M117 timing chain tensioner help

[s class]

Hi guys,

The piston on the M117 chain tensioner has a vent hole in it. I'm sure I've read somewhere that the vent hole should point up (to allow air out), whilst on my new tensioner, its assembled with it pointing down. The workshop manual makes no reference to this, but shows a cut-away drawing with the vent hole pointing down.

??

 

[WGB]

With my 450 motor I just took the new one out of the box and screwed it in after filling it with oil (which made it much stiffer than oiless).

Do you really think it is a vent hole or is it an oil bleed hole.

If it is indeed an oil bleed hole to control pressure and possibly allow lubrication of the pivot point it won't make much difference if it is up or down.

I'll have a poke around my manuals and also go and look at the old one I removed and see which way the hole is aligned but won't get a chance until tomorrow night.

Bill

 

[s class]

Thanks Bill, I appreciate that.

 

[Styria]

Sorry S-Class, I can't help you with this one - I have never done any work on an M117 engine. Regards Styria

 

[s class]

- I have never done any work on an M117 engine

You are a lucky man. Replacing the chain and tensioner on the M117 shortly after the same job on the M100 has given me quite some distatse for the M117. It is considerably more inconvenient to work on than the M100- both in terms of engine layout and ancilliaries location.

 

[WGB]

Hi S-class,

I looked at my old M117 tensioner that I had removed from my 450 previously and the hole in that one is at right angles to the previously discussed up and down positions and would have pointed to the front of the car.

I'm sure it doesn't really matter but at least if left pointing down any sediment would drain out more easily.

Bill

PS I do have some 117 specific literature that I haven't read through but will do so later tonight and post anything I find.

 

[Styria]

You know, S-Class, I am pleased that at long last someone has actually agreed with me that the M100 engine as in 6.9's is just so much easier to work on and service. In fact, this also applies to suspension work, and the rest of the 6.9 components are shared with all other 116's as well.

So, anyone that speaks of increased 6.9 complexity is a little off the mark - certainly from an accessability point of view anyway. Regards Styria

 

[WGB]

The 117 motor sits lower in the car so the plugs are a little harder to change but the aircon compressor is easier to remove. The biggest mechanical difference is the non-ratcheting tensioner which means the plastic sliders need to be 100% as the chain contacts them a lot more often.

The suspension on the non-hydraulics needs the correct spring compressor and once you have that they are about on a par to work on.

I pored through some manuals last night (sounds a bit extreme, had a glance really) but didn't come across anything in any offical M-B maual.

Chilton's Repair and Tune up Guide 1974-85 gives the following passage about V8 tensioners - " Since December of 1974, a venting hole has been installed in the tensioner to prevent oil foaming. If you have a lot of timing chain noise, use this type of tensioner, which is identified by a white paint dot on the cap."


Bill

 

[s class]

Thanks for all the ghelp guys - Bill especially.

I went ahead and started it up today, and I'm quite pleased with the results.

Some background - last year I had my thermostat fail in the partially closed position, so one weekend I remedied that. While I was at it, it occured to me that chain problems are endemic to the M117, and I had never checked the stretch on that car. I pulled off the right hand valve cover and discovered 14.5 degrees of stretch. I was so shocked I did not start the engine again, and parked the car pending repairs. I checked my mileage log, and it turns out that was July 21 last year. It took until this year to get around to doing the repairs, and its taken months because I've been distracted by other issues.

I replaced the chain, and cam sprockets, plus the three upper chain guides, and the tensioner rail lining. I also put in a new tensioner. I tried to do the correct thing, priming the tensioner in oil, but the new chain was so, well, unstretched, that the tensioner rail was moved very nearly to its outer extreme, requiring the tensioner plunger to be compressed to its maximum to fit the tensioner. The chain ended up as tight as a drum skin on all travels, and I was unhappy with this. I ended up removing the tensioner, draining the oil and refitting it. I then was able to deflect the tensioner rail about 2mm with firm hand pressure.

Before firing the engine, I cranked with the coil disconnected until I had oil pressure. I then reconnected the coil, and it fired first time. 11 Months after it last ran!

There is not much difference in performance, which surprised me, but it now idles very smooth. THis had been a problem before - idle was terrible.

Happiness. Now I can get on with the sale of this car.

 

[WGB]

Pleased you're pleased.

I think a good 117 tensioner does hold the chain very tight but an old one is very sloppy.

What was your timing like in degrees ATDC with the new chain and sprockets?

Bill

 

[s class]

With the marking on the RH cam lined up, I got about 2.5 degrees on the crank. I then checked both cams with the proper valve lift method, and found that :

LH side : spec is 6.5 deg ATDC, mine is 7.5 deg ATDC

RH side : spec is 4.5 deg ATDC for a new engine, 6.5 deg ATDC for a used engine. I got 7.5 deg ATDC.

Considering that I am selling this car now, this is more than good enough.