Need Help Diagnosing Engine Knock


IHC in the early to mid-fifties.

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Golden Jubilee
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Post Thu Apr 15, 2021 8:15 pm

Need Help Diagnosing Engine Knock

I finally got around to putting on a functional muffler, and now I can hear the engine noises. I have a knock, sounds like the diesel pump on an old tractor (but this is an SD 220), or like a hammering on the block. My first thought was either wrist pin or connecting rod knocking. My understanding is that those knocks usually get louder with RPM, and as the engine warms up. This one is loudest at cold idle, and can't really be heard while driving at highway speed. Compression is 120 - 130, with #1 at 130, #5 at 120, and the rest at 125. I set the valves with each cylinder on TDC, hot. Then to verify, I checked again with the engine hot and idling. And that's when I discovered that the knocking stops when I put the feeler gauge on the #6 intake valve. That's when it is gapped at .019 to start with. Pulling plug wires doesn't diminish the knock. I'll try to get a leak down test done on it tomorrow, but I'd welcome any thoughts on what would make it hammer with the valves set correctly, and then stop when the gap is removed entirely on one intake valve.

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Post Sat Apr 17, 2021 5:30 pm

Re: Need Help Diagnosing Engine Knock

Do you know if this engine has been rebuilt? If it is original, what is the mileage?
I Googled, "diagnosing a gasoline engine knock" and got a bunch of opinions. It was an interesting read. I will not go over it all, but it might be of interest to you. You tube has some information.
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Golden Jubilee
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Post Sat Apr 17, 2021 5:44 pm

Re: Need Help Diagnosing Engine Knock

Sound like the problem is #6 intake rocker.
Just remember, you are asking me to diagnosis something I can't see, hear or feel.

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Post Sat Apr 17, 2021 9:47 pm

Re: Need Help Diagnosing Engine Knock

I was thinking the same thing about the rocker. I wanted you to say it first.
I would rather have tools I do not need than to need tools I do not have
Opportunity is missed by most people because it is dressed in overalls and looks like work.
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Golden Jubilee
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Post Sun Apr 18, 2021 5:59 am

Re: Need Help Diagnosing Engine Knock

I've been googling for a few days, but haven't found anything that seems to describe what I have. The engine was completely rebuilt, including new valves, valve guides, and even new rockers and rocker arm shaft. It has 80,000 miles on it since the rebuild, well-maintained and mostly long distance driving. I can't find any looseness in the rocker arm, but that's hard to feel at the back of the engine. I can't hear it with a stethoscope on that rocker arm. Leak down on that cylinder is about 11%. One other clue - it goes away on deceleration. I know it's hard to diagnose engine trouble by description and not being there, but I sure appreciate your thoughts and suggestions. Will do more checking.

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Post Sun Apr 18, 2021 7:31 am

Re: Need Help Diagnosing Engine Knock

nikkinutshop wrote:I was thinking the same thing about the rocker. I wanted you to say it first.

Ahh, wanted me to be wrong 1st! :t1809:
Flat cam lobe, or a flat cam follower (tappet) are a possibility. If you have a dial indicator, you can check another intake push rod lift against the lift on #6 for comparison.
Piston slap or wrist-pin bushing/ wrist pin clearance are another possibility. All these should have been noticed on assembly but could be overlooked. Whoops, missed that you have 80K on the rebuild, I just read rebuild. There could be most anything with that many miles. Drop the pan and check the bearings wouldn't be out of order.
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Post Sun Apr 18, 2021 7:56 am

Re: Need Help Diagnosing Engine Knock

I don't think there's a "wrong" in this. It's best guesses based on what I can give for information and over long distance, and it's appreciated. I'll see what I can do with a dial indicator for comparison. The difficulty there is working by myself, trying to turn the engine and read dial indicator at the same time, but will see what I can come up with. A good idea. New pistons, pins, pin bushings and rod and main bearings on rebuild, but that doesn't mean that any part hasn't worn out.

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Post Sun Apr 18, 2021 8:05 am

Re: Need Help Diagnosing Engine Knock

I am curious, where did you find new rockers and a rocker shaft? Also, who was the engine rebuilder? Was this a home build or a machine shop build? How much experience does the rebuilder have?
I would rather have tools I do not need than to need tools I do not have
Opportunity is missed by most people because it is dressed in overalls and looks like work.
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Post Sun Apr 18, 2021 9:33 am

Re: Need Help Diagnosing Engine Knock

My guess is when you slip the feeler gauge in the running engine, you are holding the intake slightly off its seat and "unloading" that piston.
It could be as simple as a little excess clearance of the piston fit in the bore. This would also be the case on deceleration, when the pressure on the piston would be low. It would increase when the cyl fires and the piston "rocks" in the bore. Unfortunately, the only real way to be sure is to tear down and measure. If it is, the piston can be "knurled" to increase the size of the piston skirt.
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Post Sun Apr 18, 2021 9:55 am

Re: Need Help Diagnosing Engine Knock

I used to watch Ebay and pick up about any engine parts that came up NOS and cheap. Found a full set of rocker arms on there years ago and held on to them. The rocker arm shafts are, or at least were, available through the Case/IH ag dealers, as they were the same as used in the tractor, combine, cotton picker, etc. Now, as far as the quality of the rebuild, well, ahem, uh, the machine shop did the machining, balancing, measuring of fit in cylinders, etc., but I did the rest. Not the first, but still subject to suspicion I'll admit.

Piston slap is sure a possibility, since that cylinder would run hottest and probably have the least oiling. I'll do more checking, but I was of the impression that wrist pin, connecting rod or piston slap would be heard once per revolution. This noise is certainly every other revolution, ie occurs with the valve train or ignition.
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