Case Porosity at Main Bearing Web

rdimarco · rdimarco's Garage

While flushing my case squirters I found a few pores in the main bearing web actually communicate with the oil passage in the bearing web. As I was flushing, small amounts Oil/solvent was coming out a couple of the porous holes nearest the oil passage. Could a bit oil coming out between the web and bearing shell cause a problem or increase chance of a spun bearing?
Should I try to seal these up, and if so with what?

Thanks,

Flieger · Flieger's Garage

If it were me I would try to have that welded. Those holes could initiate cracks as well.

rdimarco · rdimarco's Garage

Have you seen one crack there before? This SC case has 150K miles (street) on it, I would have guessed if it hadn't cracked by now then cracks would be unlikely.

Flieger · Flieger's Garage

I am not an expert -- I was hoping by bumping the thread that one of the more knowledgeable members would chime in.

But;

The holes are stress concentrators and aluminum will fatigue fail eventually under cyclical loading no matter how low the stress (most apparent on airplanes). So the holes will shorten its life but the lifetime would have been designed to be very long anyway so it might not make any difference to you. Maybe the load cycles are not so pronounced there -- the two banks of cylinders balance out the force on it?

afterburn 549 · 06-11-2012, 05:00 PM

slippy slope
with welding you are now doing a line bore and a bunch of other steps...If it was airplane I would be concerned.....
So..I would say you have oil pressure on the back side of that bearing shell?..Not good.
I dont know if I want to tell what i would do...........or not........clean it and JB Weld the imperfections. Just make dam sure you are below contour.
If you spun a bearing..is the Big end round on the rod?
Are the main bearing holes round when bolted together?
What does the other side of the saddle look life?

AlfonsoR · 06-11-2012, 08:34 PM

What did the crank and bearings look like? If they look good and if you intend on keeping your car on the street, I would be tempted to leave it as is.

I don't believe there is any concern with stress risers. Maybe too simple thinking but, if a hole in the web was a significant stress riser, then you would find cracks around the holes that are designed to be there in the first place. Airplanes are a different story, the structures under go many pressurization/ depress cycles.

afterburn 549 · 06-12-2012, 04:26 AM

If you can find NO reason for the bearing failure..I would be concerned about the oil pressure behind the bearing shell making it float (hydraulic lift) up against the crank......thats all I can think if

BURN-BROS · 06-12-2012, 05:03 AM

We have taken apart a fair number of cases with this type of issue. All of the cases were from high mileage cores with no issues as a result of the porosity. Porsche also accepted these cases during the inspection and assembly process as well.

chris_seven · 06-12-2012, 08:02 AM

I would think that it is unlikley that this type of porosity would result in any crack propagation.

To create a fatigue crack the local stresses would have to relatively high and there would need to be a surface traction vector that would exceed the stress needed to cause fatigue crack initiation. I wouldn't worry.

I would try to fill the holes with a low viscosity araldite but cleaning out all of the oil could be tricky and the adhesive may not bond to the surface.

rdimarco · rdimarco's Garage

The bearing, crank, and journal are all in good shape, no visible or measurable problem so far. No bearing failure, I just wanted to prevent one in the future. I was concerned that oil pressure under the bearing shell might not be good. I may try to dab a tiny bit of JB Weld or similar into the leaky pores with a pin, keeping the sealant below the journal surface.
Thanks for all your input.