Engine alignment

[Thistle]

I'm shortly going to be installing a replacement inboard diesel engine. The existing bearers will, I think, be suitable but I'll need to move and replace the mounts. Access to the shaft coupling will be very limited, probably requiring a couple of extra joints in each arm. Because the new engine is slightly longer than the original, I doubt if there will be room for a flexible coupling. All suggestions as to how I should best go about aligning the engine will be gratefully received.

Thanks!

 

[tugboat]

Correct engine alignment is obviously essential to the longevity of the installation, so you are going to need reasonable access to the coupling area in order to use feeler gauges to set it up. Your stern gland is there too so you need to be able to access that quickly in case of emergency (leaks). The drive needs to incorporate some sort of flexible coupling to absorb vibration and to allow for the inevitable settlement of the engine mounts. I get the impression you maybe need to modify the boat to suit your choice of engine, or maybe rethink the choice of engine itself?

 

[alahol2]

I've recently re-engined our boat and you will need to be able to get at the coupling in order to align the engine. There are also at least 8 bolts back there to tighten. There's a description of what's involved on my website. Follow the link below.

 

[Davolas]

When we re engined a couple of years ago. I made a dummy engine out of hardboard. To position mounts, check clearances and achieve rough alignment before fitting the engine.

Cut basic profile of plan and side elevation from manufacturers dimensions. (Yanmar installation guide had all necessary details) or measure carefully from engine. Epoxy templates together and add webs for stiffness. Add template at each engine mount and piece of broom handle with plywood dummy flange for propshaft. very carefully check all dimensions are correct and particularly that proshaft length and squareness are correct in relation to mounts.

Can be lifted in and out for checks, I used mine to drill and tap mounting holes on new engine beds and rough align propshaft. Engine dropped straight onto pre installed mounts and only needed slight adjustment to allow for sag of mount as I had to guess how much that would be.

Took about 4 hours to make and saved me loads of time and effort during the installation.

Good Luck

Steve <font color="black"> </font>

 

[brianhumber]

Very few designers think about access for these items

However not to fit a good flexible coupling would in my opinion be a very bad idea.
Lifetime of your shaft seal even if its old packing type will be reduced.
Whilst you are having the grief of changing the engine i would also suggest the rest of the transmission is surveyed.

 

[brianrunyard]

As the engine will move slightly due to the engine mounts you need a flexible coupling, even if it means mounting the engine further forward.
Withou a coupling engine vibration will be transmitted to the shaft and could cause problems between the shaft and stern tube, and between the sterntube and hull.

 

[macd]

I'm in the process of re-engining, including completely new beds, and fully agree with Davolas. Getting the alignment right BEFORE offering up the engine will save lots of time and aggro later. Like him I made up a template (securely fixed to a length of shower rail which stockist claimed to be 25mm but was actually one inch, same as prop shaft), with 5mm datum holes drilled for centres of the four new engine mounts. These obviously based on engine manufacturer's drawings. Clearly it's crucial to get this square and aligned in all three dimensions, which involves compensating for any sag due to the weight of the template. It helped that the cutlass bearing was new, so didn't permit any slop of its own. Luckily in most installations the mounts offer more up and down than sideways lattitude. If you can't get the heights spot-on, it's better to have the beds slightly low than high, since you can shim up but cannot shim down.

 

[poriordan]

Hello there Thistle,

Think I've been through the same problem a few times with yachtmasters. Getting an engine in and out is a nightmare. Was even at a point one stage where I was going to take a flooring section out to make things that little bit easier. Think about this when doing any alterations as it pays off afterwards. Stupid question I know, but have you any room to move the propshaft back ? Could you cut a hole /groove in the rudder to get that that extra clearance needed ? I have done it on a 400 hp trawler - all worked fine !

Patrick.