Engine Replacement/Rebuild questions

[71dsp]

The other week, my wife tried starting her 99 to go to work (140k miles). I wasn't there, but she said the engine made a metal on metal scraping & knocking sound. She immediately shut the engine off, but when she tried to restart, the engine would not start. When I got home, I checked a few things (oil, plugs, etc), but the engine wouldn't start.

I decided to do compression and leak down tests. Compression numbers were not promising, 135, 145, 45, 145, which are well below spec. Leak down was worse, 20%, 20%, 80%, 15%. No air from the exhaust, some from the intake, and I couldn't tell how much was coming from the bottom end (valve cover was off); however it sounded like a lot of it was coming from the spark plug holes!

Cam timing was perfect and plugs looked okay.

I pulled the head yesterday, and there is a TON of carbon on the pistons. Valves look fine with none of them being obviously bent. Cylinder walls still have a cross hatch pattern on them. No scratches.

I also measured crank end play last night. 0.007" - 0.008". It's not really bad, so to speak, but more than I was hoping for.

So far I don't see anything that would be the source of the knocking noise. I let her hear a video of an engine with rod knock and she said the noise wasn't that loud. Also when I was cranking the engine over during the compression tests, the idiot "gauge" would move to the normal mark showing that the engine was at least getting some oil pressure during cranking.

At a minimum I'm going to freshen the head up. Now I'm trying to decide whether or not to rebuild the block. We won't be doing a turbo or anything like that on her car, so the rebuild will be using OEM parts. I do need to replace the input and output seals on the transmission as one of them is leaking.

She's also had this persistent leak since about 50k miles. It's not enough to drip, but it wets the engine bottom side of the engine. I thought it was the front main, so I replaced it when I replaced the timing belt. During this tear down, I can clearly see that it's not coming from the front main. The metal around the front main is very, very clean. The oil appears to be coming from either the PS pump or the AC compressor. Has this happened to anyone else?

Any suggestions would be greatly appreciated.

Also, I seem to recall that Mazda sells an engine rebuild manual for the Miata. I'm going to call Trussville about it today. Does anyone know the exact name for it?

Does Mazda use various sized bearings to fine tune bearing clearance like Honda? I don't happen to have a parts manual for the Miata like I do the Prelude. Speaking of, does anyone have a parts manual for a 99 Miata?

[71dsp]

Found some parts manuals here. I'm downloading them now: http://www.mazdaspeeddevelopment.com...miatapubs.html

Maybe it's worth it to start autocrossing the Miata to get in the Mazda Motorsports program. I won't be doing nearly as much racing with the Prelude as I hoped this year anyway.

[Mark52]

The Masdaspeed Development program is great, in my opinion! Sometimes you can even slip in a body parts order and they won't notice it! (Autocrossers are not eligible to purchase body parts through the program ). I rebuilt my 2000 engine with all new seals, bearings, pistons, rings, etc. purchased thru their parts program.

[71dsp]

Do you mind sharing how much it cost for the parts? :)

[Mark52]

Do you mind sharing how much it cost for the parts? :)

It's been several years ago that I did it, so I don't have the invoices. You ought to go ahead and register with them and say that you are building a Miata to race, then you'll have access to the parts lists and be able to see what the cost is for what you need. The way you find the cost is to enter the part# as if you are going to order it, and it shows up in your shopping cart.