How Bad Does This Sound? (Tapping Noise)

[TheDude7B7]

Hey All-

Trying to diagnose a tapping noise. A little background first... Last year this noise started to develop about 2 hours after a complete overhaul. Engine seemed to run fine regardless of the tapping. Great power and able to push the boat at hull speed. Figured it was a valve issue. This was in October. I had to go away on a trip and decided to start troubleshooting the sound in November, and as it turns out, there is coolant in the engine. Turns out the torque wrench I was using was old and out of calibration, so the head bolts never got tightened properly, leading to a blown head gasket. Wasn't too upset because I figured I was going to have to tear down the top half of the engine to troubleshoot the tapping noise. Since the valves were stuck so bad from coolant water, I decided to install new valves and guides (one of the only things that was not replaced in the overhaul). Pretty easy, but took a back seat to family, job, and some deck repair.

Fast forward to this month. Got the engine back together. Started almost instantly. Runs amazing, idles smoothly at 700ish RPM and doesn't miss a beat in and out of gear. Only problem is, the tapping noise is still there. Given that I just did the valves and the problem persists, I'm not sure if that is the issue. Based on other posts, I experimented with removing a plug wire from each cylinder while running, and while the tapping would recede a bit, it was still there, and no change based on which plug I pulled. Also listened to the engine with a stethoscope and couldn't really locate the tapping.

I ran a compression test and got the following results:

Dry
#1: 100, #2: 97, #3: 100, #4: 100
Wet
#1: 101, #2: 100, #3: 102, #4: 105

The biggest difference was on #4. That plug had the tiniest bit of oil.

Here is a video of the engine running. First half is running it up from idle to round 2000 RPM in increments. At about 0:55 I put it in gear and run it up to 2000 and down again.

https://youtu.be/xBZt0NO6VGs

And here is another video of moving the phone around the engine while it is running at around 1200 RPM in gear.

https://youtube.com/shorts/jAbBsiUpMAA

As far as temperature, the fresh-water cooling keeps it at 180ish degrees. After the engine is fully warmed up and the oil is hot, the temp gets a little hotter and I start to notice a little smoke in the exhaust. Somewhere between white and blue smoke, but def not black. I have dye in the coolant and there does not seem to be any coolant leaks. So I'm thinking it might be a little oil burning off when it is hot.

Hopefully that is a good amount of info. Really appreciate any thoughts you guys may have. I really don't want to have to pull this damn engine out again. It's taken so much time from other projects.

[Dave Neptune]

That is a very nice looking engine, kudos for the set up.

I do hear a lot of valve noise so you may check the clearances again. It is quite common for them to need a readjusting after a rebuild once it has been run for a while.

I do hear another noise that sounds more piston related however pulling the plug wires one at a time should isolate it demonstrably. So I suggest removing the alternator belt as it could just be accessory drive noise to check. Another thing would be to retard the timing just a smidge and see if that noise abates, however the valve noise will still be there.

The numbers look great. RE the smoke does it dissipate as it moves away from the boat? Blue or rather oil smoke won't but condensation from moisture will. Not to worry. You may notice a bit less "smoke" from backing the timing off a bit. Are you using anything in the fuel?

The A-4 is rather forgiving as far as timing goes and it is easy to put in to much advance. If the noise eases a bit after retarding it a bit leave it there.

Taking the time to establish a timing mark at TDC can really ease tuning by using a timing light for adjustments. If it is just power timed and you did not back it off a smidge after doing so go for retarding it a bit now. The engine will run smother and yield better economy and longevity with 34~36* of total advance. There are a few links on this site that are excellent for doing so.

Dave Neptune

[TheDude7B7]

That is a very nice looking engine, kudos for the set up.

I do hear a lot of valve noise so you may check the clearances again. It is quite common for them to need a readjusting after a rebuild once it has been run for a while.

I do hear another noise that sounds more piston related however pulling the plug wires one at a time should isolate it demonstrably. So I suggest removing the alternator belt as it could just be accessory drive noise to check. Another thing would be to retard the timing just a smidge and see if that noise abates, however the valve noise will still be there.

The numbers look great. RE the smoke does it dissipate as it moves away from the boat? Blue or rather oil smoke won't but condensation from moisture will. Not to worry. You may notice a bit less "smoke" from backing the timing off a bit. Are you using anything in the fuel?

The A-4 is rather forgiving as far as timing goes and it is easy to put in to much advance. If the noise eases a bit after retarding it a bit leave it there.

Taking the time to establish a timing mark at TDC can really ease tuning by using a timing light for adjustments. If it is just power timed and you did not back it off a smidge after doing so go for retarding it a bit now. The engine will run smother and yield better economy and longevity with 34~36* of total advance. There are a few links on this site that are excellent for doing so.

Dave Neptune

Thanks for the kudos Dave. Had to cram alot in a small space Yankee 30.

I'll play with the timing when I go out on Monday. Will def check the valve clearances in the next few weeks. Already removed the alternator belt and that wasn't the source.

As far as fuel, I have a bit of Marvel added to it. So that might be contributing to it the smoke.
*
What is the piston noise that you are hearing? I could take a video of removing each plug wire.

As always thanks for the advice

[Dave Neptune]

The noise is sort of a thump but nothing definitive. When you had the belt off did you try loading the accy drive pulley with a block of wood? Sometimes the loading will change the noise.

The noise I hear could even be created by to much timing. Also to much timing can increase oil consumption as the shock of it allows oil to get past the rings especially old ones and new ones not fully seated.

At what ratio are you adding the MMO to the fuel? Anything richer that 100:1 can smoke a tiny bit.

Dave Neptune

[TheDude7B7]

The noise is sort of a thump but nothing definitive. When you had the belt off did you try loading the accy drive pulley with a block of wood? Sometimes the loading will change the noise.

The noise I hear could even be created by to much timing. Also to much timing can increase oil consumption as the shock of it allows oil to get past the rings especially old ones and new ones not fully seated.

At what ratio are you adding the MMO to the fuel? Anything richer that 100:1 can smoke a tiny bit.

Dave Neptune

Gotcha, so a piston noise would be lower pitch noise, not the higher pitch noise of the tapping? Also, I forgot to mention that I used a BPM meter to measure the frequency of the tapping noise and it is half of the RPM of the engine. Not sure if that is helpful.

I didn't load the pulley when I had the belt off. Will try that before I mess with timing so see if that makes a difference. I just use the block of wood to provide some friction?

In regards to the MMO, I'm thinking there might be more than 100:1. I misjudged the angle of putting it in the tank and dumped more than I would have like in. So maybe that is part of the smoke issue.

All good stuff. Thanks

[Dave Neptune]

Half speed noise would be valve train, engine speed would be rotating assembly like pistons, rods and crank shaft.

Yes just put a load on the pulley by bracing the wood (2x4 works fine) against something. No drastic pressure required.

Dave Neptune

[Al Schober]

Hey Dude,
Please tell more about the BPM device. Sounds like a handy tool (that I don't have...).
Oh yeah, when you're in the hole checking valve clearances, also give the springs an eyeball. Any look different, perhaps broken?

[TheDude7B7]

Half speed noise would be valve train, engine speed would be rotating assembly like pistons, rods and crank shaft.

Yes just put a load on the pulley by bracing the wood (2x4 works fine) against something. No drastic pressure required.

Dave Neptune

Just got back out to the boat. Power timed the engine as mentioned above, engine runs great but no change in tapping noise. Also pulled the belt off and put some load on it with a block of wood. No noticeable difference.

I think I'll just plan on checking the valve clearance when I pull the exhaust off in a few weeks to make some dimensional tweaks.

This has been quite a journey. Thanks so much for all your input. More to come....

[TheDude7B7]

Hey Dude,
Please tell more about the BPM device. Sounds like a handy tool (that I don't have...).
Oh yeah, when you're in the hole checking valve clearances, also give the springs an eyeball. Any look different, perhaps broken?

I use liveBPM on Android, but really any DJ-focused app that can use Hit-Hats to detect BPM will work. Metronome apps will also work. You can speed up the frequency until it matches the noise you are hearing. It's a little trickier because you have to get used to listening to two things at the same time, but having one side of a pair of headphones in helps alot.

[joe_db]

Take the alternator belt off. I have more than once found odd noises to be alternator bearings going bad.