Early aluminum valve covers: how flat is flat?

[Neil '67 911S]

Listers,

Ol Ivory ('67 911S) has warped aluminum valve clovers. Both lowers (exhaust) are warped by 0.002 in, one upper is warped 0.014 in and the other 0.024 in. Clearly, the uppers need to be machined flat again.

Anyone know what the "flat" spec is? Using a set of orange silicone gaskets, perhaps the lower VCs are flat enough?

Thanks!

[1QuickS]

Standard milling practice would result in a maximum of plus/minus flatness across the surface of 0.002", maximum, more likely 0.001".

Is the flatness resulting in oil leakage?

I was experiencing oil leaks with the silicone gaskets and the six stud lower valve cover. Since I have a Bridgeport mill I decided to purposely mill my covers so that the middle was lower relative to the ends. This provides additional clamping force to the ends of the covers which I deemed to be deficient compared to later covers with more studs to clamp the gasket tightly.

I clamped the ends of my covers to my mill placing a spacer in the middle which resulted in more material removed in the middle than at the ends.

My results were worth the effort, no more leaking from the lower covers.

[Neil '67 911S]

Standard milling practice would result in a maximum of plus/minus flatness across the surface of 0.002", maximum, more likely 0.001".

Is the flatness resulting in oil leakage?

I was experiencing oil leaks with the silicone gaskets and the six stud lower valve cover. Since I have a Bridgeport mill I decided to purposely mill my covers so that the middle was lower relative to the ends. This provides additional clamping force to the ends of the covers which I deemed to be deficient compared to later covers with more studs to clamp the gasket tightly.

I clamped the ends of my covers to my mill placing a spacer in the middle which resulted in more material removed in the middle than at the ends.

My results were worth the effort, no more leaking from the lower covers.

Hi Paul,

Thanks for the speedy reply. I was tinking that 0.002 in might be adequate.

Oil leak? Of course. From where, hard to tell. Engine is up on the stand, and of course, tipping it from one side to another causes any drips to run/possibly change direction.

Top of the cylinders where the spark plugs go, is dry. None of the rocker shafts have moved, all the bolts are snug.

One cam housing drain tube is slightly suspect; the other 3 are dry.

More burned oil on the driver's side heat exchanger but more on the shop floor below the passenger's side. The suspension set at stock ride-height, which I believe is slightly nose-down.

Intake valve cover gaskets are the slightly green variety without "traces." Exhaust valve cover gaskets are a thinner cork? I remember torqueing the M8 lock-nuts atop, buna sealing washers topped with the correct aluminum washers to 5 ft-lbs last valve adjustment which was years but maybe 5k miles ago.

Both intake valve covers are warped on a diagonal. Clamping as you suggest sounds like a decent idea after the surfaces have been milled flat. However, I just checked with a flat edge and found that all four covers crest in the middle of the clamping face but all four of the cam tower gasket surfaces are flat. My guess is that the Factory already did what you do. What I do find is that each valve cover seems to have a "happier" side but unfortunately, I didn't mark which cover went where.

Since the car sat in a garage for nearly 30 years, perhaps the valve covers "took a set."

I'll take a look at the imprints on the gaskets next but I thought I'd toss these comments out there first.

[1QuickS]

Try this:

Clean and dry assemble covers to cam towers, tighten the nuts to "finger tight". Use feeler gauge to determine gap situation. What I achieved after milling was zero gap in the ends and about 0.015" gap (guessing as this was long ago) at the middle.

Since there are no fasteners at the corners of the covers it is easy for the gasket to resist sealing AND the cover will warp. The covers are not that rigid and the gaskets do "push back"; this force can yield the cover out-of-flat.

I did not machine or even check upper covers as they were not leaking. Oil rests against lower cam cover so a weak seal will weep oil.