[freedomgli]

Nice work! I didn't have the time or patience to photo-document the process when I did mine. Thank you for making the effort for the benefit of the community. The job isn't all that hard, just a little tedious. I also used the 949Racing guide when installing mine. Here are some extra notes I made to supplement their instructions:

Adding Zerk Fittings to your Mazda Miata Control Arms
Applicable to 1990‐2005 Mazda Miata with Aftermarket Polyurethane Bushings

General Instructions
• This guide contains pictures of a Mazda Miata with Zerk fittings installed in the control arms to facilitate lubricating the pivot points when you’ve installed aftermarket polyurethane bushings. These pictures are intended to serve as a guide but they are not definitive and you are solely responsible for your own actions.

• Use common sense when installing Zerk fittings. Make sure you can readily access them with your grease gun and they don’t cause interference or inhibit suspension travel.

• Zerk fittings are not absolutely necessary but they will allow you to readily maintain the lowest possible friction in the suspension action over time. You could disassemble your suspension and pay for another wheel alignment each time you need to lubricate the pivot points but it’s easier to leave the suspension alone and simply lubricate the pivot points with your grease gun.

• If you run out of the Hyperlube grease the bushings come with, 949Racing recommends Superlube available at Ace Hardware stores. Personally, I use a synthetic grease from Royal Purple in my grease gun and it does a great job so far.

• 949Racing used 6mm threaded Zerk fittings but there are a few different types of grease fittings that will do the job.

• The basic procedure is to remove the control arms from the vehicle, press the old bushings out, drill holes for the Zerk fittings, deburr and tap the holes, install the grease fittings, lubricate and install then new bushings, lubricate the mounting hardware and then re‐install the control arms. Subsequently, you can maintain the lubrication with your grease gun.

• Take care to locate the Zerk fitting at the exact spot where the two halves of the bushings meet so injected grease fills the space between them. For the one piece bushings, remove the steel sleeve, locate the drill in the hole you just made in the control arm then drill all the way through the plastic bushing, then reinstall the steel inner sleeve.

• The rear upper inner (R_U_I) control arm only has enough room for a Zerk fitting if your suspension has droop travel less than OEM. Check your RUI with dampers installed at full droop before you pull it all apart. See Canaille's method above for an alternative solution if your suspension has interference.

• For lowest friction and best suspension action, 949Racing recommends lubing once a year in most climates, or twice a year if you drive the car in really wet climates.

What is a Zerk fitting?
• A Zerk fitting is a threaded grease fitting that is screwed into components that require lubrication. The patent for the Zerk fitting was granted to Oscar U. Zerk in January 1929, and the assignee was the Alemite Manufacturing Corporation (thus the eponymous names for the fittings). Today many companies make these grease fittings.

• Zerk fittings can be installed in ball joints, universal joints or parts that contain bearings.
They are commonly used on heavy industrial machinery. They used to be common in automotive applications but have largely been phased out in favor of “maintenance free” components that get thrown away and replaced with new ones when they wear out.

• The lower section of the Zerk fitting is threaded and is screwed into the component you wish to keep lubricated. The non‐threaded part of the fitting is a grease nipple to which a grease gun is attached when grease needs to be injected into the part. The nipple usually contains a ball check valve so that grease can only flow one way into the fitting.

• Installing a Zerk fitting requires drilling and tapping a hole in the part, then screwing in the fitting. Installation is made easier if the part is already removed from the vehicle.

• Zerk fittings do have a finite life span and will need to be replaced on occasion. They can get clogged, rusty, get broken or mysteriously disappear. Keep spares handy.

What size Zerk fitting do I use?
• Zerk fittings are available with straight (UNF, UNEF) or tapered threads (NPT, NPTF, PTF, SAE‐LT, BSPT, Metric).

• Zerk fittings are available in straight, 45° and 90° and flush nipple configurations.

• Using 6mm Zerk fittings on your Miata would allow you to stay consistent with the rest of the metric hardware used on the vehicle.

• SAE ¼”‐28 fittings are readily available and they are popular for many automotive applications. The threads are close to the same size but they are not interchangeable with 6mm Zerk fittings and their bodies tend to me much larger than 6mm Zerk fittings, making them less ideal for confined spaces.

• Use the size/configuration Zerk fitting best for your particular application and grease gun.

• Be sure to use the proper size drill and tap for whichever size Zerk fitting you choose.

What size drill / tap do I use?
• M6 x 1.00 Zerk fittings require a 5mm drill bit and a regular M6 x 1.00 tap to cut the threads. If you don’t have a 5mm drill bit you can use a #8 or #9 drill bit. Unless you have a complete drill index, you probably don't have a #8 or a #9 drill bit, either. Go ahead and use a 3/16" drill bit. The Miata control arm is relatively thin and soft. My M6 x 1.00 tap had no trouble cutting threads in a 3/16" hole.

• It is recommended that SAE‐LT taper threads be assembled into 1/4"‐28 UNF, Class 3B, straight threaded holes having a modified maximum minor diameter of 0.2151 in. to insure 75% minimum thread height. Therefore, you should use a #3 drill bit. If you don’t have a #3 drill bit you can use a 7/32” drill bit. Most people have a 7/32” drill bit laying around,
making SAE ¼”‐28 fittings a popular choice.

How do I drill the hole?
• Safety goggles!

• Secure the control arm in your bench vise. Be sure to use protective rubber jaws so you don’t damage the control arm.

• Mark the location of the hole you are going to drill with a center punch and hammer. It should be exactly in the center of bushing.

• Use your electric drill to make just one hole per Zerk fitting. Don’t create two holes by drilling all the way through the other side of the control arm.

How do I make the threads?
• Once you have drilled the hole you must remove any metal filings and smooth any sharp edges with a Whirly‐Gig deburring tool or a file or a utility knife

• Carefully start the tap in ‐‐ the most important thing is to keep it STRAIGHT. Screw in a few turns, back up a turn. Screw in a few turns, back up a turn. Don't force it. Use a cutting fluid like TAP Magic or WD‐40 to keep the tap well lubricated while cutting.

Installing the Zerk Fitting
• Clean the threads to ensure there are no contaminants.

• Screw the Zerk fitting into the threaded hole by hand to reduce the possibility of cross-threading the hole.

• Continue tightening the fitting with a wrench until the hex flats on the fitting bottom out on the part's surface.

• Do not over‐tighten! Zerk fittings are relatively fragile and easy to break if you over-tighten them.

 

[freedomgli]

You're over thinking it. There is no need for concern. Just do what everyone else does and you'll be fine. When you pump the grease into the Zerk fitting it follows the path of least resistance. The bushings are a tight fit inside the control arm. They are split in the middle and have grooves on the inside that channel grease between the metal inner sleeve and the polyurethane bushing. Pump in grease until it comes out the sides. Wipe up excess grease. Done. Piece of cake!