Saturday, January 25, 2014

My Spec Miata 1.6 Engine Rebuild has begun!


I last posted about this in July.  Shortly thereafter, work got busy, summer happened, bought a house, moved, did some house renovations and I'm finally getting started on this project.

I started this project with a lot of research.  I'm fairly handy with a wrench but I've never opened a motor before so I educated myself about the rebuild process.  I'll make another blog post with helpful videos, posts, pictures and books and such that I used to educate myself but for now I'll focus on my progress.  While wrenching, I mostly refer to the Miata Factory Service Manual (aka FSM) and the Miata Enthusiasts Manual.

I bought an engine stand from Harbor Freight for $65 and got the engine situated using my engine hoist.  Also cleared some space in the garage so that I can work on this.  Here is my work space:
Following the FSM and the Enthusiasts Manual, I removed all the stuff on the front of the engine, the valve cover, head and oil pan.  All of this was easy as it was pretty detailed in the books and it is honestly pretty obvious how to get these parts off.  Progress was quick.  I made an effort to take pics of everything so that I could reference the pictures when putting the engine back together again.  I also tried to mark parts so that I could re-install them in the same position that I removed them from.
The camshaft journals are marked so didn't need to do anything here.
Cams off:
With the cam removed, the HLAs come off by hand.  I almost lost them when I started rotating the engine.  I got an egg crate and labeled the location that I removed them from.  
The cam journals look pretty rough.  The markings you see here don't feel rough or scratched up.  I'll need to revisit this later.  Right now I'm focused on rebuilding the bottom end.
Engine pan off.  Easy peazy.
Some minor gunk (oil pan sealant?) in the oil pickup but mostly clean beyond that.
Head is off.  
This is why you should you DISTILLED water in your coolant system and NOT tap water!  Those are mineral deposits from minerals in tap water from the previous owner's mechanic. :(  The cooling passages also have this crap.
Pistons look OK from the top.  Carbon deposits on the top of the pistons.  You can see more gunk in the coolant passages too.
View of the underside.

Removing the timing cog on a SNC 1.6 Miata 

I was making great progress until I got to the timing belt cog.  It wouldn't budge.  I spent a good long time Googling about how to remove this bitch of a part and tried everything I read.  Some people suggested 3 prong gear pullers.  Tried a few different ones and they didn't work.  The FSM says that the proper tool is a steering wheel/gear puller.  I tried that too but the bolts included in the kit do not fit the threads in the timing cog.  I wasn't sure what I was going to do about this....

I wound up posting about my issue on the local Miata club forum (Bay Area Miata Drivers).  Thankfully, a fellow club member (and total stranger) from the local Miata club offered to lend me a tool he fabricated for this job.  So he mailed it over and long story short - it worked.

Here is the custom tool I used to remove the timing cog on the SNC 1.6 Miata.  I used the screw driver just to keep the crank from turning.  The timing cog fought me the whole length of the crank shaft but it did eventually come off.  Of course I broke it in the process while trying to manhandle / pry the damn thing off but I didn't plan on re-using it anyway.  I could now continue to dis-assembling the bottom end.
Pretty rusty and gunky as you can see:
Here is is cleaned up and dried off from it's bath of penetrating liquid.  The keyway looks in good shape so I can re-use this crank.

Dis-assembly of the bottom end

Things progressed quickly from here.  Following the dis-assembly procedure of the FSM, I removed the oil pump / front cover.

Then the rear cover:

Measuring engine clearances

Time to start measuring.  The FSM and Enthusiast manual both suggested measuring clearances before tear down.  I figured it would be a good idea also so that I can compare clearances when I assemble.  

I bought a feeler gauge and checked the clearances on the Connecting Rods and wrote down the measurements.  I had never done this before.  I had expected that the connecting rods would have a fixed position on the crank.  Turns out they move front and back along the crank shaft so as I inserted feeler gauges into the gaps, the connecting rod would move slightly allowing me to progressively insert larger feelers until such a point as the maximum range of the factory tolerances was met.  It actually took me a while to figure out what was happening so pay attention when you do it.  Turns out my clearances were within spec.  Goodie! :)
The FSM also said to use Plastigauge to check oil clearances on the connecting rods and main caps.  I was tempted to but I didn't have any and was making such good progress that I decided to skip that step and complete the dis-assembly.  I marked the connecting rods using a punch as the Enthusiast Manual suggested so that I could be sure to use that same piston and rod in the same cylinder.  I noticed that the main caps had unique numbering so I noted these numbers in my note book.  The FSM and Enthusiast Manual specifically state to NOT attempt to punch these caps so take note.

Eventually, we ended up with a bare block.  Well almost.  I removed the oil piston squirters later.

The cylinder walls all looked good.  There were no ridges at the top of the cylinder bores.  The cylinder bores felt pretty smooth.  I'm going to send this out to the machine shop to clean up and measure the bores with their super accurate and expensive bore gauges and then figure out what parts I need to buy.

I need to have a good look at the pistons and the bearings.  I'll post more about those in another post.

Thanks for following along.  Let me know if you have any questions or advice.

Friday, January 3, 2014

Comparing thermostats - Mazda OEM vs NAPA

I took a bunch of pics and measurements of various thermostats when I was testing them on my Miata.  I thought I would share them in case you are curious.  I compared and measured them looking for differences to substantiate why the OEM might be 'better' as some people say but could not notice any difference in materials using my naked eye or primitive measuring tools.  Even the spring feel similar when compressed using my hands for force.   Not very scientific but good enough to establish that the NAPA stuff is not made of weak springs or materials that are flimsy.

First, let me start by saying that I only compared the OEM Mazda thermostat with the NAPA sourced thermostats.  The Miata uses a generic, common sized thermostat with a 52mm / 2 1/16" diameter.  NAPA was the only parts store that would give me a hard time when I ask for a generic 2 1/16" thermostat in 180* or 160*.  Every other part store would only look up the Miata and sell me whatever the stupid system said was the one.  Just walk into NAPA and ask for a generic thermostat in 2 1/16" and 180* temp with the part/reference number of 142 and they should be willing to help you.

Here is a pic comparing the OEM thermostat with the 180* #142 Napa thermostat.  The NAPA is shorter but it makes no difference as it fits the thermostat housing / water outlet housing perfectly.

Here is a pic of the inside of the thermostat housing (aka water outlet housing as the part's store books refer to it...).  The thermostat can be shorter and still fit.  However, it cannot be longer / taller the the OE and fit.

Here is a pic [attempting to] measuring the size of the hole that the water circulates through when the thermostat opens in NAPA vs OE.  I couldn't find my calipers so I used a tape measure - sorry.  The diameter of the hole is very similar.  Perhaps only a mm larger in the NAPA.  Napa on the left.  OE on the right.

OEM thermostat:

Hope that was interesting in some way.

Should you run a thermostat in Spec Miata?

Well... it depends.

This is a question that arises often.  I've read all the threads on various forums and opinions on both sides of the question.  Some say get rid of it that it is a failure point.  Some say that the cooling system needs the slight bit of restriction of the thermostat to prevent against boiling the water in the head.  I did some research into this topic and figured I'd share.

Some background on the Miata thermostat
The Miata uses a generic, common sized thermostat with a 52mm / 2 1/16" diameter.  NAPA was the only parts store that would give me a hard time when I ask for a generic 2 1/16" thermostat in 180* or 160*.  Every other part store would only look up the Miata and sell me whatever the stupid system said was the one.  Just walk into NAPA and ask for a generic thermostat in 2 1/16" and 180* temp with the part/reference number of 142 and they should be willing to help you.

Let's get to it
Let me start by sharing some facts from a well known Spec Miata builder and engineer Dan Tiley of Ti Speed Engineering.  He was also a Development Engineer and NASCAR.  Refer to this thread:;f=44;t=003785;p=0#000001

Dan's comments:
I absolutely disagree with the idea of targeting your run hot coolant temperature at 160, 170, or even 180. There are several reasons for this. Your Mazda engine has an iron block and aluminum pistons, which have very different coefficients of thermal expansion. The cylinder diameter will "grow" fractionally at a rate of approximately 7e-6 units per degree F. The pistons grow at nearly twice the rate at 13e-6 units per degree. What this means is that your the clearance between the piston and cylinder wall is larger at lower temperatures. My dyno tests have shown very repeatably with back to back runs that the car will make x HP cold, and will increase with each run and then starts to decrease again after 210, due to the ECU beginning to pull timing. To make the absolute most power, you want that piston to cylinder wall clearance to be as tight as possible. Of course, once the car starts heading for the 240-250 range, that clearance becomes 0 at which point the engine starts to try to make it's own clearance.

My point is that it's a delicate balance act. Peak power is achieved in the narrow window of tightest possible piston to cylinder wall clearance, and the point where the ECU pulls timing.

I can assure you that 100% of the ECM tuning was done with a 192 thermostat installed. Running at a lesser temperature means that you're operating in a region where your fuel and ignition maps are not optimized, thus robbing you of HP's. 

Target 195-205F for your running temperature. I've tapped into the stock Mazda CTS (Coolant Temp Sensor) and read this digitally live on my on-board display, and note the temp while making dyno runs.

Focus on the bold text where he says that the target temp should be 195-205* F.  I exchanged a few emails with Dan on the topic.  He's a smart dude.  He races in the South East US where it gets hot and humid in the summer.  At one point he used to run a thermostat.  Now that the front of the pack of the top prepped car drafts and bump drafts, he has found that he needed to remove the thermostat in order to run optimal temps.

So, like I said, it depends - on your water temps.  Install a coolant / water temp gauge on your car to ascertain what your operating temps are and determine what you should do.  I installed an Autometer Elite gauge with Peak and Hold functions measuring water temps from the back of the head - which is the hottest point in the Miata's cooling system.

If your temps are too low, run a thermostat so that you can get the operating temps up to the target 195-205* F.  If you see temps too high with a thermostat, test without the thermostat and see where your temps are.  I have done this testing here in northern California running at Thunderhill, Sonoma and Laguna Seca raceways.  I'll share my results.

OEM thermostat
The OEM thermostat opens at 192* F.  Lots of people on miata forums and some on spec Miata forums and race forums will go on and on about the OEM thermostat and how you must run an OEM thermostat or your car will spontaneously combust and aliens will come get you.  Yeah.  You can safely ignore them.  Dan Tiley confirmed as much in my email exchange with him.  I've had good luck with NAPA thermostats.  They seem well built.

In my car, running the OEM thermostat, a Koyo 52mm radiator, starting position around the middle / back half of the pack, minimal drafting, northern CA temps ranging from ~60-90* F in dry air, I would typically achieve operating around 210-215* F.  Sometimes as high as 220* depending on ambient temps and the length of the session.  30 minute sessions resulted in slightly higher temps (215+) toward the end of the session.  On hot days, I could feel the power decrease as temps rose and the session or 20 minute race.  The Miata ECU will pull timing as engine temps increase.  You can feel the power difference.

This is what the OEM thermostat looks like.  Note that I removed the 'jiggle pin' which would typically have occupied the space between that arm on the right and the small right protrusion on top.

NAPA 160* thermostat
I briefly experimented with the NAPA 160* thermostat.  This is sometimes referred to as the #42 NAPA thermostat since that is their part number for it.  I read a bunch of people on talking up the thermostat and l tried it.  It sucked on my car in northern California temps.  The engine would not get up to temp - which means excessive wear and low power.  The cooling temps would barely hit 180* F on a hot summer day.  Regardless of what 1950s hot rodders say, those temps aren't appropriate for the Miata.

NAPA 180* thermostat
I next tried the NAPA 180* thermostat.  This works well for me.  Coolant temps typically stay at 200* with this the 180* thermostat.  They'll basically range from 195-205*.  I once observed cooling temps of 208* once when running in ~100* F ambient temps in the middle of August in Willows, CA at Thunderhill Raceway.  Never higher than that.  Power stayed consistent from the first lap to the last lap.  Like Goldilocks and the 3 Bears, the 180* thermostat was just right!

Here is a pic of the NAPA 180* thermostat - part reference number 142.
*Note: Do not use the crappy, paper thin generic gasket pictured above.  It won't seal.  Don't ask me how I know.... :(  Use an OEM or Fel-Pro gasket.  NAPA should have Fel-Pro.

The NAPA 180* looks exactly the same as the 160*.  If you have one installed in your car and are curious about what the temp rating might be, try looking underneath it like so.  This is the 160*.

Comparing the 3 thermostats, it seems like the engine would typically run about 20* F hotter than the thermostat opening point when driving at race pace in mostly clean air - meaning I wasn't drafting lap after lap like some of the guys at the front do.

Now, all this will vary depending on your ambient temps, humidity and how much drafting / clean air you have in your races.  The point is that although some people say that thermostats should be removed, other say thermostats should be kept, others say only run the OEM thermostat; the final answer as it relates to your car, in your region, in your race conditions is going to vary.  So test and figure out what works for you.

If you do wind up doing some testing and can confirm what works in your region, please come back here and share your experience so others can be well informed.