Losing a rod bearing in 350. Advise?

[fostrem]

So I've got quite a knocking when I accelerate in my 350 SBC. When in park and I rev it there is NO knock. When I get to a cruising speed there is a slight knock. When accelerating there is one hell of a knock. So I'm guessing it is a rod bearing.

For the time being would it be safe to run thicker oil with some stabilizer until I decide what to do?

I have never touched a bottom end, could I replace it with ease and without taking out the engine?

Part of me wants a shop to do it the right way but how much would they charge? If it is expensive I'm almost tempted to buy a crate engine and sell the working heads/ short block.

I need suggestions, any input is helpful.

Thanks,

Finn

[INSIDIOUS '86]

Leave it be till its fixed. Thicker oil won't change a thing. It would be better serviced with the engine out but you can drop the pan and figure out which rod is bad. If your extremely lucky and the crank is still smooth with no grooving you may be able to replace that bearing and the one next to it as a precaution. Then check the mains for any shrapnel. Otherwise you pull the crank and polish the rod throw on the crank and order the appropriate size bearings for rods and mains.

Either way if you have a rod knock the engine was either over reved or misassembled or just plain worn. All of those are warrant enough for a teardown and overhaul in my book. Jays machine shop on hwy99 does great work.

The more you run it the more damage you do. There is no oil cushion between the bearing and crank. The bearing will be misshaped and will bleed all the oil pressure off and the mishaping wipes the oil off like a scraper the only thing that keeps mass damage happening is that soft lead bearing that's getting beaten to hell.

The labor and parts involved at a shop wouldn't justify saving the engine. And for the price you can build a nice sbc that's stronger than a crate engine for about the same $$$$. Like I said jays machine shop in Everett builds race motors and street and anything in between.

[fostrem]

Thanks for responding so quickly to just about all of my questions insidious. Because money is tight and I will be needing to drive the truck this weekend, do you think I could pop in new bearings within a day? Is it worth a try? I do plan on having an overhaul within the next month or two but as of now I would like to get her running fairly well.

[INSIDIOUS '86]

In a day? It's possible but unlikely and even then the chances of everything being ok enough underneath for a rod rebearing is slim. You can try hyper lube if your pressed to drive it and zinc additive but like I said this will worsen damage and can quite possibly lead to engine seizure or failure of hard parts in which case the overheat and break. All of this of coarse will mean that it will need complete overhaul.
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[BigBlocksRule]

Check your flexplate for a crack or loose torque converter bolt. Unloaded they won't make racket, loaded they will.
And if it is a rod bearing, a new bearing ain't going to fix it, the crank has been screwed up by the bad bearing and new ones won't help.

[Desert1957]

Originally Posted by bigblocksrule

check your flexplate for a crack or loose torque converter bolt. Unloaded they won't make racket, loaded they will.
And if it is a rod bearing, a new bearing ain't going to fix it, the crank has been screwed up by the bad bearing and new ones won't help.

^^^^^^^^^^^^^^^^^^^^this^^^^^^^^^^^^^^^^^^^^

[egaray281]

i had the same problem happen to me i tried running the truck with thicker oil and like they said it doesn't work since i was on a budget and just wanted the truck to run for now i found me an engine on craigslist for $300 its a 305 out of a 90 camaro, just dropped it in last night hoping to finish it up this weekend

[manimal]

Dont be too sure a "SHOP" can handle the job either...a lot of shop are parts replacers,NOT mechanics....they will change starters,radiators,hoses,even SWAP engines...but there are MANY that could not do an engine correctly. Bearings are NOT hard. Grab a book..."How to Rebuild your Small Block Chevy" and do it yourself...then YOU WILL LEARN! win win situation! Keep us posted. and Good Luck!

[geezer#99]

K.I.S.S!!
Check your timing!
It's detonation!!

[1slo_camaro]

THERE are many factors that could be causing the knock, hell i had my exhaust hitting my trans under hard load and sounded just like a rod knock (ive done everything from a small valve tap to completely snapping a crank in half and many things in between) before you go buying anything or replacing anything do some research into what other issues you could have. if it truely is a rod knock you should be able to at least hear it faintly at idle or without a load. its really hard to diagnose your truck over the internet. i would recommend a engine shop take it to them and ask them to take a look, most wont mind taking a quick look at it.

Best recommendation if money is tight.... give me a week or two and let me find the set of stock rod bearings i have laying around you can have and get a book and pull the bottom end. you will have to get your crank micced and probably polished, if you are lucky you could get away with a polish and new bearings. also while you are down there i HIGHLY recommend get a new oil pump in there just incase you have pieces of the old bearings in there that will cause pre-mature failure of the bearings. bearings arent expensive or hard to replace. just pull the motor, throw it on a stand drain as much possible oil as you can so you dont have any old oil in there, flip the motor pull the bottom end out, take the crank to a engine shop and have them check it and give you a thumbs up and polish it, take it home with a boook on how to rebuild a SB/BBC and go to town, make sure you torque the bolts properly as well.


Good luck with it, its not a hard job to do just can be a pain sometimes. and/or you get like me, i see no reason to pull a stock motor to replace a stock motor, so it turns from a weekend job to a 2-3 month job.....


OR!

find a used motor in a junkyard or craigslist for a couple hundred bucks. throw it in and hope it lasts you long enough to get your other motor either rebuilt, bored/stroked, freshened up. whatever you want to do. just take your time and think about your money, time and knowledge of the job.

[BigBlocksRule]

Originally Posted by geezer#99

K.I.S.S!!
Check your timing!
It's detonation!!

^^^^^^^ this, too!!!!

[cyclefreak207]

like manimal said, a lot of shops are just replacers... check out my build thread, there's quite a few good pictures from the two engines we rebuilt this weekend, and dropping the pan and personally I say it's easier to push the pistons UP and replace the bearings. hopefully none are scored up from the bearing spinning.

I also had a similar noise like you say, accelerating was noisy, revving in idle wasn't. torque converter bolts were loose as could be. you can take the cover off and use a long 9/16ths wrench to tighten them. Do one, then bump the motor till the next one is within reach, and then do the third one. then check again for tightness.

[JellyBeanDriver]

Originally Posted by manimal

Dont be too sure a "SHOP" can handle the job either...a lot of shop are parts replacers,NOT mechanics....they will change starters,radiators,hoses,even SWAP engines...but there are MANY that could not do an engine correctly.

Agreed. I'm always hearing horror stories from co-workers about shoddy work at 'shops'. Most cannot even diagnose a problem to the root cause.