Scored Main Cap Bearing - Ouch

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blewbyoutobad

blewbyoutobad

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I have a new 340 motor that I had the shortblock built and cant get rid of an oil leak at the rear. After changing the pan gasket several times I am confident it is not leaking and decided to go in and replace the rear seal. When I pulled the rear main cap this is what I found. Motor has less than 500 miles and good oil pressure. I have no idea what could cause this except some debris left in the engine after build. Now what?
Thanks FABO

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Better check the rod bearing too. Crank may end up needing polished. Did you do the rebuild or did a local shop do it. May end up rebuilding the whole engine again to get it cleaned and figured out.
 
Did the bearing do the job and take all of the damage? If It didn't then I'm sure you already know whats next.
 
Ouch! Not totaled but not right. Do you know what the oil clearance was on that one? You may find other bearings that look the same.
 
yes, the crank is scored. ,Yes a reputable shop did the work. Has to be junk left from the rebuild. not much sense in going any further.
 
That's a bummer but you got lucky really, It could have been much worse.
 
You might have the machine shop check the crank for straightness & have the align bore checked also. JMHO
 
That STINKS. Sorry to see your issues. Get in touch with the shop that did the work ASAP. How does the cam look. Any flat lobes.
 
show us the crank journal. bearing could have taken the hit only. If its apart, look at the rest.
 
blewbyoutobad said:
I have a new 340 motor that I had the shortblock built and cant get rid of an oil leak at the rear. After changing the pan gasket several times I am confident it is not leaking and decided to go in and replace the rear seal. When I pulled the rear main cap this is what I found. Motor has less than 500 miles and good oil pressure. I have no idea what could cause this except some debris left in the engine after build. Now what?
Thanks FABO

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Sure looks like debris scoring to me.
Think about how and where the oil gets to the bearing and it becomes fairly obvious.
Some of that junk probably got in the rear main seal causing the leak.
 
I would check the other main bearings, a few of the rods bearing , and #8 rod bearing. This is to try to determine if the debris is general or localized.

If it is just in this #5 main, then it may have just been a chunk of debris in that oil passage, which IIRC is separate from the main oil gallery that feeds 1-4, and the lifters and heads.

That is not horrible scoring, not great but not horrible IMHO... and is not all across the bearing, so not likely to be a bent crank. The wear in front of and behind the scored area looks pretty typical. Could you take a pix of the main journal and post it here?
 
Main journal, no raised areas. Damage is all in center where oil hole is. Talked to shop and they said to order new bearings and replace this journal. Motor is still in car. Also suggested using some scotch brite to clean up the crank, clean and rotate then do the other half. Nothing to lose at this point. Had to be some debris. I will pull main cap next to it and rod cap.

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Someone didn't chamfer the oil hole either before or after the crank was ground. That's what did the most damage. Then the junk came from that.

Look at all the mains and I bet you find the same thing.

Also, there is some water patterns on the bearing. If they didn't line hone it, they should have. None of them are ever straight, round or sized the same after years of use.
 
It is very important to hot tank the block after removing every plug from the oil passages. Then clean the block. and then clean it again. Never let it in the open always keep it bagged until it is buttoned up. Also every part should go in a sonic cleaner that goes in the motor. Heat shield taken off the intake and cleaned. . You would not believe how many fresh motors come here looking like yours. Shops think throw the new parts in and send them down the road. I
If you wouldn't have had the leak you would have never saw this until it was to late.

I wouldn't let him touch it again . Take it as a lesson learned and move on to a shop who takes pride in their work. I have mentioned this once in a thread. When taking your engine to a shop. Ask to see the shop and make sure the machines are clean and on piles of metal on the floors around them.

Look at the out going work such as heads and short blocks, They should all be bagged and on a clean shelf.

Would you sit on a shitter without looking at the underside of the seat? Some people only clean what they have to to get by. You have to watch out for your own *** in this world. LOL.
 
I'd also remove and disassemble the oil pump and inspect, making sure it turns easily and doesn't have excessive scoring. I mean the pan is off already, so do it!
And clean the pick-up tube.
 
A lot of people don’t knock out the vertical plug in the oiling system under the rear main cap. Without doing so there is no way to properly clean an engine block.
 
Everything my son works on is cleaned before it hits the machines and after. He will not put parts that don't look like new in the mills. Also all parts are laid on clean towels and then covered at night. Like your putting the kids to bed. He sprays every machine down with CRC lube every night. I once set a coffee on the mill. He flipped out. Dave leaned on it one time and he flipped out. That is the kind of shop you want to take a motor to. He learned this working for an old time machinist . Not from me that's for sure.

Look for a clean machinist in your area that cares about their reputation.

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Mmmmmm.... Scotchbrite is frowned upon. The carbide particles get get everywhere. I'd lightly polish with 600 or 400 wet-or-dry. Crank is not great but no horrible. I would plastigauge it too.

Good idea on the pump examination. A lot of scoring there indicates a general level of dirt/debris. But that can only be told if this was a new pump at rebuild. Again, examine more mains/rods to see if this was a general problem or localized. The more info you have, the better the decision, IMHO.

Not sure I am following the comment on the chamfer being no touched.... looks chamfered to me...??? But I might not be seeing it right. It looks like the debris was caught around the hole and spun around and around before it disintegrated.

How is this engine to be used OP?

BTW, I don't see the factory knurling/fine grooves on the seal surface. Maybe it may not be visible. But if that is gone, then I think you need to change away from the rope seal. And if that is a rubber rear seal, it looks kinda burned/melted to me....???
 
You guys are the best. And Old Man your son is terrific. Wish his shop was in Houston area. The oil holes are chamfered, hard to see in pic. I am going to use 400 & 600 wet or dry to clean up the journal. I am doing this under the car in my shop. When i work on something I am anal about cleanliness, maybe I should have done the short block assy. I plan on checking all the mains since I have to order a set of bearings. I will also check some rods to see whats going on there. Anymore of this scoring and the engine comes out. Engine is a street engine, knurling is there on crank for seal. Thank you all for your input. I will keep you posted.
 
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blewbyoutobad said:
You guys are the best. And Old Man your son is terrific. Wish his shop was in Houston area. The oil holes are chamfered, hard to see in pic. I am going to use 400 & 600 wet or dry to clean up the journal. I am doing this under the car in my shop. When i work on something I am anal about cleanliness, maybe I should have done the short block assy. I plan on checking all the mains since I have to order a set of bearings. I will also check some rods to see whats going on there. Anymore of this scoring and the engine comes out. Engine is a street engine, knurling is there on crank for seal. Thank you all for your input. I will keep you posted.
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Cut the can of the oil filter, that will tell you alot.
If the filter element is loaded with trash you can almost bet all that crap went through the engine.
 
blewbyoutobad said:
You guys are the best. And Old Man your son is terrific. Wish his shop was in Houston area. The oil holes are chamfered, hard to see in pic. I am going to use 400 & 600 wet or dry to clean up the journal. I am doing this under the car in my shop. When i work on something I am anal about cleanliness, maybe I should have done the short block assy. I plan on checking all the mains since I have to order a set of bearings. I will also check some rods to see whats going on there. Anymore of this scoring and the engine comes out. Engine is a street engine, knurling is there on crank for seal. Thank you all for your input. I will keep you posted.
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I would leave the crank alone unless the damage is bad enough to catch a finger nail on. The only way I would polish a journal is out of the engine and on a crank polisher.
 
oil holes are chamfered. and oil to #5 is back from the filter directly, 1-4 goes a different path. did junk in the pump go thru a cheap filter?
 
Marcohotrod said:
oil holes are chamfered. and oil to #5 is back from the filter directly, 1-4 goes a different path. did junk in the pump go thru a cheap filter?
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Put a 1/8 rod down through the oil pressure sending unit hole on top the rear of the block. If it falls straight through the block (with the rear main cap off) the 9/16 plug was never installed. If you fail to install this plug oil isn’t diverted to the oil filter.
 
toolmanmike said:
I would leave the crank alone unless the damage is bad enough to catch a finger nail on. The only way I would polish a journal is out of the engine and on a crank polisher.
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I have done them in the engine and in the car a bunch of times without a problem.
A fine (600) crocus cloth strip with a little oil on it and make sure the oil hole in the crank is clean after.
Q tips for that.
 
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