Volvo Penta MD2020 exhaust elbow blocked

tawhiri

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I removed my exhaust elbow today, because I suspected it was blocked, as the engine would only rev up to 2100 RPM.
My suspisions were confirmed. However the exhaust is also bloked but I do not know how much is normal. see pictures.
How much shold I remove from the exhaust.
elbow (Small).JPG
Elbow
Exhaust before (Small).JPG
Exhaust before cleaning
Exhaust after (Small).JPG
Exhaust after cleaning
What is the best way to remove the carbon. I spent about 2 hours to get to this stage

Thanks A
 

PetiteFleur

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This is exactly what happened to my elbow on my Perkins Perama - it's the same engine. Mine only had a 10mm hole in the middle! The original hole was I believe about 45/50mm diameter BUT when I started to dig out the coke, my screwdriver went straight through the cast iron so had to buy a new elbow, which was a VP item not a Perkins as it was cheaper..... When fitted it was like a new engine, 3600 rpm flat out.
 

Yngmar

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Just did this, although my MD22 elbow was much less clogged (the good old Perkins engineers that designed it made the injector a separate piece and that was where all the clog was). On the elbow I used degreaser spray first to remove any oily residue that would prevent the acid from working, then citric acid (brick cleaner is stronger and may be warranted in your case). Be careful not to pour anything into the exhaust manifold though. Commonly heat is also used to burn the carbon deposits to ash - same reason your engine likes to be run at high RPM once in a while (for an hour or two), it clears the crud out.
 
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I had the same problem with my MD2010 …took the exhaust elbow off and left it soaking in caustic soda solution for a few days. Came out clean as a whistle. No scraping required.
 

aluijten

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Tranona

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Approx how many running hours has it done before it got like that?

_______________________

Hopefully the OP will tell us. However hours run is relatively unimportant. Coking up is caused by the way the engine is used. Short runs at low loads, followed by long periods of inactivity. In other words, typical light leisure yacht auxiliary usage. My old 2030 ran 3500 hours as a charter boat in the Ionian and the elbow has never been removed - nor is there any need other than curiosity.

To avoid, or at least delay the build up of carbon, run the engine on load (around 2200-2400 for a VP 2020 or 2030) using motor only, with regular short runs at over 3000 and always long enough to get fully warm.
 

RichardS

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Hopefully the OP will tell us. However hours run is relatively unimportant. Coking up is caused by the way the engine is used. Short runs at low loads, followed by long periods of inactivity. In other words, typical light leisure yacht auxiliary usage. My old 2030 ran 3500 hours as a charter boat in the Ionian and the elbow has never been removed - nor is there any need other than curiosity.

To avoid, or at least delay the build up of carbon, run the engine on load (around 2200-2400 for a VP 2020 or 2030) using motor only, with regular short runs at over 3000 and always long enough to get fully warm.

A couple of weeks ago I removed my YM30 elbow after 3200 hours, mostly under charter, and it was totally free of build up. There was a layer of loose black soot which wiped off with a cloth to reveal shiny stainless steel underneath. The only problem was a small crack in the outer weld at the manifold end (Tranona has mentioned this issue previously) which was weeping sea water but I've fixed that with epoxy. I reckon that I should get another few years out of it!

But perhaps I should have posted this in Practical Boat Bodger! :)

Richard
 

ChrisCalthrop

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Hi, I have MD2020 with Exhaust Riser - as opposed to the exhaust elbow - in 27ft Sabre 27. Looks like this:
http://www.ropewalkmarine.com/products/40362-3581031.aspx
The water flow blocked... after months of gradually slowing top revs.. I found that it was coked up as described above.. The route of the water pipe within the Riser is not clear so having discovered how to clear it I wanted to post the method:

There are non-removable plugs around the outer band, see image, from manufacture. the main water inlet hole into the exhaust is opposite the plug at the downstream exhaust end - where your rubber exhaust pipe attaches. Use a hook of wire to scrape toward the plug. You can offer the wire up on the outside to get the right length. Mine was so blocked that it looked flat like there was no hole. By blowing in from the water inlet with you mouth you can tell if it's clear or not. I was at sea so could not use my brick acid which was back at home. I don't know if there is another hole/inlet but I did try scraping opposite the next plug up too to feel bare metal.
I also scraped and flushed the box shaped section below the water inlet.
Incidentally the revs are now back up to 2500ish but I have never had these figures of 3500.. Maybe something else is wrong? Perhaps someone can enlighten me.
I only just returned from a Holland trip. Ramsgate to Breskens in one hit and return after a weeks cruising, so am pretty happy it happened outside my own creek at conyer where I could calmly work on it..
I used 1800rpm the whole way there and back as my water hoses around the heat exchanger were swelling at 2100 and I could not figure out why..... now I know..!
Chris
 

Tranona

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Incidentally the revs are now back up to 2500ish but I have never had these figures of 3500.. Maybe something else is wrong? Perhaps someone can enlighten me.
I only just returned from a Holland trip. Ramsgate to Breskens in one hit and return after a weeks cruising, so am pretty happy it happened outside my own creek at conyer where I could calmly work on it..
I used 1800rpm the whole way there and back as my water hoses around the heat exchanger were swelling at 2100 and I could not figure out why..... now I know..!
Chris
Almost certainly you have the wrong propeller. You should be able to achieve 3400rpm. Your coking up problem is almost certainly directly linked to the incorrect choice of propeller as you are overloading the engine leading to inefficient combustion and unburned fuel.

To give you an idea as to how much to big your prop is, 1" of change in pitch or diameter changes revs by approx 250-300 - so you are 3-4" out. Reduction in pitch definite and probably an inch down in diameter. Check the recommended size on the Propcalc programme on www.castlemarine.co.uk
 

ChrisCalthrop

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Almost certainly you have the wrong propeller. You should be able to achieve 3400rpm. Your coking up problem is almost certainly directly linked to the incorrect choice of propeller as you are overloading the engine leading to inefficient combustion and unburned fuel.

To give you an idea as to how much to big your prop is, 1" of change in pitch or diameter changes revs by approx 250-300 - so you are 3-4" out. Reduction in pitch definite and probably an inch down in diameter. Check the recommended size on the Propcalc programme on www.castlemarine.co.uk

Thanks for the suggestion. The boat came with prop and engine installed new in 2002. I don't get much over 2600rpm in neutral though.... Mind you I have never tried / thrashed it since clearing the exhaust elbow riser... I think this Exhaust Riser has a more restrictive effect than an exhaust elbow. The height of the antisyphon tube might be restrictive too.
That propcalc doesn't work on my win7... will have to try on another laptop
 

Tranona

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Thanks for the suggestion. The boat came with prop and engine installed new in 2002. I don't get much over 2600rpm in neutral though.... Mind you I have never tried / thrashed it since clearing the exhaust elbow riser... I think this Exhaust Riser has a more restrictive effect than an exhaust elbow. The height of the antisyphon tube might be restrictive too.
That propcalc doesn't work on my win7... will have to try on another laptop

Something seriously wrong if you cannot get more than 2600 with no load. It should whizz up to 3600 when the governor kicks in. Worth checking the revcounter. The high rise manifold (not sure why you need it?) should not affect the running of the engine, nor does the antisyphon valve. Have a look at the schematics for wet exhaust systems in the Vetus catalogue (p84 in the latest version) to see if you actually need a high rise as from what I have seen of Sabres, don't think your exhaust outlet can be well below the waterline - which is the reason why a high rise might be fitted. Normally a water trap and swan neck loop is sufficient.
 

ChrisCalthrop

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Hi Tranona,

Thanks that is exactly what I think about the Riser.... and height of engine in the Sabre 27 sailing yacht (not American Sabre motor boat in case you thought that) but it was installed as such by whoever installed it in 2002... the riser costs £450 compared to the elbow at £145 so they might have persuaded the previous owner "belt and braces".. he was the type.

I will have another test next time for rev limit.. and will get the riser off for an acid bath too some time soon as it may still be partially blocked.. although the water pumps as well as it ever has...

Either way I don't need 3500rpm.. the boat pushes along well at 1800 and the consumption graph shows that's a great rpm to run at.
 

Tranona

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Hi Tranona,

Thanks that is exactly what I think about the Riser.... and height of engine in the Sabre 27 sailing yacht (not American Sabre motor boat in case you thought that) but it was installed as such by whoever installed it in 2002... the riser costs £450 compared to the elbow at £145 so they might have persuaded the previous owner "belt and braces".. he was the type.

I will have another test next time for rev limit.. and will get the riser off for an acid bath too some time soon as it may still be partially blocked.. although the water pumps as well as it ever has...

Either way I don't need 3500rpm.. the boat pushes along well at 1800 and the consumption graph shows that's a great rpm to run at.

You are still running the engine at too low revs because the prop is too big. It should be sized so that you achieve 3200-3600 at WOT. This will give you a cruising speed at approx 70% or around 2300. Constant running at 1800 is not good for the engine. Fuel consumption is linked directly to power used, not revs. If correctly propped you should reach maximum hull speed at the revs suggested, but of course you rarely need that, although it is good to give it short bursts at near those revs from time to time.
 

tawhiri

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Well she is has just done 1000 hours to date. I did put a Kiwi prop on several years ago, and possibly this is not loading the engine up enough. I will buy a new elbow and fit it next year. The original I will clean and keep as a spear.
Are the Stainless elbow better than the Volvo elbow?
 

aluijten

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Are the Stainless elbow better than the Volvo elbow?
Well for a starter they are stainless.... But I don't expect them to be less susceptible to carbon build-up. On the other side the "clogging-up" debris is a mixture of rust and carbon, so it actually may be a bit better. I've ordered one myself from the USA but as it's still in transit I can't tell.
 

Tranona

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Re: Volvo Penta MD2020 exhaust elbow Riser blocked

Well she is has just done 1000 hours to date. I did put a Kiwi prop on several years ago, and possibly this is not loading the engine up enough. I will buy a new elbow and fit it next year. The original I will clean and keep as a spear.
Are the Stainless elbow better than the Volvo elbow?

If you have a Kiwi you can easily adjust the blades to reduce the pitch. Sounds like they are set at too steep an angle. Although you have done 100 hours - just look at the state of your exhaust! - and you are not getting full revs. Not particularly relevant now, but your set up would not be signed off for warranty if the engine were new. It would have to achieve minimum 3200 at WOT on load.
 
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