A Knock from the 2.25

[rbbailey]

This is a 2.25l replacement engine I got when my last one lost its bearings. It starts and runs well, seems to have power enough.

However, over the summer oil pressure kept dropping during idle when the oil had really gotten up to full temp. There were times when the engine would actually sputter after going up a hill. Someone suggested that I might simply have a low idle setting, and I think he may have been right. After the engine was warm, I adjusted the idle just a tiny bit at the carb, and it seems to have fixed the issue. But I can't really get out and test it now because after the last few drives I've had a knock develop.

I think it has been on the edge of my hearing for some time. But it is distinct now. It is coming from the back of the engine, somewhere near the middle top of the block. I can't really pinpoint it, but I think it may be most noticeable at that rear of the exhaust manifold.

Other than the knock, the only symptom might be that if I am at idle, then rev the engine quick a few times, some grey smoke does blow for a second or two. It is faint enough that I would have to have particular lighting to catch it on camera.

The knock itself is medium low in tone, and it has a ring, or metallic sound to it. Video linked below that actually does capture the knock, but not really with the same tones I hear in real life.

The last engine I had knocked from right down low in the center of the block. And it had a deep wooden sound to it.

This is not a priority. I want to get the 110 on the road before I dive into this. But I figured if I get lucky, maybe one of you will know what this sounds like, and maybe I can justify a repair sooner than later.

https://flic.kr/p/ztpKhZ

[Les Parker]

Hi,
Sorry to learn of this. Does the noise increase/decrease when the revs are raised?
Do you have a way of checking the oil pressure?
I would suggest dropping thee oil sump and checking the mains and rod bearing surfaces.
Let us know what you find.

[rbbailey]

The noise seems to go away when a bit of RPM's are added. But hard to tell. I will start it up tonight to try to listen for that.

The PSI gauge seems to be accurate. It runs at about 34-40, idles at about 12, down to a hair under 10 when hot. I need to get a second opinion on that to make sure it actually is accurate.

[bugeye88]

Hi RB,
This reminds me of a similar "strange Knock" I had with a 2.25 engine that was a replacement engine. After much searching for a cause, it turned out to be Piston Slap. A condition arriving from several rebuilds on the engine, each one taking a bit off cylinder by boring. Eventually it is just too much and overbore pistons and rings just can't make up for it and the piston moves about a bit during its stroke causing the knock. Some have run an engine in this condition for some time with no real problem other than the knock and slight increase in oil consumption. most eventually fail in some way though.

Cheers,
Rob
Bugeye88

[Les Parker]

Another thought is an out of round tappet roller.
Try adjusting the valves and if they need re-adjusting immediately, I would figure this would be the most likely candidate for renewal.

[rbbailey]

OK, this is good stuff to go on. I'm going to do pressure test, look around with the camera in the pistons, adjust the valves, and go from there.

Is there anything to doing a cold vs. warm vs. hot pressure test?

[rbbailey]

OK. I looked in on the cylinders, they were all pretty much the same. A coating of carbon in center, clean on edges. 3rd was a bit more dirty. All plugs were the same, dark, not oily, just carbon. #4 was a bit grey/brown.

Compression test: I don't think I did it right. At first I cranked for 6 seconds. But the numbers were very inconsistent. As in, 6 seconds would be 50 psi. Then on the same cylinder, 6 seconds would be 60 psi. Then something else.

So I cranked until the pressure stopped rising, 10-12 seconds. When I did it this way, each cylinder rose to between 87-90 psi, then would not go higher.

So then I opened the valve cover and adjusted the valves. Again, I actually don't know what too tight or loose is, so I did my best to get them equal at .010. When I started, #7 and 8 were so tight I could not get a .008 blade in there. Same with #1. All others were pretty good.

No change in the noise that I can tell. Runs fine.

A few things to note:
The knock can be heard while in idle. A small amount of gas and the knock goes away. I can't tell if I hear it at all while driving. When the gas comes off, as the RPMs drop back to idle, the knock quickly returns as the RPMs settle, but it is not rhythmic. Then you can't hear it for a few seconds, but as the idle stabilizes the knock goes back to its rhythm.

[lumpydog]

With the compression test, 6-10 cranks should do it. You need to test with the throttle open. Push the gas pedal down all the way. That will get you more accurate results.

[slowmo]

Lumpy's right, but your compression seems ok to me. Did you check the timing? For it to make that kind of knock the timing would have to be way off, however. Be sure to remove the vacuum advance at the carb and plug it at the carb when checking the timing at idle.

If the plugs had a carbon build-up you are running rich. Before fiddling with the carb, get the valve clearances, plug gaps, points (dwell angle), and timing (in that order) spot on. Then lean the carb to spec. Monitor the plugs in a hundred miles for condition.

[lumpydog]

I listened to your video - and a few other videos that you also posted to flickr - covering the same noise (you can just move to the next "image" (https://www.flickr.com/photos/bhcmbailey/21969015268/in/photostream/) in the account.

That sounds to be metallic and sounds to be knocking at the rhythm of a single valve to me. Have you tried running with with valve cover off? You can do this and at idle it won't make a big mess with the oil. Place some paper towels at both ends where they won't foul the rocker arms to catch any oil seepage.

With the valve cover off, does it still make the sound? If no - one of the valves may be contacting the valve cover (this happens - sometimes hitting the screw that secures the red valve tolerance = .010 plate).

If you still hear the sound, get a 3ft section of heater hose (or garden hose) and place one end to your ear and block your other ear. Move the hose end around the engine and listen to each valve. Listen to the distributor/distributor shaft area. Listen to the lower engine. Where is the knock most pronounced?

Sometimes a specific valve is the cause and you can adjust (tighten and test, tighten and test) and see how it effects the noise. A feeler gauge will tell you the distance from the highest surface on the rocker arm, to the valve. But if the arm is worn/recessed where it contacts the valve - the arm/valve gap could be much more than what you think it is.

In any case, using a hose section will help you localize the problem and narrow it down a bit.

P.S. Try Slo's idea first. If your spark is too advanced, you get knock. But usually a very rough idle too.

[rbbailey]

The timing was done by a pro this last summer. I ran it with lid off, cause I thought maybe that was the issue as well, but the noise is still there. I have been listening to different points on the engine, and it is coming from the rear, nearest the exhaust valve. That valve was very tight, could not get .008 between there. Set it to .010. No change.