Gearbox Troubles?

[john4647]

My boat is powered by an Isuzu 25 hooked to a PRM80 gearbox. It has done 2000+ hours from new in 2007.

When I last had the boat serviced at the end of April this year, I was surprised to see a charge for Automatic Transmission Fluid on the invoice. On querying this I was told by the servicing engineer that the PRM80 should take ATF. However, in my handbook it states that mineral oil should be used and I had always used that in the past.  

On first use after the service I noticed that the revs/boat speed were fluctuating when the boat was first started (for about 10 minutes running)

On contacting PRM I was told that my gearbox, being 2007 or earlier should not use ATF but the mineral oil as in the handbook.

I informed the servicing engineer who kindly came back to the boat and changed the ATF for mineral oil.

All was well for about 30 or 40 hours running after that (no fluctuations in speed or revs).

However yesterday and the day before on first running the engine from cold the revs refuse to go over 800 and the boat will not drive faster than about 1mph in forward or reverse. This is accompanied by a light screeching noise. After about 10 minutes running the noise stops and the boat behaves normally and I am able to cruise at 1500 revs which is my normal cruising speed. I wonder if anyone can shed light on what my problem may be?

[Tony Brooks]

This makes little sense to me. have you checked the prop for fouling.

 

Low engine speed & power + screeching suggests a seizure but I would not expect that to clear itself.

 

Low speed and power with no screeching normally suggest either air in the fuel or fuel starvation.

 

Try taking the alternator belts off and turning the alternators by hand in case one is seizing when cold. If you have a very large alternator maybe your batteries are flat so the belt is screeching and the alternator load is holding the engine speed down. more info on alternator size required and charging current when the problem shows itself please..

[hider]

Water pump could screech but I doubt it would hold back the engine to this extent.

As the PRM 80 is a dual cone clutch as far as I remember it cannot select forward and reverse at the same time.

Have you asked PRM  what the effect of using ATF in a box intended for engine oil could be?

 

Have you checked that there is nothing wrapped on the prop?

Quote

 

 

[john4647]

Tony, Thanks for the reply.

 

I check the prop every day prior to running. There is and was no fouling issue. The screeching was very apparent, so presumably not a fuel problem.

 

The alternator belts are tight (also a daily check). There are two alternators both Lucas design flatbacks @ 80amps each.

 

Both batteries are at 13.7v. (static).  I have not checked the charging current but batteries are only 12 months old and have never been flat.

 

 

Hider, Thanks for the second reply.

 

PRM say that ATF should not be used on PRM80's prior to 2007. They advise that mineral oil only should be used but declined to say what the consequences might be.

 

I check the prop every day prior to running. There is and was no fouling issue.

Edited July 3, 2019 by john4647

[hider]

If you are convinced that it is the gearbox screeching I would drain the oil and see what is in it. Listen to it with a length of hose close to your ear and the box.

If there is bronze dust in the oil I would suspect that the cone clutch is damaged.

Ensure that the gear linkage is moving the gearbox lever correctly in and out of gear without excessive travel or free play in either direction.

[john4647]

12 hours ago, hider said:

If you are convinced that it is the gearbox screeching I would drain the oil and see what is in it. Listen to it with a length of hose close to your ear and the box.

If there is bronze dust in the oil I would suspect that the cone clutch is damaged.

Ensure that the gear linkage is moving the gearbox lever correctly in and out of gear without excessive travel or free play in either direction.

Thanks again.

I will be back at the boat next week and check both the oil content and gear linkage.

[BruceinSanity]

How much trouble did the “engineer” take to flush all the ATF out? @Tony Brooks, how bad for the box would it be to have a mixture of ATF and mineral oil swilling round?

[john4647]

58 minutes ago, BruceinSanity said:

How much trouble did the “engineer” take to flush all the ATF out? @Tony Brooks, how bad for the box would it be to have a mixture of ATF and mineral oil swilling round?

Hello, I don't know as I was not present at the time.

I don't blame the engineer because if you look at the PRM website, it specifies ATF !

What they don't make clear is that PRM80's manufactured prior to 2007 use mineral oil. This is what my handbook says and what PRM told me on the telephone.

[Tony Brooks]

1 hour ago, BruceinSanity said:

How much trouble did the “engineer” take to flush all the ATF out? @Tony Brooks, how bad for the box would it be to have a mixture of ATF and mineral oil swilling round?

I have no idea but if there was no reaction that caused the oils to thicken I doubt there would be any effect.

 

I was given to understand that the change from engine oil to ATF was brought about by problems with the clutches. If that is correct I have some doubts about what PRM reportedly said  because the problem would have occurred with boxes that were already in service so possibly made before the date given. Also the manual for my Spanish Built ZF mechanical box said it uses engine oil but when I bought the boat out of the hire fleet I found that it had ATF in it. Having consulted the Bukh inland agent about I continued to use ATF, which I think may have better lubricating properties for gearboxes, for the last 19 years without problem. A further advantage is the manual says the box should not have multi-grade engine oil in it so if I went back to engine oil there would be plenty of room for confusion when the family takes the boat out.

 

Th OP seems a fixated with the noise and loss of power being caused by the gearbox. I still think a high charging current might be the problem, especially if he has something like a Sterling A to B or a VSR fitted that parallels the alternators. I would love to know the charging current when the problem occurs.

 

 

 

[john4647]

2 minutes ago, Tony Brooks said:

 

Th OP seems a fixated with the noise and loss of power being caused by the gearbox. I still think a high charging current might be the problem, especially if he has something like a Sterling A to B or a VSR fitted that parallels the alternators. I would love to know the charging current when the problem occurs.

 

Hello Tony, nothing fancy about the Alternator setup. No sterling Devices or anything else.  Just a 2 x 80amp, with one alternator charging the Engine battery and the other charging the Leisure batteries (2 of these).

I don't rule anything out but I do suspect the gearbox as I know the addition of the ATF did originally cause a problem which was apparently cured when it was replaced with mineral oil.

 

[Tony Brooks]

 

From your post I don't think that statement holds water. I agree that something made the engine lose power around the time the gearbox oil was changed. I also know that changing the oil again seemed to cure the problem but that is far from proving the problem ever was the gearbox. Coincidences can and do happen. It could just as  easily be a fuel filter problem that was presumably changed at the same time as the original oil change or even a fuel tap left partially closed.

 

I have given you another scenario that is known to produce an apparent loss of power and a squealing noise.

 

This is why it is vital that when you get back to the boat you use Hinder's listening tube or a listening stick/long screwdriver to try to isolate where the sound is coming from.

 

In fact fuel starvation may prevent the engine revving enough on start up to energise the alternator and screeching sound could be the warning buzzer. This is just another known possibility, hence my asking for the charging current when the problem occurs. 80 amps plus and the engine will not rev until it has started dropping indicates excess alternator load. Zero amps means the alternator has not energised.

 

I simply can not see how the wrong oil in the box of an inland boat can load the engine sufficiently to hold the revs down and them magically cure itself. If the box were seizing up I would expect it to get worse, not better. Even if a   cone clutch is breaking up I would except ether an inability to get neutral or the loss of power and noise to keep getting worse.

 

I inadvertently ran my mechanical gearbox for several ours without oil and it got noisy and stiff to  engage but it did not screech or load the engine.

 

Anyway I await the outcome with interest.

 

 

[john4647]

Hello Tony,

 

Understood. I am back at the boat next week and will take a piece of tube with me and use as instructed. I also have a clamp on ammeter so I can check the individual charging currents.

Will report back then but in the meantime many thanks for taking an interest.