Crank bearings

Mike the mechanic · 11-11-2002, 09:35 PM

Hey guys,I finally started to take my engine apart for my big project. The engine has under 75,000 miles on it (119,000kms) and I am wondering if I should change out my crank bearings while it is apart. I feel it is logical to replace them since all will be apart anyway, but then again I find it pointless to replace parts that don't need replacement.
Everything in the top end is flawless, by the way.
How many miles do these bearings in our engines typically last? I will probably split the case tommorow and I can post some pics of the bearings in the evening.
Let the comments begin!
Thanks

KevinP73 · 11-11-2002, 09:46 PM

For as easy as it will be to replace them now it's kind of a no brainer. Think of how upset you'll be later when you find out you should have changed them when you had the chance. Besides if you're going to rebuild it, why not go 100%
Just my humble opinion

A Quiet Boom · A Quiet Boom's Garage

An ounce of prevention.......

Mike the mechanic · 11-12-2002, 05:43 PM

Yeah, I posted that pretty late last night, woke up this morning wondering why I even bothered posting about this. Here's some pics of the open case, let me know what you guys think of the bearings. Funny, the intermediate shaft bearings are "showing copper". WTF? Is this usual in our engines?
Thanks

silverc4s · silverc4s's Garage

Yeah, Mike,
That Intermediate shaft does a LOT of work. Think about it..

Zendalar · 11-12-2002, 08:08 PM

Replace them all.

And if copper/brass is visible the bearing MUST be changed.

Superman · 11-12-2002, 08:46 PM

Intermediate shaft bearings don't work that hard, but they're small. Yes, it is typical for them to show copper like that. They'll work fine for a half million miles probably, but they show copper like that.

Crank bearings get wear spots too. The one closes to the flywheel will have dark wear spots at opposite ends. Also, the bearings will catch particles leaving them embedded in the bearing. That may be why the crank bearing on the end in the picture looks duller.

They're all probably perfectly serviceable but it's still a no-brainer. Replace them all.

speeder · speeder's Garage

I am having a similar dilemma, actually whether to even split my case on 120k mile SC motor. I removed #5 rod to check that bearing, it shows very minimal wear. If I do split case, I am 99% sure of what I will find, main bearings that look like yours and wear on I.S. bearing.

Everyone here says that it is a "no brainer", I am not so sure. He has the original bearings in mint condition, they are worn-in to the crank, zero chance of reinstalling a faulty/defective bearing. And they appear to be in close to "like new" condition. For me it is not a "going cheap" decision, could care less about the cost of new bearings, just whether it would be an improvement on what is there. I.S. bearings would be replaced, natch.

Can anyone out there convince me why it would be wise to replace them under these conditions, other than just an opinion, ("it's a no brainer")? TIA.

Zendalar · 11-13-2002, 01:25 AM

Well...try scraping with you nail, first the graphite looking area, then the area which has the copper visible.

Every mechanic (engine rebuild shops) that I have spoken with have told me that if copper is visible, the bearings should be changed.

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by speeder
I am having a similar dilemma, actually whether to even split my case on 120k mile SC motor. I removed #5 rod to check that bearing, it shows very minimal wear. If I do split case, I am 99% sure of what I will find, main bearings that look like yours and wear on I.S. bearing.

I'm not answering the question but it seems #6 is the one that usually goes first. I have one in a bag it you need it - it looks like bran flakes.

-Chris

AFJuvat · 11-13-2002, 04:46 AM

Quote:

Originally posted by speeder
I am having a similar dilemma, actually whether to even split my case on 120k mile SC motor. I removed #5 rod to check that bearing, it shows very minimal wear. If I do split case, I am 99% sure of what I will find, main bearings that look like yours and wear on I.S. bearing...

...Can anyone out there convince me why it would be wise to replace them under these conditions, other than just an opinion, ("it's a no brainer")? TIA.

Why is because it is just good safe practice. With the large investment of time and cash rebuilding, why would you even consider putting it all at risk (however small) with some used bearings to save a maximum of $200?

True, the I-shaft bearing tends to wear first - the mains seldom wear at all on a properly maintained engine - they swim in oil.

Be safe, be sure, replace the bearings...

AFJuvat

speeder · speeder's Garage

Thanks for the replies, I've pretty well decided to replace them if I split the case. It was never a question of $$, if anything I tend to replace parts that could have been re-used in a rebuild, I just was not convinced that new ones would be a true improvement over what is (presumed to be) there.

Like AFJ said, they tend not to wear out period, and certainly not before my motor needs its next rebuild, (I figure another 100k miles it will be P/C time). Also Chris, thanks for the reply, Walt from Competition Engineering is the one who told me to check #5 rod bearing, he said that if any show wear it would be that one. (Not sure why). It was in "close to new" condition, crank journal appears to be perfect/new condition. These motors were really built, especially the bottom ends. Funny, but I also asked him about replacing perfect main bearings, he laughed and said something along the lines of, "if you don't, the sky will fall". And they have lost count of the number of high quality 911 rebuilds they have done. Lost count many years ago.

But I'll change 'em, what the heck.