loctite fix for crank keyway

5/20/2018 Loctite Fix for Crank Keyway

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Loctite Fix for the early (1990-1991) Miata Engine

Pictures

Introduction

Diagnosis

Instructions

Parts needed

Pictures

Results

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 mocrank 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 o

Some Photo Highlights

Getting ready to open timing covers. Radiator is drained. Intake plumbingand coolant hoses removed. Accessory belts off. It's far easier to work withthe plastic pan under the motor removed.

I also removed the fans and dropped the sway bar. Some people alsoremove the radiator at this point, as it's a few more bolts.

Valve cover is off. Timing covers off. I rotated the crankshaft to top dead centerand marked the belt with white paint (white-out) so I could easily put it back thesame way. However, it's easy to align the belt.

As I did not replace the belt, I left the little coolant hoses in place and just swungthe belt out of the way.

New woodruff key on worn crank. The keyway wear allowed the pulley to slipabout 10 degrees which would be a 20 degree retard on the valve timing. The oldkey was worn and allowed the slippage.

The new key had enough contact to align the gear and crankshaft for re-assembly.

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Clearance between pulley and crank should be checked to see i f it exceeds .20mm. This is usually done using plastigage. It's a plastic string inserted betweenthe pulley and crank and then squashed as the two parts mate. The width of thesquashed part is checked against a chart for the clearance. I couldn't fit theplastigage between the two surfaces without it being cut.

I finally snipped off a small piece of 0.20 shim from an old feeler gauge andused that as a go/no-go check. My tolerances were under the .20 number. If ithad been over, then Loctite 660 is recommended between the crankshaft andpulley surface.

I put Loctite on the crankbolt and anywhere there was metal-to-metal contact onthe gear, even on the back as shown above. It also went on the inner surface ofthe gear.. In the keyway slot, I used Loctite 660. As mentioned on the left, the660 product is only used in the keyway unless the pulley-crankshaft clearanceexceeds .0.20 mm.

This crude crank holding tooltook about two hours to make. It maintainscrank/pulley allignment while torquing the bolt. Without it, it's my opinion there issome risk that the pulley will slip out of alignment because of the wider keywaywhen the bolt is tightened.

It also locks the crank and allows easier application of torque. I highlyrecommend 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 Iwas 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 toset within minutes after assembly. I worked quickly. It took less than 15 minutesto mount the pulley, bolt on the fixture, spin on the crank bolt and torque theassembly.

It's very important to allow 24 hours for curing. Since I was in no rush, I gave it 48hours before I did any further work on the engine.

Comments on Crank Bolt Torque:

The shop manual torque on the small crankshaft bolt is a nominal 85 ft-lbs. Since this procedure was originally described. some users have chanced goinghigher on the torque, hoping that the bolt is strong enough to take it or that Mazda used a higher grade steel in later bolts. There is no documentation to supportthis and it is is left to the user. Perhaps an additional 10% is not unreasonable. I left it alone though. .

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