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Shaft Diameter

Shaft and Log Diameter

Q: I'm considering installing a Dripless Shaft Seal in my 1987 C34 and need to know the Stern Tube (Shaft Log) Diameter. Per the West Marine catalog, it should be either 1 1/2" or 1 3/4" for a 1" shaft.


The shaft log measures 1 5/8 inches OD, The correct PSS size is 1" shaft x 1 1/2" tube. I requires a little stretch to fit. This is the size recommended by the PSS technical guy. Installation is simple and straightforward. The difficult part may be removing the flange from the prop shaft. Easiest way is to unbolt the flange place a roundish object somewhat less than the 1" shaft diameter (I used a large nut) and tighten the flanges together. This should exert enough pressure to push the sheaf out of the flange. If more persuasion is required the apply some heat to the flange. When reassembling the flange to the shaft use some antisieze compound, it will make thing easier to take apart in the future. The only cautionary note is to be really careful when sliding the fixed stainless steel part OD the seal over the shaft. It is a very tight fit and has 2 O-ring which must not be damaged. It is easy to cut the O-ring as they slide over the key way on the shaft. Polish the shaft lightly with very fine wet or dry paper to remove any nicks that might cut the O-ring. No modifications to the shaft length are required. The whole job can be done in 1/2 hour or less. Don't worry about stories of catastrophic failure, PSS claims they have never had a report of one.


I have done this installation, and it is pretty easy. The diameter of your shaft tube is 1 1/2", and that is the size of PSS you should order. As I was preparing for this installation, I had some initial trepidation about the size, because I measured the tube size to be 1 5/8", and I did not know whether the 1 1/2" PSS would fit. However, once you get the old hose off of the tube, you will find a smooth metal tube without extra fiberglass all over it, and it will be 1 1/2". This job should be done out of the water, because you have to uncouple the shaft from the engine, and you don't want it to drop out the back of the boat. I can imagine that certain daring souls might be tempted to do it in the water, but I wouldn't.<g> Also, if you haven't replaced your cutless bearing yet, this would be a good opportunity to do so. The only other potential difficulty is separating your shaft from the coupling. Mine came apart easily, probably because it had very little corrosion, so take this into consideration. If you have a problem, you can insert a block of wood/metal between the shaft and the transmission flange, and use the bolts to jack the shaft coupling off of the shaft. WHen you first start up after the installation, you will see a line of carbon on the hull as the bearing wears in, but this is nothing to worry about. Just remember to "burp" the bellows every time you go back into the water, and you won't have to worry about tightening packing again.

Ralph Caruso

I recently had this job done at a Marina. They had to cut the shaft to get it off. When I looked into it over a year ago at a different Marina they also indicated that this might be necessary so cutting the shaft may be a fairly common necessity. Also the rear engine bolts needed replacing so the engine could be aligned properly. It is apparently important to let the boat sit in the water for a day before doing the final engine alignment

John Coulthard

Technical Editor Ron Hill Comments:

There are a number of solutions out there. With a 1" shaft most of the "bellows" units like PSS will fit. You might also consider "drip free packing" which I wrote up in the May 1992 Mainsheet . I've used it sense the spring of 1991 and still have it installed today(with a dry bilge). I saw it's still available at West Marine. Any advantage of the packing over the bellows unit ? If the bellows were to break - for what ever the reason - you have a real EMERGENCY and had better find a travel lift fast. If the normal flax/dripless packing leaks all you need to do is stuff more flax /dripless packing or even stuff pieces of shoe lace /rag in the packing gland to temporally stop the leak.