Mercruiser 4.3 knocking noise

[Jrhinehimer]

Definately sounds like a rotational eng noise. Its a short video, but my 2 cents is it sounds like a rod cap is loose, or a valve is way out of adjustment. You say its idling smooth so that rules out a valve adjustment.

My fear is a rod cap or something similar. Guess Ill pull it back out and see what I find.

 

[Scott06]

My fear is a rod cap or something similar. Guess Ill pull it back out and see what I find.

Correct I think you may have to send it back to the rebuilder. I assume the noise is different than the knock on the original engine ?

 

[Jrhinehimer]

Correct I think you may have to send it back to the rebuilder. I assume the noise is different than the knock on the original engine ?

It actually sounds very similar, which is why I was trying to rule out everything I moved from one engine to the other just to make sure it wasn't something I carried over.

 

[Scott06]

It actually sounds very similar, which is why I was trying to rule out everything I moved from one engine to the other just to make sure it wasn't something I carried over.

Only thought is coupler, flywheel or starter. Is starter not fully disengaging and hitting flywheel? might be worth pulling it and taking cover off bottom of flyhweel cover to see. Balancer hub up front? Did you swap balancer and flywheel from the old to new engine? May be a mismatch between non balance shaft and balance shaft engines?

 

[Jrhinehimer]

Only thought is coupler, flywheel or starter. Is starter not fully disengaging and hitting flywheel? might be worth pulling it and taking cover off bottom of flyhweel cover to see. Balancer hub up front? Did you swap balancer and flywheel from the old to new engine? May be a mismatch between non balance shaft and balance shaft engines?

I thought about the starter as well, that will probably be my next step. I reused the Starter, Flywheel, Flywheel cover, and coupler. The balancer up front was already installed on the long block when I picked it up. I would think if the flywheel and balancer were out of balance with each other the engine would vibrate/shake but I am not getting that at all. It actually moves less then my 2020 Silverado engine... lol

 

[Lou C]

It does sound like metal to metal contact, with a flapper it will make a lower pitched sound due to the rubber coating.
It would be interesting to see if it makes the same noise with the engine out of the boat.

 

[nola mike]

My fear is a rod cap or something similar. Guess Ill pull it back out and see what I find.

Maybe try disconnecting plug wires one at a time. If the noise changes in one cylinder only, that might be your culprit. Also should be able to pinpoint starter noise pretty easily with a stethoscope. I'd expect rocker or valve train noise to be more prominent on one side as well...
Did you run the engine on a stand before install?

 

[Scott06]

I thought about the starter as well, that will probably be my next step. I reused the Starter, Flywheel, Flywheel cover, and coupler. The balancer up front was already installed on the long block when I picked it up. I would think if the flywheel and balancer were out of balance with each other the engine would vibrate/shake but I am not getting that at all. It actually moves less then my 2020 Silverado engine... lol

Yeah since you are pulling it anyways would check the starter. or pull the starter and see if it looks nicked up... but it is almost easier to pull the engine to get the starter out...

4.3L Flywheel (1987 & Later Engines, 14

4.3L Flywheel (1987 & Later Engines, 14" diameter)

www.michiganmotorz.com

this lists the flywheel as the same for all '87 and up 4.3's which would cover both balance and non balance shaft engines.

 

[Lou C]

I've been wondering about this myself, because at one point I was thinking of getting a new 4.3 Vortec when you could still buy them new (don't think you can any longer). I would have thought there were differences in the flywheel and harmonic balancer going from no balance shaft to balance shaft, but that doesn't seem to be the case. There is also the issue of many changes in the 4.3s over the years, even the differences in the same years depending on if it was built in Tonawanda NY or Romulus Mi, that is signified by T or an R in the GM serial # on the block.
With all the possible variations and problems from mixing and matching parts I just decided to go with a 5.7 V8 when I repower. I do like the good fuel economy of the 4.3 especially with Quadrajet with the small primaries.

 

[Jrhinehimer]

Maybe try disconnecting plug wires one at a time. If the noise changes in one cylinder only, that might be your culprit. Also should be able to pinpoint starter noise pretty easily with a stethoscope. I'd expect rocker or valve train noise to be more prominent on one side as well...
Did you run the engine on a stand before install?

I didn’t run it on the stand, looks like I should have

 

[Jrhinehimer]

Yeah since you are pulling it anyways would check the starter. or pull the starter and see if it looks nicked up... but it is almost easier to pull the engine to get the starter out...

4.3L Flywheel (1987 & Later Engines, 14

4.3L Flywheel (1987 & Later Engines, 14" diameter)

www.michiganmotorz.com

this lists the flywheel as the same for all '87 and up 4.3's which would cover both balance and non balance shaft engines.

I’ll pull it back out this weekend when I get the chance, it’s not to bad to do. Question, do you know if the starter is the same on the balanced vs non balanced?

 

[QBhoy]

I’ve heard a balance shaft being noisy on a 4.3 bortec mpi recently. It didn’t sound quite like this and was particularly evident just when you stop it, more than anything else. Not sure what this is.

 

[nola mike]

I would have thought there were differences in the flywheel and harmonic balancer going from no balance shaft to balance shaft, but that doesn't seem to be the case.

IIRC, both engines are internally balanced, allowing swapping of balancers and flywheels.

 

[Scott06]

I’ll pull it back out this weekend when I get the chance, it’s not to bad to do. Question, do you know if the starter is the same on the balanced vs non balanced?

yes chevy has only two starter configurations based off flywheel size straight and staggered bolt pattern. Don't recall which takes which but depends on if you have the small 12.75 ish "or newer 14" flywheel.

 

[Scott06]

I didn’t run it on the stand, looks like I should have

Easy to do don't really need a stand it can be sitting on blocks.

 

[Lou C]

4.3 takes the staggered pattern

 

[Jrhinehimer]

4.3 takes the staggered pattern
View attachment 360305

The one in the boat is the smaller one and I am using the same flywheel so as long as the block is the same I should have no issues unless the starter is not disengaging all the way? Thank you all for your help on this, I really appreciate everything!

 

[Lou C]

You might try removing the starter and testing it to watch the starter gear.
Yep the big one is the old Delco direct drive starter, not so much fun to change because they are so heavy. The new PMGR starters weigh like half as much. Just be careful with the bolts.

 

[boosted4life]

Any new on what the noise was?