View Full Version : Please help! Broken crankshaft?

06-19-2005, 03:51 AM
The shop that is working on my 1991 SC said the crankshaft is "bent".

Two years ago, they replaced the harmonic balancer for me with a Ford balancer. When the car broke down this time with the same symptoms, I was somewhat surprized when I was told the harmonic balncer was shot again. So, I read some posts and relized I should have had them install the aftermarket HB recommended by most on this site. So, I forked out the bucks, took the aftermarket balancer to them, and a day later they told me the crankshaft was bent.

The guy at the shop said I should dump the car. I trust him for his honesty, but from knowing him over the years, he isn't the most knowledgeable when it comes to SCs, and doesnt like jobs where he can just swap out parts.

The reason I was hoping for a second opinion is because I thought crankshafts "break" or "don't break" as opposed "bending" out of shape.

What should I look for to know that the crankshaft is truely shot?

Also, fearing the crankshaft is shot, what are my options?


06-19-2005, 04:41 AM
there are 4 main bearings that hold it true. what makes him believe the crank is bent? could be the original crank bolt broke and the piece of the bolt is still lodged in the crank,which doesn't allow the balancer to properly seat. just a thought. :)

XR7 Dave
06-19-2005, 09:57 AM
A crank can in fact bend. I would be curious to know how he determined that it is bent though. If he determined it through deductive reasoning (it breaks balancers and is therefore bent...) then I'd want more proof. These balancers are the weak spot so I'd be suspicious more of the balancer.

Crankshafts are not necessarily perfectly straight right from new anyway, and a forged crank such as ours is more "flexible" than a cast crank. There are many "degrees" of "bent" so I just think I'd be very skeptical of any claims that it is bent beyond use.

I don't think anyone has ever lost a crank after installing a steel balancer. Anyone who has can feel free to speak up though. I do know of people who have lost several balancers in a short time and then finally installed a steel one not to have any more troubles. Still doesn't mean the crank wasn't bent though.

Personally I'd install the BHJ balancer. If in fact the crank did break later on, the cost of putting in a used motor won't be that much more than replacing the crank now. And vrs junking the car, well if it breaks THEN you can choose to junk it if you want. I don't see how you really have much to lose by putting on the new balancer unless he can demonstrate to you that the crank is in fact shot.

Just my opinion. :)

06-19-2005, 11:57 AM
Dave you took the words right outta my mouth!!! :D

Jason Wild
06-19-2005, 12:20 PM
Maybe he can not get the BHJ on because it needs to be honed out to fit the crank. this giving him the idea the crank is bent.

06-20-2005, 12:04 AM
wasn't sure if you said the car will still run or not. if it runs, and the crank is bent, you should here the motor start to knock. after a while, depending on what kind of crank it is (it should have a material limiting factor), if the crank is out too much, you'll be getting uneven compression in cylinders and eventually start to lose power. Usually though, before this happens, the crank will basically snap, and trust me, you WILL know when this happens. It happened to me during a test drive with my dad's friend's Lincoln Continental. Nice car, but crank broke 2 miles out of town, resulting in a 45 minute hike for the truck to tow it home. It sucks. Another way to test is there should be a small crevice between the bell housing and the back of the pan. Listen for any chattering between the pilot bearing and the thrust bearing, if you can get the rear end up on stands and drive it. If not, another way would be to make sure yor HB is sitting right then use a mounted caliper to measure the "sway" in the HB when you turn the engine over. If it goes out by more than a certain allowance, the crank could very well be bent.

06-20-2005, 02:18 AM
Thanks everyone for the input so far. I am going to check with my mechanic tomorrow and get some more info as to how he concluded the crankshaft was bent.


06-20-2005, 04:10 AM
never seen a SC bent one yet:|, use a dial indicator on the snout, bad balancer install is my guess :confused:

06-20-2005, 04:58 AM
I'll tell you this much, my LX broke a harmonic balancer a little over a year ago. I replaced it and all seemed to be fine. About 6 months later, it broke another one. However, after putting a new one on, I found out the crankshaft had broken too. I think it had been bent from the first time because the balancer wobbled slightly, even though it felt perfectly tight. Now the 3.8 NA is externally balanced meaning a broken balancer may be harder on its crank than on a Supercoupe, but I would certainly investigate it further.

06-21-2005, 03:05 AM
Well, after talking with my mechanic first hand, I think I got the (or inferred the real story) The story changed a couple times even as he told it. First it the crankshaft was bent...then it was the HB not seated correctly....then it was the bolt was broke off inside(as Huckleberry suggested) and he couldnt get it out...then it was that they tried to get it out and they think they got most of it....then it was that there werent enough threads left to seat it properly....Long story short, the most I could firgure out is that in the process of getting the broken bolt out, they stripped the threads or cross threaded the new one, and now there is noway to get the new hb seated properly without taking it to a machine shop to be rethreaded (if that's even possible)

Any suggestions now that it appears the actual crank is not bent, but the threads are stripped and/or there may even be parts of the old bolt left in there causing the problem? They still had the HB seat bolted on to the crankshaft and it was tight as a drum with no play, so it must be threaded to something?



06-21-2005, 09:39 AM
clean the holes, get a longer bolt and have the balancer HONED TO FIT :rolleyes: , they might have ****ed it up trying to draw it up with the bolt :D

06-21-2005, 10:14 AM
Thats why I did mine myself I do have a mechanic I trust but.................The SC is quirky car too work on with many custom aftermarket parts :D

06-21-2005, 10:57 AM
I've had the bolt snap a couple of times prior to getting a BHJ. The last time it happened, the threads in the crank got all messed up from drilling the pilot hole for the extractor. I figured I was in for a trip to the machine shop, but decided to see if I could tap new threads (had nothing to lose). I got a tap that was one size larger diameter than the original bolt and cut new threads. The "old threads" worked as a guide for the tap. I now have a slightly larger bolt (length and diameter) holding my BHJ in place. No problems for a several years now. You can tap new threads in the crankshaft without removing it from the car if you take your time.

06-21-2005, 11:43 PM
Thanks again everyone...

AsScLoWn Im not sure what you mean by "hone" ...hone the balancer? Were specifically...I thought the BHJ was balanced at the factory and shouldnt be messed with. Or are you refering to attempt to retap the hold for the crank bolt?

My mechanic has all but washed his hands of it saying the threads were shot and he tried 'everything', So I need a little more detail to walk him through what exactly needs to be done and convince him its worth another try.


06-22-2005, 12:01 AM
He just said he thought the crank was bent, and now he's having trouble with the threads on the crank, sounds fishy, you dont tap a bent crank. Either he does not know what he's doing, or he doesint want to fix it, I would suggest you tow your car to another shop and get another opinion.

06-22-2005, 12:12 AM
He just said he thought the crank was bent, and now he's having trouble with the threads on the crank, sounds fishy, you dont tap a bent crank. Either he does not know what he's doing, or he doesint want to fix it, I would suggest you tow your car to another shop and get another opinion.

Thats exactly what I did one shop that was down the street from where I live (who went out of business) I let work on my car in a no start situation could not figure it out just started "hanging parts" a couple of weeks I figued they were trying to pump up the bill ,I called atow truck brought it to a reputable shop and never paid the bill because tey cased more damage than my car had in the first place ......in other word get your car outta there!!

BT Motorsports
06-22-2005, 02:10 AM
gator2000, where are you located?


06-22-2005, 02:34 AM
beats me, the only BHJ I had done was years ago, theres a clearance from the inside bore of the balancer to the outside of the crank snout, the inside of the balancer is actually smaller than the crank snout, but comes smaller than what the specs call so it can be honed out to fit a variety of cranks. Call BHJ for the interference size, its might be .003"( I dont know, just an example!!!), meaning if the crank snout is 1.000 in diameter the inside of teh balancer should be .997 in diameter. Then whoever is installing it needs to put the balancer in the freezer for several hours if they want to expand the balancer to ease the install, also put some lube on the crank snout, to help it slide on. I use a block of wood and hammer to start it on, make sure the KEYWAY IS LINED UP or it will shear, tapping the inside bore then impacting with an air gun, DONT DO THIS, use the proper install tool :D. Yea you could re-tap the crank hole bigger and use a larger bolt like someone suggested, but use a 10.9 strength bolt if its metric, I dont know ask him for details, depends on the availability of bolts and taps washers etc (stock washer can be enlarged) blah blah blah blah blah blah?!?! blah

06-22-2005, 02:16 PM
Thanks everyone,

The reason I'm asking everyones expert advice in the first place is to see if a scecond opinion warranted. I didn't want to run up towing charges just to find out theres nothing that can be done.

After being armed with more info, I believe that my mechanic was just covering for the fact that he stripped the threads and so he said the crankshaft was 'bent'. After he got 'most' of the broken bolt out, either the bhj didn' seat right..(maybe needs to be honed to fit, or the crankshaft needs to be retapped). In anycase, either because he knows he messed it up, or becasue I have known him for several years, he is not charging me for any of the work he has done on it...its not a "run up the charges" deal. Like I say he's an honest guy, but he is definitely out of his comfort zone. He'd be willing to try a few other basic things without charging, but again, I would have to walk him through it to convince him there might be other things that can be done.

06-22-2005, 02:56 PM
um i was on something when i typed that, i changed the air hammer part, should of been air impact :rolleyes: and I had the diameter of the balancer at 9"s :eek:

06-23-2005, 02:51 AM

I'm loacted in the Tampa Fl area. If you know any good shops or machine shops in the area that could give a second opinion let me know.


06-23-2005, 04:00 AM
if the crank snout is 1.000 in diameter the inside of teh balancer should be .997 in diameter. Then whoever is installing it needs to put the balancer in the freezer for several hours if they want to expand the balancer to ease the install
Freezer, huh! Last I heard, warming the part expands it, & chilling the part shrinks it. So if you want to freeze something, freeze the crank. You have a "Drive In Freezer", Right?


06-23-2005, 05:46 AM
sweet :D , yea freezing shrinks it :rolleyes: , i hope the guy doing it would of realized that :confused: , just dont melt the balancer, you can spray nitrous oxide or something on the crank and hope it doesnt shatter if it receives any shock ;)