TMD41a again

[boatmike]

Following my previous post I am still trying to calculate the optimum props for my Aquastar 33. Searching for reasons why max RPM is down I investigated further and noted steam from port engine at WOT. Engine temperature OK and plenty of water coming through so I stripped down the exhaust elbow and found the "exhaust brake" (volvos technical term not mine) was sticking shut. This gismo is a solenoid operated butterfly which is supposed to close when starting and running at idle but opens when revs increase. Have only seen this on TMD41a and similar engines. When Volvo originally advertised the TAMD41a they made a big fuss that it met the very stringent emission requirements for use on Lake Constance. I think these abortions were their solution to achieving this on starting and serve no useful purpose otherwise. Interestingly both engines start and run very well although there are no heating elements in the cylinders for starting. The port engine one sticking closed has been causing the elbow to overheat and obviously won't reach full power with an exhaust restriction which is possibly why I can't get more than 3400rpm out of either engine and steam out of the port one. I have now removed all the carbon build up in the elbows water channels and will put everything back together and perform sea trials soon. My question is this however. As I see this gismo as unnecessary for normal starting and running, should I just remove the solenoid actuators from both engines and run with both exhaust brakes permanently open, or does anyone see a useful purpose in retaining them? Do later versions of the TMD on TAMD have them or is it just the early versions?

 

[snowbird30ds]

Mine doesn't have the flaps in, I assume someone has previously changed the exhaust elbows and just left them blanked but there's no obvious spare connectors around, mine does have heater plugs in the inlet manifold.
You will get a good bit of white smoke on start up without the flaps but it clears once warming up, I've heard of people wiring them in the open position due to the sticking problem.
I believe it was just the early versions that had the flaps.
VolvoPaul will be the guru on these.

 

[colhel]

I have the tamd41a and mine are permanently open after I noticed the solenoid wasn't working but also the lever on the elbow had disconnected. When I first locked them I wasn't sure what position was open or closed and the first time I locked them shut and when I opened the throttle I could barely get anything above 2000rpm. After locking them in the correct position, the engine felt transformed for the better.

Tamd41a exhaust solenoid

 

[boatmike]

Yay! Good old Forum! That's what I thought. Colhel's link to another thread seems to confirm what I thought. I think Snowbird has a b or later engine not the a series and they don't have these abortions. While the exhaust elbow on mine was on the workbench I removed all the carbon from the waterways ( 70% blocked) and removed the offending butterfly plate from the spindle. The spindle is still in place but won't shut off the exhaust at all now regardless of its position. Will test it and if it's OK like that I will take the other one off too and examine the waterways to see if that needs decoking too. I will also remove both of the solenoid actuators to avoid any associated problems. Once I get them both running at a reasonable RPM I can do meaningful sea trials. Thanks again folks. Even when you suspect you know what the problem is its good to hear others confirm it.