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Nov 04, 2023

How to replace Volvo Penta shaft seals: A step

An uncharacteristic dripping of seawater into his Beneteau's usually dry bilges

An uncharacteristic dripping of seawater into his Beneteau's usually dry bilges heralds an unscheduled haul-out for Stu Davies…

As the launch cradle dropped us in, Bruce called out his usual, "All OK?" before disconnecting us from the slings. We’d splashed our Beneteau 381 after a lift and antifoul at Bruce's yard in Faro this summer and I’d performed my usual dash below to check for any leaks and to burp the Volvo-type seal.

I noticed the shaft seal didn't immediately stop dripping when I released it as it usually does, but as it did stop dripping after a few seconds it wasn't a major concern. I made a mental note to grease it again and to keep an eye on it.

My engine is a Volvo Penta MD22 with an MSE2 gearbox and a shaft drive through a Volvo Penta dripless seal and a rubber cutless bearing – a system is commonly used on Beneteaus and other French boats.

The dripless seal is sold by Volvo Penta but is used on other boats for other engine combinations. There are also ‘pattern’ versions made and sold by other manufacturers.

Article continues below…

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Changing the shaft seal is an easy job, but make double sure you have all the necessary tools and parts before commencing and allow half a day if it's the first time you’ve done it

Two weeks later, I did a check of the seal, more by accident really, and was horrified to see it dripping. My bilges do dust rather than moisture so this was not a good sign.

I got on the phone to Bruce's Yard to see if he could lift us and then got on to Sopremar in Portimão to see if they had a new one in stock.

The answer was yes on both counts and Bruce could lift us immediately. Off we set, it was only a couple of miles down to the slings ready for work to commence.

At this point I must confess that I’d used a Volvo rubber shaft seal clone previously. There are a few of them on offer now, quite a bit cheaper and supposed to be just as good.

The Volvo Penta one is about £90, the clone £70, but the Volvo one in Portugal cost me €150, and with the cost of the lift… Ouch!

The Volvo seal is a rubber moulding which consists of what looks like a rubber cutless bearing and two lip seals.

The ‘bearing’ supports the shaft at the inboard end which also has a small water feed to it from a through hull fitting. Some manufacturers use part of the exhaust cooling water discharge to lube them.

To change the seal is quite easy. Four prop shaft flange bolts are removed to separate the flanges at the gearbox. The flange is held to the shaft by a nut and a feather keyed taper.

1. Holding the flange boss with Stilsons I undid the flange Allen nuts. The shaft was then slid back to allow access to the central nut (24mm) which is inside the prop shaft flange and then once that was undone a two legged puller was used to pull off the flange.

2. I used two 8mm bolts through two of the flange fixing bolt holes and the puller after loosening the 24mm nut and I left it in place to centre the puller screw and to stop the flange popping off.

Note that the new lip seal is noticeably smaller than the bearing so it is a close fit on the shaft.

4. This protects the lip seals in the new seal while it is slid along the shaft and mounted. The clamp was put on the seal loosely before mounting.

5. With the new seal on the shaft, the split protector was removed and the two 6mm Allen bolts with nuts tightened to clamp the seal to the fibreglass hull tube making sure that it is centred on the tube and shaft. The flange was then fitted to the taper on the shaft, making sure the feather key was orientated correctly so the flange could slide all the way onto the taper.

6. I put some lithium grease on the nut threads and load washer in an attempt to prevent stainless steel galling over time, and then used some Stilsons to again hold the boss of the flange while I ‘leaned’ on my breaker bar to tighten the nut.

Tighten the puller up and then give the boss of the flange a sharp tap with a hammer to shock the taper into releasing. Make sure you don't lose the feather key after removing the flange and also mark it to make sure it goes back in the same orientation.

They can have slightly different dimensions and it's possible for the key to stop the taper on the flange from mating correctly if it's put back differently.

The seal is held onto a fibreglass tube bonded to the hull, by stainless bolts through a clamp, which are undone and then the seal is slid off the shaft. The new one came with a plastic split protector which was inserted into the new seal with lots of silicone grease on it.

While the boat was out of the water I decided to change the exterior cutless bearing as well. This had felt good when I’d inspected it before launching a month previously but there was about 1mm of lift in it now. Luckily I had a spare on board.

The cutless bearings on Beneteaus are simple fluted rubber ones and are not difficult to change, but the prop and rope cutter have to be removed which can sometimes prove difficult.

Once you’ve got these off two plastic 6mm screws locate and hold the bearing in position.

1. The propeller is held on by a 20mm thread nut, locked by a stainless steel tab washer, on a feather key taper. To get it off I have a serious three legged puller.

2. First of all the rope cutter was loosened, this is just an 8mm Allen grub screw. A chisel and screwdriver was used to pry down the tab on the stainless lock washer and then a large adjustable spanner was used to undo the right hand thread prop nut. I usually use a piece of 2×4 wood to wedge the prop against the skeg – my wife Laura is not afraid to hold this for me! Then a 2lb hammer came in to play to help the spanner undo the nut. I left the nut loose on the shaft to stop the prop falling on our toes when it jumped off the taper.

3. The three legged puller was fitted to the back of the prop and was tightened fairly hard, then the end of the jack screw on the puller was hit hard with the hammer, the shock was sufficient to break the grip of the taper and the prop came loose.

4. The prop and rope cutter were then slid off and then the cutless bearing could be eased out after undoing the two 6mm plastic screws. The bearing is rubber and came out easily.I had an issue previously where a rope went around the prop and forced the seal well up the glassfibre tube. to extricate it I drilled a couple of holes in the rubber and threaded some long self-tapping screws into it and was then able to grip the screw heads and pull it out. I mention this only so that if readers do have difficulty getting the seal out then this is one way to do it.

5. The new bearing was slathered with Volvo blue silicone grease and fitted back with the plastic locating screws.

6. Calcium deposits could be seen on the old bearing and I suspect that either prop fouling that was cleaned off on the previous lift or antifoul had got up the shaft housing and was maybe something to do with the premature wear.

7. So while I had the gearbox coupling off to change the Volvo shaft seal inside, I pulled the shaft out as far as I could and cleaned off quite a lot of calcium deposits.

8. I ensured the taper and feather key were clean and that the prop slid all the way home on to the taper before fitting the rope cutter loosely and then refitting the prop and tab locking washer. Be aware that if the taper key isn't fitted properly, it can ‘jack up’ the shaft on tightening and prevent the prop gripping the taper correctly.

9. The nut was hardened up the same way that it was removed. I checked that it was all the way up and that the washer tab was in the same place as when it was undone. Then all that remained was for the tab to be eased back over with a screwdriver and cold chisel to lock the nut.

10. With the tab bent over and the prop nut locked (above) I could tighten the grub screw in the rope cutter. The cutter fits flush against the prop, leaving about 15mm between it and the cutless bearing (below) to allow the prop shaft to move with the drivetrain as the load comes on and off and to allow lubricating water to get to both the cutless bearing flutes and the Volvo seal flutes.

One of the most common mistakes in nautical terminology is referring to cutless bearings as cutlass.

The technology was a serendipitous discovery made in the 1920s by American mining engineer Charles Sherwood who discovered when he ran out of his usual bearings that the abrasive muddy water ‘cut less’ into the shafts of his pumps when he used fluted rubber instead of lignum vitae bearings.

Hence he soon patented it as his ‘cutless’ bearing. The other spelling is of course a pirate sword, confusingly also nautical, but the mix-up is so rife that even several online chandlers have them listed as cutlass bearings!

This feature appeared in the August 2022 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat's performance, take out a magazine subscription to Britain's best-selling boating magazine.

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