Apexi N1 Damper Installation and Info Guide
The Apexi N1 Damper is a replacement harmonic balancer for the 1990s Mazda Miata (1.6L and 1.8L engines). It replaces the stock rubber-damped crankshaft pulley with a unit that uses a polyurethane intermediate ring instead of rubber. The main reason people buy it is that the stock dampers on these engines tend to separate from the harmonic balancer over time, especially when driven hard or subjected to high RPM sustained loads. Once that rubber degrades, you get crankshaft windup under load and potential timing chain damage. Not an emergency situation but a long-term reliability fix that matters if you do any track days or tune your Miata. Installation is straightforward but not trivial. You need a 22mm socket on the crank bolt, a breaker bar, and ideally a hub puller or a proper pulley remover if the stock balancer is seized. The bolt torques to about 148 to 157 foot-pounds depending on your source. I use 152 foot-pounds as a happy medium. You also need to mark the crank sprocket and the harmonic balancer alignment dots before removal so you know the timing reference is correct when you put everything back together. Here is how the actual install goes. Start by removing the serpentine belt. Then remove the upper engine cover and the accessory bracket that sits above the harmonic balancer. This bracket is held by two 12mm bolts and a 14mm nut. Once that is clear you can access the crank bolt. The bolt is under significant preload so use a long pipe on your breaker bar if it does not want to turn. Never try to hold the engine with the starter to break it loose. That will strip the starter ring gear teeth and you will be buying a new flywheel.
After the bolt comes out the harmonic balancer should pop off. Sometimes it does not. I have encountered several where the steel hub was pressed onto the crankshaft taper and had corroded in place. In those cases a proper hub puller works best. A slide hammer can work but I have seen more balancers get damaged by hammering them than by using a puller. If you do need to use a slide hammer make sure you are pulling from the bolt holes in the balancer face and not prying against the engine block. The aluminum block will not survive that. Before you slide the new Apexi N1 Damper onto the crankshaft, clean the taper surface on both the crankshaft and the inside of the balancer bore with a clean shop towel and some brake cleaner. Any debris left in there will change the seating depth and throw off your timing marks. This is the kind of thing that gets overlooked and then causes headaches later when the timing seems off after reassembly. The taper fit is supposed to be a light interference fit. It should slide on with hand pressure after the old one comes off. If it does not want to go on easily do not force it. Clean the surfaces again and check for burrs or corrosion. One specific issue I ran into on a friend's car was that the alignment dot on the Apexi damper did not line up with the timing cover mark when the balancer was seated properly. The crank sprocket mark was off by about two teeth. What happened was the old harmonic balancer had been installed incorrectly years ago and the timing chain had stretched slightly to compensate. When we put the new damper on and torqued it properly the timing was off enough to cause a rough idle at low RPM. The fix was to remove the timing cover again and check the camshaft timing marks. They were correct so the issue was that the crank sprocket had been installed with the timing chain too loose. We tensioned the chain properly and rechecked everything. The timing marks aligned after that. It took about 45 minutes to diagnose and fix once we realized what was going on. I wish we had checked the chain tension before removing the old balancer.
The polyurethane insert in the Apexi N1 Damper is firmer than the stock rubber. This means you will feel more vibration through the clutch pedal and the chassis at idle than with the original damper. It is not unpleasant but it is noticeable. If you run the car daily and commute in traffic you will notice it more than if you drive it on weekends. Some people add an aftermarket engine mount to compensate for the reduced isolation. Others just accept it. The tradeoff is that the damper will not separate under hard acceleration or high RPM loads the way the stock unit can. If you are planning to install this yourself here is what to budget. The damper itself runs roughly 200 to 280 dollars depending on where you buy it. You will likely need a new crank bolt because the OEM bolt stretches when torqued to spec and Apexi recommends using a new bolt each time. That runs about 8 dollars at the dealer. You will also probably need new serpentine belt tensioner seals if you remove the tensioner assembly. Not expensive but easy to forget. Total parts cost is usually under 350 dollars if you already have the tools. Tool cost is the real variable. If you need to buy a 22mm deep socket and a hub puller set that could add another 60 to 120 dollars to the project. The download for the manual is typically available on the Apexi website archive or through third-party parts sites that host documentation. Search for "Apexi N1 Damper Manual PDF" and you should find a version posted by community members. The manual itself is short, maybe five pages. It covers installation torque specs, part numbers for the various Miata years, and a warning about not reusing the OEM crank bolt. Nothing exotic. Most of the useful information is not in the manual but in forum posts from people who have actually done this job. Forums like MX5Nutters, Miata.net, and NASIOC have detailed threads with photos and torque values from real installs.
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Common mistakes to avoid. Do not use an impact wrench to remove or install the crank bolt. Impact tools will stretch the bolt and potentially damage the crank threads. Hand torque only. Do not apply threadlocker to the crank bolt unless you are in a very dusty or dirty environment. The bolt is torqued to a high value and the friction lock is the primary retention method. Threadlocker can make future removal a nightmare and is not recommended by either Mazda or Apexi. Do not reuse the stock harmonic balancer bolt. It is a torque-to-yield bolt and stretching it again will cause it to fail prematurely. Replace it every time. Another thing people get wrong is the timing mark alignment. The timing cover has a fixed mark and the harmonic balancer has a painted dot. When the damper is correctly seated the dot should align with the cover mark at top dead center on cylinder one. If it does not, check your crank sprocket timing mark against the camshaft timing marks. One rotation of the crank should bring both cam lobes into the correct position for cylinder one TDC. If the marks do not line up after seating the new damper you have a timing issue unrelated to the damper itself. This is usually caused by a jumped tooth on the timing chain during previous service. The N1 Damper is a solid upgrade for street and mild track use. It is not designed for heavily built engines with significant turbo or supercharger kits. If you are running more than 250 horsepower at the crank with a forced induction setup the polyurethane insert may not be sufficient and a heavier duty damper or a billet aluminum unit from a company like Sunfab or SPP would be a better choice. The Apexi unit is good for stock to moderately modified naturally aspirated engines. That covers the vast majority of Miata owners who ask about this part.
If you decide to go ahead with the install take your time with the crank bolt removal. That is the step that causes the most trouble. Use penetrating oil on the bolt threads the night before if they seem stuck. A 3/4 inch breaker bar with a 22mm socket and a four foot pipe over it will handle most situations. If you still cannot break it loose after that, a professional shop with an air impact and a proper puller will sort it out in about fifteen minutes. The actual damper replacement portion of the job takes roughly 90 minutes from start to finish for someone who has done it once before. First time expect two to three hours. Factor in the time spent cleaning up old RTV and replacing seals if you disturb anything on the accessory mounts.
