Loud popping noise after warm up

[JOHN COOKSON]

Me 2

And I gotta say, those sooty plugs are really bugging me.

But then again the grungy plugs may be from over use of the choke (post #14) and\or not really warming up the engine.
The only way to tell is to put a new set of plugs in and lay off the choke.

TRUE GRIT

[ndutton]

Could also be from an intermittent rich condition via carburetion problems (float/valve/fuel bowl level) affecting the power/RPM but I don't see how that would explain the noise. There's an awful lot we still don't know.

IF you try the original bench configuration suggestion and IF bringing in a particular component returns the symptom don't call it good just yet. Keep adding components and testing after each one until the installation is complete. We've heard more than once of multiple issues.

Why was this engine a candidate for rebuilding in the first place??

edit:
Just listened to it again. I'm still thinking valves and more than one.

[Marian Claire]

Have you had a chance to test with the boats wiring harness bypassed? I may have missed the results.
As a general question to the forum: Would the simple test in post #12, voltage at coil + during poor running/popping, pick up a failing connection/short etc in the wiring upstream of the coil?
Dan S/V Marian Claire

[JOHN COOKSON]

Loose Engine Mounts?

The engine mount situation did change bench ->boat.

Listen to the video again in post #1. At idle the noise is present. At high RPMs the noise is absent. As the throttle is backed off the noise starts happening with decreasing frequency.

So here we go. At idle the engine is hitting or bouncing on something. At high RPMs the engine torque lifts it up off the loose mount(s) and holds it there. The result is no bounce and no noise. As the throttle is reduced the engine settles back to it's idle position with the characteristic decreasing frequency of the noise that is present at idle.

TRUE GRIT

[ndutton]

John,

Perhaps I'm mistaken but I understood the variation in RPM was a direct result of the problem rather than throttle manipulation. The ticking starts and the RPM drops on its own. Dan??

[Dan.Sev]

Heres another video, this is after i fixed the valve spacing issue. I also ran it up a bit past idle so you could hear it. When i move the camera to the side of the engine you can hear the tapping a lot louder, so im 90% sure its coming from the that side My next step is removing the valve cover and running it to be sure. Then if it is, then ill be picking up all new lifters and springs.
[YOUTUBE]gwsXQtHPjxY[/YOUTUBE]

[67c&ccorv]

What exactly did you rebuild during the rebuild process?

After listening to the videos it sounds to me like the noise is getting worse - if it isn't your valve assembly then my thinking is it is a connecting rod going to failure.

[Mo]

hmmm...

What exactly did you rebuild during the rebuild process?

After listening to the videos it sounds to me like the noise is getting worse - if it isn't your valve assembly then my thinking is it is a connecting rod going to failure.

I agree. I'm almost sure I hear sticking or starved lifters. What's the oil pressure. Now, I'm sure I hear a knock there as well. You need a stethoscope...a long hose that you can hold to one ear and move from place to place on that engine to find the noise. I've used fuel line hose and a real stethoscope with the amp off it in the past...both work. Should have no problem locating the noisiest spot(s).

It is possible that the noise is valve assembly but I think this has progressed into a knock. I'm wondering if when it was bogging down in the first video if that was caused as she spun a bearing or something....I hate to be the bearer of bad news but I think she needs surgery...out she comes.

[edwardc]

After listening to the second video, I'm afraid I agree with Mo. I think I hear rod knock, which means you really don't want to run it any more and risk turning a major inconvenience into a disaster. Really seems like the only recourse is to pull her and open her up. (

[ndutton]

A spun bearing might be indicated by a compression test. My project engine ran but knocked like Hell, a bone jarring, teeth rattling deep knock. I did a compression test and found three cylinders @~100+ PSI and one @ 85. Pulled the head and slowly turned the crank by hand. #2 piston didn't reach the top of the cylinder like the rest and started moving down later than #3. Flipped her over, removed the pan and #2 had no bearings. The shrapnel was glommed on to the oil pickup screen.

The first measured indication was the lower compression in #2 due to slightly less piston travel.

edit:
Watching Dan's video in post #66 I wanted to point out the personal restraint I've displayed in this thread. Seems the meds are effective.

[Dromo]

If you look at the both videos on post #33 you 'll notice on # 2 cylinder,
the intake lifter still has some movement just when Dan stops cranking it over.
Almost like the spring is pulling the valve up .
I didn't think anything of it at first , then I thought ,
What is the chances of the cam stopping at the same place twice ?
Maybe a weak spring or something and the drop in RPM is probably unrelated.
Cheers Rick
P.S. in the first video pay attention to the third spring back from the left , in the second video ,the forth spring back # 2 intake

[Mo]

There may still be a valve issue there as well but that sounds like a connecting rod at the very least. Bottom line is that it has to be taken apart and find out what is going on.
A few reasons that I can think of where something like this might happen so soon following a re-assembly.
- Bearing being put back on different journals than they came off.
- Torque specs not followed (usually people are meticulous about those).
- Another reason could be putting new bearing in a crank or cam shaft that is worn and hadn't been machined.

Sorry to see this happen...I wouldn't run it again and just start the process of getting it out and taking it apart. It's a setback, but don't let it get to you...all the best.

[Dan.Sev]

What exactly did you rebuild during the rebuild process?

After listening to the videos it sounds to me like the noise is getting worse - if it isn't your valve assembly then my thinking is it is a connecting rod going to failure.

she got all new bearings, resleeved cylinders, new pistons, new crank shaft, and a new head. So I dont think its a rod or bearing problem. Heres the original rebuild post. I didn't replace any of the valve train components, just had them cleaned up. I am kinda worried about the cam shaft because the lifters were mixed up so now they will create a different wear on the lobes of what i think is probably the original cam shaft. I ran into a lot of cooling problems too when i originally bought the boat. Another thing i was thinking was that overheating of the motor could of warped the lifters causing them to stick when she warms up. Who knows, probably just gonna replace it all. You are right, she is probably gonna have to come back out. This sucks... lol.

[Mo]

Dan,
I know you have done the work but you have to recheck everything. Something is definitely not right there and it is not only top end...take the time and haul it apart. If there's a rod problem you will notice something on the bearings...it sounds like a rod / wrist pin letting go.

[Dan.Sev]

Dan,
I know you have done the work but you have to recheck everything. Something is definitely not right there and it is not only top end...take the time and haul it apart. If there's a rod problem you will notice something on the bearings...it sounds like a rod / wrist pin letting go.

Got it. Ill check it out.