Author Topic: Best way to torque the crank bolt (Read 8893 times)

wannam42 · « **on:** July 01, 2012, 03:58:09 AM »

Hey guys,

After watching this video http://www.youtube.com/watch?v=Ex_yJ_V5UH8, I could not help but wonder if the process hurts the main bearings at all when the crank bolt on the m42 is torqued to spec using a torque wrench with a really long handle or extension.

Yes, the video is about the harmonic damper install on a v8 but it got me thinking about the main bearings on our engines.

Anyone use an impact or a torque multiplier? I feel that's the safest since *I imagine* the crank doesn't flex too much so the front main bearings don't get "pressed" on (however so slightly) vs using a torque wrench with a long handle. The problem with using an impact, of course, is that you won't know what the tightening torque was.

Am I just over thinking it since the forces generated during engine operation, especially at high rpm, might well exceed 253 ft-lbs of force being acted on the bearings. But then you could argue that the oil under pressure provides a hydrodynamic barrier.

Your thoughts would be greatly appreciated. Thanks.

bmwman91 · « **Reply #1 on:** July 01, 2012, 08:17:15 AM »

I can't get on Youtube where I am right now. Was the video showing someone locking the crank via the starter ring gear?

I think that an impact gun would be more damaging than slowly hand-torquing. Relatively static loading like that probably will not hurt anything.

DesktopDave · « **Reply #2 on:** July 01, 2012, 09:02:06 AM »

I do agree with the video, mostly. Tapping a harmonic balancer on to our crank is a good way to damage the insufficient thrust bearing we have. However, the BMW crank bolt is far beefier than the GM part that he demonstrated.

I'd vote for using the BMW crank locking tool along with a decent torque wrench.

wannam42 · « **Reply #3 on:** July 01, 2012, 03:50:53 PM »

bmwman91, the video shows the crank was locked via a hammer handle being jammed up against the crank. He did say there were many ways of locking the crank.

My thinking on the impact wrench is that it doesn't load the crank with a weight that is far from the axis of rotation if that makes any sense. The only thing is that you need to be sure the impact wrench doesn't deliver more than 250 lb-ft of torque.

DesktopDave, which crank locking tool are you referring to - the flywheel locking tool or the crank counter holder tool (http://www.SamstagSales.com/bmw/bmw88886112150.jpg)?

If it's the latter, I can imagine that the crank counter holder tool would allow you to apply more torque using a torque wrench and prevent (in theory) any force from being exerted on the front main bearings. I imagine that the crank counter holder tool would need to be at 90 degrees or less so you can push/pull on it while pulling/pushing the torque wrench if that makes sense.

bmwman91 · « **Reply #4 on:** July 01, 2012, 06:23:02 PM »

Aaah. Intiutively, it seems like a bad idea to be jamming stuff between the crank and block. Dave is correct that the best way is to lock the crank in place with the OEM tool, or one that does it similarly. In my case I found a big piece of 1/2" steel plate and drilled holes in one so that it could be bolted to the crank nose and rest against the chassis. Without going too far into math or anything, the closer you can get the locking implement to the bolt you are yanking on, the less loading you will place on the bearings ALSO assuming that the angle of the breaker bar you are using is very close to the angle of the locking bar. Doing it this way puts no longitudinal torque on the crank, whereas stuffing a block of wood up there puts all of it on the crank. If you are working the breaker bar at a similar angle to the locking tool on the crank nose, you will also minimize the radial forces developed on the bearings.

As far as installing the harmonic balancer goes, I have no idea why one would need to hammer it on. If you do, then something is either dirty or maybe you need to hit the woodruff key's edges with a file, clean it all and put a little clean oil on it. The crank bolt will push it all together anyway.

wannam42 · « **Reply #5 on:** July 02, 2012, 08:48:34 AM »

I think I'm understanding what you're saying but could you make it more concrete with a drawing?

http://www.realoem.com/bmw/showparts.do?model=BE53&mospid=47480&btnr=11_1521&hg=11&fg=18

For the life of me I can't figure out where the crank holder tool needs to be in the diagram above.

bmwman91 · « **Reply #6 on:** July 02, 2012, 09:54:44 AM »

The OEM one has a single tooth on it. It bolts onto the front of the motor and the tooth sticks into the harmonic balancer, between its teeth. You tug away with a breaker bar and it is held by the balancer. I have never liked that design since it seems an unreasonable amount of stress to put on the balancer.

I got a big piece of steel and machined it so that it can be bolted to the crank. You remove the 6 bolts holding the accessory pullies, remove the accessory pullies and damper, and bolt the steel plate on. It is long enough to rest against the driver's side frame rail, where I put a block of wood for it to rest on. Then I crank away with a giant torque wrench until it is at 240 ft-lbs.

Getting the bolt OFF is super easy. I put a wood block on the driver's side frame rail, attach a 18" breaker bat to the crank bolt and turn the key in the ignition. WHAM! The starter motor can almost always break the bolt loose after a few tries. Just position the breaker bar about vertical and run the starter. Only run it for 1-2 seconds as it will probably overheat if you try to run it while stalled against the wooden block. Usually 2-3 tries gets the bolt loose.

wannam42 · « **Reply #7 on:** July 02, 2012, 11:06:37 AM »

Ok I get it now. I always figured that the pulley and harmonic balancer / vibration damper were secured by the crank bolt. Doh!

Clearly, they aren't because they're bolted to the hub. Doh!

Thanks for clearing that up, bmwman91. I imagine I'll be pulling against the crank holder tool while I push the torque wrench with my foot!

The engine is off the car so I'll be using an impact wrench to remove it. I've seen what you described re the starter to remove the crank bolt.

dhirsch · « **Reply #8 on:** July 02, 2012, 11:33:05 AM »

I've been able to take the crank bolt off and put it back on using a large spanner and some bolts w/washers threaded into the harmonic balancer. The spanner is long enough from what I remember to hit the ground below the car or a frame rail. It worked very well and the spanner can be used for other things like removing the bolt from the trans output flange.

The part number for the KD tool is 3900 and it's called a "universal pulley holder". You should be able to find one way cheaper than the OE tool.

using washers and the extra nuts on the spanner is important. If they're not used the spanner can slip away from the vib. damper and will just bend the bolts rather than provide the holding power needed.

A link to the picture with the spanner on the damper is below
https://dl.dropbox.com/u/58198780/spanner.jpg

wannam42 · « **Reply #9 on:** July 03, 2012, 11:05:32 AM »

dhirsch, thanks and I also found your old post. I wish I saw that before I got the crank holder tool.

So for tightening the crank bolt, I will use the method described by bmwman91: crank holder tool + torque wrench to prevent loading the main bearings which was my original goal.

I've read that torque wrenches are recommended to be pulled/pushed from 2 o'clock to 3 o'clock (30 degrees of travel). Anyone subscribe to this?

bmwman91 · « **Reply #10 on:** July 03, 2012, 05:43:40 PM »

I have never heard that before. Any background on it?

wannam42 · « **Reply #11 on:** July 03, 2012, 07:49:51 PM »

The link isn't active anymore but here's a copy http://web.archive.org/web/20080506104118/http://www.mondello.com/Pages/Articles/1/1.htm

keflaman · « **Reply #12 on:** July 03, 2012, 09:20:41 PM »

Quoted from the article:

"Most people don�t know how to torque fasteners properly."

"When you torque anything, keep the torque wrench at about two o�clock and pull the wrench to three o�clock. Do not pull past this point because your angle will get too far off. This is when you pull past your torque point and over-torquing takes place. Always pull into your torque range, not past it."

I think most people intuitively do it this way to begin with, although I can't say for sure what the author talking about with 100 percent certainty.

wannam42 · « **Reply #13 on:** July 04, 2012, 08:08:05 AM »

IIRC, the picture was showing him torquing a head bolt which would explain the 2-to-3 o'clock pull. It would be difficult to pull with constant force beyond 3 o'clock since your wrist will start to bend - unless, I think, of course you're using the left hand.

So if the bolt you're fastening will require vertical final torquing, like the crank bolt, does this still apply? I would think 3 o'clock (or slightly just above it) would be my starting point since it's the easiest way to put all of your weight on it.

keflaman · « **Reply #14 on:** July 04, 2012, 10:11:26 AM »

Okay, that's about what I got out of it and I'd agree with you.