The Stovebolt Site Forums The Shop Area Engine Shop Is this a rod knock? 235 engine with video

Hello all, I have a few questions.

I just had the head rebuilt on my 235, which is great since the old one was cracked, had worn guides, sunken valves. The motor will now idle down to 500ish rpm, when previously it would die below 750. Now that I have everything together, I have a few questions.

At idle I have a knocking noise, which goes away above 1000 rpms. There is no change in noise if I pull spark plug wires off, and the noise seems to be coming from the pan somewhere. Does this sound like a rod knock? Most rod knocks I found on Youtube were less rhythmic. If so, am I probably looking for a new crank when I rebuild the bottom? I'm just trying to estimate costs.

Thanks, Vince

http://s1206.photobucket.com/albums/bb458/vincejohnston/?action=view&current=VIDEO_0011.mp4

Oh, and sorry for the horrible video, it's from my cell phone. But at least the sound is pretty clear...

Thanks again.

That sounds like a lifter noise to me. Sometimes a manifold gasket leak can also make a similar sound.

Thanks Dave. I've checked the lifters twice now, but I will again tomorrow. I know I can check for an intake leak with propane, is there any test for an exhaust leak, other than noise?

Also, would a manifold leak explain why my manifold vacuum drops to almost 0 on quick acceleration from idle?

It is normal for vacuum to drop on acceleration.
Is this a solid or hydraulic lifter engine?
Blocking the tail pipe momentarily can change the sound if it is an exhaust leak.

Well it definitely is not a rod knock. I would take a piece of 3/8 plastic hose, put one end to my ear and poke around with the other end. I find it to be a good listening tool and it is very directional.

It is a manual lifter engine. When I pulled the valve cover off yesterday to adjust the valves, I left the motor running for a minute or so. The sound seems to come at a faster pace than any one rocker, more like twice the speed.

I'll ask my buddy to put something over the exhaust, I assume I would hear noise around where the leak is coming from, right?

Thanks again.

I had a similar noise in a flathead one time. It turned out to be a dent in the flywheel cover and the teeth were nicking it as they went round. I hammered the dent out and that was the end of the noise.
May you be so lucky.

Has the pan been off for any reason while you did the head?
It sounds like a crank lobe frequency to me. I had a similar but slightly lower toned knock after my reassembly. I wound up taking my oil pan off close to a dozen times trying to locate the 'knock'. I pulled things apart and checked and rechecked but couldn't find the origin of the knock.
I finally set up my video camera and recorded the engine turning over with the pan off. Then I checked the sound track in my software editing program and saw where the knock occurred, then I could see it was at the bottom of the #3 (or is that #4?) lobe and the only thing possible was that return line. It was just barely missing the line when I would turn and check by rotating the crack by hand but once the centrifugal forces came into play it no longer missed.

When you adjusted the valves did you check how much wear was on the contact face of the rockers where they hits the top of the valve?
The rockers are known to wear significantly. The problem is that the rocker is wider then the valve stem and wears a recess in the rocker. Then when a standard width feeler gauge is used it bridges the wear point and gives a false reading.

Wow, thanks for all the ideas.

I'm going to grab a stethescope from Harbor Freight on my way home. They're on sale, and I have a coupon.

I'm also going to drop the pan this weekend, and take a look around. I didn't when I removed the head, but it's got a very small leak anyway, so changing the gasket is probably in order. Is there anything I should know beforehand? Anything special outside of removing all of the bolts around the rim?

Finally, when I pulled the rocker assembly off the head, I cleaned each rocker and the tube they sit on pretty well. I'm not sure how to check the rocker wear, but each one was smooth, and rounded. There wasn't a valley in the center of the rocker arm, they were rounded yet flat. If that makes any sense. Also, if I remember right, on the face where the rocker rubs the valve stem the center was silver, with a darker outter ring. Is that normal?

Fuel pump? Seems to be the right frequency and location. Excessive clearance causing the pump rod to slap the cam? Or maybe a stuck lifter?

I had a problem where I wasn't getting much oil to my rockers and they were pretty noisy like that. The rear connection of the oil supply tube that is located behind the pushrod cover was completely blocked with crud. Here is a picture:

[IMG]http://i7.photobucket.com/albums/y261/bohon/56%20Chevy%20truck/Blockage019.jpg[/IMG]

Here is the same hole after cleaning:

[IMG]http://i7.photobucket.com/albums/y261/bohon/56%20Chevy%20truck/Blockage021.jpg[/IMG]

Joe, is that the hole that has a copper line running out of it? I think I'm getting enough oil to the rockers, but I'll check that out too.

Mine was metal. Yours might be copper. It's behind the push rod cover. As soon as you take the cover off, you'll see it. The area shown in the picture is where the rear-most end of the tube threads into the block. In the photo I have removed the fitting the tube threads into but the fitting itself was packed full of crud, too. I don't know the history of your engine, but mine sat for many years. I had to eliminate all the suspects from the rockers to that particular fitting and this included the overflow tube that loops over the rocker arm assembly, the drilled-out head bolt next to that tube, the passage in the block that leads down behind the push rod cover, the tube behind the push rod cover, and finally, the fitting I showed in the picture. There is a threaded plug on the passenger side of the head that you can pull while the engine is running and see if there is any oil coming out. If so, you should be good. In fact, that's the first thing I'd do before taking stuff apart.