Engine Tapping

[sunnnnseeeker]

Hello,

I ran a can of Seafoam Spray Top Engine cleaner and lube through my A4. It did increase the max RPM from 2000 to 2100 on open smooth water and the engine seems a little smoother at 1600 cruising. During my recent two week cruise, with lots of motoring, the engine started a tapping sound at 1600+ RPM. I suspect it's a valve. I have had the boat for 17 years and it's never made this tapping noise before.

I have read many of the entries on valve tapping here and the reason I am posting is because some people stated they hear the tapping at low RPM and not high. Mine is opposite, I hear it at high RPM. If I cover the flame arrestor on the carburetor it does suppress the tapping noise. I suspect the noise is still there and I am hearing it through the carburetor when not covered. Wondering if anyone else has an engine doing what mine is?

The valve clearances have not been check, probably since the engine was new in 1975, 1300 hours. Compression numbers were 95, 95, 75, 105 before the Seafoam. I am going to do the Seafoam again and then check compression. The 75 bothers me and the max RPM of 2100 is lower than I would like. Indigo prop. I am probably expecting too much with the engine cleaner but it did help and it's cheap and easy.

1975 C&C 30.
Chesapeake Bay

[Dave Neptune]

Did the "tapping" start abruptly? Valve tapping noise usually increases over time not all of a sudden unless something breaks. If the noise did start all of a sudden it could be a broken valve spring nothing un-heard of on an A-4.

Listening to the engine can also be an indication of where or what the noise is. Listen to the engine through the oil fill cap this will give a good indication of it being piston related.
You can use a long screw driver or something solid with one end on your ear and the other poking around. This can often isolate the sound for easier identification. A stethoscope works great for this and there are automotive types.

Is the noise steady or does it fade in and out? Determine if it is a ticking or a thumping if you can.

2100 RPM's is low for an Indigo prop, we can work on tune at a later date.

Dave Neptune

[sunnnnseeeker]

Thanks Dave.

The tapping started after I did the SeaFoam cleaning, which did improve engine performance a little bit. It's quiet at 1500 RPM and below. The tapping gets louder as the engine increases RPM's and is constant. Doesn't matter under load or not.

I did run the engine 30 seconds at 4500 RPM after the SeaFoam, thinking it may help clean. Is that excessive and could have broken something? But I did not notice the tapping after this. I noticed it while on cruise a couple weeks ago.

Would a broken spring reduce performance? If something was broken, wouldn't it be noisy at any speed?

Nathan

[edwardc]

4500 seems excessive. Although Universal never seems to have published a "Redline", it advertised the engine as "30HP", which the power curve shows that it achieves at 3500 RPM.

In 2007, Don published this nice chart:
https://www.moyermarineforum.com/for...39&postcount=2

[sunnnnseeeker]

Thank you Edward. Nice to see that chart. I made a typo, I ran the engine at 3500, not 4500. 4500 would be really screaming. So that is comforting I didn't break anything because of doing something dumb.

Nathan

[joe_db]

Before you do anything else, take the alternator belt off. I went nuts chasing a noise that turned out to be a bad alternator bearing. They can make a variety of noises including tapping.

[edwardc]

Nate,

It's still possible that a valve spring broke. This is not uncommon for an A4.

A broken spring provides less closing force on the valve and may allow the valve to "float" off of the cam follower at higher RPMs, causing s "tick" as it lands.

[sunnnnseeeker]

Yesterday I went sailing. Engine does not do the tapping until it warms up. Thoughts?
Nathan