'90s Chevy truck elusive engine knock. Rod/Main bearings, or what?

Removed 4 front bearings today. Main bearing #1 is kinda rough (far right in pic), the journal has some scoring too. Might be able to work that out a little (??). Rod bearing for piston #1 has a little more wear than #2. Main bearing #2 is not too bad, and the journal for it is ok. So, do I fix it the best I can and see what happens, or pull for a rebuild. My three options are: 1: fix/repair. 2: Rebuild 3: Replace with new long block. There are no rebuilders in my area (podunk rural). Anyway, here's a pic. from Right to left: Main #1, Rod #1, Rod #2, Main #2:

Bearings.jpeg
 
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I mean if the journals are looking good, the cheapest/quickest would just be to roll-in new crank bearings and inspect the rest of the rod bearings. If the rod bearings have any grooves in them, would want to replace. If smooth, still good. As mentioned earlier, Plastigauge will tell you where your clearances are at currently which may make the decisions for you.

It all depends on your budget and what you want to do with it. A rebuild would allow you to upgrade speed parts along the way. Stock long block would be fairly reasonable and you would have a new bottom end.
 
Exhaustgases said:
And hows the oil pump etc.? Looks like one of those Toyota machining debris main bearings there. :ROFLMAO:
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Its original, seems to be ok physically, screen was clean. Will be replaced once I get going with the bearings. Assuming I can tidy up the journals.
 
DuckRyder said:
I think if i was that far I would roll a set of main and rod bearings in it. provided there was nothing egregious looking on the crank (any of it fail the ol fingernail test?)

You don't really have anything to lose. What is it a couple hundred bucks?
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The 1st main journal has the most scoring. Not super deep, just slightly into the surface. If I can get it looking better, I'll certainly do all the main & rod bearings. Plus a new oil pump. The truck is not a daily driver, just 1K-2K a year now.
DuckRyder said:
Also while not cheap it seems like you can still get a stock replacement and a couple warmed up versions from GM.
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Yes, I've checked out a few of those in case this repair doesn't go well.
 
GM part# 19432778 is the 4-bolt main, Forged Crank crate LO5. Summit Racing has them in stock. Has a 3 year, 100,000 mile warranty that's good at any Chevrolet Dealer.

Getting a good polish on the crank journal is going to be difficult.......Maintaining journal concentricity may be impossible. Debris management will be paramount.
 
How much money / time would you be willing to put into this project?
At the very least, the engine should come out so that you can put it on a stand and pull the crank. If the pins and mains measure something close to serviceable, then new bearing shells and an oil pump and you've got your 2k mi. / year truck back in service.
A bit more time / money would be to replace the cam drive and the cam bearings (the kind of damage you saw on the main / pin shells indicate the cam bearings are probably bad also). If the cam and lifters are bad, a cheap cam kit with lifters would be just fine. All of this without any machine shop work, but as others have noted, the crank may not be in spec, but for your purposes it may be just fine.
Even more involved would be to pull the heads, pop out the pistons and measure the bores. If they're not horrible, a ball hone job and new rings will get you a bit fresher engine. Again, without machine shop work, but close enough for jazz.
With the heads off, you can at least put on fresh valve seals to reduce oil consumption, even if the guides are a bit sloppy.
Put the parts list together to see what sounds reasonable. If you can rent an engine hoist (or tree limb and chain fall), and get a cheap engine stand, you're in business. You've got the skills.
 
Ignitiondoc said:
How much money / time would you be willing to put into this project?
At the very least, the engine should come out so that you can put it on a stand and pull the crank. If the pins and mains measure something close to serviceable, then new bearing shells and an oil pump and you've got your 2k mi. / year truck back in service.
A bit more time / money would be to replace the cam drive and the cam bearings (the kind of damage you saw on the main / pin shells indicate the cam bearings are probably bad also). If the cam and lifters are bad, a cheap cam kit with lifters would be just fine. All of this without any machine shop work, but as others have noted, the crank may not be in spec, but for your purposes it may be just fine.
Even more involved would be to pull the heads, pop out the pistons and measure the bores. If they're not horrible, a ball hone job and new rings will get you a bit fresher engine. Again, without machine shop work, but close enough for jazz.
With the heads off, you can at least put on fresh valve seals to reduce oil consumption, even if the guides are a bit sloppy.
Put the parts list together to see what sounds reasonable. If you can rent an engine hoist (or tree limb and chain fall), and get a cheap engine stand, you're in business. You've got the skills.
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As this stage. I'm still trying to evaluate what was causing the knock. It obviously has some bearing issues (still have a few to remove). A couple posters here said it could be wrist pin related. As soon as I can get things checked out, and get it back together, I'll make a decision on where to go with my options. Wife wants a new engine, or if need be, a new truck. I'm in my 70s, it's no picnic being under this truck!
 
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I know i'll take some heat for this, but i wouldn't mess with the crank, if i thought it truly needed messing with i'd pull the engine. it doesn't have to be perfect it just needs to not have anything that's going to catch the new bearing. Same for a piston skirt or wrist pin WRT to pulling engine.

In my view - that far in if nothing else is obvious slapping a set of bearings in it is a diagnostic aid - in other words the knock will be gone or not.

Unless you have the knowledge, tools, space and willingness to rebuild it yourself - id just stick a crate motor in it...

The bad influence side of me mentions a 350/357 and HT 383 aren't that much more in the grand scheme of new engines... though i suppose issues with the TBi might ensue.
 
Took about 3-4 hrs of work to get the scoring out of the rod journal for pistons 1&2. This is right over the truck's crossmember, and hardest one to reach with 5" of clearance to do the laborious sandpaper trick (600 grit thru 2000, polish compound and polish). Didn't care for the shoestring method, so I used an old Hanes knee sock to do the back & forth tugging, wax on, wax off! I'm going to have to get some measuring tools to see what size bearings I will need. WilI just do them all, and see what happens. I can see I'll be under here for a few weeks, lol.

rod journal.jpeg
 
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So, here's the plan. I've ordered a micrometer for measuring the journals. Will check with NAPA and order some of the bearings for initial fitment testing using a plastigauge. I wish there wasn't so much science involved with these bearing sizes. Anyway, I will proceed slowly and try not to make any mistakes. Will update when I get some of the bearings installed, hopefully next week. Thanks for all the replies, they've been very helpful.
 
Exhaustgases said:
And did you find the knock?
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Main bearing # 1 was in rough shape, looks like a vinyl record. Rod bearings 1&2 had some excessive wear too. I assume these issues were causing the knock. Haven't remove all of the bearings yet, those in the middle area seem to be ok (will still replace). I've not found anything else that would be contributing to a knock. I'm still poking around in there, so might find something else?
 
Almost done with the new bearings. Maybe I can get it fired up by next weekend and see if the dreaded knock is gone.

I have a question. I used Lucas assembly lube all the bearings/journals. Will I need to use an oil pump primer attachment tool to pump some oil through the engine, or is that overkill with doing basic bearings/oil pump replacement?
 
Just Dropped In said:
Almost done with the new bearings. Maybe I can get it fired up by next weekend and see if the dreaded knock is gone.

I have a question. I used Lucas assembly lube all the bearings/journals. Will I need to use an oil pump primer attachment tool to pump some oil through the engine, or is that overkill with doing basic bearings/oil pump replacement?
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I didn't catch it, did you install a new pump or no?

If yes, I would prime it before first start. You need a specific style primer rod that seals the oil galleries in order to verify flow to the rockers.

Assembly lube keeps the bearings/journals happy until oil hits it, with a dry/empty pump, that time is delayed.

I'm not a professional engine builder by any means but Id rather be safe than sorry.
 
I agree, i would prime it if its possible,

Been 30 years or so since I've been in a small block chevy but tif it possible to drop the oil pump drive, try not to... ;)
 
Slight setback. Was going to replace the oil sending unit and that danged "brass" elbow fitting/adapter broke off in the block. Fortunately, I was able to get the broken threaded portion out of the block fairly easy. No one locally sells a replacement, so I had to mail-order an aftermarket unit. On a happy note, priming the oil pump worked, as I had around a half-qt or so squirt out onto the back of the engine/trans and floor, lol.

While I'm waiting for the part, I adjusted the rockers as they were quite loose. As it stands right now, I'm not 100% convinced I've resolved the knock issue, as It could still be wrist pin related as some have mentioned. If that turns out to be the case, it's back to the drawing board. Hopefully, I can fire it up by end of the week and find out.
 
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