff out, its going to take at least a week and a half to get stuff back.
  8. Replace all non reusable bits as well as all parts with lifespan (belts, gaskets, over torqued bolts)
  9. Get a case (at least!) of carb cleaner spray cans in addition to the kerosene. The hi pressure blasts are great for hard to reach places.
  10. Have a permanent work spot that is dry, adequately lit, and flat.
  11. Invest in good, solid cast 4 leg jack stands. Your lower back will thank you, as well as your piece of mind.
  12. A $60 creeper is small potatoes compared to the $3000 labor bill you're saving by doing this yourself. Ditto the $30 Big Mac coveralls. Get them.
  13. Don't fix more than you initially planned (known in the car restoration hobby as ship wrights disease) or you'll never get finished.
  14. Relax, its not brain surgery, just a bunch of mechanical parts.
hmmmm, I guess this was probably more than you wanted to know.....

Miq Millman   mmillman@ptdcs2.intel.com	  503 642 6139   (Aloha site)
AL4-55  Intel, 5200 NE Elam Young Parkway, Hillsboro, OR 97124-6497
See also miq@teleport.com