VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 216 knock

The '41 coupe I just bought has a Canadian 216 from 1948 or 49. It has a slight knocking sound at idle, but it goes away when you rev up the engine. The oil pressure gauge shows I have plenty of oil pressure. When each plug wire is removed, there is no change in the sound. Which was a good feeling! A friend with more mechanical know-how than me came over yesterday, and we listened with a long stick at various locations, but didn't locate the source of the sound. Anyone have some suggestions? I was hoping to drive it about 400 miles next month, but I think I better check this out first.
Thanks,
Sid

If the knocking noise doesn't go away when you pull a spark plug wire then it could be a main bearing that is knocking.

Also, check for a slightly bent push rod knocking against the push rod cover.

It can also be a wrist pin (fairly common problem but not often fatal or serious) or even piston slap (also not often fatal). There are also a few other possible sources. Most are not a serious (short term failure) problem. What happens when you load the engine at low speed (like let the clutch partly out while idling)? Does the noise get louder?

Thanks for the ideas Chipper. I'll try the load test in a few days. And thanks also to Dog re: the main bearing possibility, but I'm still hoping for something easier to deal with. Could a fuel pump make a knocking noise?
Sid

Use a stethoscope or a section of garden hose ( held to your ear and to the suspected area) to help isolate the knock.

I second the hose method for listening. I use a smaller diameter clear plastic hose. I find it is very directional and I can get results by pointing the end without actually touching anything.

A rod knock is a fairly harsh sound and will be worst after a qucik flick of the throttle as the rod "floats". That is the most feared knock for me!

I just did some more testing. I put it under load in gear, and there is no change in the loudness of the knock. It is however still evident when under load. My load test was to put it in gear with the emergency brake on and let the clutch out slowly. The knock is not noticeable when driving down the street. My next test was with a piece of garden hose. The knocking sound is more apparent on the valve cover, near the front of the engine. Does this mean a lifter? a loose valve?
Thanks,
Sid

Lifters usually tap if too loose. A rod knocks and mains bump. Ford was known for mains. Dont know if they still are. But thats beside the point.

Interesting thread, my '38 has developed a knock on cold start that I thought was a rod because it goes away when the engine warms up. I was getting my mind around crawling my well fed self under the car to pull the pan and remove a shim or two. Just last week I pulled the plug wires to isolate which cylinder was making the noise and like the poster here the noise didn't go away so I guess it's not a rod. I have a mechanic's stethoscope and I couldn't isolate exactly where the noise is coming from. Does the fact that the noise goes away when the engine warms up help with diagnosis?

Wrist pin knock is common on inline Chevys. It sounds sorta like a rod but often goes away or is reduced when engine warms and oil mist reaches the pins. Most of the noise is not really the wrist pin moving but a dry pin causing resistance and pistons to rock up and down.

If the sound does not get louder when engine is loaded then chances are it is not a main bearing. Push rod or fuel pump are more likely.

Also as the piston warms up it expands and so does the wrist pin clearance.
Tony

This may sound stupid but... Check your fuel pump arm spring. My 50 216 had a horrible knocking noise intermittently so I dropped the pan to check the main bearings with plasti gauge. In my pan was a small 1/4 dia. spring 3/4" long. All my bearings checked ok but I had no idea where this spring came from. I put everything back together and continued driving with this knock. A short while later my fuel pump needed a rebuild. Guess what was in the kit, that same spring. The arm was bouncing around on the lobe that operates the pump. No more knocks now and at least I know my bearings are good.
Good luck, Bill

Thanks guys. When I get some time I'll start the engine, run it for a few seconds, shut it off, remove the fuel pump, plug the hole with cardboard or something, restart, and see if I still have noise. If that's not the source, I guess I'll remove the valve cover, and look for something odd there.
Sid

Pretty neat trick, running the engine without a fuel pump. I'm assuming you're going to use an external container with a gravity feed to the carb?

Hopefully, there will be enough fuel in the carburetor to run for a few seconds - Hopefully,long enough to see if knock is gone. If not I'll rig up a gas can and gravity feed.
Sid

If there's no spring under the fuel pump arm that's probably your noise maker.
good luck, Bill

Piston slap is common on sixes. My first experience with it was when I was checking out a recently rebuilt 216.

I had some time today, so I took the fuel pump off. Unfortunately, the knock was still there with the fuel pump removed. I'll open the valve cover next and look for anything unusual there. Thanks for all the help. It may take a while, but eventually I'll find the source of the knock.
Sid

While the fuel pump is off try prying the camshaft each direction, allow about .002 to .005 movement.
Tony

I just returned from the annual Petit Jean Mountain Car Show and Swap Meet. Had a great time! While there a friend who made his living building 216's listened to my knock and declared it to be a normal Chevrolet noise. He said it is probably a wrist pin, but said I should enjoy the car and drive it 65 mph. He would not expect any problems. Later while in the swap meet I found a rebuilt, running 216 that was to be auctioned off in the next 2 hours. I heard it run, made a bid and returned later to make the winning bid - a very reasonable price. So now my policy with the 216 in my '41 is, if she dies, she dies! I have another engine ready.

216 wrist pin noise.
A loose wrist pin can be heard best when the oil is hot and the engine is run at idle speed. Reving the engine up will make it go away for a moment. It can not be heard at a higher RPM and causes no harm.

There are a ton of old Chevys that have wrist pin noise and live with it for nearly ever. Very rare that it causes any significant problems other than owner concern. Just drive it and forget the noise. Besides you can't hear it driving down the road. If it really bothers just set up the idle speed and it will go away. Makes shifting a bit more difficult but as one wise old compatriot told me you can have two out of any three things. Once you choose the first two the third is determined. So if you choose peace of mind and no noise your bank account gets nicked.

I got called away so here are some more thoughts.
It was not unusual for the pre 1950 engines to have pin noise by 35,000 miles. Most common on cars that were driven slow and idled a lot. This was due to the fact that oil is not being thrown up inside of the pistons at idle speed or when the oil is cold and thick. I avoid letting my engines idle for prolonged period.
When I began in the dealership in 1950 it was common for 1946-1947's to be traded in with 40,000 miles or so. Was common to need a valve job at that milage and the engines were sounding "loose" due to several reasons. To make it a good engine we would just do the common overhaul job which always included fitting new pins.
In 1950 the oiling holes/groves were revised for better pin lubrication. It did help.
My 1950 with 55,000 miles has just a trace of pin noise at a slow idle when the engine is good and hot. Reving it up for about 20 secnonds gets the oil flying around the the noise goes away for a bit.
The heavy cast iron pistons also are hard on the pin bushings.
Most cars back then had full pressure oiling and a hole drilled the full length of the connecting rod. This brought oil under pressure up to the pin. Could also cause over oiling and oil consumption so was eleminated on modern engines.

I have a 29 chevy that has wrist pin knock since 1966 and that knock has never caused a problem. I did have a rod failure because the original cotter keys could rotate and wore out letting the rod nuts come off,I have since looked over some other engines and they also were missing cotter keys, GM only slightly opened these keys and they can rotate and were out.
Hi Gene see you in VA in September? Al & Mary Ann