TAMD41a woes

[boatmike]

I have done a lot of work on my two TMD41a engines which are now fitted with new ZF gearboxes, shafts and props. I have also had both turbos professionally reconditioned, cleaned out both fuel tanks and fitted new filters. The Stbd engine runs fine and gets up to 3600RPM with 1 bar positive manifold pressure. The Port engine is down on power and only gets up to 3200RPM with about 0.7 bar positive manifold pressure. It also blows quite a significant amount of oil out of the crankcase breather. I am assuming that having got everything else right that the extra manifold pressure and higher revs has now exposed a more fundamental problem with the engine and thought at first that it must be busted piston rings. However it dawned on me that a head gasket failure could be the cause also blowing between a cylinder and an oil passage. In fact possibly more likely as there is a lot of oil blowing out indicating a crankcase pressure that is quite high when running at high revs when the turbo cuts in but not at less than 2000RPM . Does anyone on the forum have experience of a similar failure with this series of engine?? Looking at the workshop manual the oil passages are very near the cylinder and I am wondering if its a common problem? ps They are TMD41a not TAMD41a but I can't seem to edit title.

 

[RobWales]

Mike, a long shot but check the 3rd post on this thread.....

http://www.marineengine.com/boat-fo...1A-OIL-LEAKING-FROM-CRANKCASE-BREATHER-FILTER

 

[kashurst]

try the simple blow by test - undo the oil filler cap and leave it on the engine. Then run the engine. As revs increase any significant blow by gas will blow the cap up. Try both engines to see if they differ. Assuming the rebuilt turbo is OK you could just have an air leak.

 

[boatmike]

That's a thought Rob thanks. It wouldn't explain why the engine is down on power but the oil pressure is down on this engine too so an oil leak in the rocker oil feed pipe might explain this too.....

 

[boatmike]

Don't really understand what you mean by an "air leak". Where from? I am obviously getting excessive crankcase pressure to blow out of the breather. It can only be coming from a head gasket leak into the oil galleries or past the pistons cant it? Where else?

 

[[2068]]

A compression test would be revealing.
I'd have thought a blown head gasket would be more likely to pressurize coolant and cause an overheat.

 

[boatmike]

A compression test would be revealing.
I'd have thought a blown head gasket would be more likely to pressurize coolant and cause an overheat.

Yes I agree. If the gasket failed between the water jacket and cylinder I would see oil in water and the tell tale evidence of slimy emulsion in the rocker boxes. If it failed between the cylinder and the rocker box oil drain galleries though it could cause the problem? Dunno. A compression test will almost certainly reveal if the problem is related to one or more cylinders but wont tell me what the problem is until I strip it down. I may be clutching at straws here and hoping that I can find the problem in the top end of the engine. I still think it is very likely piston rings or worse which means lifting the whole damn engine to get to the sump which I don't relish.

 

[snowbird30ds]

If the bores are a bit glazed you will get blow-by around the rings causing crankcase pressure.

 

[RobWales]

From memory of when I used to run a pair of AD41's in an SS 34 a few years ago......
Am I correct in thinking/remembering that there is a blow off valve of some sort to the rear of these lumps quite near to where the breather cannisters are situated?
Mine dumped oil into the bilges on one occasion due to high crank case pressure which caused thses valves to open (sure I'm not dreaming this btw) anyway I was advised to replace the crankcase breather filters because if these are blocked then pressure will build causing said problems..........
I did and hey presto....never happened again.

 

[boatmike]

From memory of when I used to run a pair of AD41's in an SS 34 a few years ago......
Am I correct in thinking/remembering that there is a blow off valve of some sort to the rear of these lumps quite near to where the breather cannisters are situated?
Mine dumped oil into the bilges on one occasion due to high crank case pressure which caused thses valves to open (sure I'm not dreaming this btw) anyway I was advised to replace the crankcase breather filters because if these are blocked then pressure will build causing said problems..........
I did and hey presto....never happened again.

That is a very useful contribution Rob. I assumed the oil was coming though the filter. Now I see that there is indeed a pressure relief valve just forward of the filter that may well be where the oil came from. I must admit the crankcase breather filter is the only one I have not replaced. If it turns out it is that simple I owe you one! I will check to see if the filter is blocked and try that first..... Thanks!

 

[RobWales]

They get forgotten at the back there Mike, I do remember the oem units being very expensive.....hence picked up some copies from Keypart, hope it proves to be the problem....
PS mine only ever dumped the oil at high revs...on dirty breathers...good luck.

 

[boatmike]

They get forgotten at the back there Mike, I do remember the oem units being very expensive.....hence picked up some copies from Keypart, hope it proves to be the problem....
PS mine only ever dumped the oil at high revs...on dirty breathers...good luck.

Again you are correct Rob. £45 EACH! from Volvo. Half that from keypart and elsewhere. They should arrive today and I can get out on the boat again early next week to trial them. I am now trying to decide if high crankcase pressure would cause performance to suffer and explain why this engine is down on power compared to the other. It is of course still possible that I have other problems as well but changing one thing at a time will tell.
Thanks again
Mike

 

[oldgit]

Again you are correct Rob. £45 EACH! from Volvo. Half that from keypart and elsewhere.I
Mike

Those crankcase filters are available from ordinary motor factors.
From memory they were an American import bearing a well known name and around half the Volvo price. Pre BREXIT.

 

[boatmike]

Well having now fitted new crankcase filters I am now clear that this is not the problem. I have been trying to come to the conclusion that it was not blowing past the pistons but I guess it is now the main suspect. I just hope its rings alone and the pistons are not damaged as they are out of production....... Only one way to find out I guess. Oh well, Should keep me out of mischief this winter :-(

 

[RobWales]

Well having now fitted new crankcase filters I am now clear that this is not the problem. I have been trying to come to the conclusion that it was not blowing past the pistons but I guess it is now the main suspect. I just hope its rings alone and the pistons are not damaged as they are out of production....... Only one way to find out I guess. Oh well, Should keep me out of mischief this winter :-(

Oh bugger!

 

[boatmike]

Just found that I can get complete piston, liner and ring set still at £385 per pot. (plus VAT of course). Worth stripping the booger down then I suppose. If I am lucky it will be just new rings. I can then evaluate cost and see if its worth doing.......... Boat comes out in December so I will have fun times this winter! Grrrrr..........

 

[RobWales]

Just found that I can get complete piston, liner and ring set still at £385 per pot. (plus VAT of course). Worth stripping the booger down then I suppose. If I am lucky it will be just new rings. I can then evaluate cost and see if its worth doing.......... Boat comes out in December so I will have fun times this winter! Grrrrr..........

Surely you're going to run a compression test on each cyl before proceeding? might just be one bad pot.........

 

[snowbird30ds]

If it's a glaze up then one of the tricks is to feed a spoonful of vim into the intake with a bit of load on the engine, I've seen it done on old aero engines to good effect and the compression comes back up too, if the rings need changing anyway it's worth a shot.
I'd be tempted to disconnect the turbo air pipe and feed it direct though not through the turbo.
It scuffs the bores and rings and lets them bed in again.

 

[[2068]]

If it's a glaze up then one of the tricks is to feed a spoonful of vim into the intake with a bit of load on the engine, I've seen it done on old aero engines to good effect and the compression comes back up too, if the rings need changing anyway it's worth a shot.
I'd be tempted to disconnect the turbo air pipe and feed it direct though not through the turbo.
It scuffs the bores and rings and lets them bed in again.

This is not a good idea on a reasonably modern turbo diesel. You could turn one duff set of rings into knackered bearings and a new turbo.
Compression test followed by strip down if one or more cylinders low is the way forwards.

 

[boatmike]

A compression test may well show which cylinders are causing the problem but if I am going to strip down the engine anyway I am certainly going to pull all the pistons to inspect condition and measure wear. I have never seen an engine (particularly a diesel) where one cylinder has broken or siezed rings and the rest are in perfect condition. It is false economy to just recondition one pot and leave the rest. Even if they are not the cause of the problem they will get the same attention.
As for stuffing it full of abrasive........... Er No..........