KAD44 / 290 Exhaust Bellow

[Dazzajohm]

Here's an interesting one I wonder whether anyone has come across.

I've had problems with the exhaust bellow bursting. Not long after i got the boat this time last year we heard this pop at cruising speed but couldn't work out what it was. Anyway there were some other issues with the boat and it was lifted for work under warranty and we found the burst bellow. Obviously this was replaced then when the boat was launched, on the first sea trial, as soon as she was opened up we heard the pop again.

Anyway I had her taken out a few weeks ago for the annual maintenance and as suspected the bellow is split again. Needess to say now the boat is out of warranty I'm using another engineer who is well spoken about in the marina who suspected the exhaust outlet in the 290 must be blocked. He sent the leg off to a specialist in Brighton I think to get it thoroughly checked over and they have said they cant find anything wrong with it least of all what could be causing the exhaust bellow to burst like that.

Anyone had / seen anything similar?

Cheers

 

[scottie]

Just a thought but was the 290 normally used with the 44?

 

[Dazzajohm]

Just a thought but was the 290 normally used with the 44?

I had thought of that too and after some Googling have found other boats with that combo on.

 

[BruceK]

bursting or coming off? I have no direct experience but I believe from conversation there is a marked front and rear to the pipe and this can also be absent with aftermarket pipes. Get it wrong and they are prone to coming off. Sounds plausable as I had a similar issue with a mercruiser exhaust. Worth confirming if this is the case, anyone?

 

[jimmy_the_builder]

I had thought of that too and after some Googling have found other boats with that combo on.

My Targa 37 had KAD44's with DP-E drives.

 

[Dazzajohm]

bursting or coming off? I have no direct experience but I believe from conversation there is a marked front and rear to the pipe and this can also be absent with aftermarket pipes. Get it wrong and they are prone to coming off. Sounds plausable as I had a similar issue with a mercruiser exhaust. Worth confirming if this is the case, anyone?

Nope, bursting...

Like there is some kind of blockage and when I open up the throttle the exhaust gas cant escape.

Have tried to attach a photo

 

[nicho]

My Targa 37 had KAD44's with DP-E drives.

Same here.

 

[BruceK]

Nope, bursting...

Like there is some kind of blockage and when I open up the throttle the exhaust gas cant escape.

Have tried to attach a photoView attachment 69192

The term 290 leg seems to be used to describe a plethora of legs including the DP C through E for clarification

Do your drives look like this


or this

 

[CLB]

I would imagine the latter. They will be DP-E I guess.

 

[Dazzajohm]

The term 290 leg seems to be used to describe a plethora of legs including the DP C through E for clarification

Do your drives look like this
View attachment 69193

or this

View attachment 69194

Mine is like the first picture.

 

[BruceK]

AQ 290 DP. That does seem an odd pairing. Even my KAD42's have DP-D drive.

 

[Dazzajohm]

AQ 290 DP. That does seem an odd pairing. Even my KAD42's have DP-D drive.

Odd pairing? In what’s way just so I understand the concern?

Does that mean the leg and engine are incompatible though?

 

[BruceK]

Truthfully I don't know about their compatibility but the drives predate your engines by a good few years. Was your boat re-engined?

 

[CLB]

Mine is like the first picture.

I may be wrong, but they look like early 290 drives and, as far as I know, were never mated to kad44 from the factory. Someone may correct me if I'm wrong, but if that is the case, your problem could be bigger than you thought.

 

[Dazzajohm]

Truthfully I don't know about their compatibility but the drives predate your engines by a good few years. Was your boat re-engined?

Yes - I've got a Princess 266 which orginally came with twin petrols but was re-engined with a single diesel

 

[BruceK]

Well the gear reduction will be a problem for you for starters. The reduction ratio's for the AQ290 DP will be limited to either 1.95:1 or 2.30:1 as standard (unless that was also fettled with) whereas the KAD 44 reduction was 1.68:1 . You may absolve this issue on a revs side by having finer pitched props on but the question is whether your drive can absorb the torque of a diesel in the long run.

 

[scottie]

Well the gear reduction will be a problem for you for starters. The reduction ratio's for the AQ290 DP will be limited to either 1.95:1 or 2.30:1 as standard (unless that was also fettled with) whereas the KAD 44 reduction was 1.68:1 . You may absolve this issue on a revs side by having finer pitched props on but the question is whether your drive can absorb the torque of a diesel in the long run.

That’s the easy bit you can change the lower unit thus changing the ratio but still leaves the torque issue
You could also change the exhaust there is /was a blanking kit and adapter to have a separate exhaust which would avoid back pressure issues

 

[zt260]

As far as I am aware the kad44 was mated with the dpe drive( mine was)
So if yours is not a dpe drive then the pairing is wrong

Regds ash

 

[Dazzajohm]

Well the gear reduction will be a problem for you for starters. The reduction ratio's for the AQ290 DP will be limited to either 1.95:1 or 2.30:1 as standard (unless that was also fettled with) whereas the KAD 44 reduction was 1.68:1 . You may absolve this issue on a revs side by having finer pitched props on but the question is whether your drive can absorb the torque of a diesel in the long run.

Ok, much to my dismay this seems to make sense, as I was told to boat should achieve 30knts, but in reality I've struggled to achieve 15knts - 18knts at cruising RPM. Part of me sending the drive off to a specialist is to get the ratio checked as even trying different props performance doesn't seem to improve.

 

[BruceK]

That’s the easy bit you can change the lower unit thus changing the ratio but still leaves the torque issue
You could also change the exhaust there is /was a blanking kit and adapter to have a separate exhaust which would avoid back pressure issues

Yes agreed ...

(unless that was also fettled with)

I know the Americans have a mod to change their Mercruiser thru-prop to a seperate underwater exhaust and they favour further mods for thru-hull exhausts but not seen anything like that for Penta, The difference here is by venting out the anti cavitation plate, once on the plane there is no back pressure because it's already out the water.