Use Hylomar on OM642 Turbo pedestal gasket??? - PeachParts Mercedes-Benz Forum

87tdwagen · #1 03-05-2022, 12:40 PM

Hi all,

After much probing, it seems that my OM642 has a oil leak in the turbo pedestal gasket, so far seems to be the bottom gasket. Arrg.

The PO had the oil cooler seals done some time back, and I cannot see anything indicating an oil cooler leak, there is residual oil towards the rear of the valley but it seems to come up from the base of the turbo pedestal which is higher, as well as oil deposits in a portion of the head casting by the turbo which is accessible only from the turbo end rather than the oil cooler which is isolated by relation.

So, I may have to yank the turbo and do the pedestal seals.

What's your thoughts on using Hylomar on both surfaces of both the upper and lower pedestal seals? I have used this product for years on head gaskets and according to its product info it is for metal to metal surfaces which in this case perfectly describes the turbo pedestal seals. The operating rating is from -5to250 degrees C.

Any concerns or input as to why I should or shouldn't use Hylomar in this application?

TIA

Murkybenz · #2 03-05-2022, 01:08 PM

No need for the Hylomar or anything like that , just replace gasket.
Now there are two types of gasket the thick solid one and a thin waxed card type one which can tear and is most likely the one you have that is leaking.
Now to stop the thin one from tearing when fitting turbo if you get two long bolts of the correct size thread about an inch and a half long and cut a slot for a flat blade screwdriver in one end you can thread these in and sit the gasket in place and there is no turbo sliding around which is what tears the gasket when refitting it.
Once fitted just unscrew them and use a magnet tool to pull them out one at a time and refit the correct bolts.
The bottom gasket has a dowel that positions it … I fitted my turbo by fixing pedestal first and then doing the above … not sure if it is possible to fit pedestal to turbo and fit as one unit but possibly trying to do it may tear gasket

jay_bob · #3 03-10-2022, 06:20 AM

There are 2 versions of that tower gasket, the factory one and the aftermarket ones.

The factory ones have little ears that capture the tower holes and keep it from moving around.

The aftermarket ones are just flat.

I think I used dental floss to hold things in place while setting the turbo on the times I did it with an aftermarket gasket. Get things in position and the bolts started and slide out the floss. Use that polymer tape kind "Glide" it holds up better.

87tdwagen · #4 03-10-2022, 08:07 AM

Thanks for the input, this has been valuable. While I was approaching this from making a more leak free joint, your experience is indicating that the gasket placement on reassembly and securing it is paramount. I was not aware of how finicky this was.

I have the aftermarket late design metal gaskets, so will take your advice into consideration and report back when the job is done. One of the reasons I was leaning towards the use of Hylomar is that it is really tacky, and should theoretically aid in keeping the gaskets in place on reassembly, as well as adding a bit more overall bonding and seal to the entire gasket, but may combo that with the bolt or floss methods you have both outlined.

From what I have researched so far, it seems like the turbo has to be removed from the upper pedestal mount first, in order to then have access to the lower pedestal bolts to the head. Is this correct or does it all come out at once, turbo and pedestal together?

jay_bob · #5 03-10-2022, 04:09 PM

You want to pull the turbo off the stand and then take out the stand afterward. But if you’re just swapping or removing the turbo then the stand doesn’t have to come out. Only if you’re going deeper (oil cooler seals) does the stand have to come out.

Reassembly you put the stand onto the engine, and then put the turbo onto the stand. The troublesome gasket is the one between the turbo and the stand.

Check this thread I go through the whole process of pulling and installing the turbo (twice).
OM642 VNT Turbo actuator issues

87tdwagen · #6 03-11-2022, 10:44 AM

Thanks Jaybob, great write-up and thanks for clarifying which was the troubling gasket. I assumed the procedure was similar and could not see the bottom stand gasket being difficult with the turbo out, but can see how the top gasket could move around.

Are the bolts from the turbo to the pedestal one-time use also?

I see that you have them listed in your parts list. Since you did this twice, did you have to go thru 2 sets? Or reused the new ones, from first attempt?

I'll prob have to source some more parts, I did not account for the pedestal bolts either to the turbo or the head, did not think they were one-time-use. I have new ones for the exhaust end.

jay_bob · #7 03-12-2022, 08:14 AM

Yes those bolts (the big black ones with T45 heads) are torque to yield so they are single use. General rule, if WIS calls for a torque that is a Nm plus a further angle, that requires a new fastener each time.

That list encompasses everything (bolts and gaskets) you have to replace if you pull and replace the turbo.

I did pull it twice, first time tried cleaning the VNT vanes but the second time was to install a replacement turbo. In the box with the replacement they give you a couple of the gaskets but that's it.