Main bearing wear?
 

I’m starting the tear down on the 455 I bought last year, the motor was rebuilt at some point and then stored for a few years before I got it. My goal is to freshen up the short block with new rings and bearings then replace the cam, chain, etc. and run it with a fresh set of heads as a temporary fix while I (eventually) send out the numbers matching motor.

I pulled the first three main caps to inspect and get a better idea of what’s going on internally. The bearings are Clevite .010’s and have some wear that looks a little odd to me. Either way they’ll be replaced and so far the crank looks perfect so I’m just trying to better understand what I’m looking at.

I guess you do not want to answer my polishing question I put up in your first post on your bearing issue.

Non the less here is some possible help for you and I would suggest you go to the Cleveit 77 site and read up on bearing failure conditions and in particular page 20 which deals with the proper polishing of a crank.

Different post Steve, I saw that post by another member. This motor had no known issues, I’m just trying to get a better idea of what’s going on internally.

Nothing serious that I can see that says something failed. The bearings are not pulled down to the Babbit anyplace, the overlay appears to have gotten smeared some on one bearing. Hard to say what may have caused that though.

my guess is that's from needing a line hone. It was fine from the factory but it would be better with a hone. that being said if you didnt know it was there it wouldnt make a dfference. Do you know what the clearances are?

I’ve got some plastigauge and I’ll be checking clearances shortly. The goal like I said is to clean it up with new bearings and rings, after seeing the bearings I’ll make sure that I run brushes through all of the oil passages as well just to be safe.

I second the line honing recommendation. Uneven wear from misaligned mains. If the only uneven wear was Pic#2, (high spot), I would have said a spec of debris was on the saddle when the bearing was installed.

That’s disappointing, I was hoping to avoid the machine shop since this is a temporary engine and I’m trying to save some money for the numbers matching engine build.

Diluted oil with gasoline then left sitting can cause bearings to wear-smear on restart.

checking with plastigauge is step 2, first you should lay the crank in only the number 1 and 5 bearing and get a magnetic dial indicator to check for run out on the center of number 3 .

Even though the crank is iron they do bend.

I see nothing of worry there at all. I’d run it as it sits . Main caps also walk around a little at times. You can see this where the bearing caps meet the block. It may be minuscule but they move. I’d bet that more about debris in the oil than anything else.

Use longer main dowls. makes a big differance.

GT

Be sure to run a clean out brush thru the oil passages in the crank also as a lot inexperienced home builders miss this important final step.

I checked clearances on the three main caps I pulled and with plastigauge come up with clearances a little under .0015 which according to the service manual is well within spec and a little towards the tight side which I think will be better for oil pressure.

I’m going to bring those three bearings to my local machine shop and see what he thinks since he’ll be doing any machine work if necessary. Like I said I’m hoping to just run it as is without machine work but also wrestling with the fact that it has factory rods and for about $450 I can get a set of China forged rods.

If he feels the cranks needs work then I’m going to ask him if it makes sense to do a hone with a set of fresh rings keeping the forged flat tops since they look pretty clean (which matches what I was told about the engine having low miles since the rebuild). Swapping the rods and doing a polish to the crank. I’m trying to save a few bucks since this will only be in the car for a season or two while I build the original motor but also give me something decent to sell when I’m ready for the real build.

Besides 450 for new rods tack on a 250 + balance job that will need to get done also.

I’d shoot for .0025 or so on the mains

Not arguing but trying to understand because the 72 service manual lists specs as .0005”-.0021” or .003-.0019 for the small valve #1 location?

Absolutely and I’ll be speaking to him about that because I realize that I don’t need new rods but all the suggestions of replace the weak Pontiac rods or at least upgrade them to ARP bolts at about the same or more cost has me worried and while I don’t want project creep it seems like now is the time to do it if I’m going to do it.

If I had one thing I was allowed to change in a Pontiac engine and that was the only upgrade I was allowed it would be the Rods. The biggest flaw in a Pontiac engine has always been the connecting rods.

Whatever you spend on rods will make the engine that much more valuable. I wouldn’t even buy an assembled engine without good rods unless I planned to disassemble it and replace them

If all the bearings are around .0015 someone could have done a little hand polishing and took the high spots down. Was the motor rebuilt at a shop? My opinion is to run it with those bearings if just a temp refresh.