940 Small Oil Leak - Rear of Cylinder Head

Hello All,

Chasing an annoying oil leak coming from the rear of the cylinder head on my '94 940 Turbo.

Background
About 10K km (~ 6K mi), I installed a 'freshened up engine' in my car. The head was rebuilt (cleaned, skimmed, valves reground and new valve seals), new head bolts, all oil seals, all gaskets, camshaft, timing belt, water pump and hoses. Along with all fluids.

The leak started right after putting the car back on the road. It is a tiny leak running down the rear of the cylinder head, along the rear of the engine block following the edge by the gearbox bell housing and dripping of the lower bell housing bolt (passenger side). We are talking about a couple of drops every few hundred kilometres. Takes awhile for any oil residue to build up on the gearbox and transmission mount bracket.

My initial assumption was the distributor so I replaced the distributor O-rings (small and large one). I didn't replace the oil seal for the distributor driveshaft as there was very little oil inside the distributor. Replacing the O-rings did not change the oil leak.

Next I pulled the valve cover, the pedestals, and the camshaft, assuming the leak was the result of the oil creeping under the rear pedestal and / or the valve cover gasket. Put a light film of gasket maker (Permatex), under the front and rear pedestal, reinstalled the camshaft, coated a new valve cover gasket on both sides with gasket maker and buttoned up the engine. Still leaks!!!!

It does not appear to be the valve cover gasket as it shows a light film of oil along the lower edge. Not enough leakage according to numerous 'paper towel' tests. Running my finger along the back of the cylinder head always results in a very 'wet' (oil), finger.

Any thoughts on what I am missing here?

Go back and check the distributor shaft seal again. They're always baked, especially on the turbo cars. Be sure to check the shaft bushings as well. A seal can't work on a wobbly shaft.

The procedure for changing the seal can be found here.

https://www.volvoclub.org.uk/faq/VolvoB230ShaftSeal/DistributorShaftSeal.html

Detailed drawings of the tool are here.

https://www.volvoclub.org.uk/faq/SpecialTools.html

I have the same issue, very frustrating.

Hello All,

Finally got around to pulling the distributor and going through the disassembly process. If you follow the procedure as outlined in the UK Volvo club (link in hiperfauto post above), please beware of two potential issues,

I did the distributor on both my 940s - both had oil seals that were basically bits of hard plastic. On the turbo the drive pin was a PITA to remove, the NA was a piece of cake. Due to the very large number of blows on the turbo drive pin, the bushing in the housing moved. This became readily apparent when I started to reassemble the distributor - huge amount of end play. When I compared the two distributors it was readily apparent what had happened. It is easy to tap the bushing back into its correct place. So keep a close eye on that when disassembling.

The second potential issue are the fiber washers (yes, plural). It appears the washer on the rotor side has a fiber coating and both washer on the drive side have a fiber coating (coatings face each other). On my turbo the fiber was gone on the rotor side and could be rubbed off with a finger on the drive side. These washers are NLA. I was unable to find fiber or mylar material as suggested in the Volvo UK article. I ended up making washers from the heat resistant cooking sheets for BBQ use. These are extremely tough. The down side is you need to have a hollow cutter to make the 1/2" hole in the centre. I happen to have a set of cutter for making gaskets but not everyone may have this luxury. Cutting the outer circumference is easy with scissors. This material is thin so you will have to make a number of washers to equal the required thickness on the drive side. The rotor side will only need one.

Lubricate well with engine assembly oil and double check the end play. It should be close to zero.

IPD is the only place I know of the sells (only a few dollars) an after market (MTC), repair set that includes the seal and both O-rings (black ones). They also sell the seal separately if you prefer using the better quality 'green' O-rings for the distributor housing (large one), and small one at the end of the drive locating shaft.

CAUTIONS;
1. take lots of pictures.
2. mark the drive to shaft orientation BEFORE disassembly.
3. use the punches as recommended in the Volvo UK article.
4. CAREFULLY seat the new oil seal - you have ~2mm of fore / aft room to play with to avoid the new seal mating with the original seal groove on the shaft.
5. try to use a vice / punch for assembly and not a hammer / punch - its a lot easier on the components.

Hope it helps.