1997 4.3GL Temporary Knock

[Jprevat]

Hey guys, I have less than 20 hours on a rebuilt 1998 4.3 GL. It has an intermittent knock that has me stumped.

If I keep it below 3k then it runs really well and no sounds out of the ordinary. After running 4k or higher for more than a few minutes then it develops a knock. After bringing it back down to idle for 5 minutes then the knock goes away.

This is a video I took that will explain this a lot better than I can.

 

[alldodge]

Doesn't sound good, but I don't hear a knock

 

[Scott Danforth]

Detonation?

 

[Jprevat]

Thank you for the input. I honestly think I may be looking at a lifter issue. I put in a new sealed power set on assembly but I encountered this sound almost immediately. So I swapped back in a few of my original set and the noise became less pronounced. I feel like they may be bleeding down causing some noise.

I suppose I should pick up a mechanical oil pressure gauge to make sure I'm not losing pressure when the knock comes up.

 

[Jprevat]

Scott, if I am set on the correct base timing how could detonation be a problem? I have some octane booster in my truck. Should I get some 91 octane and throw in the booster and see if it subsides?

 

[alldodge]

IMO detonation comes in at higher rpm and would stop immediately when rpm was lowered. Still not making out much of a knock, but maybe U joints

 

[Jprevat]

I had the outdrive off last year and they were nice and tight. I greased them up and bolted it back up. I'm debating if it would be worth it to pull the drive again, undo the water pump belt and see if the noise persists. I was thinking flywheel but that is a very distinct sound. I got another video yesterday I'll upload in a minute to see if you can hear it any better.

 

[Jprevat]

Ok here is the other one.

 

[alldodge]

I'm hearing a real low tone type knock. Does the knock stay this low at higher rpm's

 

[Scott Danforth]

when you rebuilt it, what specifically did you do?

the knock in the new video sounds like the balancer shaft is out of time or the u-joints are bad

 

[Scott Danforth]

when you rebuilt it, did you replace the balancer shaft bearings and gears?

 

[Jprevat]

The knock does not get loud. When I give it enough throttle to plane off I honestly can't hear it over the engine.

I picked up a complete short block from a reputable engine builder. It did not have the cam or balance shaft installed. With the help of an experienced mechanic helping I installed everything except the balance shaft. He installed it because I wasn't sure how.

It does have a small amount (32nd of an inch or less)of play in it but I assumed that was normal.

All bearings in the lower end were replaced along with the rings. I had my heads cleaned and check and valves replaced.

Thank y'all for helping me out with this btw.

 

[Jprevat]

The more I read up on the balance shaft the more I am thinking I may pull the drive gear for it and see if that's causing the noise. Makes me think I should have done some research and pulled it from the get go.

 

[Scott Danforth]

The motor needs the balance shaft or you need to change flywheel, damper and mounts. Would be easier to get rid of the slop in the balance shaft

 

[Jprevat]

Thank you for that bit of common sense.

I'm just getting frustrated I suppose. I guess I need to run it and produce the knock then pull the outdrive before it cools down, crank it, and see if the knock persists. If it doesn't then I know I am looking at u-joints.

If it is still there then I will look at the balance shaft bearings.

The outdrive didn't make any sound on the previous engine so I doubt that is the issue but it would be the easier of the two.

 

[Lou C]

I would pick up a mechanics stethescope and see if you can better localize it. See if the scope picks up the sound when you put the probe on the front timing cover ..

 

[Scott Danforth]

Pull the drive, then run it

 

[jimmbo]

loose bolts on the flywheel/coupler? When the engine was replaced, was the driveshaft alignment checked?

 

[Scott Danforth]

did a google search for 4.3 knocking

plenty of forum hits for this with the S-10 forums. many have to do with the balance shaft pin and gear holes wallowed out, allowing the balance shaft to move.

the OP stated there was 1/32nd of slop when he put the motor together

the drive gear pin and gear are supposed to fit like the cam gear does.

should only have backlash of gears which is only read with a dial indicator.

 

[Jprevat]

Can the front bearing be purchased seperateley from the balance shaft?