Issues with 60x tensioner - alignment and shearing bolts - PeachParts Mercedes-Benz Forum

JHZR2 · #1 10-11-2022, 09:17 PM

My latest w126, my 91 350SD with 206k has a few bugs. Nice car, keeper, but sorting it out has been interesting.

When I bought it, the tensioner was in disrepair:

I put in a new shock and it was mildly better but still not right.
I replaced the tensioner. Simple once I got the old one loose. Drove maybe a quarter mile and the new pulley’s bolt (reused old bolt) sheared off…

When I pulled the system off, the new stabilus shock was somewhat misaligned. When I pulled the whole thing apart, the top rubber was halfway pressed out.

Like there needed to be a washer between the shock and the head. Is there? There isn’t one on my car, and the FSM doesn’t show one between the shock and head, nor the EPC.

There’s just too many things not going right, which to me indicates an issue. But what? Why?

The sheared pulley bolt could have been me. I’ve done quite a few of these, and have not used a torque wrench for the pulley bolt. Maybe I should because the FSM says 14nm which isn’t much. But I’ve never broken one before. I don’t gorilla them down that’s for sure.

Maybe I also have a bad (new) stabilus damper. It’s hard to get it right in there. It seems to be a bit loose even with the new tensioner. I’m not sure just how much motion the tensioner should allow when cinched down to the lower part of the damper.

Any thoughts on this? The car is new to me, and it seems like there is something not quite right in the setup. How much of it is me vs the car vs something else ai can’t tell. It isn’t rocket science.

Any ideas?

Thanks!

optimusprime · #2 10-12-2022, 09:17 AM

The tensioner can be fitted to either sides of the bracket Fitting it to the wrong side of brkt will throw it out of line .

87tdwagen · #3 10-12-2022, 09:42 AM

No washer at shock to head mount. There should be a washer behind the tensioner Part # 23 based on your style tensioner. From your other thread, you mentioned that the tensioner bolt threads were damaged, any sign of that before installing new?

The backface of the tensioner in your pics shows some scars, not sure how this happened, but that outer face should not be in contact with anything, only the center section where the bolt goes thru and the washer backspaces it from the timing cover.

Possibilities that come to mind:
Tensioner mount washer missing causing alignment issue
Tensioner threads where damaged causing tensioner to mount at an angle, again alignment issue.
Possibly a bad pulley out of alignment elsewhere in the route, water pump, power steering etc.
Possibly locked up AC compressor that when activated caused excessive force on tensioner pulley.

The threads on the timing cover will be the most challenging, if they can be re tapped and cleaned up, would be great. If damaged or if the timing cover mounting boss was stretched/bent, a new front timing cover may be the only solution to that.

JHZR2 · #4 10-12-2022, 11:38 AM

Quote:

Originally Posted by 87tdwagen

No washer at shock to head mount. There should be a washer behind the tensioner Part # 23 based on your style tensioner. From your other thread, you mentioned that the tensioner bolt threads were damaged, any sign of that before installing new?

The backface of the tensioner in your pics shows some scars, not sure how this happened, but that outer face should not be in contact with anything, only the center section where the bolt goes thru and the washer backspaces it from the timing cover.

Possibilities that come to mind:
Tensioner mount washer missing causing alignment issue
Tensioner threads where damaged causing tensioner to mount at an angle, again alignment issue.
Possibly a bad pulley out of alignment elsewhere in the route, water pump, power steering etc.
Possibly locked up AC compressor that when activated caused excessive force on tensioner pulley.

The threads on the timing cover will be the most challenging, if they can be re tapped and cleaned up, would be great. If damaged or if the timing cover mounting boss was stretched/bent, a new front timing cover may be the only solution to that.

Tensioner mount washer was definitely installed. M

The tensioner threads are damaged now when I pulled this one out. But they weren’t damaged before, and the new tensioner moved properly.

I looked over the pulley system and didn’t see anything out of alignment/how that could happen.

The AC isn’t working so I don’t think that’s it. Pulley spins nicely. Only operate in economy mode.

I think you’re onto something regarding misalignment. But what I don’t know. I’m inclined to remove the radiator and condenser and do a time sert insert in the timing case.

87tdwagen · #5 10-12-2022, 03:22 PM

I guess you could try placing a straight edge across pulley faces from the hub pulley and see if they all align. Inspect all of the pulley bolts and any protruding center hub for evenness, possibly a pulley mounted with a tilt. Next would be to check the pulleys themselves with a straight edge to make sure they are true.

Last thing that comes to mind is replace that serp belt, its got a lot of cracking, and if worn in by your bad tensioner before, it is likely skewed now on a good set up and not traveling true under load.

Good luck

JHZR2 · #6 10-13-2022, 12:16 AM

Quote:

Originally Posted by 87tdwagen

I guess you could try placing a straight edge across pulley faces from the hub pulley and see if they all align. Inspect all of the pulley bolts and any protruding center hub for evenness, possibly a pulley mounted with a tilt. Next would be to check the pulleys themselves with a straight edge to make sure they are true.

Last thing that comes to mind is replace that serp belt, its got a lot of cracking, and if worn in by your bad tensioner before, it is likely skewed now on a good set up and not traveling true under load.

Good luck

Sure, it needs to be replaced. Had gotten one online that was The actual MB part, but the part number was wrong and it was 20mm too short,,,, went to AZ to get a continental belt, and it’s some subpar variant.

I’ll have a new quality 2120 belt soon. Hopefully continental contitech is still legit.

I have to think that I tightened the bolt too much which damaged it.

I also still don’t really know why the shock rubber shifted so much, like a washer’s worth…

87tdwagen · #7 10-13-2022, 04:19 PM

Hopefully it will all work out with fixed pulley and belt. The shock bushing shifting is strange. I can only imagine that the pulley shearing created some excessive force, enough to damage the tensioner threads, so I assume that was from the tensioner being violently jerked, twisting the shock bushing in the process. It and the threads had to have a lot of lateral twisting force applied to be damaged like that IMO. Maybe from over tightening, maybe not.

The oddity for me is that the old tensioner is similarly damaged at the shock fork, from a twisting force rather than the vertical force normally applied thru the pulley. Not knowing the history it's hard to tell. If your timing cover looks original, inspect it closely for damage especially around the tensioner mounting location, it may no longer be true, may not have been before you started either, maybe from prior damage. Best of luck, a mystery indeed

JHZR2 · #8 10-13-2022, 06:54 PM

Quote:

Originally Posted by 87tdwagen

Hopefully it will all work out with fixed pulley and belt. The shock bushing shifting is strange. I can only imagine that the pulley shearing created some excessive force, enough to damage the tensioner threads, so I assume that was from the tensioner being violently jerked, twisting the shock bushing in the process. It and the threads had to have a lot of lateral twisting force applied to be damaged like that IMO. Maybe from over tightening, maybe not.

The oddity for me is that the old tensioner is similarly damaged at the shock fork, from a twisting force rather than the vertical force normally applied thru the pulley. Not knowing the history it's hard to tell. If your timing cover looks original, inspect it closely for damage especially around the tensioner mounting location, it may no longer be true, may not have been before you started either, maybe from prior damage. Best of luck, a mystery indeed

Thanks. The damage on the old one was from the shock rubber bushing coming off. Could something have twisted? Yeah I guess so (?). I thought it had just vibrated in place. This engine does allow a decent amount of tensioner up and down movement.

I can’t imagine something is seizing up occasionally to cause funny forces. But something is obviously moving in a strange direction.

I could have sworn that one of my 603 cars, maybe my 1993 300SD had a washer between the shock and the head, which is why I asked. If that shock is misaligned, it would pull and cause all sorts of funny issues.

87tdwagen · #9 10-13-2022, 08:06 PM

Quote:

Originally Posted by JHZR2

Thanks. The damage on the old one was from the shock rubber bushing coming off. Could something have twisted? Yeah I guess so (?). I thought it had just vibrated in place. This engine does allow a decent amount of tensioner up and down movement.

I can’t imagine something is seizing up occasionally to cause funny forces. But something is obviously moving in a strange direction.

I could have sworn that one of my 603 cars, maybe my 1993 300SD had a washer between the shock and the head, which is why I asked. If that shock is misaligned, it would pull and cause all sorts of funny issues.

It may need a washer to be perfect, you can always try and see. My 86 and 87s did not come with them, but who knows if the exterior dimensions in the head redesigns in later years, had any impact. I'm not sure how much impact a1mm washer either way wou,d have on the proper function of the tensioner, there's already a bit of play in the bushings. Should be fine.

Either way once assembled and running you can visualize any belt runout and or pulley wobble if any thru the rpm range. If no probs, chalk it up to another case of der gremlins seeking tribute.

JHZR2 · #10 10-13-2022, 08:47 PM

Quote:

Originally Posted by 87tdwagen

It may need a washer to be perfect, you can always try and see. My 86 and 87s did not come with them, but who knows if the exterior dimensions in the head redesigns in later years, had any impact. I'm not sure how much impact a1mm washer either way wou,d have on the proper function of the tensioner, there's already a bit of play in the bushings. Should be fine.

Either way once assembled and running you can visualize any belt runout and or pulley wobble if any thru the rpm range. If no probs, chalk it up to another case of der gremlins seeking tribute.

I went out and looked at the 602 in my 91 300D. No washer.

Hmmm. Could have sworn there was one on some car.

I mean, a bit of misalignment can make all sorts of issues. I’ll need to go look at the 93 tomorrow…

JHZR2 · #11 10-14-2022, 05:34 PM

Quote:

Originally Posted by 87tdwagen

It may need a washer to be perfect, you can always try and see. My 86 and 87s did not come with them, but who knows if the exterior dimensions in the head redesigns in later years, had any impact. I'm not sure how much impact a1mm washer either way wou,d have on the proper function of the tensioner, there's already a bit of play in the bushings. Should be fine.

Either way once assembled and running you can visualize any belt runout and or pulley wobble if any thru the rpm range. If no probs, chalk it up to another case of der gremlins seeking tribute.

So this is where the shock lies just sitting natural.

I checked the 603.971 in my 1993 300SD.

No little bracket between the shock and spring holder, and definitely a spacer.

I looked at my 602 in my 1991 and 1993 and they don’t have spacers. Must be a difference in the newer 6cyl heads (?).

I got a small aluminum washer at the hardware store. Good enough??

I torqued it all down to spec.

I need to let the tensioner loctite cure so I won’t put the spring on and run it for a day or so.

87tdwagen · #12 10-15-2022, 09:24 AM

Looks good.
It's hard to say what came with what beyond what the EPC parts diagrams show. These cars are old and have had who knows how many people working on them, how many parts were lost or decided not to be used by previous wrenchers. So long as the shock is vertically aligned between upper and lower mounts it should be fine.

Now that front Z bracket between the shock and the spring holder, IMO, is important, it serves as the stop for the spring holder, applying full spring tension on the assembly. Without it, it is conceivable that a sharp jolt to the belt will allow the spring to release tension enough to pop the belt off. That is why it must be loosened and unhooked from the metal stud on the spring block in order to then pivot the block to remove tension to change the belt.

It's hard to tell from the pics if your spring block has the stud or not that locks into the fork end of the Z bracket (item 95). Your bracket looks a bit mangled either from an extreme belt jolt, or possibly someone previously trying to pivot the block to change the belt without releasing the bracket first. It can be straightened out . The engines without it should get one added IMO.

JHZR2 · #13 10-15-2022, 11:38 AM

Quote:

Originally Posted by 87tdwagen

Looks good.
It's hard to say what came with what beyond what the EPC parts diagrams show. These cars are old and have had who knows how many people working on them, how many parts were lost or decided not to be used by previous wrenchers. So long as the shock is vertically aligned between upper and lower mounts it should be fine.

Now that front Z bracket between the shock and the spring holder, IMO, is important, it serves as the stop for the spring holder, applying full spring tension on the assembly. Without it, it is conceivable that a sharp jolt to the belt will allow the spring to release tension enough to pop the belt off. That is why it must be loosened and unhooked from the metal stud on the spring block in order to then pivot the block to remove tension to change the belt.

It's hard to tell from the pics if your spring block has the stud or not that locks into the fork end of the Z bracket (item 95). Your bracket looks a bit mangled either from an extreme belt jolt, or possibly someone previously trying to pivot the block to change the belt without releasing the bracket first. It can be straightened out . The engines without it should get one added IMO.

Thanks… yeah I was surprised to not see the bracket on my w140, and the black plastic spring holder didn’t have the small nipple that it latches into. The w140 has been set up like that for tens of thousands of miles.

The bracket on the w126 is bent but latches a bit. I can change it.