Phil C55

I have done a search and there is conflicting info, could someone who has access to a shop manual for C55 please list the torque spec for the bolt. I'm replacing mine soon and just want it right. Thanks, Phil

c32AMG-DTM

Not specifically what you requested, but in case it helps: C32 idlers are torqued to 20 Nm. A dab of thread-locker (loctite or equivalent) on the threads is recommended by many.

GTibunny8v

10nm according to WIS.

Phil C55

Is that for the bolts holding the tensioner assembly to the motor or the idler pulley. The reason I ask is the original was considerably tighter when removed than 7 ft. lbs. of torque.

MIKESV8

smart man right here folks. replace them before it's too late....like me.lol

Phil C55

Not sure it's smart as much as scared, I made the mental picture of my car completely disabled on the side of the road all over a plastic roller with a substandard bearing. The fact mine has clear wear signs (wobble) at only 33k miles shows what a POS this idler is. MB should give you a new one when this is the service life. Better yet, fix the design/build flaws so it's the last one you have to buy.

Viper98912

I thought it was 15Nm?

Phil C55

That's what I'm running into. I have now heard 10Nm, 15Nm, 25Nm, 65Nm, 15 ft. lbs., 18 ft. lbs., etc.

The 25Nm/18ft. lbs sounds right for a bolt this size and application, but I would really like something definitive from MB.

splinter

^ Listen to this man. Locktite’s 242 is ideal for critical fasteners such as these.

http://www.loctiteproducts.com/p/t_l...r-Blue-242.htm


Is this the one you’re asking about? “Bolt connecting guide pulley to coolant pump” = 20 Nm:

Phil C55

Thanks Splinter, I'm pretty sure that's it. At least it gives the bolt dimensions so that's an extra verification. I just saw a long bolt disappear back into the engine, didn't pay attention the pulley is on the water pump. That too is a check though. At this point it looks like 15 lb. ft. is correct. I probably won't use any loctite though since MB didn't. If it's needed, they use it. The casting supports the bearing and the bolt just keeps the inner race from turning. Thanks again.

splinter

Anytime.
Fact is my various (C32) OE replacement pulleys’ mounting threads were coated with a blue substance of unknown origin.
Much like dealership-supplied chassis fasteners et al. Just saying. :)

Phil C55

I do have some 242 blue in the tool box, I suppose a drop couldn't hurt. I know it's the last time I'll have this bolt out. I put all of 1270 miles on my car this year. I just did an oil change before putting it away for the winter. Nine quarts of Mobil 1 with 1270 miles on it.

GTibunny8v

Saaboteur

When I was doing some work on my C43 - both the 4.3 and the 5.4 I have - I went with 20Nm. The bolt that holds the idler pulley in is very long, and goes through not just the water pump ("coolant pump"), but the timing case and into the block. I see the screen grabs show both 20 and 25 Nm. In the whole scheme of things, 5 Nm difference equates to not even 4 ft lbs. Heh, the $20 torque wrench you can get at any auto parts store probably has a 4 ft lb error!

What I'm interested to know is if there is enough clearance to get that bolt out without removing the rad. My understanding (though I never did it) is that the bolt is too long to be removed from a C43 without removing the rad. Money-one (with a 55K in his C43) had recommended doing the idler pulley with the engine out of the car (as part of a swap process) or pre-empting it by cutting off a bit of the bolt so as to enable it to be removed from the car without removing the rad. Just eyeballing it, I think there might be some more room between the engine and the rad on the C55 as opposed to the C43, but it's difficult to say until one tries to get the bolt out.

Phil - please update when you do the job!

Phil C55

I can update right now, I already took it out and looked at the pulley. The bolt has plenty of room (it does have to go between a couple of the fan blades, but comes out easy). The whole thing is a five minute job.

Phil C55

But that chart says 9 Nm for the pulley on the coolant pump. Splinters chart shows it being a 40 mm long bolt which is only about 1.5 inches and this bolt is 4-5 inches long which would be 100-125mm. Why is this so difficult????


BTW, anyone who says this bearing fails due to over tightening, hasn't had it apart. Can't happen, the bolt holds the inner hardened steel race ONLY and it is holding it against a cast aluminum fitting. The aluminum would react to the pressure long before the steel would. Not only that, holding the inner race is exactly how roller bearing on a motorcycle axle works and some of those have a tightening spec of over 100 lb. ft. of torque with zero effect on the bearing and some bikes don't have a bearing much bigger at all either.

Phil C55

I put my new idler and a new belt on last night just because it was so easy to do and inexpensive too. Odd, the idler which is the exact same made in Germany INA brand part still isn't 100% wobble free and it's brand new. Don't get me wrong, it's not all sloppy and falling all over the place, but if you grab it, you can feel a little movement. It's smooth as silk and doesn't feel like anything is wrong so I am going to leave it, but it still seems a bit odd to me.