Lycoming IO-360 A1A Bent/Spalled Cam? What is that sound?

[Moooney Pit]

Hey gang, can anyone tell me what that sound is? Is it a bent/spalled cam?Here is a link to the video i made of it. Thanks for your help. 

 

[EricJ]

You could try a mechanic's stethoscope (or a long bolt) and try to isolate the location of the sound if it isn't already evident.

[PT20J]

Hard to see how a cam would get bent as it's pretty beefy and supported by several bearings and what would bend it? Spalling shouldn't create a sound like that. That sounds like something is loose. Maybe a counterweight. Bent pushrod? Did this have a prop strike or something? Might need to pull a cylinder to look inside the crankcase.

[Moooney Pit]

20 minutes ago, PT20J said:

Hard to see how a cam would get bent as it's pretty beefy and supported by several bearings and what would bend it? Spalling shouldn't create a sound like that. That sounds like something is loose. Maybe a counterweight. Bent pushrod? Did this have a prop strike or something? Might need to pull a cylinder to look inside the crankcase.

I bought it used, from a company called BAS. They sell used aircraft parts, and motors. They said it didn’t have a prop strike. The sound is coming from the cam gear, I just don’t know why. When you rotate the crank, the cam gear will make a “click” or skip sound. Not sure really what it sounds like, kind of hard to describe. From what I can gather, I think a pushrod is being slammed back after opening/closing a valve, which in turn is slamming the tappet back into the cam. I check valve clearances, and they are all in spec. I might have to double check though. Thanks for watching the video. 

[EricJ]

31 minutes ago, Moooney Pit said:

I bought it used, from a company called BAS. They sell used aircraft parts, and motors. They said it didn’t have a prop strike. The sound is coming from the cam gear, I just don’t know why. When you rotate the crank, the cam gear will make a “click” or skip sound. Not sure really what it sounds like, kind of hard to describe. From what I can gather, I think a pushrod is being slammed back after opening/closing a valve, which in turn is slamming the tappet back into the cam. I check valve clearances, and they are all in spec. I might have to double check though. Thanks for watching the video. 

It should be easy to take the valve covers off to see what's happening with the rockers and pushrods.   If one is suspect, remove that rocker and see if the noise goes away.

[RLCarter]

Kinda sounds like a valve clicking as it closes? I would pull the valve covers as mentioned above and see if the sound changes location, watch the valves to see if one sticks/hangs, if you can’t see anything then remove 1 (one) push rod at a time to isolate which valve on which cylinder needs looked at, if it’s still clicking with all the push rods removed remove the cam gear, you should be able to spin the cam and listen/feel for the click.  If it still clicks with the valve train completely disconnected it’s in the rotating assembly (crank, rods, pistons). Will be interesting to see what is found, so keep us informed 

[Fly Boomer]

7 hours ago, Moooney Pit said:

I bought it used, from a company called BAS. They sell used aircraft parts, and motors. They said it didn’t have a prop strike. The sound is coming from the cam gear, I just don’t know why. When you rotate the crank, the cam gear will make a “click” or skip sound. Not sure really what it sounds like, kind of hard to describe. From what I can gather, I think a pushrod is being slammed back after opening/closing a valve, which in turn is slamming the tappet back into the cam. I check valve clearances, and they are all in spec. I might have to double check though. Thanks for watching the video. 

Web site says “You may return parts or request a replacement within 90 days of the purchase date with no penalty. We'll also pay the return shipping costs if the return is a result of our error (if you received an incorrect or defective item, etc.).”

[jetdriven]

It could be the impulse coupler 

[Moooney Pit]

8 hours ago, M20Doc said:

Did you try holding the tachometer drive shaft while you turn the engine over?

I haven’t tried that yet. However I tried a few things. I removed all pushrods from each cylinder, and the sounds goes away, although when I checked the clearances, they were all in spec.  I tried installing a pushrod, individually on each side of the cylinder, I.e Intake by it self, and the sounds comes back, for both intake or exhaust, on each cylinder as well. 

[hammdo]

May need to do a wobble test on the valves to see if it’s a morning sickness thing (guides need reaming)…

-Don

[jetdriven]

On 7/27/2023 at 6:40 AM, M20Doc said:

With the accessory cover removed?

No

[N201MKTurbo]

It could just be the dry tappets taking up the clearance. I seem to recall that sound when I put my engine together. Considering that the engine is that far apart, Pull a cylinder or two and take a look inside. It will only cost a couple of o-rings and a few minutes.

[Moooney Pit]

On 7/28/2023 at 4:10 PM, N201MKTurbo said:

It could just be the dry tappets taking up the clearance. I seem to recall that sound when I put my engine together. Considering that the engine is that far apart, Pull a cylinder or two and take a look inside. It will only cost a couple of o-rings and a few minutes.

I was thinking along those lines as well. I pulled #1 cylinder off, and rotated the crank. I installed #2 intake pushrod, to see when the sound is about to start at the cam gear. I found just before and after the apex of the cam lobe, the sound is heard at the cam gear. The cam gear seems to “slip” or catches up with the speed of the rotation to the fuel pump idler gear, after that point of the cam lobe. I’m hoping this is normal, until you actually run the motor, and get oil circulating etc. What do you think? 

Edited July 31, 2023 by Moooney Pit

[N201MKTurbo]

37 minutes ago, Moooney Pit said:

I was thinking along those lines as well. I pulled #1 cylinder off, and rotated the crank. I installed #2 intake pushrod, to see when the sound is about to start at the cam gear. I found just before and after the apex of the cam lobe, the sound is heard at the cam gear. The cam gear seems to “slip” or catches up with the speed of the rotation to the fuel pump idler gear, after that point of the cam lobe. I’m hoping this is normal, until you actually run the motor, and get oil circulating etc. What do you think? 

That makes sense. As the cam pushed the lifter against the valve spring, the gear would be on one side if the gear lash, after going past the apex, the valve spring would be pushing on the cam and back driving the cam, pushing it to the other side of the gear lash. 

I have a feeling that after it is up to speed, inertia would keep this from happening.

This is a part of engine operation I have never considered before.

[Pinecone]

The question to me is, how much play is normal in that gear mesh.  Is yours a bit loose?

[N201MKTurbo]

4 hours ago, Pinecone said:

The question to me is, how much play is normal in that gear mesh.  Is yours a bit loose?

The gear lash limits are in the table of limits in the overhaul manual.

[Pinecone]

Then it would be a good idea to check this.

[A64Pilot]

On 7/24/2023 at 11:38 PM, RLCarter said:

Kinda sounds like a valve clicking as it closes? I would pull the valve covers as mentioned above and see if the sound changes location, watch the valves to see if one sticks/hangs, if you can’t see anything then remove 1 (one) push rod at a time to isolate which valve on which cylinder needs looked at, if it’s still clicking with all the push rods removed remove the cam gear, you should be able to spin the cam and listen/feel for the click.  If it still clicks with the valve train completely disconnected it’s in the rotating assembly (crank, rods, pistons). Will be interesting to see what is found, so keep us informed 

I’m thinking sticking valve myself, and pulling push rods will make it stop if it is.