I tore down my 454 last weekend and have the crank out. This engine has about 10-13K miles on it. 6 of the rod bearings had worn through the soft coating on the bearing nearly all the way across. The wear is on the top of the bearing directly under the rod I-beam I had one incident with intermittent oil pressure early this summer, and the engine did overheat once to around 260 deg. When I put the motor together, the plastigage said the rod journals had 2 to 2 1/2 thou clearance.
Anybody have any ideas why these bearings did this?

Also, I noticed I have some minor scoring on the cyll walls. There is a noticable wear mark at the bottom of the cyllinders in two places. It looks as though the piston skirt is causing this rubbing when the crank rolls over BDC. This is not a stroked motor.
This has me baffled also.

Thanks
Dave

I would say you are very lucky. It sounds like you had more than a little problem with oil pressure. Look at everything a motor that runs without oil pressure can hurt just about every moving part.

Do the bearings or connecting rods show any signs of heat? How are the remaining cap bearings? What do the mains look like? Considering the mileage, I'd suspect abrasion first from contamination of the oiling system. Loss of lubrication means heat, which totally destroys all bearings, including the mains. Accelerated wear is a slower process but no heat is involved. If the worn bearings do not show heat discoloration or melted material, then another factor was involved. The condition of the bearings will tell what has happened. Look at all the remaining bearings in the engine.

Kas,
Absolutly no sign of heat. No discoloration or "moving" metal.
Mains look fine, except for the score marks in a couple where I picked up a chunk of a broken rocker arm pushrod seat. The side broke out and some small pieces were circulated through the pump and into two mains. Did not loose any oil pressure from that episode. I guess it wouldn't bother me so much, but it happened so soon, and the wear pattern is only on the side of the bearing extending to the center. Doesn't go all the way across. ? ?

Dave

Dave,

Chevy bearing wear should extend all the across the rod bearings. The maximum wear or load is +/-20 degrees from TDC on the compression stroke. Having a wear pattern that doesn't extend across the bearing suggest an abnormality in the loading pattern. Piston contact with the cylinder walls is also not normal. Check piston/connecting rod alignment. Check for bent connecting rods. Was the crank reground .010 under or so? Were the connecting rods reconditioned at the last rebuild? We're looking for a reason why your 454 wore the bearings the way it did.

I think the shrapnel from your rocker arm incident may have caused the wear due to the particles in the oil. I had a similar experience when I had a torque converter balloon and wiped my thrust bearing when the engine only had 1500 miles on it. I had the stock oil bypass and it sent the grit throughout the engine. Scored the main bearings pretty well and the rod bearings were worn down to the copper in a few places. Looked like sombody used 80 grit to sand the bearings. What did the cylinders leak down at?? If they are good, just have the crank polished and install new rod and main bearings. I tore my engine down completely and had it hot tanked and new cam bearings installed. May have been overkill but I didn't want any chance of that stuff recirculating after all the work to teardown and re-assemble. I cleaned the pistons in carb cleaner to get the carbon off and they looked like brand new. Had the crankshaft polished and checked clearances and reassembled with new bearings. So far its been OK. Also, I am running a plugged bypass and stock pressure relief spring and have had no problems with it.

------------------
David

1968 Chevelle Malibu

Dave,

Even though you have .002" oil clearance, the oil film between the bearing and the crankshaft is only .000040" thick. Not much room for the oiling system to clean things out. Cleanliness is the #1 issue in bearing health.

Dave,
If I understand your post correctly as far as the point of wear, I would say it is either too much bearing clearance, or possibly a detonation problem. It might have also happend when the oil pressure was low.
Check out Clevit's site...they have some good info on bearings. I think somewhere on the site is a bearing failure chart with pics. Any chance of getting a pic of your bearings ?? http://www.clevite77.com/Motorhead/techstuff/

------------------
Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100

kas, Crank was ground under .010.
I miked the crank immediatly and found the journals paralles within .0001.
I hope you are wrong about the bent rods. http://www.chevelles.com/forum/eek.gif

Bill,
I have a camera and will try to post a pic. I do know that I did have a problem with pinging at one time. Nursed the car home and backed the timing off.
I posted this question on Clevites site.
I will copy their response here.

thanks
Dave

Dave,

if they looked like this...

http://www.chevelles.com/showroom/427TRI/427L88bearings.jpg

We've kinda determined it was from contaminated oil, or NO oil at high rpms ( HV pump and stock cap pan) AND too much timing. The apex of each bearing showed more wear.

You run a HV pump?>?>

BTW, these bearings had over 30K HARD miles on them, so its not as bad as it looks, well, I did pull the whole enchillada apart.

[This message has been edited by 427L88 (edited 01-02-2003).]

427,
Well, sort of.
Difference is mine have copper showing on the upper bearing, on the apex or the centerline of the rod. And, the wear does not go all the way across the bearing. It is almost like Bill suggested, there was too much clearance or it was low on oil. Which I am ashamed to admit, did happen once.
My bearings only have about 13K on them.
I will try to post pics tonight from home.

Dave

[This message has been edited by SS_Dave (edited 01-02-2003).]

Also, if you run too much side clearance, the oil wont stay where it belongs, ON THE ROD BEARINGS.

BillK,

Here is a picture of my bearings.

http://www.chevelles.com/showroom/SS_Dave/rodbearings.JPG

Little fuzzy, but the best I could get.
You can see where the copper is coming out.
Wear is not even. I think the low oil incident caused this.

Dave

BillK,

Some "mild" detonation??? Or will low oil pressure "ONCE" do that to them???

I ask b/c they look like maybe they were hammered at some time in their running...pdq67

btt.

Bill? U out there?

As I was reading this I was thinking detonation the whole time. I will have to agree with Bill on the bearings. What compression, timing and octane are you running? Do you have a picture of the skirts? Do you run an air cleaner on the car at all times? Dust (dirt) will do wonders to a cylinder wall.

------------------
Mike Hurta
(Aug98)
Gold#25
Lake Jackson, Texas
www.chevelles.com/feature/aug98.html (http://www.chevelles.com/feature/aug98.html)
http://chevelles.com/showroom/hurta2.jpg
www.chevelles.com/showroom/hurta.jpg (http://www.chevelles.com/showroom/hurta.jpg)
www.chevelles.com/showroom/hurta4.jpg (http://www.chevelles.com/showroom/hurta4.jpg)
www.chevelles.com/showroom/Aug98/HurtaBurnout.jpg (http://www.chevelles.com/showroom/Aug98/HurtaBurnout.jpg)
www.chevelles.com/showroom/Aug98/Sept27Hurta.jpg (http://www.chevelles.com/showroom/Aug98/Sept27Hurta.jpg)

the cylnder wall damage is from too much heat, that is heat damage, I would have the crank checked to see if it is straight it may be bent, I had one like that it ate up the bearings because it was not rotating properly

Dave,

A picture paints a thousand words.

Your photo shows concentrated loading in the crown of the bearings. This only happens two ways: 1. from excessive bearing clearance or 2. from overloading, such as detonation.

Do not see any heat damage. If it were a dirt problem, you'd see all kinds of bearing surface damage, scratches, displaced bearing material, etc.

Thanks for the opinions.

I took my stuff the machine shop saturday.
The guy there builds motors for all kinds of racing. Says that the bearings wearing were from excessive clearance. Now I checked all rods and mains and all were 2.5 to 3 thou.
Mains were 3, rods were 2.5. I ran 20w40 oil.
This guy wants to cut them all at .003 and run 20w50 Penzoil. I think the same thing is going to happen. This is a street/strip car, mostly street. The motor has 10K on it. How many miles does a drag car see with .003 bearing clearances and heavy oil?
Any opinions are welcome.

Dave

I had a motor exhibit very similar wear patterns on the rod bearings, and also the main bearings. Turned out after chasing it through several sets of bearings that the remote oil filter I was using was causing a restriction. Even with -10AN lines and fittings, the 90's did it. Happened to catch a glimpse one day of my oil pressure gauge dropping 10 psi when the motor revved over 4000rpm. It did it consistently. Removed the remote from the system and it cured the problem. Those bearings definately look oil starved. Do you run an oil cooler or remote filter?

No oil cooler or remote filter.
Although I was considering putting a remote on it, you have convinced me otherwise.

I freely admit, I ran the motor at the track when it was low on oil, once. I didn't notice anything at the track, but driving home, I noticed the needle on the gauge bouncing every once in a while. It never went below 25 psi, but that does not mean there werent starved bearings somewhere.
That was early spring, and my oil pressure was still good. I didn't think any harm had come of it. Maybe that is not true. So far, the combination of larger than stock clearances and low oil might have done the dirty work.

Get a GM serviced manual and stick to their specifications for the bottom end. The GM oiling system is more than adequate for a street/strip engine. Don't go crazy with the compression and timing and the engine will last a long, long time. Make sure you wire brush and flush all the oil galleries while you have the engine apart. Hot tanking alone won't get the job done. With 4:10 gears in a Chevelle, I put on well in excess of 160k miles on my stock L72 427 with no bottom end problems what so ever. Upon disassembly the crank and bearings were both in good shape. Worked for me.

[This message has been edited by Keith Tedford (edited 01-14-2003).]

Keith,
This is were opinions differ between engine builders for racing and crate motors.
It seems the high performance people like .003 clearance on bearings along with heavier oil and an HV pump. I think they came up with this theory from bearing clearances on some of GMs high performance motors. Some had clearances at .0029. I think they figure that if GM opened up the bearings in high output engines, then they should too. And, whats a tenth?
I argued this point with the shopo that is grinding my crank and balancing right now. He insists that .003 with Penzoil 20w50 and a Melling HV pump will outlive stock clearances and bearings. He has also recomended Federal Mogule 3/4 groove mains.
How do you argue with someone that does it for a living? I am nervous about it to be honest.

Dave