Kad32 twins - one down on boost - please help

[Bavnavkad]

Hi guys, wondering if you can help me as I have a bit of an issue.

I have twin kad32 done 640 hours each, both engines not long serviced.

The issue that's arisen over last few outings is this:

Hi guys wondering if any one can shed any light on an issue that I'm having. Or if any of you have solved it before now, basically it's this.

Last couple of trips, I have noticed that the starboard engine is low on rpm, I.E when both throttles are at cruise of 3000rpm everything is sweet.

If I advance the affected engines throttle to WOT, it increases only around 100rpm, but if I leave that throttle WOT, and advance the good engines throttle. The good engine advances to 3600 perfectly and in turn slowly brings up the rpm of the starboard engine to nearly 3450, if I then only back of to 3000rpm on the good engine, the affected engine also drops back to circa 3100rpm.

So no actual issue until WOT. Otherwise everything else is performing as it should. Planes perfect, no noises nothing.

So coming back to dock, stripped down the air side to check turbo shaft, but cast elbow screw snapped so it wouldn't come off with out removal of turbo. So I've managed to put it back as it was whilst checking all air joints from air box and supercharger to turbo, all appears OK.

However doing an idle check let's me know both super charges work as expected and cut off at the right time. Both engines with NO load rev to 4000rpm as they should, however on the affected engine. After the supercharger has cut off, I get a small cloud of black smoke.

Both intercooler have recently been removed and serviced.

Filters and belts oils etc all brand new genuine.

Good engine had new turbo 80hrs ago ( 1 year ) wonder if its now time for other side

Aim to take it out this week with boost guages, but that won't tell me what the issue is exactly will it? I already think I'm down on boost as both engines always were perfect to 3600 @ 35kt I'm now cruising at 3k @ 28kt

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So today I took the boat out for a boost test with calibrated pressure guages and nipples to test each engine and my results are as follows.

Basically this is the threshold I should be getting from both engines boost according to workshop manual.

I made a nipple and had a professionals guage and calibrated. So. This is the minimum requirement for each engine. Under load

Supercharger at 2000rpm ( no turbo ) 10.1psi

2500rpm - 25.1psi
3800rpm - 23.9 psi


Bearing in mind my starboard won't get to 3800 I had to just compare engines boost.

It's as follows

Starboard engine ( suspected down on boost )

Supercharger at 2000rpm I got 17psi ...

2500rpm I got 18psi
3100rpm I got 13psi
No black smoke under load

Port engine ( with new turbo from GA 2021 )

Supercharger at 2000rpm 20psi
Turbo
2500rpm - 25psi ( bang on )
3000rpm 21psi but then once on plane dropped to 14 consistent...

So I'm not really any further forward other than I am certain boost is down on stbd.

However Supercharger should only give 10.1psi however more I can't see being an issue?

Any input from you guys is really appreciated as I'm at a bit of a loss now as to where the issue may lie.

Thanks in advance

 

[kashurst]

looks like your starboard turbo is tired. The port engine is trying to compensate but at higher rpm the electronic ecu will not allow overfueling/black smoke conditions.
Check for airleaks but I think its turbo time.

 

[Bavnavkad]

Thanks kashurst for your swift reply, I really appreciate it

The engine is fully mechanical bar sensors, it's the kad32. Black smoke at no load idle revving but after supercharger cuts off, but minimal, port does not do this.

Then no black smoke under load but down on power. Its weird and frustrating.

What I don't want to do is replace turbo for 1500 and not resolve it, understandably.

Do you think 17 and 20psi @ 2000rpm from super charger is an issue when the book stated 10.1psi

 

[Momac]

.....the electronic ecu......

I may be wrong but think the kad32 does not have one of those.

 

[Bavnavkad]

You are right, no ecu, mechanical engines. Just some sensors

 

[kashurst]

apologies 32 is mechanical but it does have smoke limiter on injection pump. I still thinkk you have a tired turbo and the other engine is struggling to compensate.

 

[Momac]

Props could be damaged or otherwise mis matched leaving one engine to do more work than the other. Could the props be swapped between engines to test this? I have changed duo props with the boat in the water.

If the turbo is worn in my limited experience, does this not result in oil bypassing the turbo and being ejected via the inter cooler? Possibly not but just a suggestion.

 

[Bavnavkad]

apologies 32 is mechanical but it does have smoke limiter on injection pump. I still thinkk you have a tired turbo and the other engine is struggling to compensate.

Yes, it does have a smoke limiter on the pump, 100% with a tube to manifold. I kind of agree with that turbo issue. Hmmm

 

[Bavnavkad]

Props could be damaged or otherwise mis matched leaving one engine to do more work than the other. Could the props be swapped between engines to test this? I have changed duo props with the boat in the water.

If the turbo is worn in my limited experience, does this not result in oil bypassing the turbo and being ejected via the inter cooler? Possibly not but just a suggestion.

Props all good, last owner forgot thrust washers. So guess what, had to fully rebuild both drives and replace 4 props, so they are genuine j8 volvo props, and 2 months old, prior to this issue sort of a month ago, both engines were OK.


I agree with the oil thing, hardly any oil in the intercoolers, just a very very light mist that the manual states is normal as the oil seal is of the piston ring type, so at low rpm will bypass a mist of oil 100% normal.

However I understand a really bad turbo could also dump oil, but heard even without oil loss they can fail
. I'm so lost

 

[BruceK]

However Supercharger should only give 10.1psi however more I can't see being an issue?

Your SC helps spools up the turbo so figures you are seeing could be SC + turbo boost combined. To me it sounds like turbo bearings are gone.

 

[Bavnavkad]

Your SC helps spools up the turbo so figures you are seeing could be SC + turbo boost combined. To me it sounds like turbo bearings are gone.

Thanks for your reply, I feel lots of people are pointing at turbo, so I think that's the route I have to go down, however at first inspection today. I notices the smallest amount of oil mist around the seal between turbo compressor housing and the pipe to aftercooler, so I am wondering if that could cause a notable drop in performance, the oil mist was extremely small, but tells air can escape there. But equally there is a drain hole in the intercooler, would this have any effect do you think?

 

[gery w]

What rpm can both engines achieve max in neutral? Should be around 4250 rpm.

Check for boost leaks in the pipework between the turbo and the inlet manifold (soapy water solution in a spray bottle) is best for this.

Remove exhaust elbow from turbo and inspect the exhaust housing for corrosion and excessive clearance between it and the turbo blades.

 

[Bavnavkad]

What rpm can both engines achieve max in neutral? Should be around 4250 rpm.

Check for boost leaks in the pipework between the turbo and the inlet manifold (soapy water solution in a spray bottle) is best for this.

Remove exhaust elbow from turbo and inspect the exhaust housing for corrosion and excessive clearance between it and the turbo blades.

Thanks for your reply, your input is much appreciated.

both engines in neutral rev to around 4050 4100rpm , both very equal in revving. However in neutral but not underload at high rpm there was small amounts of black smoke emitting from exhaust, however can't see this underway with load. Could be because it's minor blacking?

Yep, next route will be to test the air inlet to manifold, is this possible to do in neutral with superchargers engaged? As it's going to be dangerous to do this underway I feel.

In regard to elbow, do I need to drain down coolant to inspect this? Or can I simply undo the clamp and then the elbow?

 

[david_bagshaw]

critters growing on the low output engines props? dirt in fuelfilters of that engine?

 

[gery w]

Thanks for your reply, your input is much appreciated.

both engines in neutral rev to around 4050 4100rpm , both very equal in revving. However in neutral but not underload at high rpm there was small amounts of black smoke emitting from exhaust, however can't see this underway with load. Could be because it's minor blacking?

Yep, next route will be to test the air inlet to manifold, is this possible to do in neutral with superchargers engaged? As it's going to be dangerous to do this underway I feel.

In regard to elbow, do I need to drain down coolant to inspect this? Or can I simply undo the clamp and then the elbow?

You may be able to check this on the supercharger, check the flap in the y peice and also where the hard elbow connects to the turbo as there is a o-ring in there.
No need to drain coolant to remove exhaust elbow as it is raw water which is injected at that point.

 

[Bavnavkad]

critters growing on the low output engines props? dirt in fuelfilters of that engine?

Thanks for reply, had brand new genuine j8 props as they were fitted with from new

 

[Bavnavkad]

You may be able to check this on the supercharger, check the flap in the y peice and also where the hard elbow connects to the turbo as there is a o-ring in there.
No need to drain coolant to remove exhaust elbow as it is raw water which is injected at that point.

Thanks for your reply, I think 10.psi should be enough to show any leaks right. Once it's engaged I know that it's making boost so just a case if 10psi is enough to cause the leak.

The y with the flap has been removed and checked and all is OK, and the inlet elbow on the turbo has a broken screw so I can't get it off, tried to remove compressor housing but wasn't able to remove all the bolts. But would a leak that side cause any issue with turbo? I would assume it would affect the supercharger boost, but I could be wrong. Assumed the leak would be after the compressed air

 

[QBhoy]

Hi. On the affected engine…does the supercharger come back in at all, after it should have or has cut out ? I’d think it’s more than likely a turbo issue…and or elbow.

 

[Bavnavkad]

Hi. On the affected engine…does the supercharger come back in at all, after it should have or has cut out ? I’d think it’s more than likely a turbo issue…and or elbow.

Tha ks for your reply.

The supercharger cuts off around 2500 2600 rpm, then it stays off unless I bring back down the revs to that range. I suppose it kicks in to stop boat just literally dropping of the plane.

Sounds like turbo to you?

 

[QBhoy]

Tha ks for your reply.

The supercharger cuts off around 2500 2600 rpm, then it stays off unless I bring back down the revs to that range. I suppose it kicks in to stop boat just literally dropping of the plane.

Sounds like turbo to you?

I’d say it probably is. I have not long replaced a turbo and elbow on a kad32 single engine boat. Was lacking a little power and supercharger having to help more than it should. Your issue might be getting disguised a little more, having the other engine to help it along. Sent the turbo away to AET. Great job. Back on and the boat is running tremendously now. I’d take the turbo off and send it away before it completely goes and damages the casing too. Much cheaper to refurb just the turbine cartridge instead of the whole thing further down the line.