Broken Crankshaft Key, Anyone seen this before? (Pics)

[Boomdeeze]

Found my timing off one tooth so I started to retime it. Got to the crank and the alignment plate was way off. Dug a little deeper and found the culprit. Anyone seen this before? Should I be ok with a new key, gear and plate with the crank in that condition?

Enjoy:

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[rEclipserGST]

Damn dude! HOW?

 

[randman2011]

Yes, I have seen it. Never on a DSM, though. It was a common problem on early 1.6L Miatas (lots of info here) and the info is probably relevant to you. The bad news is that nothing is reuseable. It's a very rare and expensive problem to have, but if you've ever wanted a stroker motor, now is the time!

I know what makes the NA6 susceptible to keyway damage. The bolts would have to be really loose to have enough play to cause that much damage, though.

-edit-

I just looked more closely at the pictures. That's exactly what happened. Someone used harmonic damper bolts that were too long. They likely never engaged far enough to hold the damper to the crank pulley because they had bottomed out on the crank trigger wheel. Idk how long the engine ran like that, but there's your cause. Are the bolts shown in the crank sprocket picture really the ones that were on the car? Those things are gigantic!

That key locates your timing belt. Any play in that key translates directly to both play in the camshaft positions and exponentially increased wear in the keyway. If the keyway fails entirely, it will take out the pistons and valves and, if you're really unlucky, the head and block as well. You could get away for a short period of time by replacing the sprocket and crank trigger wheel and key, but you're trading a rebuild now for a more extensive rebuild later. I have never heard of cranks being repaired, but that MIGHT be a low cost option. It would still need removed, though, so you might as well replace it.

 

[1990TSIAWDTALON]

Yes, when my balancer bolt came loose, it did the same thing. I broke the keyway and wollered out the crank pulley. Still have them laying on my work bench after eating all 16 valves and ruining 1 rocker and putting a crack in my VC when all hell broke loose from the crank pulley spinning on the crank.

 

[Boomdeeze]

I just looked more closely at the pictures. That's exactly what happened. Someone used harmonic damper bolts that were too long. They likely never engaged far enough to hold the damper to the crank pulley because they had bottomed out on the crank trigger wheel. Idk how long the engine ran like that, but there's your cause. Are the bolts shown in the crank sprocket picture really the ones that were on the car? Those things are gigantic!

No those were not the bolts used, I had to buy some long bolts to thread through the timing gear to push it off the crank, the broken key wedged it on there.

It appears the new key will sit in there without moving as it’s just the end top portion that appears to be rounded. Any possibility to fill that rounded portion in to make it lay snug against the key so it has no movement? Possibly some titanium putty or JB Weld(I know, I know)?

 

[Devilsfutbol17]

Yes, when my balancer bolt came loose, it did the same thing. I broke the keyway and wollered out the crank pulley. Still have them laying on my work bench after eating all 16 valves and ruining 1 rocker and putting a crack in my VC when all hell broke loose from the crank pulley spinning on the crank.

Happened to me as well. Problem started with the clutch after a few passes at the track. Wouldn't shift into any gear. Rev matched my shifts most of the way home before the balancer bolt came loose on the freeway and the car stalled. Clutch was garbage, valves were garbage, crank was garbage, etc.

 

[streetraceboi]

Replace the woodruff key and you should be good to go as long as it stays lined up in its position

 

[jakk220]

No those were not the bolts used, I had to buy some long bolts to thread through the timing gear to push it off the crank, the broken key wedged it on there.

It appears the new key will sit in there without moving as it’s just the end top portion that appears to be rounded. Any possibility to fill that rounded portion in to make it lay snug against the key so it has no movement? Possibly some titanium putty or JB Weld(I know, I know)?

I would not be JB welding anything in there. You might be able to save the crank with a new Woodruff key but I would probably be replacing it if it were me. You more than likely have some bent valves at the very least.

 

[rEclipserGST]

How far do you think it was driven with it loose?

One time I turned over my engine inside the shop on the lift. The ratchet untorqued the key since the car was close to the ground. I didnt realize until I was out front the shop idling. And started hearing a tapping sound. Pinpoint was timing area right where the key was. I torqued it. Sound gone. That was probably at least a year ago. I daily this slow car.

 

[Boomdeeze]

The car was still running great, the valves never hit. The crank gear was still in it's position, maybe off by a tooth. I had the bolt come loose about a year ago and I tightened it, didn't notice anything until now.

I ordered a new crank key, I was talking JB weld to just fill that top bent part so the key would be snug. All the JB weld would be doing is help supporting the very top of the key, the bottom looks to be in good shape.

 

[donniekak]

I had a similar failure. I replaced the crank, key, both timing gears, and the plate.

Any play at all will wallow out the keyway more until you break another key.

 

[1990TSIAWDTALON]

I didn't have any damage to the crank itself or none that I have found yet, keyway is tight, but the timing gear should be REPLACED, please don't reuse it with the keyway all wollered out. We all talked about this before when mine first happened, that was A YEAR AGO ....dam time sure gets away. Consider yourself lucky. After my incident, my son checked his bolt and by god it was loose too. My car still isn't back together.

 

[Boomdeeze]

I ordered a new timing gear, alignment plate, rear spacer(balance shaft pulley delete), and crank key. If the key fits snug, I will just apply a little JB to the curved/bent portion to add a little strength. I believe it is just the very top/front part of the key cutout that is damaged. Will snap a few pics when I install the parts tomorrow to see what we are working with.

 

[motomattx]

As silly as it sounds you could probably very carefully tack weld the new key in a few spots and then file it flat, of course that would be the last time the key would ever come out of that crank, but if it comes down to replacing the crank anyway or tacking it into place, I would tack it and then next time the crank has to come out, replace it then. I would venture to say that its the high rpm running that is causing this, has anyone had this happen that runs their engine below 5k rpm? I dont remember seeing it happen on any stock Dsm's, it might be a combination of poor quality balanced reciprocating parts and high rpm without an aftermarket dampener.

 

[1990TSIAWDTALON]

I attribute my failure to no balance shafts (vibrations). Yes I turned mine 8700.

 

[Boomdeeze]

I attribute this to the crank bolt coming loose which cause all the stress of the rotating assembly to be put on the crank key. The pressure of the bolt/washer on the crank absorbs most of the stress but it goes on the key when it loosens.

 

[1990TSIAWDTALON]

Fully agree!!! ^^^ I think my bolt came loose because of the vibrations which led to the rest of my problems (well my mechanical problems ).
Josh, do you still have balance shafts???

 

[Boomdeeze]

I don't. I do have a Fluidampr pulley and I used locktite on the crank bolt, unsure if it was blue or red. This time I will make sure both are thoroughly cleaned and apply an obnoxious amount of red locktite while tightening it as tight as possible with my Snap-On 1/2 Impact haha

 

[jakk220]

I don't. I do have a Fluidampr pulley and I used locktite on the crank bolt, unsure if it was blue or red. This time I will make sure both are thoroughly cleaned and apply an obnoxious amount of red locktite while tightening it as tight as possible with my Snap-On 1/2 Impact haha

An obnoxious amount of lock-tite is not going to help you. It could actually hurt you. At this point I would replace the crank bolt as well. Make sure that when you are torquing the bolt you are not just sticking the half inch drive into the head of bolt and torquing it. You need to use a socket that goes over the crank bolt head.

Torque the bolt properly with a torque wrench. You should not be using an impact for this. If you over torqued it last time then this could be part of your issue. You WILL break the lip off of the timing gear if you over torque it. You could also break the bolt off in the crank or destroy the threads. And if you were luck enough for all of that not to happen you are still stretching the bolt threads which will cause it to back out on you no matter how much loctite you use.

I am still against any kind of JB weld job in this area.

 

[bastarddsm]

If it was me, I'd use a mic to measure crank snout and see how much it's worn compared to another good crank. If it's less than maybe 0.002", I assemble it like stock except I would coat the first half of the inside surface of the timing pulley with red loctite, and then 1-2 drops of red loctite on the threads and rub it in. Torque to 105ft*lbs. That's my method and it works. I make a bunch more power than about anyone who has posted, and go 10k now days.

The key does not transmit torque. The friction on the thrust faces it what transmits torque. Keep loctite off the thrust faces, and only on the radial surface of the pulley.

 

[jakk220]

I make a bunch more power than about anyone who has posted, and go 10k now days.

I am not saying you are wrong, but I don't see much of a correlation between the power you make and knowledge on the topic. I know people and shops that can build you a car that will put down 700hp+ on a dyno, but yet I would not trust them to gap my spark plugs properly.

Just like the people that have 8,000 posts and spit a bunch of BS to people... It's just a number. At the end of the day its the quality of content that matters.

 

[Boomdeeze]

I am still against any kind of JB weld job in this area.

I would only be using it as a glue type situation and to fill a very small gap, what would be the downside of doing this rather than installing it bare with that gap on the top part?

I have a race this weekend so removing the crank to swap out is not in the picture. The crank has minimal damage compared to others I've see fixed.

 

[jakk220]

I would only be using it as a glue type situation and to fill a very small gap, what would be the downside of doing this rather than installing it bare with that gap on the top part?

I have a race this weekend so removing the crank to swap out is not in the picture. The crank has minimal damage compared to others I've see fixed.

I just don't think the JB weld is going to have much of an effect on it. If I had no option of replacing the crank I would just leave it.

 

[Boomdeeze]

I just don't think the JB weld is going to have much of an effect on it. If I had no option of replacing the crank I would just leave it.

Do you think it could have any negative effects?

 

[jakk220]

Do you think it could have any negative effects?

I suppose you got me there. I can't really think of any immediate negative effects. However most things I have had go wrong I thought the same thing about haha.