Knock in the crankcase at idle, 2f (1 Viewer)

[Fast Eddy]

While I was working on smog crap yesterday, there was a time when I heard a rattling noise at idle. I got a piece of pipe and tried to figure out what it was, hood? heat shield? I crawled around and came to the conclusion that it was in the crank.

It was only at low idle, 600 rpm or so. It was only on one of the runs. When I started it later it didn't do it. I will admit that my oil pressure gauge is bad. I've got another one to swap in. I'll try to get to that today. I checked the sending unit with a meter and it seems to work, and I have oil pressure. I suppose it's possible it's low at idle. What would cause that?

Any other anecdotes about rods or thrust-clearance knocks at idle would be appreciated.

 

[Poser]

It is my experience that low oil pressure at idle is due to increased cam/main/rod bearing oil clearances being larger than spec.

With that said, without a real instrument providing you a number, this is all simply conjecture. When ever I have a vehicle in the shop that someone says has an oil pressure issue, after verifying that there is in fact oil in the crankcase, I attach a mechanical instrument and see what there is for oil pressure, cold at idle, cold 2K RPM, hot at idle, hot at 2K RPM.


It was posted out here someplace many years ago now that Toyota states that <10#s of oil pressure at idle is acceptable.

What oil weight are you running?

 

[Fast Eddy]

15w-40 Rotella. I've got a way to add a mechanical gauge. I'll go pick one up.

Edit: Not so easy. I'll have to order it.

The only reason I have to think I might have low oil pressure is this isolated event.

 

[Pin_Head]

Low oil pressure and rod knock is not an intermittent problem; here one time, gone another.

 

[Fast Eddy]

Low oil pressure and rod knock is not an intermittent problem; here one time, gone another.

What else would be knocking around inside the oil pan?

 

[sggoat]

It is my experience that low oil pressure at idle is due to increased cam/main/rod bearing oil clearances being larger than spec.

With that said, without a real instrument providing you a number, this is all simply conjecture. When ever I have a vehicle in the shop that someone says has an oil pressure issue, after verifying that there is in fact oil in the crankcase, I attach a mechanical instrument and see what there is for oil pressure, cold at idle, cold 2K RPM, hot at idle, hot at 2K RPM.


It was posted out here someplace many years ago now that Toyota states that <10#s of oil pressure at idle is acceptable.

What oil weight are you running?

No hijack here, but info and some questions--I have a somewhat similar issue(I think). When the rig is first started, oil pressure is up in the 60psi range. After the engine gets to op temp(and run for a few miles), it drops to the expected 55 psi. if I stop for a traffic light, the pressure drops to just below 40 psi(650 RPM) I don't think this is abnormal, but based on Poser's post, do I need to be concerned about clearances?( engine temp is ~ 195 deg F, oil is Castrol 10W-30-location is So. Florida-ambient outside temps average about 85 deg F.(new water pump, rodded rad, new OEM t-stat, new hoses). Maybe this info can help, and maybe someone can tell me if I have an issue ready to bite me.

 

[Pin_Head]

What else would be knocking around inside the oil pan?

All kinds of things that have play: Trust clearance on the helical cam gear and distributor that happens to resonate at a particular speed and temperature.

 

[shawnfj40]

All kinds of things can cause a nocking sound. Engine timing is one and over heating can sometimes thin the oil to the point of knocking. It can be be more than just worn bearing surfaces. Working gauges are a good start to finding the source. You can also test the vacuum Advance on you distributor and your timing.

 

[Fast Eddy]

LOL. It's not timing. It sounded like someone hitting the block with a hammer. I've been all around the dizzy in recent memory. It works. I'm guessing it's a low mileage engine. It's from an '86 and has compression numbers 140-140-132-132-140-140. It pulls a steady 20 in hg at idle.

It's not like I was pulling a boat up a hill. It was sitting in my driveway idling. It does not overheat. I drove it on a 300+ mile wheeling trip to Pismo last month.

If I had any thought that I had a major issue I'd pull it out for a diesel swap in about one second.

 

[tornadoalleycruiser]

did ya try it with the smog pump disconnected? Not sure how legal that is in the republic of Kalifornia.. but i've had them knock really loudly before they go south for the winter.

 

[Fast Eddy]

I didn't, but I did lie underneath and verify that it was coming from inside the oil pan. I suppose the knock could have transferred it's way from the smog pump.

 

[Pin_Head]

Fuel pump is another possibility.

 

[brew8]

LOL. It's not timing. It sounded like someone hitting the block with a hammer. I've been all around the dizzy in recent memory. It works. I'm guessing it's a low mileage engine. It's from an '86 and has compression numbers 140-140-132-132-140-140. It pulls a steady 20 in hg at idle.


I had those kinds of numbers with a 86 2F, decided to tear it down because of low oil pressure at idle. found cylinder walls in spec had to grind the crank 10 under because of the low pressure, sits at 60 pounds at idle now. Machinist said it would run with sstd bearings but the oil pressure would stay low. In Florida I would run 20-50 oil all day.

 

[Fast Eddy]

I thought I was going to be able to run down to the auto parts and get a numeric gauge and screw it into the oil cooler, but all they had was the in-cab version with a tube (and a light and lots of plastic). I have to get a Harley gauge to screw into the block, as well as fix the stock one in the gauge panel.

 

[shawnfj40]

Hey don't bust my chops here I was just tossing out some possibilities. Checking the oil pressure is by far the most important step and your obviously working on that. It could be the canooter valve at this point. I agree with brew though compression and vacuum numbers have very little to do with journal/bearing conditions. You said that it was isolated didn't you? It happened while you were working on smog gear? Bearings don't usually stop rattling on a op temp motor. It might just be an isolated thing. Your already running 40 wt. diesel oil or I would suggest stopping that up a bit and see. Can you get the knock to repeat?

 

[D'Animal]

This 2F had a slight knock.

The F.5 had many issues working against it. One of them was all of the gasket material sucked up against the oil pick up screen.



This one caused a big constant knocking noise before it seized up.

 

[Fast Eddy]

Thanks for posting up the pics Dan. You're making me feel all warm and fuzzy.

Can you get the knock to repeat?

I warmed it up and ran it twice. The first time it knocked until I shut it off. The second time it did not, as I recall. I was working on the EGR and I didn't really start thinking about the knock until I was typing up this thread. Since it doesn't pass smog, and I'm not driving it, I probably won't get back out there to look at it before xmas.

 

[Pin_Head]

I rode to high school in a car with a bad rod bearing and it knocked all the time. I have never seen one that stopped knocking.

 

[Fast Eddy]

I had a 283 in a '47 Ford Pickup that developed a rod knock. You could only hear it at rpm and under load. It idled fine. This problem was opposite that. We replaced one bearing and hit the crank with some emory cloth. As I recall it lasted a year or so before some other bad things™ happened to that engine.

 

[Spike Strip]

I think your engine is singing that ol' song, "knock, knock, knockin' on Heaven's door..."

Sorry.

Mybad.