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I have read several posts about sealants used during an intake manifold seals/gaskets refresh. I have Curil-T on hand for the intermediate seals (rubber donuts) between the upper and lower parts of the intake manifold. I will NOT use a sealant on the gaskets at the block.

That leaves me to ask about a sealant for the gasket at the EGR tube bolted to the plenum (lower intake manifold part). Does anyone have a suggestion?

It appears that 25Nm is an appropriate torque for the intake manifold bolts. Does anyone disagree?

Should I use 2000 grit sandpaper on the interface between the intake manifold and block?

I start the tear down next Friday.
 

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Hi Tom,

I recently did a full rebuild of the intake on my 560. I've been meaning to do a write up and share pictures, but I haven't gotten to it yet. Hopefully my experience and that of others can be of help.

RE sealants for the plenum doughnuts: I used none. The service manual doesn't call for any and my (I believe original) gaskets between upper and lower plenum had none on them. With the fresh gaskets, the seal was very good. I did spend some time cleaning up everything to make a good seal. I really don't get the impression that sealant would help or add durability. Once you get the upper and lower plenum bolted back together, it's a tight seal. One minor tip: look over the 8 gaskets really closely with a flashlight / scope as you put the halves back together. I just barely caught that one of the doughnuts had doubled over on one interior side. Spend some time making sure all 8 are seated correctly to both plenum halves, then tighten down.

RE cleaning up the mating surface for the manifold gaskets: I ended up not needing sand paper. I used a plastic blade (like a razor blade but not metal) to get most of the old gasket residue off. Then I used brass brushes to scrub, which created a nice clean surface. I used a bit of steel wool at the end, but barely needed it. Same on the intake side. I think it made a good seal - no coolant leaks or anything on mine.

RE bolt torque: Frustrating that it's not spec'd anywhere in the service manual! I did a few searches and also came up with 23-25 NM. Start from the inside bolts and work out.

Let me know what other questions you have or where you stumble once you start. This is all pretty fresh in my memory and I have some pics. Sounds like you're pretty well informed, but just in case: consider what else you want to do at the same time. I replaced all of the vacuum components (lines, fittings, one check valve on the intake), replaced and adjusted the throttle position sensor, replaced the throttle gasket, replaced the big rubber boot + aluminum mount beneath the CIS fuel distributor, and serviced the flux capacitor while I was at it. ;-)

Have fun and good luck. Was a satisfying project for me. My mechanic recently did a full smoke / vacuum test and gave the job an A, no leaks.
 

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Moving to modern day high quality sealant products now readily available compared to what was around +30yrs ago i would use a smear of sealant on the doughnut gaskets.
They are notorious for causing vacuum leaks and in my own opinion it can only help avoid this issue completely
 

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Blue Hylomar sparingly on oil pan gasket works wonders at sealing, and the same for the donuts. This helps them stick in place, not used as a sealant.
 

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One minor tip: look over the 8 gaskets really closely with a flashlight / scope as you put the halves back together. I just barely caught that one of the doughnuts had doubled over on one interior side. Spend some time making sure all 8 are seated correctly to both plenum halves, then tighten down.
^This. When I did this job on my SL, I was not careful here and it was very frustrating up to when I finally figured it out.
 

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Discussion Starter #6
jsebastian, what symptoms did you experience when the doughnut was not seated correctly? How did you figure out the issue?
 

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Discussion Starter #7
My fishing trip was postponed due to inclement weather in the area. Therefore I started my tear down for the intake manifold refresh project. I have been cleaning and then applying Kroil penetrating oil for the last several weeks leading up to the job. A bolt near the coolant duct on the front passenger side had corroded and nothing that I did helped. Now I am left with the stub of a bolt. I cleaned up the remaining threads and applied heat, then more Kroil.

Does anyone have a sure fire solution to getting that bolt out of the block without needing to helicoli?
 

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Tom Kaiser
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