104 Crankshaft bolt--air impact wrench?
 

The front crankshaft seal on my 95 E320 Sedan is leaking, replacement requires removal of the harmonic balancer/pulley. Service CD shows a flywheel locking tool used to prevent crank rotation while applying torque to remove bolt. This tool is available from my dealer but is a bit pricey. So, my question for the experts--will I damage anything if I use my air impact wrench to remove this bolt? (I'm a bit concerned that I could damage the timing chain guides and or tensioner due to impact tensioning...........)

Thanks in advance,

J. M. van Swaay

I would think that its probably not a very good idea.....

I've broken the bolt loose (accidentally) on my diesel by leaving a breaker bar on the crank bolt and then cranking/starting the car. :eek: It broke it loose and ejected it right out onto the floor. :dizzy2: I promptly re-installed it and made an offering to the diesel gods. Thankfully nothing bad happened!


Might be a solution for removal though. ;)

To reinstall it you have to jam the pulley somehow. On my diesel I wedged a 3/8" extension between the balancer and the block. Worked great. I torqued it to about 180-185ft/lbs. (Well beyond the 150 max of my torque wrench)

Using an air impact wrench to break the bolt loose will not cause any issues IF you lock the crankshaft!!

If you don't lock the crankshaft the chain tensioner can POP out and cause problems (ie; broken camshafts).

Also to re-torque that bolt you will need to lock the crankshaft.

Through my years of experience I don't see a problem using an air impact wrench. I've done it many many times on a full assortment of engines. Just make sure the motor is in gear or park and it should spin right off. When you reinstall you would want to use a torque wrench on the crankshaft nut.

Provided you don't turn the crank backward, it should be fine. Worked well on my 603.

I believe that turning the engine in reverse is to be avoided.

The other method is to jamb the flywheel using a small prybar and the starter teeth, 2-man job then.

Nobody likes my idea/method? :D

I like your idea PawoSD, except I did that on purpose. Worked beautifully.

I just repalced the front crankshaft seal on M103 engine. I borrowed the tool that locks the flywheel from my friend that owns an independent MB repair shop. See if you can borrow or rent it from someone. It make the job so much easier to both loosen and then retorque the crankshaft bolt. Torque on bolt, with oil on the threads, for M103 is 148 ft lbs then another 90 degrees.

My buddy also said you can hold the crankshaft with a chain wrench on pulley with spare piece of belt on pulley to protect it from damge. I don't think I'd be strong enough to to it that way.

My opinion is that loosening with an impact gun is fine. Tightening, well... you really want to use a torque wrench and you'll need to lock the flywheel somehow to do that.

As an aside, I think the concern about reverse rotation (in moderation) is overblown. Engines frequently turn backwards a bit on their own fairly often... on a failed start attempt, when shutting down, etc. I think the only time it is truly dangerous is if the chain/tensioner/rail system is already worn close to the point of failure. This is just my opinion, YMMV!

I don't think an impact gun in reverse on a crank bolt is a very good idea unless its locked.....it could easily move the motor backwards half a turn or more....especially on a low compression gasser. Better safe than sorry.

Agreed, engines do turn backward or at least rock backward from a compression stroke often. I wouldn't do it on purpose but I'd imagine a few degrees between friends won't hurt anything.

Thanks for all the comments.

Just got to this project today, everything removed but the bolt--will probably order the tool tomorrow.

J. M. van Swaay

I've used an impact wrench on a few balancer bolts. The impact spins the bolt out so fast that the engine doesn't turn at all.

Getting the bolt out is only part of the problem. Even if you get it out without damaging the chain tensioner, you still have to retorque the bolt on assembly. The torque is 268 ft/lbs. for the M104. I don't have a clue how you can acheive that without a flywheel lock.