Editing in progress... Looking to add pictures soon.
Crank keyway and gear repair by H. Sue From a Mazda Miata BBS.http://www.miata.net/garage/hsue/LoctiteCrank1.html
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. Page 1
The Loctite Crank Fix for Bad Cranks on the '90 miata
This procedure is not my idea. It was originally posted to www.miataforum.com
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 (http://miata.net/garage/crankshaft.html
miata.net) 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 (www.roebuckmazda.com
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 (http://www.mcmaster.com
) 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!Page #2
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 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 Liquid
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.