Scratches in #8 bearing

[Dauner]

Hi everyone,

1989 911 3.2 with 212K miles going thru total engine rebuild. I was inspecting my #8 bearing this evening, and after cleaning up, saw these scratches on either side of the O-ring. I don't remember hitting on anything as I removed crank from case half, and I'm the only person to touch the part since it was installed at the factory.

Anyway, knowing the issues with #8 bearing leaks, can I just clean up the high spots on the scratches and count on ThreeBond 1211 to fill in the low spots? The outside grooves are the ones I think I need to worry about most.

Thanks,

Mark

[Walt Fricke]

In theory, those outermost scratches shouldn't matter - the O ring is what Porsche used for sealing. I think the machined groove is intended to take oil which reaches the O ring - whose grove is wider than it is even when compressed - back into the sump when enough accumulates to need relief.

But I always coat that thin outer part with the orange Loctite I use to seal the case (and would if I used one of the other sealants).

But the scratches are very strange. Us home brew guys can mess up getting this bearing properly seated onto the hole for the locating pin in the bearing, but sliding the #8 on with the crank laying in the lower case half while lifting the crank wouldn't scratch this far out.

I have always thought you seldom need to replace this bearing, but an experienced engine builder friend says their ID can open up some over time, which you can measure. Replacements aren't as expensive nowadays as I remembered them being.

If I knew what alloy the bearing was made of, I have considered having them opened up and inserts installed.

[Dauner]

Thanks guys.

I measured the ID with my telescoping bore gauge and it came in right at nominal at least for a portion of the ID.

When I was separating the case, I remember it getting hung up and needing to go up and down a couple of times. Possibly it was the crankshaft that was holding on and I was moving it up and down? Only thing I can think of. What it looks like is if you dragged a threaded stud accross it, but I just don't see how I could have done that. Once the upper case half was off, crankshaft removal and placement on the bench was pretty graceful.

I did touch it off a bit with some 600 grit, and then 2000 grit, and it's actually pretty minimally scratched right now, and I don't think I took anything off of the OD in the vicinity.

Possibly an odd fate related note, my parts supplier inadvertently sent me a number 8 bearing that I didn't order. I think about $150 part. I'm using up more unplanned $100 bills fairly early on if I decide to not ship it back.

Do you have a sense of what kind of scratch the Orange Loctite or similar can fill? A thou? 3 thou?

Not sure what it means to "index" this part. I definitely had a leak behind the pulley, but not sure the actual path the oil was taking.

I definitely don't want to "cheap out" in any way. But also am mindful of my overall budget

As a note, there were mild markings/scores at the case half locations as well. They cleaned up no problem, but still surprising that my bearing had such a rough life when everyone elses come out clean and pristine. Engine lived a happy life, and all components were in quite good shape inside the case (as well as the heads, cams, rocker arms, etc.). Have all parts back from machine shops. Waiting for my ARP rod bolts that I opted to buy, returning the factory ones per recommendations from the forum.

If anyone has been in similar situation with same or similar engine and cleaned up scratches successfully preventing leaks with some form of sealant, would be great to know.

Thanks!

Mark

[Walt Fricke]

Loctite's TDS didn't give a "how big a gap can this fill" spec. Their graph of cure time vs. film thickness had curves for 0.05, 0.25, and 0.5mm, with cure time going up with thickness.

The odds of your firing up your engine within, say, a week of when you put the case halves together are, I suspect, scant, so plenty of cure time.

[Dauner]

Thanks Walt. .5mm is a ton! I'm guessing I'm more in the neighborhood of (0.004-.006")

In reviewing threads specifically on sealants on the O-ring, it seemed to me like people were gooping quite a bit of it on, while being mindful to not let the relief groove get blocked, or any errant sealant make it's way inside the crank.

I'll need to chew on it a bit.

Thanks again,

mark

[KTL]

That orange 574 goop can fill a huge gap. Look for some hardened sealer elsewhere around the engine (like the head-to-cam housing location) and you'll find it can cure very thick.

You did the right thing dressing those scratches and it should seal fine. Just put some sealant around the edge of the bearing bore near the o-ring site and that'll provide the extra insurance against future leakage past the infamous o-ring. I don't think it's necessary to coat the entire bore of the case at this location, even though it does provide extra added insurance. The orange 574 is easy to over-apply (you want to apply it as thin as possible) and you can get a ton of squeeze out when it's applied too thick.

I also like to keep sealant away from the oil delivery hole here in the engine case bore. This oiling hole is what feeds the #8 bearing, of course. But equally important here is the oil passage also feeds the internal passages of the crankshaft to supply oil to the rod bearings. The rod bearings are fed from the ends of the crank via #1 and #8 main bearings

[proporsche]

Dauner..i did plenty of engines and i have never had to use any loctite on the outside of the 8th bearing.Never had a oil leak there either after.
Mind you, if you put a little only it would not hurt.But,friend of mine did an engine and called me that he had an oil leak right there..and after he had to split the engine guess what, he put too much orange 574 loctite and it was leaking right there.As Walt said the o ring does its job.
And yes that scratch is most likely done by you and i would not worry about it too much.

Ivan

[Dauner]

OK Thanks guys. I'll continue to clean it up and likely make a game day decision, erring toward re-using.

[KTL]

If it measures up nicely on the inside diameter, call it good and reinstall it. Usually these #8 bearing inserts show a slight amount of swiping on the ID but it doesn't amount to anything. If the ID looks nice and clean/smooth with no scratches in it, it should be fine.

There's only one way to index this bearing insert. The body has a hole in it for the dowel pin and that's the only way to install it. The reason it's doweled is because the oiling hole in the body needs to line up with the hole in the case bore. If those holes didn't line up, the bearing wouldn't receive oil and that end of the crank wouldn't send any oil to the rod journals.