O-200-A engine noises
 

I have a very neat C150M and it's serviced regularly as required. Lately, there is a noise from the engine, similar to a turbo whistle but louder. We have had the alternator rebuilt, thinking that there may have been a bearing or brush causing the noise, but that didn't fix it.
It's there with the engine covers removed, so it's not a wind related whistle. All that's left is the starter or the vac pump.
Has anyone had a similar noise? Apart from the noise, it goes well. Compression is very good, doesn't burn oil and plenty of vac.

It's unlikely that the vacuum pump is audible, and working. If it's drawing it's last breath, there's nothing you can do, it will fail harmlessly when it is done. If its high time, you might choose to change it preventatively, but it won't save you anything.

You could have one of several starter systems. The 150M is too recent to have a "pull clutch" unless the plane has been modified "backward", which is unlikely.

If it has a newer starter motor with an "injecting" pinion, have the starter checked/rebuilt. There are a number of sources of this service - no mystery there.

If it has a "key clutch", attend to it right away. A key clutch is the original configuration for that engine - it'll have a big Prestolite type starter motor bolted to a cast plate, bolted to the engine (also refer to the tech log for the engine). A person who is competent is to turn a propeller by hand, applying all the cautions appropriate should turn the propeller by its tip. If doing so enables the feel of the clutch engaging as the prop is turned backward, and releasing as it is turned forward, it's working as it should.

If the clutch does not release and engage (which can be a common fault) it's either not engaging, so the engine cannot be started, or it's not releasing = serious problem - do not run engine.!

Diagnose, and PM me if you like. If it's a starter clutch problem on the O-200, I have a lot of experience with these...

Let me know what you find...

I have recently gotten checked out on an LSA aircraft with the lightweight O-200D engine. When I shut the engine down, it seems to come to a very sudden stop almost the way a Rotax engine does(which is strange in itself).

I don't remember the O-200A engine on the Cessna 150 stopping in this manner. Is it just my imagination or is there a reason for this.

Inlet manifold leak?

Metal or wooden or composite prop? The C150 has a metal prop which will have a greater flywheel effect than either a wooden or composite prop.

I have a metal prop in very good condition. We have also investigated the inlet manifold as a possible cause. Everything appears ok but until things are removed, we can't be 100% sure.
Thanks so far your replies.

A forged aluminum alloy propeller according to the POH. But perhaps weight makes a difference.

As Fark'n'll posted: you have a leak at one of the rubber hose connectors on your intake manifold.