Sunday, March 30, 2014

More engine rebuild complications - Miata Piston Rings

I recently ran into another set-back.  Some friends were over to help me with the assembly.  The plan was to install the piston rings onto the pistons and then install the crank and pistons.  The plan quickly went to hell...

If you, like me, have never assembled an engine before or handled a piston, you would have never thought that those little dinky piston rings are engineered for a very specific orientation on the piston.  Let's review using this naked piston as a reference.

The bottom most set of rings are the oil control rings.  As I understand it, the purpose of the oil control rings is to retain a little bit of oil to lubricate the piston to cylinder wall during the up and down stroke.  This bottom most ring is actually 3 pieces.

The second or middle ring is the 'scraper'.  It scrapes the side of the cylinder of oil to keep it out of the combustion chamber - the semi-circular, bowl shaped area between the top of the piston and the bottom of the valves.  It is OK for oil to be present in the cylinders up to this point but not above.  If oil makes it to the combustion chamber that means that the piston rings are sealing properly, results in low compression and the oil dilutes the combustion and results in blue smoke out the exhaust.

The top or first ring is the compression ring.  It is responsible for compressing the air from the intake manifold with the fuel being injected from the fuel injectors while the spark plug ignites the mixture and creates the big boom that forces the piston back down the cylinder and makes the engine run.

The original Miata Factory Service Manual published in the early '90s provides information on how to install the piston rings.  The oil control rings don't have an up or down orientation but they do have to be 'clocked' in a certain fashion for purposes that I don't really care to learn...  The second/middle ring does have a top and bottom.  This one is easy to figure out which was is up just by looking at it.  The top/first ring is a fucking bitch.  That's a technical term...

The image below is from the FSM published in the early 1990s.  I state the publishing date for a reason.  A reason that cost me a week of time in this build...  This early version of the FSM states that the top ring is marked with a letter 'R'.  Guess what?  Things have changed since the 1.6L Miata engine was first manufactured and this version of the book was published.  The new piston rings that I sourced from Mazda Motorsports do not have the same markings as they used to.  The top / first piston ring can now either be marked with an R, marked with a dot, have a bevel on the edge that is supposed to be oriented upwards or it could have no frickin' marking at all.  A more recent publication of the Hayes manual (which I don't have) states that the top / first ring will be marked with a dot.  That still doesn't help since mine don't have a dot...  Hmmm...

Since I bought my parts from the good guys at Mazda Motorsports, I called them to get insight and learned that the version of the FSM I was using had been updated.  They emailed me the most recent version of the FSM which states the following with regards to piston ring orientation.  Pay attention to #2...
Yeah...  Great....  Where's that face palm meme?  That would fit well here...

Thankfully, I got this sorted but lost a week which means delays when I can get started racing again.  I'm enjoying the engine build but tripping over this was annoying.  Regardless, thanks to friendly Miata people posting on and the guys at Mazda Motorsports, this mystery was solved.

The oddest part is that we couldn't even see a bevel or taper in the top / first piston ring.  3 of us tried to find some sort of mark that would distinguish which was was up or down but we couldn't.  The top set of rings did have one obvious visual marking - a white paint dot - but no mention of how this paint mark relates to orientation can be found anywhere.  The only time I was able to visually see the beveled /tapered edge on the inside of the first ring was when I stacked a couple of rings together and held them over a white background like in the picture below.  If you look close enough, it looks like there may even be a smaller bevel on the bottom side of the piston ring also.  Either way, I wound up installing the top ring with the white mark on the right - which placed what I thought was the most noticeable beveled / tapered side upward.

With this mystery sorted, I was finally able to start assembly and I made great progress!  I'll make another post on that in the next couple of days.  Hope this helps someone else out in the future.

Sunday, March 9, 2014

Testing and Cleaning the Miata's Fuel Injectors

Since the engine is apart, now would be a great time to send out the fuel injectors to get tested and cleaned.  Lots of places to choose from including:

Normally, I would have used Advanced Autosports since I get many of my race parts from them but I forgot they offered fuel injection services so I sent them to RC Engineering.  I mis-placed the fuel injectors from the core 180k mile engine during my move so I removed the fuel injectors from the '91 engine that was in the car with 91k miles.

I was surprised at the test results!  2 injectors were dripping.  Dripping is not good for power.  The other 2 injectors were better but not great.  Never would have expected dripping injectors at 91k miles.  The previous owner of that motor must have neglected fuel filter changes and gotten some gunk through the fuel filter and into the injectors causing the 'dripping' condition.  Glad I got this done.  $107 well spent I think.

You may want to consider sending your injectors out for servicing if you haven't.

Cleaning, cleaning, cleaning engine parts for the rebuild

Well, since I won't have time or budget to make the first two races of the season, I've lost some of my motivation in getting this rebuild done quickly.  So I slacked off this weekend and did other things - like have fun.  I did spend some time in the garage today cleaning some ancillary parts and checking to see if I'm missing any parts for the rebuild.

Cleaning the Throttle Body and Intake Manifold

A clean intake is a good thing.  Might as well do it since the engine is apart.  Better airflow, cleaner air = reliable power.  This really took a lot longer than I expected to get the internals of these parts clean.  Lots of nooks and crannies that you need to get into with engine block cleaning brushes.  

I started with the intake manifold and throttle body.  I started by removing the electricals.  Marked which clips belonged to which injector and removed the fuel injector harness:
Next, removed the throttle body from the intake manifold.  I don't think it had ever been removed before.  It took some effort to separate the throttle body from the intake manifold.  I realized I will need a throttle body gasket since it fell apart during dis-assembly. :(  Both the throttle body and intake manifold were pretty nasty and gunky inside.  Yuk!  You can't really see inside the intake manifold in this pic but it was just as nasty (if not worse than the rear of the throttle body you see in the pic.
Here is an attempt to view in the intake manifold.  Looks nasty in the pic.  It was just as nasty in real life.

Decided to start with the throttle body.  I busted out the carb cleaner and brass wire brushes and got busy on the throttle body.  Here is a during shot.
Almost done here.  Spent a ton of time with the wire and nylon brushes getting all the nooks and crannies of the throttle body clean.  Lots of gunk in there.  More than I expected considering this throttle body came from a car with only 91k miles.  Final step - trying to remove the frickin' gasket.  This thing was hard as rock.  The razor blade was the key to getting it off.

Next, moved onto cleaning the intake manifold.  I ran out of carb cleaner so I used the mineral spirits and wire brushes on it.  Turned out OK.

Inside view of the intake port.  Nice and clean now. :)

View from the throttle body opening after scrubbing with mineral spirits and long handled wire brushes.  Going to get some more carb cleaner and give it another cleaning with some nice caustic car cleaner since I have the time.

Cleaning Ancillary Parts

This is far less important than the throttle body and intake manifold but I had some time to kill and wanted to do something brainless so I cleaned up the water outlet, head-to-block bolts, piston squirters, coolant hard lines and other bits and bobs.  Pics!

Lots of work.  Some with little value but I like clean engines so I'm happy with the time spent since I have some time to kill right now.

Sunday, March 2, 2014

Miata Engine Rebuild Complications....

So...  Turns out the original 'short nose' crank that was on this motor is damaged. I discovered this when I was test fitting a new woodruff key and timing cog that I had ordered from Mazda Motorsports.  I ordered a bunch of parts and a rebuild kit from them.

Remember from my earlier post where I had a difficult time removing the timing cog from the crank?  I should have taken that as a sign that the keyway in the 'short nose' crank was damaged.  Actually, it was the second sign.  The first sign was that the large 21 mm bolt that holds the timing cog and pulley on the end of the crank was hand tight.  That bolt should have around 100 ft/lbs of torque holding it on so for it to be hand tight is a bad sign.  When that bolt is loose, the woodruff key, pulley and timing cog are not properly attached and causes the pulleys to wobble. is full of threads on the issue and YouTube has various videos on the topic.

The machine shop must have missed the issue with the keyway when they were checking the crank over.  Here is a pic of the issue.  This keyway is no where near as bad as some of the horror stories you see on the forums.  I could fit a .229 mm feeler between the woodruff key and keyway.

I briefly considered the 'Loctite Fix' that you read about on but after researching it further and getting input from people, it is more of as a repair to get you by for a while and can fail again.  Since the motor was apart, there was no point in putting it back together with a damaged part.  Especially on a race car.  I decided to get a replacement 'big nose' crank.  Click to research Miata crankshafts.

I decided to pull the running 'big nose' crank motor that was in the car so that I could use the crank from that engine.  So I invited a few friends / Spec Miata competitors over and we pulled the motor last Saturday afternoon.  Yes, competitors in my region are also friends!  The racing community is very supportive of its members.  Victory Machine graciously offered to clean and prep the new crank without charge so I dropped it off.  It turned out great.

So I now have all the parts that I need to assemble and rebuild the engine.  I spent a lot of time with carb cleaner and engine cleaning brushes cleaning up all the oil and coolant passages and chasing the threads all over the block in preparation for assembly.  Time to get busy bolting it together and testing clearances with Plastigage.  Should be a learning experience.