aligning engine with a Vetus type 6 coupling

Same as any other coupling. Undo the nuts on the inboard end of the gearbox coupling and slide the whole coupling and shaft back to create a gap between the face of the gearbox output coupling and the flexible coupling. If you suspect it is way out then take the bolts out and see if the coupling will come together without distortion. Bear in mind the coupling is designed to cope with misalignment unlike a solid coupling.
 
Not sure why that should be the case. The whole purpose of the rubber bushes in the coupling is to isolate the movement of the shaft from the gearbox.
 
Tranona said:
Not sure why that should be the case. The whole purpose of the rubber bushes in the coupling is to isolate the movement of the shaft from the gearbox.
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Not really, the flexible coupling facilitates a degree of misalignment though any forces caused by the misalignment are resisted by the the flexible element and much of it then transferred to the shafting and hence the bearings etc, the allowable misalignment quoted by the coupling manufacturers are what the coupling can handle, not necessarily what the particular shaft assembly can cope with...... with the exception of some specialized shaft couplings that actually require a given degree of misalignment then you are generally better off making the alignment as good as possible
 
This coupling like the others seems to be designed to cope with small angular misalignments but not lateral ones. In an ideal world you would disconnect the coupling at the gearbox side, centralise the shaft in the stern tube and then check that the engine is aligned to the shaft in the side to side and up / down sense. In other words when the shaft is slid forwards does it mate up with the gearbox flange or is it displaced a bit either to one side or up and down.

After doing that, then you would check that the face of the gearbox flange is parallel to that of the coupling ie check the angular alignment. Easiest way to do this is with the coupling and flange only loosely connected , to measure the gap at 90 degree angles aiming to get this gap to be the same at all 4 points to within a thou or so.
 
Thanks again. I'll slacken it off and have a look. She's back in the water now so more drastic investigation will need to wait until the winter.

The issue arose with me trying to install a new cutlass bearing into the Y bracket. The old one was worn slightly with maybe 1.5mm play and rumbling a bit. I pushed it out with the shaft in situ (bits of angle iron, tubing and big studding as a press) and installed a new one. The shaft was then very tight - too tight to turn by hand. It got tighter the more I pushed the bearing in. The wear on the old one was more at one end than the other. In the end I put the old one back the other way round and it all felt better. But obviously it's not quite right and I need to sort it more properly. Hence thinking about the alignment. My guess is that the Y bracket is not quite in line - it's a 1984 boat and things get caught round the prop etc. although there's no evidence of damage. I might explore mounting a slightly smaller od cutlass bearing in epoxy to ensure it's in line?
 
Replacing the cutless with the shaft in place is not usually a good idea as you are forcing both faces to fit at the same time. First it is worth checking that your new cutless was exactly the right size - for example a 38mm is not exactly the same as 1 1/2" and on a new bearing the clearance is very small so will be difficult to turn until water is running through, even with the correct size. If you are going to put in a new bearing without removing the shaft (perhaps because you have to also take the rudder out), then disconnect the shaft from the engine. It is unlikely that the Y bracket is out of line as they are pretty robust and unless the inboard end of the shaft is in a fixed bearing the coupling will take up any small misalignment.
 
It's a 30mm shaft and a 30mm id cutless; I'm slightly less certain about the id of the Y bracket - I pushed a 45mm od grp shell bearing in but it stuck at about half way and the studs began to complain. I sanded the grp lightly and it went in more easily, and measures about 49.9mm od now. I could put a 1.75 od bearing in and rely on epoxy to hold it in line, or stick with the nominal 45mm and put up with it being stiff until wet. I was wary that if too stiff it would turn in the Y bracket despite the grup screw - the GRP shell is soft. The old cutless (now back in) was brass-shelled and measured about 44.7mm od. Remember the shaft was in place all this time so I couldn't find a way to measure the id of the Y bracket, and it appeared even to have a slight shoulder at the forward end. Nothing is simple is it, esp the first time?

Anyway, it sounds like I should have more faith and trust that the new one will loosen up when wet.
 
If you have a non standard id bracket it might be worth considering having a composite bearing machined to fit - although you do need to know the id. You can set these in epoxy so don't have to be a press fit. Speak to H4 Marine owner NeilY posts on here regularly.
 
Your Dehler being a foreign boat is likely to be metric and 45mm though it could be 1 3/4 inch which is 44.45 mm. What you need to do is to get the old beariung out together with the shaft and apply a pair of calipers to the ID of the Y bracket. At the same time you can check that there is no obstruction in the form of a grub screw for example.
 
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