V belt question... - PeachParts Mercedes-Benz Forum

Shern · #1 04-24-2019, 01:46 PM

I am the most recent victim (self-inflicted of course) of the alternator tensioner bolt. Heard some chirping, went to tighten the belt and the bolt snapped in the middle. I've installed a new one and I can tell the cap nut has already destroyed the threading... that said, it's on and adjusted for now.

Now I'm no stranger to the adjustment process. I have a copy of the FSM and loosen all requisite bolts before spinning the tensioner.

While I was in there, I pulled all the belts. All three were Gates brand that I installed new 3 years ago (about 40k miles) and both the power steering and A/C belts still looked new. The alternator belt was cracking and had a few threads loose on the sides.

The FSM states that all belts should be tensioned to 40-45kg.
Here's the thing. The PS pump at maximum adjustment gives me belt tension of only 25kg. The AC compressor at maximum adjustment also gives me 25kg on the cricket. The alternator is the only belt I've been able to adjust to 40kg.

All the sizes are correct (1030, 875, 1145).

Have I been over-tightening the alternator belt? Is it important to maintain belt tension balance? In other words, better to have all belts at the maximum tension of the loosest belt (25kg)?

Diesel911 · #2 04-24-2019, 06:00 PM

Others might know what belt tensioner you have but there is more then one type. Without knowing what you have it is a head scratcher.

Do they show a belt tensioner gauge in the FSM?

Are the belts you used SAE or metric. Continental makes Metric Belts which is what I have on mine.

I have always just adjusted belts with the imprecise deflection method and drove enough with them to get them hot and stretched and rechecked them. Functionally that has normally worked for me on all of the vehicles I have owned.

Shern · #3 04-24-2019, 06:23 PM

Metric belts, fsm specified lengths.

I don’t claim to be not overthinking things

The belt tensioner gauge they show is called a cricket -which I bought.
No chirping, no issues so I might just leave well enough alone.

My suspicion however is that I was overtightening the alternator belt.

JHZR2 · #4 04-24-2019, 08:18 PM

Quote:

Originally Posted by Diesel911

Others might know what belt tensioner you have but there is more then one type. Without knowing what you have it is a head scratcher.

Do they show a belt tensioner gauge in the FSM?

Are the belts you used SAE or metric. Continental makes Metric Belts which is what I have on mine.

I have always just adjusted belts with the imprecise deflection method and drove enough with them to get them hot and stretched and rechecked them. Functionally that has normally worked for me on all of the vehicles I have owned.

The krickit is shown in the fsm. IIRC for a 240d, all belts get 50kg initially then 40-45 after. My observation, having just done 240D belts, is that the krikit is a great, simple and valuable tool, but sensitive to placement location on the belt, and how it’s pressed.

Was very easy to get exact on my 240d the other day. Getting the right sized belts over the pulleys was the bigger issue.

OP, was your adjuster bolt well oiled? I’ve found they need to be. Also need to be doubly sure that the other bolts are actually sufficiently loose that the alternator can move in it’s adjustable range.

Shern · #5 04-24-2019, 08:25 PM

It's possible I'm using my krickit incorrectly, because I'm 100% using the right sized belts, and am at the maximum adjustment travel and still getting 25kg.

The alternator adjuster.... no I didn't oil it, and that's not a bad idea.
But getting that tight has not been an issue. In fact, I'm fairly certain that I've
been over tightening it.

Quote:

Originally Posted by JHZR2

The krickit is shown in the fsm. IIRC for a 240d, all belts get 50kg initially then 40-45 after. My observation, having just done 240D belts, is that the krikit is a great, simple and valuable tool, but sensitive to placement location on the belt, and how it’s pressed.

Was very easy to get exact on my 240d the other day. Getting the right sized belts over the pulleys was the bigger issue.

OP, was your adjuster bolt well oiled? I’ve found they need to be. Also need to be doubly sure that the other bolts are actually sufficiently loose that the alternator can move in it’s adjustable range.

JHZR2 · #6 04-24-2019, 10:04 PM

The one thing I’ll hypothesize is that the belts may be stretched beyond useful life.

I couldn’t tighten down the MB OE belt on my ac compressor anymore for whatever reason. It doesn’t take much. See my old and new belt overlaid.

These cars seem to be precariously close between not being able to get the belt over the pullies, and not being able to tighten.

Shern · #7 04-24-2019, 10:49 PM

A good theory, however my belts were new with this issue : /

Diesel911 · #8 04-24-2019, 11:22 PM

Is this they type of bracket that you have?

In the other pic is a cheap replacement if the skinny rod breaks off on the tensioner. I believe it needs bit longer large bolt. (someone from another forums idea.)

Instead of the double nuts you could use self locking nuts.

JHZR2 · #9 04-24-2019, 11:50 PM

Quote:

Originally Posted by Shern

A good theory, however my belts were new with this issue : /

Hmmmm. I didn’t take that away from the OP. Bummer.

Technique with the krickit is to go very slow. You can go fast and an overshoot reads as more deflection or less tension. It takes a bunch of tries
To get a feel and a consistent read. Pressing faster/harder is not better.

okyoureabeast · #10 04-25-2019, 01:27 AM

Quote:

Originally Posted by Diesel911

Instead of the double nuts you could use self locking nuts.

Awe, thanks for posting my fix for the alternator adjustment bolt. That's my old house's kitchen counter top and you can see my leg in the pic

It came from this thread: http://www.peachparts.com/shopforum/diesel-discussion/290803-stuck-v-belts-alternator-bolts-frozen-tension-bolt-broken-2.html

But the eye bolt repair came from someone else suggesting it. It was this guy here: http://www.peachparts.com/shopforum/2616765-post14.html Very simple, yet very clever and above all cheap.

The only difference I would do now is sandwich the eye hook with two washers.

I'm glad my cheapo fix from 2010 has helped others over the years.

Shern · #11 04-25-2019, 01:51 AM

Diesel911 -yes, that's the bracket.

I plan to utilize this cheapo fix at some point in the future... think i'll just keep it around should I need to pull my alternator again and get nervous about cracking another $50 bolt.

JHZR2 · #12 04-25-2019, 10:01 AM

You sure your alternator pulley is the right diameter?

Shern · #13 04-25-2019, 11:37 AM

That's a thought I've had...
though it wouldn't be the alternator pulley, (because I have plenty of adjustment room) I would be the pulleys on both the power steering pump and the york AC compressor.

JHZR2 · #14 04-25-2019, 12:08 PM

Interesting that you have a York compressor. My 81 240D has an R4. Have you checked the FSM if the belts are different for the two compressors?

The copy of the fsm here:

http://www.peachparts.com/shopforum/diesel-discussion/368295-1982-240d-alternator-water-pump-belt-size.html

Indicates the same size from 1979 on (I know you said you have the right size belts earlier in this thread), but there are other fsm resources that show belt routings and other sizes.

The PS pump is the one with the longest run, but is also the easiest. The AC is the hardest to get on IMO, and I realized that the spacers weren’t right, so it had some extra slack in addition to the stretch. But my 81 has an R4...

Shern · #15 04-25-2019, 01:52 PM

You're right. Research and reality have turned to goo.
It's a delco.

Checked the FSM for all combinations of belt sizes.
Thought perhaps there might have been a slightly shorter PS belt, or AC belt for a previous version... nope.

It's weird. I'm either using my Kricket like an idiot (near certainty) or I'm missing something really basic here. I'm taking the car into my indie tomorrow to install an axle, will inquire and report back.

Quote:

Originally Posted by JHZR2

Interesting that you have a York compressor. My 81 240D has an R4. Have you checked the FSM if the belts are different for the two compressors?

The copy of the fsm here:

http://www.peachparts.com/shopforum/diesel-discussion/368295-1982-240d-alternator-water-pump-belt-size.html

Indicates the same size from 1979 on (I know you said you have the right size belts earlier in this thread), but there are other fsm resources that show belt routings and other sizes.

The PS pump is the one with the longest run, but is also the easiest. The AC is the hardest to get on IMO, and I realized that the spacers weren’t right, so it had some extra slack in addition to the stretch. But my 81 has an R4...