Sail drive corrosion

[evgen]

Hello,

I am new to this forum, but not new to sailing and bavaria boats.
I am wondering if someone could help me out with saildirve corrosion on my photo...
I noticed this corosion on two different sides of gearbox.

Can someone explain how to prevent this from corroding further more? And if this is dangerous? There is no negative pole on the engine, also zink protectors are regullary changed. Oil in the gear box is slightly milky... or it's not prefectly clean... but there is no water present.

[Impavidus]

Evgen. Hi.
It looks to me like there has been a lot of salt water in the engine bay at some time.
There are a number of ways this could happen and without looking at the engine it is hard to say how this has happened. However, I have seen a blocked heat exchanger result in forcing water past the rubber connector (large rubber elbow on front of engine with 2 jubilee clips)  the result is pressurised seawater gets forced into the engine cooling side of the heat exchanger past the jubilee clips if they are not tight. Hot water, from both the cooling system closed circuit, and salt water from the raw water system cascade/spray all over the engine bay from the header tank overflow and the twist cap on the top of the engine. Again it?s a possibility but I have seen this a couple of times. The telltale signs are rusty components in the engine bay and around the sail-drive gator, rusty water residue in the gator and rusty water or dirty water in the engine header tank, that?s a job to get rid of. I see some of these in your photo.
Oil in the sail drive should be clean, not milky. The latter suggests that you have emulsified oil (oil and water mixed) in the sail drive. That?s not good, it will need to be drained, flushed, and the cause of the water ingress rectified. This could be as simple as the oil drain screw O ring not sealing or more likely a failure of the oil seals in the lower leg output shaft. Sadly I have to say that the water may also have damaged the bearing surfaces and the gears internally. You will need to investigate.
The paint damage you have pointed out is corrosion under the powder coat finish to the sail drive. It does not look terminal but it is best treated. This is can be done with the sail drive out. The sail-drive is an aluminium casting. You will need to clean back to the solid metal. Wash of the oxidisation with a chemical cleaner, then use an aluminium self etch primer and two coats of a reputable smooth finish enamel.
I notice that the jubilee clips on the hoses are rusty at the screw in your photo. This would indicate they are not 316 stainless steel. You must change these (with the valve shut just in case) as if they rust they could fail eventually.
I am sorry to be the profit of doom but you need to look at the sail-drive out of the boat and for the extra expense change the gator gasket at the same time if it shows any signs of cracking or damage. If it older than 6 years its probably best to change it now rather than take the drive out again in two years when your insurance company will probably insist its changed in line with Volvo?s recommendations.
Did you have the boat surveyed when you bought it? A good surveyor should have pointed out all the above to you in his/her report. You may have some redress if they did not.
On the positive side. Removing the sail-drive, gearbox and engine is relatively simple once the boat is out of the water. Parts will cost about £400, depending on the gears and bearings. You will need to have a competent engineer set up the shims that determine the amount of drag (torque) it takes to turn the shafts in the sail drive. Its not difficult but you need to know what your doing. You may get away with a good clean down internally and a protective oil on the rusty bits and on the sail-drive. Dont let oil or paint get on the sail drive gasket. The sail-drive milky oil can only be changed with the boat out.

A long reply, if you need any help or more information drop me a line.
Good luck.
Best regards
Ant.

[Nigel]

Could just be a leaking raw water pump, or hose.

[Salty]

Looking at the picture Evgen has provided and the corrosion on one of the parts above as well as the faint trail of rusty water staining down the side of the green painted engine, I'd say the problem could well be from somewhere more or less above that point such as, for example, where the raw water is injected into the exhaust system, or it could be from a water leak somewhere else that is tracking along something above until dropping off at that point.

[Yngmar]

I think there are two separate issues here. One being the corrosion on the gearbox casing, which may well just be from seawater in the engine bilge (or dripping down from above), but still requires the saildrive to be removed to clean up and repaint properly (it's too close to the diaphragm to go near with a steel brush). Check the date stamped on the diaphragm and if older than 7 years, replace it too (yes, I know they last much longer, but if you're lifting the gearbox and saildrive out it'd be silly not to replace it). Next time you're running the engine, take a peek in there with a flashlight and have a look around for any wet spots or drips from above the corroded spot. Exhaust elbow and impeller pump being typical candidates.

The other issue being the milky oil in the gear box, which means there is water in the lubricant. The most likely cause of this is the bottom shaft seal, which doesn't require the saildrive to be removed, but does required the boat to be out of the water. You might be able to confirm this if you listen closely when unscrewing the (cold) saildrive dipstick. If you hear a faint hiss of air escaping and the level is slowly rising, you're definitely getting water in from the bottom (leave the dipstick and filler cap screwed in tight until you can get her lifted in that case).

[evgen]

Yes, this could be two separate issues, but i am afraid that the corrosion that is visible on the picture is the same corrosion inside.. and that is why the oil is milky... Motor has only 2100 hours. on the motor and below there are no traces of leaking.

[Impavidus]

There is a lot of information to absorb here. Some valid points to. From fellow members.
Agreed, there are a number of issues that you need to look at.

Quick summary?
Why is there emulsified oil in the sail-drive?
1.   Is the O ring drain on the bottom of the leg secure and keeping the water out? Change it they are cheap.
2.   Are the oil seals behind the drive shaft face plate intact? Change them they are cheap.
3.   Has the water in the drive (remember it will separate out somewhat when drive stands for some time) damaged the bearings and or the gears? Simple visual inspection will confirm this.
4.   You will need to flush out the drive and possibly change the gator.
5.   If the boat is out the water you can address the paint and corrosion problems on the sail drive at the same time. It will be cheaper in the long run.


Where has the salt water in the engine bay come from?
1.   Has raw water got in the sealed (fresh water) cooling system and contaminated it (look for cloudy or rusty water in the header tank) if so it will have over pressurised the fresh water system and this will have come out at hi level from the header tank overflow and the engine cap on the top of the heat exchanger.
2.   Volvo engines can leak from the exhaust injection point on the manifold. This normally drips in to the engine bay on the manifold side.
3.   The raw water pump seals can fail. The one on the water side of the pump usually goes first and drips raw water on to the pump drive shaft, spraying drips of water around the engine bay. Easy fix, simply replace the seals its a simple job.
4.   The original Volvo exhaust muffler/mixers are prone to leaking where the stainless steel end caps suffer from crevice corrosion. Detectable  able from the rusty water at the lower end of the muffler. Simple fix change for Vetus fibre glass/plastic unit.
5.   The anti siphon valve can block, it is high up in the raw water feed pipe well above the engine. I have seen this put salt water spray into the engine bay.
6.   Are all the raw water pipes secure and double clipped with quality 316 stainless clips?
7.   I have seen salt water seeping in through the anode fixing points, its a slow seep that leaves a rusty trail.
8.   Check all the exhaust hose and clamps, the do leak if not secure.


If you have any problems PM me and I can talk you through the checking while your on your boat.

Best regards.
Ant

[BillGiles]

It all seems doom and gloom, but can I say that we had milky oil in our sail drive and it was not a huge problem. Firstly, if the oil is not very milky and the oil level has not risen very much then there has not been much water ingress into the leg and gearbox. We monitored ours until we could get a lift out at some future date. But we did avoid long motoring trips in the meanwhile. When lifted out and on the advice of the local Volvo engineers we took out the gear mechanism, bearings etc at the bottom of the leg. The shaft had a few marks and scratches on it where we had had 3 (yes 3) occasions of ropes and nets around the prop. We took the drive shaft which goes to the prop with great trepidation to the Volvo agent. The engineer said 'Oh we can remetal that' and for pounds few the job was done. Reassembly was simple and the problem has not recurred (fingers crossed) in 6 or 7 years. We did put new seals in the bottom of the leg though which probably cost more than the re-metaling (and might have cured the leak anyway - but you never know). (PS, make sure that you keep all the shims and washers in order, if you read the book about setting it all up, you will never do it, use your camera to carefully record the position of everything.)