1991 BMW 850i

page 3

  1. Charcoal canister refurb
  2. Acoustic cover refurb
  3. Valve stem seals
  4. Cam timing
  5. Oil pan gasket
  6. Intake gaskets



The charcoal canister on these cars are notorious for rusting due to being located under the washer tank (which often leaks). The purpose of this canister is to absorb any gas fumes from the gas tank when the engine is not running. When the engine is running these fumes are sucked into the intake manifold and burned off. It is a very simple device that is simply packed with activated charcoal and some gauze filters. They cost about $130 to replace but can be rebuilt for a lot less and so that is what I did...

The washer bottle (located above the charcoal canister) was cleaned with hand cleaner. I replaced the grommets that seal the washer pumps and level sender and also replaced one of the pumps which appeared to be leaking.

The charcoal canister was sanded and primed with rust reformer.

I then drilled out the 4 dimples that retain the end cap.

This is the end cap and filter that hold the charcoal granules in place.


Looking down inside the canister with the charcoal removed you can see a removable gauze filter..


This is the activated carbon I used. It is a bit coarser then the original stuff but should be fine. It is primarily used to clean aquarium water and this cost me only $14 on Ebay (shipped).


I refilled the canister, re installed the white filter and end cap  (now held in place with 4 x 4-40 SS hardware), then cut out and installed a new outer filter as the original disintegrated when I removed it.


Here's the finished rebuilt and painted charcoal canister with new hoses ready to be re-installed in the car (after I replace the valve stem seals).


The engine acoustic cover was looking a bit sad and the rubber gasket had detached so I spruced it up...

I thought the brown residue on the gasket was old glue but I now believe it to be Cosmolene (sprayed on to protect the engine when new). The engine cover is also covered in this stuff.

I stripped the cover with paint stripper (the only stuff I know that removes cosmolene and will not eat the plastic) and cleaned the rubber gasket with a blunt knife and my finger nails! Even after several applications of paint stripper there was still a little cosmolene left on the cover which I removed with wire wool. I also removed and cleaned the hardware with wire wool. Every thing was then washed with lots of soap and water. The gasket was glued back in place with silicone adhesive and allowed to set.


After the glue set up I applied a liberal amount of Mothers 'Back-to-Black' on the cover and gasket and the end result looks almost like new!




I Started on the valve stem seals today... I will use the rope method to hold the valves in place.

The passenger side plugs came out first - they don't look too bad. According to my records they have about 10,000 miles on them so I won't bother replacing them.


I removed both of the oil spray bars and cleaned them up with carburetor cleaner. The hydraulic lifters all look good so far - all measuring 1.91" and are nice and stiff. Checked for wear on the rocker arms and found nothing of significance.


I just picked up this tool press on the weekend for a good price ($60). Figured I'll need one of these when I get to the rear suspension. It's a harbor freight model and very sturdy.

You can never have enough tools! My Craftsman tool chest was overflowing so I also added the black husky set ($100 on craigslist) which is now just about full also!

The right tool for the job makes working on cars much easier and enjoyable. Ebay and Cripe Distributing are 2 of my favorite sources for good quality USA made tools. But I also shop Harbor Freight for some things.



I started on the valve stem seals this evening.

I used a Harbor Freight bungee cord about 3ft long to hold the valves in place. It is fed into the spark plug hole with the piston at BDC, then the crank is turned until resistance is felt. You can see my socket and wrench on the end of the crankshaft.

I used the tool below to remove the stem seals, it is designed for this job. You have to twist them and pull... they can be quite stubborn.

A 3/8" 10mm 12pt socket was used to press on the new seals. It is taped to another socket to extend its length. A 10mm 12pt socket is a nice snug fit on the new seal. You can press them on by hand. I also I tapped them lightly with a mallet just to be sure they were seated firmly.

Below you can see the valve springs (inner and outer), collets and one of the removed valve stem seals.

The old seals don't look too bad but they are noticeably hardened and blackened where they grip the valve stem.

The new seal slides over the valve stem using a plastic sleeve included with the valve stem seal kit. This avoids damaging the seal on the collet grooves in the valve stem.

Getting the collets back on after replacing the seals is a pain. I spent the better part of 1hr on the first one! Getting the valve stem tool setup right is the secret. Below is what I used initially but ended up reconfiguring it many times. There is very little room for the tool when attacking the valves closest the firewall. When removing and re-installing the rocker arms, I only used one hook on the tool so there is room to slide the rocker in from the side.

It took me a few hours just to complete the first cylinder but it became easier after that...


2 weeks later I completed the passenger side! Now I know what I am doing it is going a lot smoother and faster. Having an extra set of hands makes a big difference, especially when reinstalling the collets.

The bungee I used is quite thick, which meant I often had to reposition it to contact each valve in the cylinder. At first I had nightmares about it getting tangled up in the cylinder but it has proven to work quite well and never once got tangled on itself.


Reinstalling the rocker arms goes a lot easier if you first remove the lifter, then slide the rocker arm into position on the valve stem and to the side of the lifter and then re-install the lifter (see pic below). Now compress the valve spring while pulling up on the other end of the rocker arm until you can lift it over and onto the lifter - then release the valve spring compressor. Any other way I kept dislodging the small spacer that sits between the rocker arm and valve stem.


With the passenger side valve stem seals completed I was ready for a more relaxing job... I reinstalled the charcoal canister along with new hoses.

I have installed new rubber seals in the washer tank (for pumps and level sensor). I also spliced in some new pieces of washer hose to ensure a good tight seal at each pump. It should be watertight now.

Now that the passenger side valve stem seals are all replaced I checked and adjusted the cam timing...

First rotate the crank to TDC (clockwise to keep the cam chain tight).

And use this special tool to check the cam timing

It should sit squarely on the cylinder head but as you can see it does not. This is due to the cam chain wear (stretch) and is perfectly normal; in fact for 133K mi it looks pretty good. After loosening the cam sprocket bolts and adjustment, the cam timing is now spot on. It takes a few tries to get it spot on.

6/28 All the valve stem seals have been replaced.

These are the old ones...

They were not in bad shape for 133K mi but it made sense to change them since I had everything apart. It wasn't an easy job... definitely not for the faint hearted but it did get a lot easier once I got the hang of it. I was able to do the driver side by myself (without any extra hands).

I used blue loctite on the oil spray banjo bolts together with new seal washers.

Valve covers are now back on.

I cleaned up the engine wiring harness at the firewall; re-wrapped part of it and re-secured with tie wraps.

This thin piece of metal helps support the wiring harness across the back of the engine.

Although the existing water pump was in good shape I went ahead and installed a new one. I also refit the oil filler with a new gasket.

I dropped the oil pan and was relieved to find nothing unusual. Removing the old gasket was a pain and took a lot of scraping with the help of a heat gun. I also installed a new O-ring on the oil level sender


It is looking a lot cleaner under the engine now!


I re-installed the intake manifold adapters. I used some of Max's silicone gaskets and some gasket sealer as well just to make sure I have a good seal!

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