2 x TAMD41A - low RPM @ WOT

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bowler

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Hello all,

Long story short...

I have two TAMD41As (1600 hrs, circa 1989 in a Fairline Corniche). Both are low on rpm at WOT and have been since I’ve owned it (9 months). I am struggling to find an engineer to troubleshoot them for me so I would like to investigate what I can myself. I have lost all faith in the one that ‘surveyed’ the engines for me initially.

So far, all filters have been changed by me since I bought it and performance has been the same. Injectors and valve clearance servicing has not carried out as that is beyond my capabilities. Boat is in the water so I can’t verify prop size currently. Original fuel tanks replaced in the 90s.

Both engines start easily and start up initial grey smoke seems to clear when warmed. Tachs have been verified with a phototach at low rpm but not high yet and belts seem tight on both engines. I have also changed both sets of thermostats on both engines as they seemed to be stuck open but now perform as they should.

1) Port revs to 3600 with no smoke and runs a little hotter than SB at WOT. RPM is 4300 in neutral.

2) SB revs to 3200 with some black smoke, not huge amounts. RPM is 4300 in neutral. Aftercooler has been cleaned and appears to have been off at some point in the past as there is a weld repair around the core drain plug hole. Orange seal was also missing and elbow to housing join seems to have black sealant around it and sits a little proud of the original join (if that makes sense). I cleaned the housing and core (which was pretty mucky) but a friend who is a car mechanic said the amount of residue was not uncommon? Initially the SB required a little more throttle to keep up with the port but that has been resolved with the replaced orange seal. Max rpm had been about 3000 prior to this.

Volopaul (I wish he lived nearby) recommends getting someone to measure boost on both engines from 2800 rpm to check condition of turbos but without an engineer that is not something I will be able to do and in the short term is sadly not an option.

I am going to the boat this weekend and was thinking of the following to start with – at least then I can feel like I am making some headway:

1) Checking the SB turbo visually to see if there is anything obvious. Removing the airfilter is no problem but what should I expect opening the exhaust side? Is it straight forward? I can't see any gaskets on the volvo schematics.

2) Checking all connections and clamps/seals between turbo and aftercooler on SB engine – maybe something is amiss there causing boost leak?

3) I have also read there is a ‘smoke limiter’ on the injection pump what could lead to fuel starvation at higher RPM. That could be checked on the port engine that might explain the loss of rpm with no smoke. Is that a straightforward process?

4) Clean SB aftercooler core and housing – couldn’t hurt?

I am not scared of spanners but have only had petrol engines on boats in the past and am no mechanic and certainly do not want to break anything. I am learning about these old diesels as I go.

All tips/wisdom is welcome and thanks in advance.

D.
 
So the engines in neutral are reaching the expected WOT. So not a governor issue.

Are your hull and, most importantly, props clear of fouling ? A few barnacles destroyed the speed of both the props and boat after mid season on my Turbo 36 and same on my Corvette. If the props can't rev freely then the engine cannot develop its power.

Also have the After coolers been checked for being reasonably clean. Dirty after coolers can also destroy the effort of the turbos.
 
Hi
Obvious things to cause this would be;

Hull growth
Growth on props
Props condition
Wrong pitch on props
Fuel starvation with bug or gunge somewhere in the supply
Air filter restriction
Exhaust restriction (check outlets for growth at the flappers on hull)
Injectors blocked and needing cleaned
Tachos not accurate
Trim of boat

Etc etc. Probably nothing you won’t have already imagined. Most likely is a fuel problem I’d say. Easy fix would be the throttle cables having play and not allowing full throttle. Check the mechanism is getting as much movement by remotes. As it is by hand.

Good luck
 
Are both the props the same ?
One may be the correct pitch and size,the other something cheap/ handy bunged on to sell boat.
Although different radius easy to spot, pitch perhaps not so.
Club member recently having exact same problems.
Investigation revealed 2 different props and solved RPM problem but still black smoke from one engine when opening throttles.
Last news was smoke problems have been solved by engine adjustment.
Will find out what was done.
 
Checking that the throttle lever on the pump is reaching full travel would be a logical first move.
If one engine is down it will overload the other
3600 is nearly there so you may be looking at small things or a combination of small things
Black smoke is normally a sign of unburnt fuel often indicates overload excess weight or drag or even bad trim
Where was the boat used river or sea if it were river use and slow speed slightly over propping is not uncommon
A PM to Volvopaul may be one worthy option?
 
I had the same problem with my TAMD63P's last year, clean bum beginning of January, by June she was struggling to get enough engine speed for turbo's to spin, struggled to get on plane, and revs at WOT were down.

A lift and pressure wash, bottom & props cured the problem.
 
Do the propellers turn "easily" by hand, or different on each side ? You could try turning the axles from inside, but easier to try propellers if accessible (on land or not-to-cold water for quick swim).
This will check for engine alignment and cutless bearing pinching.

Edit : If you have sterngear then cutless bearing is of course not an issue, but engine alignment could still be.
 
Last edited:
Hello all,

Thanks for the replies. I feel better already - a problem shared is a problem halved!

To answer the questions:

Hull and props were spotless when she went in in May last year. Performance hasn't changed over time. Plus, it's in fresh water so minimal growth and she was freshly antifouled. It is coming out in a couple of months and I can check sizes properly then.

After cooler on the SB engine (the lazy one) has been cleaned by me last week. The housing has been off at some point in the past and I think it may be compromised at the housing/elbow join as there there is evidence of black sealant around the join and it is 'bulged' a bit. A the drain seal was missing so maybe another before the elbow is also missing. I plan to check that this weekend. Replacing the drain seal go me from 3000 to 3200 rpm. I will take pictures of it this weekend when I am down to show you.

I can't confirm my prop size the but the survey showed then to be in good condition with 'minor chips' on the port side (which revs to 3600). I have been told that they were replaced in the past (she was on a freshwater lake for the last twelve years).

Thanks for the link the the gauge thread. The VDO gauge plumbed straight into the intake looks like an easy job for boost pressure testing.

The shafts turn super easily by hand from inside so I don't think alignment is an issue.

I managed to get hold of a VP engineer on the phone, who of course if booked up to the eye balls for the foreseeable future! He suggested that the port engine is not getting to max rpm as the the other is holding it back, as has been noted above. So in the meantime I think I will focus on the SB engine and check all the connections and clamps at the after cooler and order up the cheaper VDO gauges and fit them for testing. I will also pull of the air filter and make sure the turbo spins freely. I will likely clean the AC on the port engine also as I'm sure it needs it.

Sound good???

D.
 
Hello all,

Gauges ordered. Also, I had look at the aftercooler on Saturday. It looks rough.

20190302_120848.jpg

View attachment 76281

I didn't see any obvious gaps at the join inside when I cleaned it last week but this does not look like it should outside. Certainly doesn't look airtight anyway. Assuming my boost readings are low this will need replacing, or likely I will replace it regardless.

I believe there are newer versions of the housing and top cover and rubber hoses. Is there anything special about the volvo hoses? They are 100 quid each!

D.
 
I was loosing boost in the exact same place!

The gap is meant to be much tighter than that.

On mine the bolt head had snapped off and the casing opens up under boost. Took it to a machine shop (good mate). Extracted the snapped bolts (2 others snapped whilst undoing the others) drilled and tapped, new bolts.....sorted!

Previous owner of yours probably tried to fix with sealant. The new casings have 10 odd bolts now so clearly happens a lot (mine had 4!) Worth a repair effort first IMHO
 
I've just been discussing my steaming issue on the phone with Andy59 of this parish and removing my exhaust elbow. On the Tamd41a there's a solenoid which we assume closes when the engines cold and opens once warmed up. If this stays closed it'll restrict the exhaust gases causing a loss in power.
 
The blackened bit is actually a lip that should be in a reciprocal groove on the housing body.

When correctly together, the join gap is tiny. I would bet there’s a ton of sealant in the groove
 
My phone is playing up.

Yup, sealant in the gap for sure. Will pull it off and see if a repair is possible.

Will check the exhaust flaps also.

Fingers crossed!

D
 
Go to a proper machine shop to have the housing drilled and tapped.

There is little room for error where the bolts go into the housing as you will see!
 
Great info indeed. I am getting excited so I think I will drive down the boat after work tonight and pull this thing off. 2 hr round trip but I might be able to get it sorted before the weekend so I can test it.

Will see how this goes!
 
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