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  • Whitfield
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Crank keyway and timing gear damage / repair
[glow=red,2,300]Editing in progress...  Looking to add pictures soon.  [/glow]

Crank keyway and gear repair by H. Sue From a Mazda Miata BBS.

The crank keyway damage seems to be to common among the little Suzuki engines both 1.3L & 1.6L.  This damage is most noticable by the vehicle showing a loss of power at low rpm's and becoming difficult to tune.  Oftentimes the crank accessory belt pulley will show a wobble.    Please follow the factory Suzuki tightening specs and avoid this from happening to you.

[glow=red,2,300]Page 1[/glow]

The Loctite Crank Fix for Bad Cranks on the '90 miata

This procedure is not my idea. It was originally posted to by a Loctite employee who goes by the handle of S oftop.
He intended it to be an inexpensive and long term fix for the worn crank keyway. My 1990 miata had this problem. With the alternative being a replacement motor I had nothing to lose by trying this except my time and some parts costs. Here's what I did.
NOTE: This procedure is for miatas where a worn out
crank keyway has already been discovered. Lamce Schall's ( garage article explains how to avoid this problem on engines that are in good condition.

No guarantee or warranty is made on the long term effectiveness of this procedure. I read about it on the Internet and simply report my experiences here. Use the info at your own
discretion. Your results may vary from mine.

Using the instructions, I bought the following parts and
supplies.  The Mazda parts came from Roebuck Mazda (
which is now Trussville Mazda.  The prices and part numbers from
October 2000 appear below.  Loctite 242 is available at auto parts
stores. The Loctite 660 is harder to find. Mine came from an industrial supply
house. If you find a Loctite 660 supplier, get a tube of Loctite 243. It's 66%
stronger than the 242, but still allows the pulley to be removed later. By the
way, Loctite 660 was formulated by Loctite for pulley and keyway repair.
July 26, 2002 - Here is a vendor with an 
web adress ( that carries Loctite

This design is found on all 1990 and some 1991 miatas.
You're looking at the crankshaft gear. The gear turns the timing belt that
rotates the camshafts, A pulley also bolts to the gear. That spins a belt for
the alternator and water pump, and a second belt for the power steering and/or
air conditioner compressor. If the crankbolt loosens, the crank gear is free to start eroding the key and keyway. With time, the crank gear slips backward, which causes retarded valve
timing and a loss in power.  The initial symptom is a gradual power loss, making the problem hard to detect. Power loss is caused by the retarded cam timing and is most apparent
under 3000 rpm. . Above 4000 rpm, the power seems to come back. Now most 90-91
miatas normally are peaky like this, but have more low end power. Some owners
detect nothing wrong and just become used to a slower car. As the keyway wears
further, the engine loses more and more power. If ignored, the keyway can get so
worn that the engine no longer can run well. That is usually not ignored. I've
read that some cars exhibit a wobbly crank pulley. I did not notice that. This
was my second miata and I had driven many others. I realized my 1990 had less
power than normal. Otherwise, it started and idled well and as the previous
owner told me "once you get up to speed, it goes pretty good."
When I read about the loctite fix in October of 2000, I decided to inspect my
motor and see what was happening. The first bad sign was that the crank bolt was
only finger tight. I got my first look at the keyway and saw that it was

Later in the 1991 production run, Mazda changed the crankshaft design to use
a stronger crank bolt.. The later design allows more clamping force on the
crank. Traditional repairs are to install the newer crankshaft that will accept
the larger bolt, or to swap in a newer engine with the newer crankshaft. These
are good approaches to follow if one wants a robust repair that will not need to
be revisited. It is probably cheaper to swap in a new or used engine than to
take out the old one and repair it.

    This procedure, in my opinion, is best suited for a do-it-yourself mechanic
because it is labor intensive. If you're paying a shop to do it, maybe your
money is better suited toward a traditional repair as there is no guarantee that
this procedure is permanent. If you do have it done, I would ask the shop their
opinion first. If they see it as a workable procedure, it's likely that both you
and the shop will be happy. In short, there is no guarantee. Proceed at your own
risk.  It's just a reassembly of the crank pulley assembly using new parts on the
old crankshaft. The use of a new crank bolt is mandatory, as bolts do stretch
and lose their holding strength if re-used. The use of loctite on the bolt
threads increases that holding strength even more. Loctite compunds on the
crankshaft-pulley contact area also serve to increase the holding strength. This
patch probably won't well if the threads in the crankshaft are damaged or if
pieces of the cranksg\fat nose have broken off.

The procedure doesn't repair the worn keyway although it does fill it with
loctite compound. . The purpose of the keyway is to provide alignment. The bolt
provides the holding power. So the repair should work without repairing the worn
keyway as long as one can align the pulley for proper cam timing.
hanks go to miata fourm user "softop" for consulting with his technical
staff at Loctite Corporation and then posting a procedure to follow and which
products to use!

[glow=red,2,300]Page #2[/glow]


The procedure is very similar to a timing belt change, except
that you re-use the old belt. Follow the samesteps you would need to disassemble the front of the motor
and expose the crank shaft.  Here are some
photos to show the scope of the project.

See a Mazda Shop Manual for comprehensive instructions on timing belt replacement.
  This page is for information only and does not represent instructions or procedures.

Some Photo Highlights

Getting ready to open timing covers. Radiator is drained. Intake plumbing
        and coolant hoses removed. Accessory belts off. It's far easier to work
        with the plastic pan under the motor removed.
       I also removed the fans and dropped the sway bar.
        Valve cover is off. Timing covers off. I rotated the crankshaft to top
        dead center and marked the belt with white paint (white-out) so I could
        easily put it back the same way.
       As I did not replace the belt, I left the little coolant hoses in place
        and just swung the belt out of the way.
New woodruff key on worn crank. The keyway wear allowed the pulley to
        slip about 10 degrees which would be a 20 degree retard on the valve timing.
        The old key was worn and allowed the slippage.
       The new key had enough contact to align the gear and crankshaft for re-assembly.
  I did have one major problem doing this fix. Even though the old crank bolt
  was finger tight when I first tried to remove it, a little bit of rust and a
  burr on the threads caused it to seize. Instead of getting out the <i>Liquid
  Wrench</i> and trying to rock it out, I forced it and it snapped off. I later
  removed what was left of the bolt with a screw extractor, propane torch, 8 hours
  of effort, and a lot of thinking. Be careful!

Clearance between pulley and crank should be checked to see if it exceeds
        .020 mm. This is usually done using plastigage. It's a plastic string
        inserted between the pulley and crank and then squashed as the two parts
        mate. The width of the squashed part is checked against a chart for the
        clearance. I couldn't fit the plastigage between the two surfaces without
        it being cut.
       I finally snipped off a small piece of .020 shim from an old feeler gauge
        and used that as a go/no-go check. My tolerances were under the .020 number.
        If it had been over, then Loctite 660 is recommended between the crankshaft
        and pulley surface.
          I put Loctite on the crankbolt and anywhere there was metal-to-metal
      contact on the gear, even on the back as shown above. It also went on the
      inner surface of the gear.. In the keyway slot, I used Loctite 660. As mentioned
      on the left, the 660 product is only used in the keyway unless the pulley-crankshaft
      clearance exceeds .020 mm.
      This crude tool took about two hours
        to make. It maintains crank/pulley allignment while torquing the bolt.
        Without it, it's my opinion there is some risk that the pulley will slip
        out of alignment because of the wider keyway when the bolt is tightened.
        It also locks the crank and allows easier application of torque. I highly
        recommend its use.  Note that
        because I was sloppy in making it, only three of the four hold-down bolts
        fit the fixture,  The bolt has been tightened to 85 foot pounds with an accurate torque
        wrench. Excess loctite is dripping off the assembly.
        The loctite 242 that I used has a long setup time, but the loctite 660
        will start to set within minutes after assembly. I worked quickly. It
        took less than 15 minutes to mount the pulley, bolt on the fixture, spin
        on the crank bolt and torque the assembly.
        It's very important to allow 24 hours for curing. Since I was in no rush,
        I gave it 48 hours before I did any further work on the engine.

  Reassembly was straight forward. The engine started after I put it back together.
  Re-alignment of the crank pulley gave me the correct valve timing again. The
  car's performance improved. Prior to the repair, my carwould take 15-16 seconds
  to accellerate from 50 to 70 mph in 5th gear. After the repair, the typical
  times were 12-13 seconds. which compares well with the 13.8 seconds reported
  by Car  Driver in their initial test report on the 1990 miata.

   I did the work in November of 2000. I now have about 2 1/2 years and close
  to 21K miles on the repair. The car is a daily driver and used for autocross.
  I have heard from two otherowners who have more mileage than I on their repairs.</p>
  Your results may not be the same. Some owners have had this repair fail after
  a month. I do not know why it works on some cars and not on others.
  • Last Edit: Monday, Mar 14, 2005, 10:28 PM by Whitfield

  • Whitfield
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Re: Crank keyway and timing gear damage / repair
Reply #1,26263.msg282516.html#msg282516

This is a link to my actual repair. 

I used information form this article along with consulting the Mechanic which I apprenticed under.  I also sought the advice of a friend and fellow Kick owner.  He is a machinist for Alcoa (Reynolds Wrap factory) and had just repaired his Kick's crank keyway.

I used:

      A like new (used) Lower timing pulley, bolt, & key.   

      A MAC Tools 12x1.25 Tap to clean the crank threads

      JB Weld to repair the Keyway
      Loctite 609 to bond the Lower pulley to the crank

      A New front crank seal

      A new timing belt

I will be reassembling the works this evening and if I run into any other issues or failures I will let you know.

More about Loctite>>>

[glow=red,2,300]LOCTITE 609 (LOC-60921)[/glow]  is [glow=green,2,300]Green[/glow]  $12 609 augments the strength of press-fitted assemblies and can be used on slip fits up to 0.005" diameter clearance. Great for spindle bearings, lip seals, and bearing races. Temp. range: -65º to 300ºF (-54º to 149ºC).

[glow=red,2,300]Loctite 620 [/glow]
Is a high temperature (450ºF), high viscocity liquid retaining compound. Provides a shear strength of over 3,800 psi on steel. Locks and secures metal cylindrical assemblies up to .015" diameter clearance. Prevents metal fretting and corrosion. Seals against leakage.

Loctite 660  Quick Metal   is [glow=silver,2,300]Grey[/glow]   1.6oz. is $20 - $30
High strength retainer for worn shafts, housings, couplings, keyways, splines, etc.  Gap Fill .010 - .020 diameter clearance.  Prevents bearing spin in housings and can form in-place shims. Cures resistant to oils, cutting fluids and most solvents.


  • Last Edit: Wednesday, Oct 26, 2005, 01:58 PM by Whitfield

  • Whitfield
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Re: Crank keyway and timing gear damage / repair
Reply #2
Runs like a champ  ;)   Still going strong...

  • Whitfield
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Re: Crank keyway and timing gear damage / repair
Reply #3
Same Song Second verse....  ;D

Someone installed the wrong crank bolt.  This one was WAY too lang and bottomed out before tightening down.

To be continued....   Replacment Suzuki Parts From "Scott" at Mike Duman Suzuki are due in today. You can reach Scott in PARTS at  1-800-438-6267  or   Here by PM'ing him " Suzukiparts1 " in this thread   (,78099.0.html   )  

OBD II engines require  a new bottom pulley with the crank sensor trigger ring.

Also included in the repair was a 12x1.25 Metric tap for cleaning the threads in the crank.  I've gotta give props to my local Car Quest for having EVERYTHING in stock including the hard to find metric tap. 
  • Last Edit: Friday, Jun 13, 2008, 09:25 AM by Whitfield

  • Whitfield
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Re: Crank keyway and timing gear damage / repair
Reply #4

Cleaned threads with a tap

Install the new crank seal.

Epoxy'd new key in place.  Due to the extensive damage I didn't use a thin sheet of paper to make the key removable.
I also smeared a thin coating of epoxy around the crank to take up the excess play / wear from the old gear dancing on the crank.  The new gear had too much lost motion.

Sand smooth, knocking down the high spots and check for proper fit.  Apply the the loc-tite and inststalll the new gear.

  • Last Edit: Tuesday, Jul 01, 2008, 05:38 PM by Whitfield

  • Whitfield
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Re: Crank keyway and timing gear damage / repair
Reply #5
A few good links on the subject...

Loc-Tite engineer screen name "Soft Top" from MX-5 Miata board.

The inexpensive fix will work as long as damage is limited to the keyway and the crankshaft is not bent or cracked. The right epoxy is a good tool for rebuilding the keyway - but it doesn't address the reason that it failed in the first place. The fact that "none have failed yet" is not decisive - remember, originally some of these engines went 100,000 miles without failure in the first instance. The company I work with, Loctite, are acknowledged around the world as the experts at this type of operation. This is the fix that our engineers came up with:

Read Lance Schall's article at

Read Skip Cannon's article at

Disclaimer: I work for Loctite. I suspect - but have not been able to prove to date that a retaining compound of some kind was used in the original assembly. If so, its failure during service or absence in subsequent re-assembly would likely be the root cause of the problem.

1. Dismantle the crankshaft and pulley and check for damage. If there is no damage then you can re-assemble. TIP - This is a good time to change the oil seal. Use a new bolt and a new key if the old one is in any way damaged.

2. Without inserting the key, slide the pulley onto the crankshaft and determine the bore clearance - plastigauges are good for this.

3. If the diametrical clearance is less than 0.2mm put a coating of Loctite 242 or Loctite 243 threadlocking compound around the shaft where the pulley seats. If the gap is greater than 0.2mm then coat the shaft with Loctite Quick Metal instead.

4. Re-assemble using a new key (make sure it is fitted in the right direction). Use a new bolt. Before inserting it put a couple of drops of the Loctite 242 or 243 on the threads and torque to specification.


If when you dismantle the engine you find damage which is limited to the keyway as shown in Skip Cannon's article then here are the steps you should take:

1. As far as possible using a small file clean up the keyway damage, removing burrs etc. from the area where the pulley seats. Take care not to file the undamaged side - this will be your reference for correct alignment during re-assembly. If the pulley keyway is damaged then it is best to use a new one. Using emery tape (not to fine because a coarser surface works better with this repair method) linish the crankshaft to a smooth slip-fit.

2. Clean the bore of the pulley and mating shaft area very thoroughly using a cloth and solvent or methylated spirits and let dry for 5 minutes.

3. Without inserting the key, slide the pulley anto the crankshaft and determine the bore clearance - plastigauges are good for this.

4. Squeeze a little Loctite Quick Metal into the keyway and fit the key. Fill the damaged part of the crankshaft keyway with Quick Metal.

5. If the diametrical clearance is less than 0.2mm put a coating of Loctite 242 or Loctite 243 threadlocking compound around the shaft where the pulley seats. If the gap is greater than 0.2mm then coat the shaft with Loctite Quick Metal instead.

4. Re-assemble using a new key (make sure it is fitted in the right direction). Use a new bolt. Before inserting it put a couple of drops of the Loctite 242 or 243 on the threads and torque to specification. Remember to keep a clockwise pressure on the pulley during assembly to ensure correct alignment. Torque bolt to specification (80-87 foot pounds).


Author's note: Keyways of this type are normally used for the purpose of alignment. Assembly forces are usually transferred to other areas such as tapers - which from the photo's seem to be absent. This means that the force locking the assembly is the clamp load exerted by the bolt then holding the pulley against the shaft shoulder and any interference between the pulley and the shaft. Even a partial loss of this clampload (bolt stretch, thermal cycling, vibration) would lead to the entire load being transferred to the key - and subsequent key failure. It would seem that this design is only good engineering practice if a retaining compound is added during assembly. That's what I suspect originally shold have occurred and that's what I have proposed.

The Loctite 242/243 or Quick Metal that you have added to the shaft cures to a tough thermoset polymer between the mating faces, keying into machining marks and micropores of the metal. This process turns the whole of the mating face area into a keyway (after alignment you could actually remove the key altogether and it would make no difference to the performance of the assembly). This assembly will dismantle with the standard puller.

The threadlocker on the bolt is also very important. Torque wrenches work on a theory called torque/tension relationship. Basically this theory determines that by applying a certain amount of twisting force to the fastener, a predictable amount of clamp load will be generated. This is only true if friction can be controlled. The quoted torque specification was valid for a NEW fastener in "as received" condition. This means that it was coated with a substance with lubricity equal to that of 30W oil. Less lubricity than this and the resultant clampload will be too low resulting in loosening. Higher lubricity will lead to more clampload which leads to thread failure and fastener stretch. The Loctite threadlockers mentioned have a lubricity controlling agent which provides lubricity in the correct range. Beware - this is a patented property of Loctite threadlockers and cannot be found in any other brand. It will also lock the bolt and prevent it from loosening.

I told you this fix was engineering quality and here's the number. After using the 242 or 243 threadlocker as described, to dismantle the assembly you would need to apply a force of 2000 pounds for every inch of mating suface area.

Sorry about the long post.

[This message has been edited by Softop (edited 12 August 2000).]