by Adam Silver
Remember how you promised to faithfully change the timing belt on your Miata every 60,000 miles? That was 20,000 miles ago. You’ve got that nagging feeling that today could be the day that belt finally snaps! So you commit to do something about it. After checking with the dealer on what this costs, you think, hmmm, you have some mechanical aptitude and what you lack in experience you’ll make up for in time and TLC. Or, if you’re like me, you suffer from DIYS (do-it-yourself syndrome). Either way, if you haven’t done this before, changing the timing belt on your Miata is not a trivial exercise.
This article won’t be a step by step guide. For that there are a couple of excellent articles on miata.net. This is a list of some of the problems I encountered doing this, and what I found that worked. This is assuming you will also change the water pump (highly recommended), and while you’re at it, you might as well put in a new thermostat, hoses, o-rings, gaskets, seals, and belts. SO...
Parts List ($270-$300 with genuine Mazda parts):
- 1 timing belt
- 1 water pump
- 1 water pump gasket
- 1 water pump to water inlet manifold gasket
- 1 water inlet manifold o-ring
- 1 upper radiator hose
- 1 lower radiator hose
- 1 thermostat
- 1 thermostat gasket
- 2 hoses from the thermostat cover
- 1 thermostat manifold o-ring
- 2 heater hoses
- 1 cam cover gasket
- 2 front camshaft seals
- 1 front crankshaft seal
- 1 alternator belt
- 1 power steering—AAC pump belt
- 1 tube ( Permatex ) Hylomar HFP
- 1 tube Permatex Ultra Grey
- 1 tube of Loctite (the thin green penetrating stuff )
- distilled water
- 1 set of spark plugs
- 1 oil filter
- 4 quarts of synthetic oil (hey, it’s your Miata!)
- Torque wrenches: (I used three!)
- sockets: (10mm, 12mm, 14mm, 17mm, 21mm)
- box wrenches: (10mm, 12mm, 14mm)
- Craftsman cross force wrenches (12mm, 14mm)
- Phillips screwdriver
- small long flat blade screw driver
- vise grips
- breaker bar
- zip lock bags (for parts)
- neon dry erase marker
- digital camera! (for remembering where things go)
- small shop vac (for sucking up old silicon seal)
- sharp scraper
- Bamboo skewers (handy for making little scrapers)
- channel lock pliers
- plastic buckets for capturing old coolant
- good work lights and small flashlight
- 1 5/16” ID PVC coupler (to tap in cam shaft seal)
- 1 5/8” ID PVC coupler (to tap in crankshaft seal)
- 1 3/32” drill
- 1 #6 x 1/2 pan head wood screw
- lots of shop paper towels
- nitrile gloves
- sheet of plastic (for under the car)
Draining the cooling system
The first thing—after getting the car on jack stands and removing the front mud guard—is to drain the old coolant. Coolant is nasty stuff. It can be a skin irritant, and will certainly kill pets that find it sweet tasting. It’s also just plain wrong, not to mention illegal, to dump coolant down the drain, in the gutter, in a hole in your back yard, or toss it over your neighbor’s fence, so be careful to collect it (all) in a bucket. You can haul it off at some point to the local haz-waste collection point—or possibly the local auto supply will take it. I used a 5 gallon bucket with a tamp-down lid from the paint department in the hardware store. I chose to flush the cooling system because the coolant looked pretty dirty. I did this by refilling the radiator with coolant and distilled water, letting the engine run until the temperature gauge was at the usual level and the fan went on, ensuring that the thermostat was well open. I then shut the engine off and let things cool for a hour or so and re-drained the radiator –this took about 3 or 4 iterations. The Miata cooling system holds somewhere shy of two gallons, so you may need an extra bucket. This seemingly messy job really isn’t that bad.
Taking Things Apart
At this point you’re ready to remove the air intake, the radiator and thermostat housing hoses and belts. As you’re doing this, get your digital camera and TAKE PICTURES of every electrical connector and wiring bracket. There are a bunch of them and though most of them kind of go back right, believe me, you won’t remember all of them or how they were oriented.
As the pulleys, cam cover, engine covers, and timing belt tensioner come off, it’s very helpful to put the bolts for each item in a zip lock bag and tape it to the part.
Also take pictures of the front engine covers, the timing belt tensioning spring, and the crankshaft pulley backplate before you remove them. Unless you have a repair manual (which I highly recommend—you can purchase a .pdf on eBay) it’s 50/50 getting it back on the right way. In general it’s a good idea to take pictures of everything before you take it apart.
Loosening the Alternator pivot bolt
This one is really buried in there, very tight, and hard to get a wrench placed in a way that you can apply any force. What finally worked really well was a 14mm wrench that Craftsman makes (the crossforce wrench) that has a 90° twist from the open end to the box end.
Removing and replacing the radiator
This is something that is recommended because “it’s just a few bolts”, but is really not necessary unless you plan to replace it. I once fried an engine on my commute because a small crack in the upper plastic housing I had been treating with regular top-ups broke open one day. The plastic used on the stock radiator gets very brittle after about 5 years. All-aluminum aftermarket radiators are pretty inexpensive, so this might be good time to replace it. Hey, with all the money you’re saving on shop labor it’s good insurance!
Removing the timing belt
It’s a good idea to take out the spark plugs. It just makes turning the crankshaft all the more easy. Always rotate the crankshaft in a clockwise direction. Once the timing marks are lined up, get the camera on level with the cam shaft timing marks on the sprockets and the back plate, take a picture, and then stare it for a few minutes until you really see exactly how they line up. Although it’s an excellent idea to mark the timing belt to the cam sprockets, I found it’s good to really study it also. I went through the exercise of transferring the old marks to the new belt, the marks on the new belt were off for some reason when I installed it. But with the pictures I was able to line it up properly.
Removing the old water pump
This is going to spill more coolant when you take it off, so be ready with the bucket under the engine.
Replacing the cam shaft seals
The classic method is to carefully cut the seals with a razor and get in with a seal pick and pull them out. But this is difficult, not to mention it’s pretty easy to score the seal surfaces on the cam shaft, seal housing or both. To avoid this, pull the front cam cap that holds the seal. The cam caps are held in with not only bolts, but a very precise internal bushing that registers the cap in exactly the right place on the engine head. What I did was use channel-lock pliers with a rag and carefully wiggled the cam caps back and forth until they were free. With the caps off, the seals pop right out.
I was able to get the cam sprocket off easy enough by using a small electric impact driver. However using the two wrench and clamp method is the best; you’ll need to do this anyway to get them back on.
A vacuum cleaner and a bamboo skewer works well to remove any old silicon seal from the flange area. Put a thin coating of Hylomar on the flange mating surface and carefully torque the cap bolts to 100-125 in/lbs. Tap the new seal in using a 1 5/16” ID PVC coupler. The seal should be flush to -.4mm to seal housing. I had to grind out the inside of the PVC coupler a little bit with a Dremel tool to get it to clear the outer flange on the cam shaft. But it worked great.
Removing the crankshaft pulley bolt
This is the 21mm bolt on the end of the crankshaft, torqued to about 120 ft/lbs. There is a SST (special service tool) that bolts to the crankshaft pulley flange to remove this. Some special tools can be created by duplicating the hole pattern in a piece of hardwood or a large washer welded to a bar. Other methods include removing the radiator and getting an impact wrench in there. I used the method of putting the car in 5th gear and applying the hand brake to lock up the drive train. That is, after saying out loud “I’m not doing this”; with a little flex and groan the bolt came right off.
Replacing the front crank seal
According to the service manual you remove the seal by cutting it and digging it out with a rag over a screwdriver. This seal is more robust than the camshaft seals making this not only hard to do, but you can very easily gouge the bearing surface on the crankshaft. I ended up drilling a 3/32 hole through the center of the seal face and screwing in a #6 wood screw 1/4”. I grabbed the screw head with vise grips and seal came out so easily it surprised me! After putting some motor oil on the inner diameter of the new seal I tapped it in with a 1-5/8” ID PVC pipe coupler. It shouldn’t be tapped flush into the housing, but with a .6-1.0mm step into the housing.
Installing the new water pump
This is straightforward except for the inlet manifold. The manifold mates at a flange on the side of the water pump, and the gasket—if you can call it that—is this thin metal thing. The inlet manifold wraps around the side of the engine and connects to a pipe using a large o-ring as a seal. It’s important that the inner diameter where the o-ring will sit is clean, and it’s very important that the mating surface on the flange to the water pump is flat. When I removed it from my car I found a paper gasket that had been glued. This meant it had to be scraped off, which really messed with the flatness of the flange. I ended up taking it to a machine shop where the flange was cleaned up and flattened on a belt sander. This was effective and a lot less costly than having the guy set up a milling machine. Use a coating of Permatex Ultra-grey on this flange. Read the directions on the Permatex tube because if this flange leaks, it all has to come apart again and it’s really buried in there. Again the Craftsman cross force wrench (12mm) came in handy to tighten the two flange bolts. These bolts should be torqued to 14-18 ft/lbs, though it’s impossible to get a torque wrench in there so that’s snug, plus.
The water pump also has a thin metal gasket. I put a very thin coat of Hylomar on it mainly to hold it in place. I checked with a mechanic friend, who said you don’t need any silicon for the water pump-to-engine seal. The water pump bolts are torqued to 14-18 ft/lbs.
Installing the timing belt tensioners
One is fixed and the other is drawn in by the spring. Of course you took a photo of this before you removed it. But If you didn’t, the spring cover has the closed face facing the fixed tensioner (facing right), with the hook curled up at that end. When applying tension to the timing belt the service manual says don’t apply additional tension beyond what the spring supplies.
Installing the Thermostat
Use a new o-ring between the thermostat housing and the engine head. Torque the bolts to 14-18 ft/lbs. The thermostat goes in the housing with the jiggle-pin at the top; the gasket to the thermostat cover with the printed side facing the engine head. Torque the cover bolt to 14-18 ft/lbs, the nut to 15-22 ft/lbs.
Put a dap of silicon seal on either side of the front cam caps and the rear (six points in all). The cover has a tightening sequence, which is on the internet. Take several passes and sneak up on the final torque values.
It’s amazing to me that a shop can turn this job in a day. If you have experience, a weekend is aggressive. I would recommend working slowly to keep up concentration—and allow about a week. Happy wrenching!
|Cam cover bolts
|Three front cover bolts
|Water pump pulley bolts
|Crank shaft pulley bolts
|Thermostat housing bolts (to engine head)
|Timing belt tensioner bolts