I had rebuilt me engine in the summer and put almost 5,000 miles on it when it started to knock knock. So Ipulled it in December and dissassembled it to find my poor bearings. Here are the possible explanations I have come up with:

When I was assembling the short block I broke a bolt off in a main cap. I realized at that point that the bolts I gave the machine shop were not the ones I got back. So I bought a new set of studs for the mains and put it together. I did not have it line bored or honed with the ARP Studs though. Could have been that.

I never dropped below the 10 psi per 1,000 RPM rule, so I don't think I ran it dry.

I noticed coolant in the oil (twice) from when I changed the intake, so I then changed the oil.

Could dirt have done that much?

I do have a freeze plug above the back main cap to prevent oil from bypassing the filter.

I did have the entire assembly spin balanced. Every part I bought was also individually balanced.

I did not have the crank turned, just polished. Maybe it needed to be turned and because it wasn't it sat too loose in the journals, or I got a set of bad bearings?

So why would this have happened?

 

Maybe no help at all but I had this happen to an engine once although not quite that bad. The stock journal crank was a bit undersized and the bearing clearance was around .004 or more. I put in a new set of Clevite .002 oversize (for undersize crank) bearings and had no problems since. I'd also suspect the coolant leaking might have some part in this.

 

Are those half-shells arranged in any particular order?

Were clearances checked when the engine was assembled?

There does appear to be some pitting, which could be the antifreeze, if it sat in the engine for any length of time.

However, I'd say not dirt. Dirt tends to score. For one reason or another, that appears to mainly be lack of lube. Either from excessive clearances, or you simply didn' t have the oil supply you thought you had.

What kind of oil were you using?

 

Looks like coolant or gasoline in the oil.

 

Those half shells are in no particular order. Just the main journals on the top and the and the rod journals on the bottom.

I did not measure the clearences once it was assembled. First one I did not and look what happens. Is it agreed upon though that it was not due to not line boring it?

Definatly not gas in the oil, but as stated before, there was coolant that I found in the oil.....Never thought it could do that damage.

For oil I used either Mobil 10W30 or the equivilent brands.

I found it odd though that on some of the bearing surfaces it was worn mostly down the center instead of evenly.

 

definitely appears to be a lack of lubrication. How long was the oil in use? What concerns me is that you did several oil changes however, this still happened...possible overtightening came to mind, but all the bearings seem spent. On the bearings with the uneven wear...possibly an uneven shaft? You ever do oil analysis on it?

 

i'll take a guess and say you didn't clean the area the bearings rest in and you had dirt run thrught it. i'd also guess you nicked the crank with a rod bolt, or two.

 

Oil was changed at every recomended interval. When I drained the oil for the final time, it did have metal flakes in the oil.
To bad I can't let you guys feel the crank. It deffinatly has ridges in it now.

 

Looks like what happens when a motor blows up, and the next owner or builder does the usual lazy cleanup thing and just dunks it with the cam bearings in it and then just pounds a new set of cam bearings in without brushing anything, and all the schmutz left over from the blowup is still in the groove behind the bearings, and it flushes right straight into the mains the first time it starts up. After that, it's pretty much a downhill spiral, of low oil pressure, dirt in the oil, parts wear shedding more metal, oil pressure goes lower, more dirt, more wear, etc.

That's why those bearings are gouged (not worn) down the middle; is because the filth that tore them up, came from the oil holes.

The solution is to take the cam bearings out yourself BEFORE you take the block in for cleanup. Specify that it be returned to you with no cam bearings and no plugs in it. Take it to the car wash, along with a couple of cans of engine degreaser (diesel fuel in a spray can), some rifle & shotgun brushes, and a little toothbrush-shaped wire brush; and spend about $10 of quarters cleaning out all those grooves, and every single oil hole and passage. Then AND ONLY THEN, put the new cam bearings and plugs in it.

 

I have never heard an explanation like that before.
Makes good sense.

I thought that the Hot tank usually took care of that stuff. Makes sense though. How do I take the cam bearings out, carefully? Freeze plugs are easy enough.

 

You'll need a cam bearing driver to take the cam bearings out. Snap-On, etc. make universal kits, or Proform has an SBC/BBC specific one for about $70 IIRC. Cheaper would be to find a used one on eBay, or if you know someone with a lathe, they could just make you one pretty easily.

 

Hot tanking doesn't dissolve metal shavings.

If you don't have a cam brg tool or want to buy one, take it to the shop, have them take the brgs & plugs out, and do whatever machine work to it that you want; and go pick the block back up BEFORE they put all that back in it, do the wash thing, then take it back to get new cam brgs knocked in. You can do the plugs yourself easily enough.

 

In case anyone comes across this in the future, here is a good site for bearing analysis:

http://www.bobistheoilguy.com/bearin...aranalysis.htm