Drivebelt tensioner bolt

[tarmacsurfer]

Dear all

I am trying to change the serpentine drive belt on my 1991 300E 12v which has the 19mm tensioner bolt and idler pulley setup. The manual says that the tensioner bolt (for proper tension) should be at the thick end of the graduated scale when tensioned correctly...but mine isn't?? Plus I just can't undo the tensioner bolt (which the manual says I need to undo first, and then the 13mm long bolt at the top next ot the water pump)...I think I'm afraid of overdoing it as I have broken a lot of bolts in the past?!?! Any ideas anyone?

Many thanks

 

[flyingtech55]

Hi Tarmacsurfer

I renewed the drive belt on my 190E when I got it because the edge was a bit frayed. The 19mm bolt was very tight. I thought I was on the wrong bolt. I removed the radiator (easy job) so that I could check that I was on the correct bolt. Eventually I had to use a two foot breaker bar and a air gun socket to shift it. I too was terrified I would break the bolt. However, it let go eventually and the job was straightforward thereafter. Removing the radiator also made it much easier to see/set the correct tension using the indicators.

 

[tarmacsurfer]

Cheers... I shall continue to try with the rad on and admit defeat and remove the thing to get better access!

 

[TheJim]

This brings back memories.
The bolt that holds the tensioner arm in place is a bastard to shift.
The thing you want to watch out for is the fragility of the tensioner. I am guessing that it is a similar setup to the 190......
The pointer on mine was off the scale and would not move when I was adjusting the tensioner. Then the tensioner broke.
If this happens, don't try and get a new tensioner because it comes as a whole assembly with the arm and everything- you don't want to know what that costs! Just tension the belt using a pry bar under the arm until you get about half an inch of deflection on the belt and tighten the bolt to hold it in place.
You do need 3 arms for that last bit.
Good luck. Best of British.
And just take the radiator out. It is quicker in the long run.

 

[tarmacsurfer]

Well I had another go, and as you guessed no joy! Looking at the fact that the tension adjustment scale says it is loose but the belt is tight I reckon my tension adjuster has gone like yours The Jim...

Looks like rad out then and 10ft long persuader required!

Cheers again

 

[TheJim]

I am trying to remember how I got mine undone now.
I think I (after the rad was out) wedged something under the arm to stop it moving on the rubber mount and then used a compound hammer on the wrench to get it undone. I seem to remember that otherwise the arm just moves and absorbs the impacts.
I shall wrack my brains some more.