Can we live with these cracks?

[wrenchhead944]

Hi
We are working on a 1970 911E .

While cleaning the block we found a couple of cracks . I was wondering if these are fatal issues . The first one is on the is on the bolt boss by the oil strainer cover . it is not through to the inside of the block and as far as we can tell it was not actively leaking. The picture does not show it well, but it is there and is not a casting marking



The second ones are by the bolt on oil cooler , just above , towards the front of the mounting boss for the front lower stud.

It looks like there is a pipe pressed into an internal passage that runs up to the oil T stat.



My question is are these a problem or are they a common issue and will not be a problem.

Any input would be great .

Thanks

Brian

[chris_seven]

Cracks are never good news and if it is still propogating then disaster will not be too far away as the crack growth rate will only increase with crack length.

If is is a brittle crack that has arrested then it may be stable but I wouldn't hold my breath.

You could try the old trick of drilling holes at the ends to blunt the crack tip and reduce the stress intensity but I would want to chase them out and have it welded.

[911Freak]

Those are some odd places for cracks aren't they?! The second one with the oil pipe: that open slot is usually sealed up both inside the void where oil cooler bolts up and the outer case area with JB weld to prevent/stop oil leaking from that area. As several qualified engine builders here on the forum do as normal practice.
I would be most concerned about this area as well. Why is it cracking and from the looks of the cracks they seem to be growing. This isn't a stressed area is it?

If you are tearing the engine down for a rebus you might want to have the cases inspected further for additional cracking in places you haven't seen yet and to get a better grasp on the severity of the noted cracks.
Might be time to look for replacement case?

Hopefully one of our resident engine builders will chime in

[chris_seven]

Originally Posted by 911Freak

I would be most concerned about this area as well. Why is it cracking and from the looks of the cracks they seem to be growing. This isn't a stressed area is it?

Unhappily you can't grow a crack without a traction vector on the surface of the crack and this always means that a stress must be present.

There are three basic modes which can cause cracks to open:



These modes can also be mixed and it is normal convention to consider that the most likley direction for crack propogation will be in a direction that is perpendicular to the plane of the maximum principal stress.

There are some exceptions to this basic rule. materials which are very anisotropic tend to follow weak planes in the material and also when local and intense plastic flow occurs cracks may grow due to in-plane shear.

Neither of these exceptions appears likely and the safe assumption is that these cracks have been produced due to relatively high levels of stress.

Why stresses have been generated in this area is the interesting question.

[Flat6pac]

I have a hard time seeing cracks on the bottom of the engine with an 8mm stud and nut holding the flange together and next to the oil drain, there is no twist in the engine.
Are you sure they are not just casting flaws in the magnesium.
The area in front of the oil cooler is a pipe and needs to be sealed as I have seen leaks there across the years of the engines.
Bruce

[BURN-BROS]

I am starting to see old mag cases form these cracks. These cases are up to 40 years old now and obviously have life spans. I personally would search for a case in better condition.

[wrenchhead944]

Update

We sent the cases out to be welded

Thanks for the input

Brian