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Volvo Penta KAD 42, Turbo screech?

Chris 540

New member
Hi all,

My Volvo Penta KAD 42 has developed a horrible screech which is kicking in at a reasonably low rev range (when moving approximately 5 or 6 knots) - noise will also kick in when in neutral and revving the engine.

Initially thought it was a belt screech, so have replaced the turbo belt, but to no avail... Now i am worried that the turbo needs replacing.

My friend suggested that there might be an air leak somewhere, and i did find a draft of air being emitted when the noise kicks in, but was having trouble isolating it.

It is a horrible noise, and is also accompanied by a burning rubber smell.

Please view the following link for a short 10 second video of the issue; (loud video, so turn your speakers down first!)

https://www.youtube.com/watch?v=-lfy9fxbmsA

Thoughts, comments?

Help me!

Thanks, Chris
 
Last edited:
That is your supercharger or kompressor, not your turbo. The thing that suddenly starts spinning in the video is the magnetic clutch that connects the belt drive to the kompressor. It is controlled by the electronics so that it kicks the kompressor in at a certain rpm. Around 1800rpm or so I think (could be wrong). Later on at around 2600rpm or so the magnetic clutch releases so the kompressor drops and and your turbo takes over.

You can't tell for sure from the video but it seems like you have 1 of 3 things happening. 1) the belt is slipping (and belt dust around that area to show that it is?). 2) The magnetic clutch is slipping. Looks/sounds like that maybe but I haven't seen one slip myself. 3) the kompressor is failing internally.

Check the kompressor oil level and colour. Should be full to the mark and still golden like new oil. The belt you just need to recheck the tightness. It doesn't quite sound like belt slip but could be. To check for clutch slip I think you could use a laser tachometer or similar and check both sides of the clutch for matching rpms. I haven't done this, but I think it is doable. You can get a cheap laser tach for around $20 or so I expect.

Another thing is that inside the kompressor are a pair of big vaned rollers that compress the air. The tolerances between them are very fine and they are coated in some type of rubbery substance. They can get sticky and make the kompressor hard to turn or even lock up. Would usually happen if the engine hadn't been run for a while. If that has happened that might make the clutch slip like you could be hearing. I would take the belt off and see if you can rotate the kompressor by hand. Note that the clutch part will turn easily as it is disengaged so you need to hold the part that connects to the kompressor internals and turn that. You should be able to turn the kompressor by hand with just a little force. It should feel smooth as silk to turn with no sticky bits etc. My memory says that you can just grab the front plate of the magnetic clutch and that is connected to the kompressor internals so try that before taking the belt off.

If the kompressor is stuck, it could be the gears or could be sticky vanes. Vanes are more likely, but if the oil is down or bad it could be the gears. When/if you talk to Volvo they will likely tell you that they are not a serviceable item and you need a new one at some very large cost. They are in fact serviceable with just normal tools and some detailed care as you disassemble it. If it is stuck vanes I would remove the kompressor from the engine and try washing some sort of mild solvent through the vanes being careful not to get it everywhere else. Maybe even a hot soapy wash. Make sure there in nothing left inside when you put it back on the engine. You don't want to permanently affect the rubber on the vanes so go carefully. Dissembling it is a fair bit of work and means carefully marking absolutely everything you remove in terms of gears and vanes etc so that you can put them back in exactly the original alignment. I can't stress enough how hard it is to put back together if you don't get this right. I took 2 of us around 3 hours extra work to reassemble one because we didn't properly mark the gear and rotor alignments.

Let us know how you get on.
 
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