Surfer69

I have a thread about knocking kind of sound coming from engine and loss of power. Now I'm wondering if it could be spun bearing. Any experts on what it would sound like. Opened intake and everything there is about right except one push rod was bent by about 1/16 to 1/8 of inch.

hudman

Mine sounded like a subtle knock. Kinda like a wooden hammer handle tapping a something metal and hollow like a pot. I could not hear it at idle but could hear it when I revved the motor slightly.

theandies

Mine sounded as described above but it was worse when I was driving and the RPM's were around 3200. I spun #6 rod bearing.

fauxrs

I have never heard a spun bearing before, but eh description above sounds like rod knock, which does not necessarily include a spun bearing. In any case if you are concerned about rod knock, and cant fully diagnose it yourself then take it soemwhere where it can be diagnosed, and dont drive it there.

Rod failure is not a good way to diagnose rod knock. If you catch it early you lose only the down time resizing a rod and installing new bearings - if you get failure, then its a whole new motor you are looking at most likely.

Fevre

When you spin a bearing it blocks the oil passage hole which causing the journal and bearing to grind at each other due to lack of oil. Once there is suffiently play in between bearing and journal you get rod knock. I had both halves of the bearing end up on top of each other really giving me rod knock. I had a Olds spin a main bearing and it squeeled like :crazy: .

slaine

My buddy recently spun a rod bearing in a 79 400 T/A. The knock was present at all rpm's. It did sound kind of wooden. It was hard to isolate the noise. But I swear it sounded like a piston was just barely hitting the head on one side. The noise traveled up the piston and out the head on one side. The piston was not hitting the head. The noise sounded like it came out the intake manifold or head, rather than a deep knock from the bottom of the engine.
Mike

Surfer69

That's what it sounds like exactly as you all are saying and what I read in archives. I'm removing heads and guess I'll pull block and take to machine shop or do rebuild myself. Might put in 262Xe cam while I'm at it.

fauxrs

Yes that would most certainly be the effect and a spun bearing will result in rod knock. I guess the point I failed to make is a spun bearing is not mandatory to experience rod knock, and rod knock is what it sounds like he has.

Its moot either way since the end result is the same.

Racer Z

Yeah I do! Had that happen a few times with my old Trans Am with a 455, sucked bad each time. You are going to have to tear down the whole engine. It sounds like a knock deep in the engine (usually louder in the wheel wells), the faster the engine spins the faster the knock. To find which cylinder, you can pull the plug wire off when it’s running, if the knock goes away, that’s the bad bearing. Just be careful not to zap the crap out of your self like I did, believe me that didn’t tickle!

ddecart

Yup. it sounds a lot like a rod knock, and not unlike a lifter noise. The main difference is that after looking around and listening all over the engine you come to the conclusion that the noise is coming from 'deep within' the engine.

My in-laws car spun a bearing when I was going to pick them up from the airport. It was pretty new and well under warranty. I couldn't place the noise as being a lifter or anything else, so I picked them up, said "You car is making noise. I don't think it's good." On the way home I was on thefreeway, went to hit thegas to pass someone and there was NO power there. Darted off at the next exit, took a side street toward home and the engine seized on me. Whoops. Pulled into a parking lot with no power steering, no power brakes, flailing my arms at some lady at a stop sign to get her to move the hell out of the way and coasted to a stop soon after.

Nope, spun bearings are not fun.

Corz

no kidding.. its cost me 3 engines. no not just the 69 either :skep:

KJL

Regarding your bent push rod, I know if you use the incorrect length intake bolts they can hit the push rods bending them and creating lots of noise. Look at the bent rod for wear marks were a bolt might have been hitting.

Surfer69

Got the heads off and no damage to pistons from top. Interesting thing is there is .030 pistons, so someone has done a rebuild on this original engine so it makes me wonder if they did a crappy job on bearing installation.

One other thing was I saw my HB wobbling a lot in the past few weeks and now wondering if that could have been a sign of something?

I looked at bent push rod and it has probably just been there for a while, not sure.

Since .030 pistons are in, I'm expecting I'll only need minor rebuild, hopefully just bearings and rings and heads cleaned up. I'll get performer 2106 type intake and install nice cam. I need to find out if cam is stock already. Open up timing cover tonight.

81' Corvette Guy

Damn..you didn't try the sawdust in the oil...come on that would have quieted down that knock. Oh well, since you got it apart..get it back together and let us know how it works...!!

Surfer69

Recommended engine shop says $800 for the whole deal, turned crank, heads, rings, bearings all within 3-5 days.

Of course that's if there is no surprises! :confused: