Warning, long-winded story:

Currently building a Superspec Cup (formerly Supermiata) car. Crappy paint and dirty, but extra baller Blackbird Fabworx cage and nice electronics:




I swapped in a 2003 VVT which was rebuilt by Treasure Coast Miata. I bought the engine second hand from a guy parting out an NB.
About the engine/car:

• Forged rods (mahle I think)
• stock pistons
• APR hardware
• mildly ported head
• skunk2 throttle body
• squaretop intake manifold
• RB header

The engine had not yet been run when I bought it, and I noticed a couple of accessory parts were not installed correctly when I bought the engine. The VVT feed line, idle control valve, and a few other things weren't hooked up right, but I fixed these things and did a timing job before installing. The engine sat for about 2 years before it was run.

Once the car was finally put together and wired (thanks Chris Allen!), it got run on the dyno at Engineering Concepts. Great shop which was very patient with my somewhat problematic car (we had to bleed the clutch when we got there and had several water leaks..).

It took a few runs to finally break in, and it blew a lot of smoke at the beginning. Eventually it stopped smoking, and it made decent power ~139whp as a baseline before adding any timing. We stopped tuning when we heard a somewhat disconcerting noise which would come and go and followed RPM. [not super exciting pull video here: [url]https://www.youtube.com/watch?v=ArCOAhdxgLQ ]

I took the car back home to try to figure out what was going on with the noise, but when I started the car back up it had low oil pressure (around 8 psi, cold idle). I pulled the engine and started taking apart the accessories to look for the noise. It turned out to be a bolt behind the water pump pulley which had worked itself loose and was rattling:

Beat up bolt

This however, did not explain the low oil pressure. Before pulling the engine I tried swapping sensors to rule out the oil pressure sensor.

I dropped the oil and cut open the filter to look for debris. The end of the oil draining from the engine was somewhat shiny, but there were no chunks of metal. The filter had a couple minuscule pieces of metal, but not like I have seen with other peoples bearing failures.


only spot with a couple pieces, the rest of the filter was clean

shiny oil, just break in?

Next I pulled the oil pump because I've read about all sorts of failures with these, and I figured maybe mine had not enjoyed sitting for a couple years and decided to off itself.

Is there something in particular I should look for in the oil pump? To my eye it looks brand new. Is there a way to check the relief valve?

Oil pump pulled from the engine



Lastly I pulled the main bearing caps off to check the bearings for wear and measure clearance. Clearances were between 0.00175 - 0.003 (number 4 was the outlier at .003):


Some scuffing on bearing #1:


worst one

I bought a new Boundary High Flow Assembled OilPump W/Billet Gears - stage 2 (72 psi), but I'm trying to decide what to do with the engine. Since the pump I pulled off the engine didn't look obviously damaged, I don't want to throw a new pump in there and still have issues.

Trying to decide what to do right now. The way I see it, these are my options (please tell me if there are others!):

1. Install the new oil pump and slap it all back together #yolo
2. Install the new oil pump and put in new main bearings.
3. Take the whole thing apart, clean and inspect everything, new rod/main bearings, hone block, reuse as much as possible.
4. Swap for another engine with good compression.

What do? (would prefer not to do option 4).

 

I'd go with #3. I'm not sure you need a hone, as long as it was broken it well, and you're happy with it. If it was originally just honed for stock pistons, honing a honed engine may just lead to low compression.

As someone who disassembles and reassembles engines and cars with months inbetween them on a regular basis, I might suggest buying a few paint pens of various colors. Every time you torque a bolt to factory specs, mark it so you know it's torqued, that way little things like timing cover bolts don't delay you further.

I should say, that if you're in a budget/time crunch, the low oil pressure could be explained by a loose pickup tube or a bad oil pump relief valve, both of which you're replacing, so option 2 might not be a bad idea, as long as you at least check and inspect clearances on the rods. Rods usually wear out first.

 

Did you check the rod bearings as well? They go way before the mains, so I am wondering how your rod bearings look if you already have one scuffed main bearing.
If you do not have much blow by or smoke, I would probably go with your option #2, but with the addition of checking and/or replacing the rod bearings as well.

 

My vote is on having the crank polished and new crank and rod bearings at the least. The last thing you wanna do is put it back together and have it lock right up again and thats a bit more material off of the mains than i'd be comfortable with.

Otherwise i agree it probably doesnt need a hone but it probably wouldn't hurt either. Possibly new rings just to refresh it while your in there. but if you hone 100% put new rings in too for the peace of mind.

 

Thank you guys for the input. I will check the rod bearings next. It sounds like they will probably need replacing as well. Seems like option "2.5" is the way to go-- replace rod/main bearings + possible crank polish. It stopped smoking out of the tailpipe, so I think the rings managed to seat somewhat, but it was still slightly smoking out of the valve cover crankcase breather (no catch can yet, just a filter).

Curly, I like the paint pen idea. I've been using one for parts of this build and it's very useful. A lot of accessory bolts seemed to rattle loose just during the dyno time. I'm sure my competition blackbird fabworx engine mounts contributed to this. I'm planning to medium loctite all the accessory things.

I'll take a look at the cylinder walls from the underside once I remove the crank. Do you think I can get away with not pulling the head if the cylinder walls look good? Or do I need to pull the rods/pistons out to install new rod bearings? Sorry if this is a noob question--trying to reduce work if I can, while still doing it right.

 

You can change rod bearings without having to pull the head.

 

No, push the pistons down close to TDC, with the crank close to BDC, careful of valves if it’s an interference build, then rock the rod sideways, replace the bearing, and obviously the bearing in the cap is easily replaced. Lube the rod, then pull it up to seat against the crank.

 

Thank you! I'll give it a shot.

 

So I got it all disassembled, but it looks like I have to take the clutch/flywheel off to get to the lower half of the mains... doh



The rod bearings definitely look worse than the mains, but I'm trying to decide whether to polish the crank. Thoughts?

Rod 1:


Rod 4:


Worst looking crank surface, I think rod 2:

 

Took the crank to my local machine shop to have it polished, but ended up needing to be ground 0.010" under for mains and rods. I've ordered the 0.010" under ACL bearing sets, but I'm unsure of the tunnel/journal specs for the new bearings. I haven't had the block machined since it is still mostly together, sans crankshaft. At the very least I'm going to check with plastigauge when the bearings arrive, but does anyone know the tunnel specs? Also most dial bore gauge sets seem to be from 2-6" but miata bearings are smaller. What's the go-to dial bore gauge for miatas?

 

Have someone who knows these engines well inspect and assembly it for you. Your going to work this engine hard so reliability is paramount. Grinding the crank was a start in the right direction. The Manley rods need to be inspected and so does the main bearing caps for shift since they have been converted to studs. Deck the block & head and have it professionally honed. I would use extra scrutiny while inspecting the pistons. Stock cast pistons will work but the ST forged (Mahle) pistonS will make more power and last longer.