Crank Seal Size

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In the middle of replacing the crank seal on our 90' but having a very hard time getting the seal in.
We are wondering; Is there a difference in size of the seal for a 90 and that of a 93-97? Could I have gotten the wrong one?


Originally Posted by CrvLvrs
In the middle of replacing the crank seal on our 90' but having a very hard time getting the seal in.
We are wondering; Is there a difference in size of the seal for a 90 and that of a 93-97? Could I have gotten the wrong one?

Yep, the short nosed and big nosed crank take different seals, one is larger than the other.  Unfortunately, the SNC seal is a lot harder to find at an auto parts store than the other one.

The difference in size is not subtle...  From recall, I'm thinking at least a quarter inch difference in diameter?
If it seems like about the right size, but you are having difficulty... I'd suggest you are just having difficulty.
The wrong one would be reasonably apparent without having to think about it too much, I believe.

Have you oiled the seal (inside and out) to help make it slide nicely? Is the bore you're trying to press it into free of gouges or burs that could be catching it?

He is here at my house and all went well until we tried to install a new seal.  The old seal was relatively new but was a butcher job of an install.  There are multiple knicks around the outer edge and best guess is it was pushed in place probably with a screwdriver and hammer.  We tried the pvc pipe but seems just a hair too big to fit.  It appears to almost fit.  We tried lubricating well but just can't get it in place.  This is the first time I had this problem.

Try to smooth out the nicks....  they are probably catching the rubber on the outer edge of the seal...

I agree about smoothing out the nicks now that we know the seal is the correct size.  The only practical way I see on doing that is by pulling the engine.  A little photo is added so you can see the old seal butchering and the nicks are shown.  Also notice a more prominent problem?
We are trying to get it all back together well enough so he can make the 3 hour drive back home.  The problems do not end there.  Will let the owner add comments and ask questions when he gets back home again.

Jim - do you think that one can be saved?  I'd be shocked if the sealing surface wasn't also gouged.  Usually if someone is that careless, they don't know what they are doing to begin with.  That's a pretty badly torn up SNC but I guess it's worth the $10 worth of loctite to try.  I think with that one, once I got a fresh seal in there, I used the loctite liquid metal on the inside of the crank gear also and just let it weld the whole gear to the crank end.  My concern is that if you can't fix it, we pretty much know it isn't going to be fixable!

Well, we gave up. Car sits at Jim's. Working on getting it back home and out of my life.

There is a bit more to it on giving up.  I don't see any other method to make the critical repairs other than pulling the engine.  I dont have a hoist.  That being the constant oil drip from the crank seal.  I do have multiple small rotary machine files and other files used for locksmithing but no way to use them to try and smooth out the torn and gouged edges that prevent the oil seal from sliding back in without mangling it.  Another concern was that big chunk missing from the shaft which is clear in the photo posted earlier.
The keyway showed no signs of slippage and the key showed no sign of wear and suspect the key and cog pulley were replaced.  It was also assembled wrong and that thin metal disk was behind the cog pulley and chewed a huge gash and hole in the lower dust cover piece.  It quot;appearsquot; that chunk missing from the shaft was filled with black gasket sealer and then all shoved together.  The posted image shows it cleaned off.  The timing belt had about a 1/8quot; tear on one side, but unable to tell age and the cogs were not chewed.
Other annoyances that made things difficult and caused grief especially when it gets to be 3 AM and start having dummy attacks.
Most of the multiple cooling hoses were not molded so they meandered all over and were held from the belts/pulleys and secured with tie wraps.  The jumble to the heat core made it impossible to remove the lower bolt to the coil pack.  Fixable yes, but why open more cans of worms.  The unused coolant nipple cap was missing, a plug fashioned from a piece of coolant hose and secured with a bolt in the open end and C clamped together.  No biggie there.
Main cooling fan did not work and the AC fan was wired to run all the time with the ignition switched to ON.  There was a gaggle of little vampire taps wired in a jumble.  Fast check shows the main fan to be good and the fan relay clicked when jumpering the TFA and GND, but not when grounding the single wire to the fan switch.  The fan switch cap was broken off and missing.  Again relatively simple to isolate and fix another time but had more pressing issues.
Unknown what type of air filter was installed, but was in a round container with a cone shaped filter that just flopped around inside the housing.  Fixable yes, but something to come back and fix.  Basically there was no filteration of the intake air.
Several bolts were missing, some from the dust covers, and all four from the bottom of both fans.  Scrounged a few from my used bolts bin, but that was not the pressing issue for this session.
Am sure Crvl.vrs can add more if he is in the mood to discuss it with any detail.

Wow. Sounds like you guys need to go find the previous owner of that car and give him a swift kick in the rump!  Why do people insist on screwing things up?

I think you should try fixing the gouges in-situ, and then the loc-tite fix.
While the chances are lower than usual of effecting a long-term solution, it should be good enough to get the car home, and may still work.  And it's cheaper and simpler than pulling the engine.
While it's not ideal to have ruts in the seal's bore..... the seal is only being stopped from entering by the peaks that stick into the space to be filled by the seal, not the ruts that will leave a void around it. You can probably scrape them off with a grave, or rub them down with some emmery paper.
Its not ideal, but if you start with the concept that its already toast, you cant make it worse, but you might make it driveable.
Unless they are huge, nicks in the outer bore are far less of an issue for actually making a seal than ones on the rotating shaft....  
Good luck.
Moderator for quot;Most Helpful Miata-itequot; of the year.



That's a shame but unfortunately, the result of uneducated backyard mechanics.  It's why I try and buy cars that have never had the TB done, especially if it's an SNC car.  I'm not sure what you paid for the car but it looks as if finding a nice, low mileage 1.6 engine might be the best route to travel.  Sorry for your troubles, as least you were mentored by one of the best in our Miata world.


Originally Posted by tom4416
That's a shame but unfortunately, the result of uneducated backyard mechanics.

The timing belt etc. was done by a quot;Garagequot; and one that definately didn't know Miata's nor seemingly care to use the shop manuals at their disposal. Or, was told by the PO to quot;do what you can to get me back on the road.quot;
Either way, upon inspection prior to purchase by eye all that could be diagnosed after severely cleaning the underside to get a clear look at the area was a very slow but steady oil leak originating from the crank seal area when under running condition on a lift. The PO said quot;it leaks very little oil so I just put some in when it's low every cpl weeksquot; leading most of us to think.... simple crank seal replacement. The woodruff keyway and housing butchery somehow wasn't mentioned.... g'figr

btw compression testing prior to discovery of the quot;nightmarequot;
cyl #    dry    wet
----     ---    ----
1         170   190              
2         145   185
3    unable to get accurate reading                    
4         170   190

What was the problem getting a reading on #3?

for some reason the tester wouldn't screw in, although the plug had no problem, threads were fine. We were going to return to it with a different style tester but didn't get to it as we had our hands and minds elsewhere.

With your permission, I will tear it down again and try a fix.  Thought about it for a few days and think found a safe method to remove the cuts and burrs and fashion a new tool to push it in better than that PVC pipe and washer.  If it works will host the tool which will cost about 60 cents to make.  Sorry, don't have the will, tools, or space to replace a crankshaft.
Been floating on IBUPROFEN for a couple of days and ready now to go at it again.  Can see the Miata in this thread.  Is quite the conversation in our neighborhood!  In can put all the pieces right in the step-van to keep from the daily rain storms.  Is that oil seal a common part at AutoZone and if so what is the size needed for the SNC?
Thanks for all the kind words, but remember I have retired 3 times and have time to do things I enjoy ... mainly taking things apart and fixing them.  I can't finish the compression check, ignition timing, or the fuel pump and FPR until it is warmed up and running.

PM sent Jim
I reiterate my previous nomination

both autozone and advance auto carry the front crank seal however depending on the location they may have to order it, $10. Neither carry a SNC bolt. Mazda only. I was quoted $16.00

Meant to host these a little earlier.  Pix 1 shows a little better the damage on the shaft and housing.  I used some mineral spirits, a rag and small wood chip to clean out the oil ring slot.  Notice the gouges and rough edges went all around the edge of the sleeve.  This pix was bleached a bit and taken after a few hours of fine filing to remove most of the protruding burrs and nicks.  Appears now after working on it in the sunlight that the old seal was never changed or badly chewed up trying to force it in place.  From the black crud removed from inside with the rag and mineral spirits, looks like someone quit and tried forcing it in and packed the slot full of black gasket sealant along with the same sealant used to fill in the broken piece on the crankshaft.
Pix 2 shows the old seal on right with the old black gloop removed.  The one on the left was a new seal and later chewed up trying to get it seated.
Pix 3 shows a Timken (made in Japan) seal on right which is a bit beefier than the replacement seal on right.  I opted for this one since unsure how well my filing would affect the smaller seal.  Think if replacing another crank seal would opt for the Timken seal.  It was an on shelf item at AdvanceAuto (about $10.60 including tax).  Most parts stores give me a discount when I ask, but not this time.  Unknown if they did not want to do it, or it is one of those items thy are not able to discount.
Pix 4 shows the key.  The pink box indicates how the key should fit in the crank shaft.  The blue circle shows the actual area this was being held by.  Also note how it is rounded on the edge and chewed up.  Not sure how any chemical bonding agent would have added any significant repair.  Then maybe talking without tools here since ahve never used them for metal patching..  The objective here was to get the vehicle from the Fl West Coast back to the East Coast.
Pix 5 is just a little tool made to evenly push the new seal in place.  It is about a 1 3/4quot; length of 1 1/2quot; ID PVC pipe.  With the 2quot; steel washer in back, the seal was pushed in place using the crank bolt.  Works fine and had these things laying around in my workshop.

Hmm   Pix 1 did not load ..  Here is Pix 1.

Quite a challange. If I may:
The real damage that would stop a good repair would be to the crank shoulder that the timing belt pulley bears against. The posted image resolution isn't good enough  to say, but it looks OK to me. Gouges there don't matter, just a preponderance of flat bearing surface to take the friction loads that transfer torque to the pulley. Bumps and burrs would be acceptable?
And damage to the threads inside the crank nose. I have a stable repair with several tens of thousands of miles that was loose enough for the bolt to wobble perceptibly in the threads, BUT, it torqued to ~100 ft/lbs, and is still running.
I'm highly skeptical of the utility of slopping Loctite 660 all over the nose and inside of the pulley. That would just make any future disassembly more difficult. The compound is to give a more stable shoulder to the keyway. I'm not convinced even that is necessary if the pulley is properly aligned when torqued down. The manual spec torque is my favorite villain for failed repairs. And for the failures of the untouched-from-the-factory crank bolts as well.
The original B6T was having untouched bolt failures before the Miata was built, but Mazda seems to have ignored it. Then blamed the more common timing belt change related bolt failures on the mechanics. Only, a lot of those were done by dealers, to the book. I figure the fresh and actually Clean new factory parts had a better chance of adequate friction at the crank shoulder to hold. Looking at the design, there is No Way the key is going to hold any repeated forces against it in operation. And it doesn't. The bolt provides the compressive force so the friction bond at the flat back face of the pulley exceeds the torque, or the parts fail. With a marginal torque for the bolt size and metallurgy involved, a certain percentage of failures happened. With the small production runs (5000 a year, world wide, it was a homologation special.) of the 323GTXs and the few 323 GTs, Mazda seems to have written off the not common warranty repairs.
With the far larger production run of the '90 Miata, the same percentage of failures alarmed the bookkeepers, and the Big Nose crank fix came out. Mazda still is in denial of the Short Nose issue, but there is that replacement crank.....
With the newer, bigger bolt, and the larger diameter shoulder of the bearing surface, along with a higher spec torque, the failures of the big nose parts is far smaller %, and acceptable for most as a risk.
I see the missing chunk as well past the load bearing portion of the internal threads in the crank nose, which is the critical load path of the part. Even the supposed bond of a lot of 660 around the nose bonding the pulley isn't much help, as the dissimilar metallurgy and coefficient of thermal expansion of the crank and pulley should have any chemical bond disrupted in short order. The stock factory parts come with a small but measurable gap around the crank nose, so there is no support there designed in.
A suggestion for the seal insertion is a corner burr remover. Like a concaved edge chisel, designed to knock off odd bits of left over machining burrs and round corners of sharp tooled parts, it should follow the front edge of the seal receptacle bore? It sure is a hard place to work, hopefully the corner burr tool can get to all the edge and remove all the sharp shoulder there. Sanding is possible but a lot harder to control and hard on not-teen aged-anymore-hands.
If there is a slight bevel left there by any method, it hopefully would match the bevel on the edge of the seal and do the small compression of the seal necessary to get it started evenly into the bore. If the seal starts properly, some gasket seal spread on the outer rim after the seal is half way in should deal with the gouges and nicks leaking oil.
Or have you successfully gotten a new seal in already?
I like the tool! I'm going to modify my plastic pipe seal tool to work like yours. I have just been tapping around the edge of the plastic, trying to keep it even. Your design is a proper seal tool, made with accessible materials. Props.