Trackspeed Engineering

Timing Belt Change

by Gary Fischman

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Changing the Timing Belt (and front crankshaft seal)

The Miata timing belt must be changed every 60,000 miles. Although the California Owner's Manual says 105,000 miles, this is just to satisfy a state requirement that says timing belts should last 100,000 miles or more. Still, it should be done at 60,000 miles. The Miata engine is a non-interference engine, meaning that the pistons will not crash into the valves. However, if you neglect this major service, you risk being stranded due to a belt break.

WARNING: Changing your own timing belt is not for the faint of heart!

If you screw it up, your engine may not run! However, if you are confident in your abilities and generally do your own work, you should be able to handle it.

Special Tools

Changing the timing belt requires no special tools. You will probably want to have a 14mm deep well socket, a 3" extension for your 1/2" drive, and you may want a steering wheel puller to remove the crankshaft pulley. (It shouldn't be necessary) Also, you may want a second pair of hands to hold the camshaft pulleys steady while you install the new belt. You will also need something to drive the new crankshaft and camshaft seals in. An appropriate piece of pipe, covered with electrical tape to prevent cutting the seal worked well for me. A long breaker-bar will be needed to remove the crankshaft bolt.

Alternatively, you can do what Bill Snyder did and make your own tool to help remove the crankshaft bolt:

It is basically a large washer (I think it was a 1 1/2" washer) that fits over the crank bolt and then there are holes drilled in it for the 10mm bolts. I then welded a piece of 1/2" keystock as a handle. The handle can be blocked any number of ways.

Archie Glasgow sent in this photo of a homemade tool that keeps the engine from turning while removing the bolt. We haven't tried it, but we see no reason why it wouldn't work.


Parts to buy in advance

The Breakdown...

Before you begin - LABEL EVERYTHING!!!! Label each part as it is taken out and also label its bolt sizes and what the part was connected to/in/between. This aids in any confusion to the novice engine worker.

  • Drain the coolant
    Into a suitable container and save it for reuse or, if you plan to replace it, for recycling.
  • Remove the large plastic air intake pipe
    Remove the hose clamps at each end and one bolt. Also take off the chrome air pipe that runs across and into the valve cover.
  • Remove the upper radiator hose
  • Remove the two water hoses connected to the thermostat housing.
  • Optional: Remove the cooling fans and the radiator. This will give you a lot more room to work. It isn't too hard. There is an electrical connector on each fan. Remove the 2 bolts at the top and bottom of each fan and lift them out. Disconnect the lower coolant hose from the radiator (accessible from the trap door on the debris shield underneath) and remove the two upper bolts holding the radiator in place. Lift out the radiator and carefully put it aside. Be careful not to damage the cooling fins on the radiator. The are easily distorted.
    Note: If you lift out the radiator, the fans come with it and you save yourself a bit of hassle trying to loosen up those 8 corroded bolts that bolt the fans to the radiator.
  • Remove the A/C belt
    Loosen the tensioner bolt, pivot bolt, and lock bolt on the power steering pump housing until the belt can be slipped off.

This is easier if you put the car in gear to keep the engine from turning. Loosen the bolts holding the pulley in place. As you remove the outside plate, pulley, and timing belt guides, make a note of the order in which they came off and the direction they face. This is important.
1992 and later: Remove the 21mm crankshaft bolt. This will be difficult. Put the car in 5th gear and engage the parking brake. Using a long breaker bar, crack the bolt loose.

TIP: Sean Archer and Vic Harder from the Canadian Rockies Chapter of MCA offered this great tip. We haven't tried it, so we're not sure what kind of caveats might be attached to it, but its sure worth a try! If you're replacing the camshaft seals or water pump as well, you won't be able to do this.

When you are ready to remove the old timing belt and apply the new one, cut the old belt in half for its entire length. That leaves lots of room to push on the new belt. Push the old belt back as far as it will go on the crank and cam sprockets, leaving approximately a 1/4" to slide the new belt over. Once the new belt is on and lined up correctly, simply cut the old one off and push the new one into place.

TIP: Kim Burgess suggests: Clamping the cams in positions aids the solitary mechanic in reinstalling the belt by 'locking' the cam wheels into position.

Place Cresent wrench on each cam at the bolt-shaped section of the cam between the #1 and #2 lobes. Position wrenchs such that they overlap and C-clamp them together to hold camshafs in position.

Inspect and Replace the Front Crankshaft Oil Seal

This step is optional. If the seal is leaking, definitely replace it. If not, you may want to let it go until next time. Especially if you have an early model with a "questionable" crankshaft.

These tips regarding the seals  were sent in by Joe Heagney ( jheagney@micromatter.com ):

Belt had obviously been changed recently, almost no gaskets   on belt covers, got the seal out and discovered that the crank nose was  ok, but the sealing surface had been gouged in several places by some  cretin trying to remove the seal, probably at timing belt change time.  After much soul searching and not a little deliberation on the familial  heritage of the cretin, I cleaned up the sealing surface by filing and  grinding with a Craytex rubber/abrasive wheel on a cordless Dremel tool,  and changed the seal. Then I thought, what about the camshaft seals? By  this time I had realized that removing these seals was a real pain in the   posterior and had discussed the problem with a friend who had taught   motorcycle repair in a former life. He suggested (here's tip number one)  that you can drill the seal with a small drill and screw in a sheet metal  screw and pull on the screw to remove the seal. He had a minerature slide  hammer puller for this, but vise grips and a hammer work since they  aren't very tight. Next he said that he had had cretin gouged motorcycle  cranks to repair and had smoothed the crank and then cleaned the gouge  and filled it with epoxy (tip number two). When I pulled the seals from  the camshafts it was obvious that the same cretin had been there as well.   To make it easy to work on the camshafts I pulled the bearing caps and  filed the sealing surface smooth and then cleaned and filled the gouges.  I used J.B. Weld, which has a long cure time, but it made a very smooth  surface when sanded with 600 wet or dry.

Richard Ohnstad sent this tip on reseating the seals:

What I finally found that seemed to be a real good fit was a 1 1/4" coupling ($1.99 at ACE Hardware). This piece has a 1 7/8" o.d., and a 1 1/2" i.d. In addition the ends are finished off and very smooth, so there was no real need to wrap the end with tape. I also used this coupling to set the camshaft seals.

CAMPULLY.jpg (25061 bytes)Inspect and replace the camshaft seals if required

Note from Chris Roberts on camshaft seals:

The only GOOD way to remove the cam seals is to pull the #5 camshaft cap. Remove the two bolts, place a rag over the cap, and grab gently with a large pair of slipjoint pliers at each edge of the cap. Alternating sides, you can rock back and forth slightly and the cap will come free, and then removal of the seals is a piece of cake with no risk of damage to the cams themselves. One important detail that must not be overlooked is cleaning up the surface where the cap sits on both the cap and the head, and then applying a THIN coat of flange sealant(hylomar is what I use) before reinstalling the cap. Then install the new seals after oiling the inner lip and drive them in until they are flush with the cap. The service manual does not advise bottoming the seals out.

Replace the Water Pump

If you plan to replace the water pump, now is the time. When you're done, come back here.

Replace the Timing Belt

  • Verify that the timing belt pulley mark is aligned with the v-shaped timing mark on the front of the engine.

Mike Stollov sent this suggestion:
I used small G clamps to keep the timing belt in place on the cam pulleys during the timing setup. Very little pressure is required & it stops annoying belt slips & you can concentrate on getting the crank pulley belt lined up properly.

Top Dead Center
  • Verify that the camshaft pulley marks are aligned with the marks on the seal plate.
  • Install the timing belt.
    CAUTION: Do not rotate the belt counterclockwise.
    Someone recently did and managed to shear the exhaust cam pulley. You'll require some help installing the belt. Someone will have to hold the camshaft pulleys steady while you thread the belt on. This will take a couple of tries to get it right.
  • TIP: Leigh Doonan suggested this as an option: Use two wrenches on the flats of the camshafts so that the handles are near each other. Then use a pair of locking pliers to hold the wrenches together. Like this:
  • Turn crankshaft 2 turns clockwise
    Align the timing belt pulley mark with the timing mark.
  • Verify alignment of camshaft pulleys.
    Be sure the marks on the pulleys are still aligned with the marks on the seal plate. If not, remove the belt and repeat from the beginning of the Replace the Timing Belt section.

Putting it back together...

At this point its a good idea to check the ignition timing and idle speed. If everything was done correctly, it should not have changed, but it can't hurt to check.


Comments from Andy Kearl:

I recently changed the timing belt on my 94 Miata. However, despite reading all the articles I could find, and referring to the enthusiast manual by Veloce Publishing I still managed to get the timing 1 tooth off on the exhaust CAM...

I did not scribe the lines on the cam sprockets, as suggested, which with hindsight was probably the wrong thing to do, but I learnt a couple of things that may be worth passing on or adding to the description on your web site.

Firstly, although obvious give yourself plenty of time, get some help if possible, and don't be put off... Follow the instruction for setting the timing prior to removing the old belt, and when you do take the timing belt off try to pay attention to how much, if any, the CAMS and crank move. Use a wrench as suggested to realign the CAMs and crank. You might like to add a couple of additional white-out marks to the CAM sprockets where they line up with the top of the cam cover backing plate. Although I made a mistake the first time I ultimately used the factory timing marks and found them to be satisfactory.

I failed the first time because I introduced an error when reinstalling the belt. In my efforts to keep the belt tight on the exhaust side of the engine I failed to notice the exhaust CAM sprocket moving slightly as I pushed on the belt. I was so preoccupied with the inlet, which moves slightly when the belt tension is removed, and worried about the crank that I simply didn't notice.

I followed the tensioning procedure and thought I checked the timing but obviously I didn't check it closely enough which brings us on to my first point. Once you have reinstalled the belt, checked the timing, tensioned it and rechecked the timing, take a break and get a coke or something. When you come back refreshed you can recheck everything again. It might seem obvious or unnecessary but it's certainly quicker than doing the job twice! I was adamant that everything was right the first time even though the car ran like crap. I didn't drive it all weekend and was resigned to taking it to the dealer, but my wife suggested I have one more look - it only I'd taken more time checking...

Needless to say when I removed the cover and turned the engine over to TDC the error was clear to see, one tooth off on the exhaust side. I removed the belt, aligned everything and reinstalled, but the same thing happened, the exhaust CAM moved slightly. The only way I could get the belt on correctly was to hold the CAM position with a wrench and get a friend to install the belt. This time I was watching everything very closely... Once the belt was on and tensioned correctly I rechecked everything and life was good, no errors! And one last thing, when I redid the timing a second time I managed to do it with the radiator, hoses and bottom shroud still in place. It tight but you can manage...

Comments from Fax Ayres:

I had one issue that I thought might deserve attention in the article. As a newb to this particular project on this car, I was unaware of the importance of the crank trigger wheel - I thought it was just some sort of dust plate. I put it on concave face towards the front of the car...and the car would not run at all. There was not mention of the importance of the orientation of this plate in the article, but a quick search in the forums turned up the issue. I removed the two drive belts and the drive belt pulley on the crank, flipped the crank trigger wheel so that it was facing convex face-forward, put everything back together, and the car started right up and runs perfectly.


Back to the Garage

21 June, 2014



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