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Kit_L · 18-12-2021, 21:01

To the Volvo Penta gurus out there:

400 hours on each engine. Start and run like new. Each engine has a supercharger and a turbo. Both engines and legs (stern drives) serviced annually since new, 15 years ago.

The panel that takes control (as in this boat has a flybridge and a lower helm position) has an '=' sign which when pressed and lit, synchronises the engines. When connected this way, both engines accelerate from idle to cruise revolutions (3,250 rpm) smoothly.

But if I have the engines separated (for docking and the like) and try to increase revolutions on both together, the port engine surges, almost as if the EDC is not managing the transition from the supercharger to the turbo (this I believe happens around 2,500 rpm). But, if synchronised, all works as expected. Now, the simply way around this anomaly is to sync the engines once underway, but the engineer in me would like to know what are the likely causes of this behaviour.

Thanks

**tkeithlu** · 24-12-2021, 06:50

Hmmmm. No bright ideas in several days. Let's see if we can narrow it down a bit.

It occurs to me that the RPM control when synchronized and when manually throttled are different. Synchronization matches RPM independent of the fuel-based throttles. The individual throttles pay no attention to RPM, they just feed in more fuel, which can have very irregular effects, such as when the engine RPM reaches the turbo threshold and bunches of compressed air suddenly arrive.

Now, does that difference in the way the two controls work give you enough clues to go looking for the details? I have not answered your question, because I don't know the answer, but here's a route to explore. Good luck on it, and happy holidays.

Kit_L · 24-12-2021, 12:42

tkeithlu: you have THE best sig. comment—that's wisdom, right there!

A question arises from your comment: when two engines are electronically synchronised, I do now know which throttle lever has priority (if in fact one does). All I know is that when the engines are synchronised, and when both throttles are moved forward approximately the same amount, the surging happens on the port engine. I will find a Volvo Penta certified mechanic at some point, and perhaps s/he will be able to answer this question, but in the meantime, that synchronisation button will be my friend! Best wises to you and yours for the festive season.

**tkeithlu** · 25-12-2021, 13:27

Thank you.

You've prompted me to Google engine synchronization and try to understand the process. I've only got one engine, so this has not been a head scratcher for me. It appears that a synchronizer adds throttle until the slave engine matches the master engine RPM.

https://www.glendinningprods.com/products/synchronizer/

So, if you throttle up on your master engine and turn on the synchronizer, it adds fuel to the slave engine until it matches RPM. I'm not sure what would happen if you added too much ordinary throttle to the slave engine, but it might not be pretty.

Given that basic idea, now I want to see one at work. Watching it doing the matching by adjusting the throttle on the slave engine, while you vary the master engine throttle would be informative.

Do you know which engine is dominant in your system? I have a suspicion that if you play with it you'll figure it out.

Kit_L · 07-01-2022, 16:37

I will need to consult a Volvo Penta guru for this, I think; I suspect the starboard engine is the dominant one (this may be a shaky inference, but my thinking is that once the engines are synced, they work as expected, but not when un-synced and it's only port engine that will not power up smoothly)—so your idea that the EDC (the 'synchroniser' in the Volvo system) will be doing the same thing is very plausible, to me at least.

I also make sure the throttle settings are close in the 1,000–2,000 rpm range before engaging the synchronising button, assuming that the system will behave similarly to the Marine Rescue vessel I drive sometimes–on this Yanmar system, the engine revolutions have to be fairly close to each other for it to work (and they do not work below 1,500rpm, either).

NBs · 08-01-2022, 00:09

hi, i have about 10 years kad44 which are almost identical to kad300.

you have a belt supercharger about 1600-2500/2700rmp in use and about 2500- the supercharger stops when the solenoid disconnects, continuing the turbo work up to max rmp.

I can see that your engines solenoid disconnects the supercharger at different times when you have the sync away, hence the power difference.

Another possible reason is the second engine's turbo gives more pressure than the second, but I think more of the first theory.

you have two switching conditions, you do not exceed the rmp value, which drops the supercharge off or you call the VP service to adjust both machine solenoid to work on the same rmp, to my knowledge this is an option to adjust.

you can check this rmp yourself, on each machine with which kompressor to stop spinning and check the rmp difference on the S / B engine, before the VP service guy.

you can see the supercharger (copressor) at the top left of the belt running all the time and the solenoid turns on the compressor and you will notice its best sound change. These superchargers are also switched on with a cold start to give better combustion and less smoke.

https://youtu.be/aFfACpeTTwQ

The KAD is a good and reliable machine if you follow a maintenance schedule, a 5500 hour old boat without much trouble.

NBs

Kit_L · 08-01-2022, 15:53

Thanks NBs. I will definitely watch that YT clip, and report back.

We took the boat for an hour run this morning, and I noticed a half-inch of water in the starboard engine bilge; I tasted it, and definitely salt. I had opened the engine hatch to shut off the sea-water cock, and I noticed slow drips from under the water pump">raw water pump. I got down into the bilge with a strong light, and the drip is coming from the pump shaft, between the impeller and the engine.

As the engine was off at this point, it was only the 6"/150mm head between the raw water strainer and the water pump that was behind the leak. It looks to me that the seal between the impeller and the shaft (assuming there is one) has died, or is worn.

It looks as though the pump is not hard to disconnect, and perhaps replacing the impeller and the seal will not be too difficult. I am looking for a parts diagram now.

NBs · 09-01-2022, 01:23

Hi,

raw water pump normal maintenance to replace the bearing and seal stefa, I recommend take both and do yourself or let a service technician replace these replacement parts, not expensive work, at least here in Finland.

Examine whether the valves are ever adjusted, this work is often neglected, you will see its fuel pipe nut output from the pump and the connection to the spray nozzle if the paint is slightly damaged the pipes are removed (mandatory work when making valve adjustment) and also see the valve cover nuts for the same paint damage if the paint surface is neat, like new, so no maintenance is done.

Also examine the coolant, if neglected, then the translucent expansion tank will be rust stained, if maintenance is done it will only be the wrong plastic color.
exchange interval 2/3 every year.

check the water pump belt wheels for leaking water to cause rust in the belt groove, if there are corrosions grind smooth or replace the new belt wheel

one more point, compressor oil change every 500 hours, you only have +400 but the machines are already old, so I recommend you do this maintenance

Tips video kompressor oil.
https://youtu.be/nAOAifOa5_o

NBs

Kit_L · 09-01-2022, 12:38

Thanks for that fantastically detailed information, NBs. I will be checking all this, definitely. I had seen that YT video already that you linked to. I have my own YT channel, so if I do end up doing any of this maintenance, I will definitely video it. There is not much on KAD-300s on YT.

The coolant, at least, looks brand new. When you wrote, "check the water pump belt wheels for leaking water to cause rust in the belt groove", you mean the fresh water pump, I assume. I will check that for sure.

The engines run like sewing machines, and I also had a diesel mechanic friend listen to the run through the whole rev. range, and all he said was, "sweet!". When the engines are serviced this year, I will definitely get the valve lash checked, as well. Sincere thanks.

Kit_L · 20-01-2022, 18:30

@NBs: I checked with the mechanic (Volvo trained) and he confirmed that the valves have not been adjusted since new. I appreciated his honesty! He said that removing the cover is a bit fiddly because Volvo does not use a gasket; you have to make a new seal using Volvo sealant. He said that it's no problem if I want it done and he has been able to remove and re-use the old gasket and we will have a tube of the new sealant standing by, in case. Yes, we will drain and change the supercharger oil too, as well as servicing the leg and the various coolers. A big service this year, in other words. Thanks for your heads-up.

NBs · 20-01-2022, 22:25

Hi,

I looked at the valve cover gasket and yes it was supplied to order, see link. Did you get an answer to the original problem?

https://www.volvopentashop.com/epc/f...38870_MD4B_001

NBs

Kit_L · 20-01-2022, 22:52

@NBs: that link is for a cylinder head gasket; can you check that?

No answer to original problem, but judicious use of the 'Equalisation' switch means it's no problem at all. And it could even be that we are supposed to use this over 1,500rpm anyway, so might not be a fault. Still thinking on this.

Thank you!