Engine Sound

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SeamusNZ
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Joined: Fri Sep 16, 2016 3:11 pm

Engine Sound

Unread post by SeamusNZ » Thu Sep 07, 2017 3:25 am

Hi from New Zealand,

I now have my Corvair engine running quite well, although there are a couple of questions that you may be able to help with. I have fitted twin exhausts to the engine.

1. The engine isn't overly noisy under the lid, but it isn't quiet either. What should the engine sound like under the lid??

2. From inside the car, the engine has a somewhat uneven throbbing sound. I'm not sure if it's the normal sound or if it's something to be concerned about.

I appreciate that it will be difficult to answer my questions without actually listening to the car running. However it would help to know if the engine naturally has an unusual sound.

I'm not referring to the sound coming from the exhausts, which I am quite happy about. It's the engine sound above the exhaust sound????

Kind regards...

SeamusNZ


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bbodie52
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Re: Engine Sound

Unread post by bbodie52 » Thu Sep 07, 2017 5:27 am

As you said, it is difficult to define the Corvair sound and to define what "normal" is over the Internet.

Unlike a cast-iron, water cooled engine, and aluminum air cooled engine would tend to transmit more mechanical noise to the outside. The heavier water cooled engine would tend to muffle some of the mechanical sounds and keep them to itself. The forced air rushing around the cooling fins might be a little noisier than a water cooled engine as well.

The objectionable Corvair sounds might emanate from the rotating idler pulley and possibly from the cooling fan bearing. As they start to age, these sealed bearings may start to squeak, or may develop a rumbling sound if the sealed bearings begin to dry out and become rough. Temporarily removing the fan belt and then running the engine for a few seconds with those rotating bearings removed from the equation may help you to identify the source of objectionable sounds. The use of a mechanic's stethoscope can also help you to localize the source of sounds from the engine. If the bearings seem to be making excessive noise you may also be able to detect a rough operation by manually rotating the idler pulley or cooling fan by hand to see if you can detect a rough operation.

The other objectionable sound from a Corvair is the clicking valvetrain noise that occurs when one or more lifters have drained their oil and have not had time to reload and close the gap in the valvetrain (as hydraulic lifters are expected to do). These hydraulic lifters are essentially identical to the hydraulic lifters used in Chevrolet V-8 engines. The problem of the Corvair hydraulic lifters is that they lay horizontally rather than at a vertical angle, because of the design layout of the flat, horizontally opposed Corvair engine. There is an oil hole in the side of each lifter. The lifters also normally rotate within their bore during operation, so that they wear evenly as they contact the cam lobe. When the engine stops, some of the lifters may stop the rotation with the oil hole facing downward. This can randomly cause some of the lifters to drain their oil content by gravity as the engine sits stopped. When the engine is restarted, a drained lifter may take a few minutes to refill from engine oil pressure before the lifter quiets down the valvetrain it is responsible for.

Perhaps these explanations will ease your concern to some extent about the noises you hear in the engine compartment. Most are normal for an air cooled aluminum Corvair engine. An air cooled motorcycle engine may also tend to sound a little more "mechanical" in the course of normal operation. But it is helpful to be aware of excessive noise that may be coming from the cooling fan and idler pulley bearings. The bearings in an alternator are also sealed and can dry out. The older generators have oil cups that allow for a few drops of oil to be added periodically to lubricate the bearings.

Your "isolated" location probably makes you the only Corvair owner in your part of the world, so listening to other owner's Corvairs for comparison purposes is probably not an option. Over time you will begin to develop a sense of "normal" for your Corvair.

:whoa: :eek: :Love it:
Brad Bodie
Lake Chatuge, North Carolina
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SeamusNZ
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Re: Engine Sound

Unread post by SeamusNZ » Thu Sep 07, 2017 2:11 pm

Thanks Brad. Excellent advice. I very much appreciate your last comment. I am still learning to develop that sense of normality. Kind regards...SeamusNZ


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