LOCTITE CRANK FIX - PART 2

The procedure is very similar to a timing belt change, except that you re-use the old belt. Follow the same
steps 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.
 

DISCLAIMER

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 Liquid Wrench 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 .20 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 .20 shim from an old feeler gauge and used that as a go/no-go check. My tolerances were under the .20 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 crank holding 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.

Here's another way to make a crank tool.

 


Here is the pulley locked down with the home made fixture. 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.

 

RESULTS

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.

UPDATE

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.

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.

Email Me (H. Sue)

Updated October 14, 2005