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I've done a bit of searching but can't find the definitive answer as to the combinations of valve cover material.
My car is a 1990 C4 (MY90) and am trying to determine whether both my upper and lower valve covers are magnesium or whether I may have an aluminium set in there also?
What are the aluminium part numbers for both the OEM upper and lower valve covers?
MY92 and later had aluminium valve covers as standard. Some earlier cars had aluminium replacements if the mag ones got badly corroded or leaked excessively. I think part numbers should end in 01 for the magnesium covers and 02 for the aluminium ones
MY92 and later had aluminium valve covers as standard. Some earlier cars had aluminium replacements if the mag ones got badly corroded or leaked excessively. I think part numbers should end in 01 for the magnesium covers and 02 for the aluminium ones
Neil
Thanks Neil. Does this mean that from the factory, the early cars had both upper and lower mag cases?
If someone could assist by providing the p/n's for the OEM aluminium upper and lower valve covers, that would be appreciated.
The Katalog doesn’t specify material type, as stated above there is a part ending with 01 or 02, but it doesn’t state the year. If you are interested in what you have it is visually easy to tell the difference between mag & ali. Unless the PO has powder coated them or something.
Check out design911 (no afilliation) they list a 3rd party and OEM part, both ali.
Both my 1990 and 1991 cars have magnesium valve covers. They have some corrosion and will eventually need to be replaced but not yet they are not leaking.
The mag covers came painted in zermatt silver which eventually turned a tanish color used up to 92 IIRC. The aluminum covers came unpainted or coated in natural aluminum finish. They were both made from the same tooling as shrinkage factors for aluminum and magnesium are the same. The only difference is the part number. The mag covers should be checked cleaned and painted if they show signs of damage to the coating. The biggest area of concern is where the spark plug cable seals to the cover trapping dirt and water which eventually break down the material at the thinner sections. I have taken warped mag covers and reworked the mating surfaces stopping them from leaking. It is the seal that seals them not the cover. tq is only 7 ft pounds.
Thanks for all of the information everyone.
I've had a look and I definitely have the mag upper and lower. My car is booked in for a new clutch and a major service next week with my mechanic. I do have some leaking from the lower covers and I was going to look into replacing with aluminium covers during the process. Based on your advice Cobalt, I might ask that he checks, cleans and possibly paints the covers as the coating has definitely begun flaking on all 4 covers.
I had the mag covers on my MY 91 powdercoated will do a valve adj soon anxious to see how they are holding up. The powdercoaters said because they were magnesium they had to bake them first to outgas them before the powder coat then of course bake them after. Not sure if all that was true but they sure acted like they knew what they were doing 😁
The external side of the mag covers is one aspect, but it is the inside condition that swayed me to buy new from Rennline. I know some have painted or powder coated with success and as JohnJ964 says there is a process to outgas the magnesium. Same goes for reconditioning the magnesium fan. Here are some pics...
04-17-2018, 11:17 PM
OEM Valve Cover - Material
