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Lycoming o-320 Valve train noise?? Watch video

William

Well Known Member
Hello a little background first. The engine does not have mags, it has dual pmags so I know it's not the impulse coupler. I've overhauled this engine last year and had all internal parts yellow tagged and assembled the engine with new Lycoming cylinder assemblies. I'm having a valve train noise that I can't track down. Don't know if this is normal or not and only noticed it when I pulled my plugs out to change them and rotated the prop. Since the video I've pulled the pushrods and the hydraulic lifters out and the noise has stopped so I know it's coming from the valve train. I've pulled the cylinders today to check the cam and tappet bodies and they are perfect as would be expected from a engine with 1-2 hours of run time. Any idea?

Thanks
Bill

https://m.youtube.com/watch?v=FC-_le1nOoM&feature=youtu.be
 
Interesting noise, but not sure I know what it is.

Did you check your dry tappet clearance for all pushrods?
 
Interesting noise, but not sure I know what it is.

Did you check your dry tappet clearance for all pushrods?

Hi Paul thanks for the response. Yes all dry tappet clearances were checked and were in the middle of the allowable range.

Thanks
Bill
 
I assume you have not run the engine yet, so, Have you spun the engine over enough so as to get oil pressure? Could be that the lifters have not pumped up yet. You could also get a mechanics stethoscope and have someone spin the prop over as you have been doing and listen at the crankcase end of the valve train to see which end the noise is coming from. Still betting the lifters have not pumped up.

Ross Scroggs
Locust Grove, GA.
A&P
RV-4 Finishing kit
 
I assume you have not run the engine yet, so, Have you spun the engine over enough so as to get oil pressure? Could be that the lifters have not pumped up yet. You could also get a mechanics stethoscope and have someone spin the prop over as you have been doing and listen at the crankcase end of the valve train to see which end the noise is coming from. Still betting the lifters have not pumped up.

Ross Scroggs
Locust Grove, GA.
A&P
RV-4 Finishing kit


Thanks for the response Ross. The engine has been run several times since being overhauled last year. I have not flown the plane yet though. Preparing for first flight and this is one of the last issues. The engine is very quiet when running. Meaning no noises out of the ordinary are heard. I only found this noise by accident during plug change.

Thanks
Bill
 
Can anyone confirm for certain that this noise is not normal? Anyone have there cowling off that could pull the top plugs and rotate there engine a few turns and see if it makes the same noise?

Thanks for all the help
Bill
 
I don't remember hearing those noises when rotating my engine to check mag timing. If I had I would have remembered.
 
That is Cam whip. I noticed it after I rebuilt my engine and spent two days trying to figure out what I did wrong. Two of the cam lobes operates two different valves on opposite sides of the engine. At a certain point in it's (the cam) rotation, the opposing forces from the valve springs transfers from one valve train to the other. At this moment the cam trys to reverse direction and gives up it gear lash and causes the click. It is insignificant and unnoticeable at any meaningful RPM, but quite noticeable when turning by hand. As you showed in your video, it always happens at the same place(s).

Larry
 
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That is Cam whip.

Larry

Okay:Cam whip. Hereafter, whenever two VAFers have a disagreement on the forums that grows heated, this shall be the official call-out. "Oh yeah? Don't like my views on downwind turns/primer/automotive conversions/pinhole fillers?! You and me - out back behind Doug's website. You need some cam whip, buddy, and I got some right here for ya!" :eek:

-Stormy
 
Okay:Cam whip. Hereafter, whenever two VAFers have a disagreement on the forums that grows heated, this shall be the official call-out. "Oh yeah? Don't like my views on downwind turns/primer/automotive conversions/pinhole fillers?! You and me - out back behind Doug's website. You need some cam whip, buddy, and I got some right here for ya!" :eek:

-Stormy

the first thing I thought of when I heard it was the "Orange Whip" that John Candy ordered in Blue Brothers.

Larry
 
I don't remember hearing those noises when rotating my engine to check mag timing. If I had I would have remembered.

Steve thanks for the response. I see you have a roller camshaft. I'm not sure the dynamics of that but I don't believe they opporate the same way as my tapet/plunger opporated camshaft, I could be wrong though?

Thanks
Bill
 
That is Cam whip. I noticed it after I rebuilt my engine and spent two days trying to figure out what I did wrong. One of the cam lobes operates two different valves on opposite sides of the engine. At a certain point in it's (the cam) rotation, the opposing forces from the valve springs transfers from one valve train to the other. At this moment the cam trys to reverse direction and gives up it gear lash and causes the click. It is insignificant and unnoticeable at any meaningful RPM, but quite noticeable when turning by hand. As you showed in your video, it always happens at the same place(s).

Larry

Hi Larry thanks for the response. I did see your thread on the subject. I still wasn't sure if we had the same phenomenon happening. Glad you're able to confirm we are hearing the same things and it is in fact just cam whip.

Thanks
Bill
 
Hi Larry thanks for the response. I did see your thread on the subject. I still wasn't sure if we had the same phenomenon happening. Glad you're able to confirm we are hearing the same things and it is in fact just cam whip.

Thanks
Bill

The fact that your noise went away when you pulled the rockers, confirms it is in the valve train and should eliminate all other accessory case related noises. It is hard to diagnose from a video, but it sure seems like Cam whip to me. Just confirm that it happens in the same prop position each time. It is a known anomaly; It's just foreign to us guys with auto experience, as it's not replicated there.

Larry
 
The fact that your noise went away when you pulled the rockers, confirms it is in the valve train and should eliminate all other accessory case related noises. It is hard to diagnose from a video, but it sure seems like Cam whip to me. Just confirm that it happens in the same prop position each time. It is a known anomaly; It's just foreign to us guys with auto experience, as it's not replicated there.

Larry


Hi Larry it's definitely happening at the same spot each revolution. That sound just sent chills down my spin. Now that you mentioned cam whip and what that is it makes sense. I will be putting the cylinders back on next week and use a stethoscope to confirm this. Did you happen to video your "cam whip sound"?

Thanks again
Bill
 
Hi Larry it's definitely happening at the same spot each revolution. That sound just sent chills down my spin. Now that you mentioned cam whip and what that is it makes sense. I will be putting the cylinders back on next week and use a stethoscope to confirm this. Did you happen to video your "cam whip sound"?

Thanks again
Bill

I did not, but I remember it sounding very similar to the impulse coupling letting go at TDC and from the same area. While I was diagnosing it with a stethoscope, I pinpointed the sound to accy case area. Once I learned what cam whip was, it made sense and confirmed things for me. The noise comes from the cam gear as it revereses it's lash, if you will, and the cam gear is in the accy case.

The sound from your video was very similar to what I heard.

I also did some layout of the cam action and confirmed that the position of the crank when the sound(s) occurred were where the cam lobe was transitioning from one lifter to the other. Further, the detail came from Mahlon; A trusted source.

Good luck

Larry
 
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