Stripped Crankshaft Pulley Bolt

[cjryan]

2000 4.0 OHV

I noticed a strange vibration a couple nights ago coming from the engine. The next day, we inspected the engine while it was running and I noticed the crankshaft pulley looked like it was shaking unusually. We tried to tighten the crankshaft pulley bolt, but it would not tighten, like it was stripped. We backed out the bolt and it looked severely worn, if not stripped.

I picked up a new bolt from the ford dealer yesterday and it has a different thread pitch than the bolt that came out. The bolt from the dealer was supposed to have be 12mm x 1.75 thread pitch, but it actually has a 1.5 thread pitch. I think someone put in the wrong bolt in the past, and just forced it in.

I want to re-tap the threads in the engine block, but I'm not sure what tap to use. My 12mm x1.5 die (from my tap & die set) doesn't rotate completely free around the new bolt. This is the largest metric tap I have. Does anyone know the exact size of the crankshaft pulley bolt?

 

[cjryan]

Update

Today we attempted to remove the crankshaft pulley bolt from my other 96 explorer to compare the bolts. We were unfortunately unable to free the bolt however; partially because the timing belt and alternator are off. There is not enough room to fit my air impact wrench near the crankshaft pulley bolt without removing the fan.

I am about 95% sure that someone put in a bolt with the wrong thread pitch. If this were true, can I re-tap the same size threads for the factory size bolt. Or will I have to go bigger because the threads inside the crankshaft are possibly damaged/distorted/stripped? My thinking is that there won't be enough metal in some areas to create the threads to the original size.

There is not enough clearance either to tap with the setup that I have without removing the crankshaft pulley first. I need a special puller to remove the pulley; I also need special tools to remove the fan, if necessary. Does anyone know if you can remove the crankshaft pulley without removing the fan?

 

[cjryan]

Update 2

So I called a shop this morning and they told me since the crankshaft was hardened steel you cannot tap new threads.

I talked to another shop and he said he may be able to tap the threads, but he needs to see the car. I think someone just needs to know what they're doing to tap hardened steel, and have a specialty tap.

If no one can do that, the guy at the ford dealer said a cheap fix would be to have someone weld the crankshaft pulley to the crankshaft. But then, I wouldn't be able to pull the pulley off again. But why would I ever need to again?

I would prefer to have someone re-tap the threads, just trying to figure out who should do it.

 

[Maniak]

I wish I could come up with an answer for you... but alas, I can't.. But, I just wanted to say thanks for continuing to put updates up. This may help someone in the future.. and Here's to hoping the solution you end up with is the right one for you...

~Mark

 

[surf]

Could the fact that the crankshaft bolt is torque to yield be the reason the thread pitch differs?

 

[cjryan]

Could the fact that the crankshaft bolt is torque to yield be the reason the thread pitch differs?

I'm not sure if the bolt is torque to yield, or exactly what that means. But I don't think that's the answer because the bolt that came out was severly distorted, and definitely had a different size thread pitch than the bolt the dealer gave me, assuming that was the right bolt.

 

[surf]

Torque to yield bolts stretch when they are torqued down. If the previous bolt was over torqued it could have stretched the threads. This is pure speculation on my part. Does the bolt the dealer gave fit the threads in the crankshaft at all or are the crankshaft threads chewed up?

 

[2000StreetRod]

Don't weld

. . . But then, I wouldn't be able to pull the pulley off again. But why would I ever need to again? . .

Why you shouldn't weld the damper to the crank:

Can't replace a failed balancer

Can't replace a leaking front crankshaft seal

Can't replace the camshaft

Can't replace the camshaft chain, tensioner, or sprocket

Can't replace a cracked front timing cover

 

[cjryan]

Torque to yield bolts stretch when they are torqued down. If the previous bolt was over torqued it could have stretched the threads. This is pure speculation on my part. Does the bolt the dealer gave fit the threads in the crankshaft at all or are the crankshaft threads chewed up?

The previous bolt actually has smaller threads than the new one, so I don't think that's the case. Yes, the threads in the crank are chewed, when I tried to put the new bolt in just a bit, the threads in the crank rounded the threads on the bolt.

 

[cjryan]

Why you shouldn't weld the damper to the crank:

Can't replace a failed balancer

Can't replace a leaking front crankshaft seal

Can't replace the camshaft

Can't replace the camshaft chain, tensioner, or sprocket

Can't replace a cracked front timing cover

Good points, thanks for bringing that up. I have the OHV, so I don't think I have the chain or timing cover. But either way, you pursuaded me not to take this route. Does anyone know if tapping hardened steel is possible? Is it just very difficult? I believe that it takes a special tap. If welding is not a option, I want to know that theoretically, the right person could tap new threads becuase I'm about 99% sure that's what needs to happen.

 

[2000StreetRod]

OHV V6 timing chain

. . . I have the OHV, so I don't think I have the chain or timing cover. . .

Actually, you have both. The photo below shows what's under your front timing cover.

 

[cjryan]

Actually, you have both. The photo below shows what's under your front timing cover.

Of course I do, that was a dumb comment I made.

I'm planning on driving the truck 5-6 miles tomorrow to the shop. I put the original bolt back in and got it as tight as possible. You tighten it to a certain point, then gets looser. So I got it right to the point before it gets loose.

My question: Will I hurt anything by driving it this short distance? I know you need a puller for the crankshaft pulley so it's in there pretty good. I just don't want there to be any problem with the crankshaft, I don't know if this could cause a timing issue. I had a bad Camshaft Position Sensor and drive unit (CPS) a while back and it caused timing issues other problems. Thanks

One more thing: Any suggestions for the type of shop to do this work. I'm planning on bringing to a engine repair shop. However, I researched to find a "machine shop" but didn't find any for that did automotive work. It was more like specialty machining stuff.

 

[2000StreetRod]

balancer is keyed

. . .
I'm planning on driving the truck 5-6 miles tomorrow to the shop. I put the original bolt back in and got it as tight as possible. You tighten it to a certain point, then gets looser. So I got it right to the point before it gets loose.

My question: Will I hurt anything by driving it this short distance? I know you need a puller for the crankshaft pulley so it's in there pretty good. I just don't want there to be any problem with the crankshaft, I don't know if this could cause a timing issue. I had a bad Camshaft Position Sensor and drive unit (CPS) a while back and it caused timing issues other problems. Thanks
. . .

The balancer is keyed so it will not slip on the crankshaft as long as the bolt prevents it from moving forward. It is usually on so tight that it must be pulled off. Even if it slipped it would not affect your engine timing. It would only affect things driven by the serpentine belt- water pump, alternator, power steering pump and A/C compressor. You should have no problems driving a reasonably short distance.

 

[cjryan]

Shop Update

So I took it into the shop today. They cleaned out the threads and put the new bolt in, but it would not torque down properly. I think it was still just turning, not able to get it tight enough. The owner mentioned something about using a heli-coil screw thread insert, but he didn't have (or didin't think) they made one that was long enough. If I can find the right heli-coil, I think that may be the route to take.

The owner of the shop is also going to give me the number for a guy who does on-location "bolt work" for heavy machinery. Basically when a piece of big machinery has a broken bolt or something needs to be tapped, they call this guy. He thinks that this guy may be able to fix it. I'm hoping.

 

[cjryan]

Heat treated hardened steel?

So I got a hold of the drill and tap guy. He said that he could put in a solid threat insert (similar to heli-coil). I told him I had a 12mm bolt and 1.5 thread pitch and he said the longest insert the made was about 1.3 inches. He thought that would be plenty of thread.

However, he said that if the crankshaft was heat-treated hardened steel, then it would not work. Does anyone know if 2000 4.0 OHV crankshafts are heat-treated hardened steel? I think he said something along the lines of "I won't know if it's heat-treated until I drill it out." This kind of worries me because then I'm really screwed if he drills it out and it doesn't work. He also will not give me any sort of guarantee that it will hold whatever torque spec that bolt needs.

This guy doesn't usually work on cars so I'll have to remove the radiator and fan, then tow it to and from his shop. He said he'd do it for $200. Anybody else have any better ideas?

 

[cjryan]

Thread Insert

So, I'm pretty sure the crank isn't hardened steel because the threads probably wouldn't have distorted if it was. I'm going to either install a thread insert myself or have someone install it.

I have someone who will do it for $200 but won't guarantee it will hold any sort of torque rating. I found a company called Full Torque who can sell me a thread insert kit for $300. That seems really pricey to me. They also claim there's is the strongest and the best (of course).

There is also Heil-coil, and I'm sure other brands out there. I saw a thread insert at Harbor freight for my size bolt (12mm x 1.5) for $80. Not sure on the brand or maximum torque it can hold. Anyone have any experience with thread inserts? Recommend any brand?

 

[NHarris]

There is also Heil-coil, and I'm sure other brands out there. I saw a thread insert at Harbor freight for my size bolt (12mm x 1.5) for $80. Not sure on the brand or maximum torque it can hold. Anyone have any experience with thread inserts? Recommend any brand?

-I know heli-coil (brand) does work well, thats what we use in the auto shop...seem to work well for those idiots that don't know how to torque anything properly (not picking on anyone), or cross threads the bolt/screw and strips out the bolt/screw and hole for the bolt/screw. (sorry for the bad description...lost my train of thought for now )
-I've personally never used any type of an insert on one of my cars. Or any other cars.
-I would be leery about going with harbor freight's. Harbor Freight for the most part has cheap stuff, thats not of great quality. But then again it may be a good product. Don't get me wrong Harbor Freight has good prices, and some good tools
-But I'd suggest heli-coil out of any brand. But read over the case of the harbor freight insert and check out where its made (I personally prefer made in USA stuff but thats my preference), and see if there is any sort of a warranty.
Good luck.

 

[cjryan]

I've done some more research and found that people have used helicoil before on a crankshaft, with mixed results. Others have re-tapped to the next biggest size. I have concern of balance issues with the bigger bolt or if I have to drill it out for an insert. I have heard of people making a guide when they drill, to make sure it goes in straight.

Is there any reason not to go with a bigger tap/bolt as opposed to an insert?

 

[cjryan]

Fixed!

So i finally got off everything to access the crankshaft, once I had the right tools. I decided to try and "clean" the threads using by 12mm x 1.5 tap even though I had been told by several people you can't tap hardened steel. The first several threads went through no problem, then it became a little harder. I had to basically turn the tap as hard as I could, back it off, and continue the tedious process over and over.

After a couple of test fittings to see if I created enough threads, I put the harmonic balancer back on. After a couple of prayers, I torqued it down the the minimum torque in my manual.... and it held! No more stripping! I meant to put loc-tite on, but I forgot in the process. I may check the torque again next week, and re-insert the bolt with lock-tite. I am so happy that I fixed this without having to use a thread insert, and without spending too much money. Luckily I am fairly mechanically inclined because the Ford dealer and two shops wouldn't even accept the job. I even took it on a mild off road trail today!

 

[jhclance]

That repitious forward/rearward turnning is how you are supposed to do when hand tapping a thread. It cuts a little forward then cleans the thread when you reverse. Cutting oil ( not wd40 PB etc lubericants) makes the job a little easier but sounds like you got it done just as well. I would deffinetly retorqe the bolt asap just to be sure it is holding. If it is torque to yield it prolly be best to leave it in and just pull it with your torque wrench.