Torqued Out Starter Mounting Bolts

[Dave 2]

I have become informed through this forum and a a couple of Gurus that I do not want to over-torque for fear of riping out threads in the aluminum block. So when I went to reinstall the Starter Motor I was dubious of Clymer's figure of 47NM or 35 Ft. Lbs. These seem so  far out of range when compared to other bolts. (55NM for the monster bolts holding the Engine to the frame). I checked another on-line source of torque values and came up with the same value. I decided to try with three incremental torque settings with the first at 20NM. [smiley=lolk.gif] The first (top) bolt made it but the second one just started spinning. The result of 20NM is the stretched out (bottom) bolt Today, with new bolts,washers and nuts I tightened the Starter Motor following Monte's suggestion of make it tight and then give it a tad extra. I would love to hear from others who may have had a similar experience and or can cast some light on why the high torque values for these bolts. [smiley=bmw_smiley.gif]D2

[Bob_Roller]

First off, if I'm not mistaken, there are holes in the engine case that the bolts pass through, no threads in the case .

Never gave a thought about torquing the nuts/bolts .

Just got them tight .

[cortina]

Good advice Bob.The BMW repair manual also states 47NM.I dont know why the torque value is so high, it does not need to be.All the bolts are doing is holding the starter motor in place and if you are worried about them coming loose then fit spring washers or nyloc nuts.I also did not torque these because I had to use spanners rather than a socket.Sometimes it is better to trust your own judgement rather than a repair manual-even a factory one.

[Barry]

Sometimes it is better to trust your own judgement rather than a repair manual-even a factory one.  

That is so true and even if the published values were correct you would never acquire the "feel" if every nut and bolt was tightened with a torque wrench. I will often tighten something by feel and then do a calibration check with a torque wrench. We tend to get drawn in to thinking that using a torque wrench is a very precise and repeatable operation when in fact it's full of potential variables that even the most accurate torque wrench can't overcome. Like material finish, friction and dry or lubricated threads. The potential error in actual clamping forces when using a torque wrench is reckoned to be plus or minus 25%. That's why really critical bolts these days are angle tightened and stretched.

[Rob Valdez 79 R65]

Just to add my agreement - the starter is held on with both nuts and bolts, so you will not have the threads in the case issue.

At least this is the case on the two rear fasteners.

The front mount threads into the threaded hole on a flange on the block, so you want to take care there.  Especially as it is a much smaller fastener than the two rears.

[Dave 2]

Hi. thanks for all your thoughtful comments. I guess using torque values and torque wrenches needs the application of "experienced feel" for the materials and tools. I like the idea of tightening the bolts with a hand tool and then checking the value with a torque wrench. I got the rest of the engine electrics back in place with out further mishap [smiley=bmw_smiley.gif]D2

[tvrla]

As you discovered, manuals aren't necessarily infallible. Common sense is something never to be abandoned.

But that can be difficult for someone new to mechanics with insufficient experience to know better. It's a difficult situation.

Glad you didn't junk anything irreplaceable and expensive! A good, cheap lesson, for sure!