Engine Swap

[agg212]

I currently have a an 1-cylinder Yanmar YSM12 (original to the boat from 1979). I am looking to replace the engine with a newer 2YM15 that I've rebuilt myself.

I am considering trying to do the swap myself, but am wondering (1) what is the best way to modify the engine bay to fit the new (narrower) engine, and (2) how to properly align the transmission to the shaft.

[tkeithlu]

There is a huge literature on aligning the shaft, from books to YouTube. In a nutshell, you must use the engine mount adjustments, primarily but not always the rear ones, to match the two flanges in every dimension. At the end, they turn the same circle with 1/1000 or less error, because your error is your vibration. You can do it; it just takes patience and figuring out what shifting the engine this way and that does to the alignment. Supposedly, you need to do it with the boat in the water, since it may sag a bit on blocks, but I did mine in the construction cradle and didn't find any error once in the water.

As for building the mounts, remember that the basic alignmnet exists in where the engine mounts are located, in three dimensions, and your prop pushes the boat through those mounts - they have to take full thrust. Again, you can do it.

[GILow]

Originally Posted by agg212

I currently have a an 1-cylinder Yanmar YSM12 (original to the boat from 1979). I am looking to replace the engine with a newer 2YM15 that I've rebuilt myself.



I am considering trying to do the swap myself, but am wondering (1) what is the best way to modify the engine bay to fit the new (narrower) engine, and (2) how to properly align the transmission to the shaft.

I have just done something similar, replacing my 420 kg 96 HP Nissan with a much smaller 50 HP Beta, all on my own. Big job, but very satisfying.

Simplest thing to do is make a quick timber mock up of the new engine that gives you the location of the feet and the drive coupling. Use this to figure out the modifications, if required, for the engine bed. And to check things like the location of the cooling water feed etc.

In my case, the model quickly showed that I’d have to replace the factory supplied rear engine mounts of the Beta (an easy job) if I were to have any hope of it fitting. This may well be what will work best for you with the narrower engine.

I used the model to get the engine beds just right then plonked in the new engine.

As noted, the alignment procedure is well described online.

[Wotname]

Don't forget you will need to change the prop.
The YSM12 uses a left hand prop while the 2YM15 is right hand.

[Reefmagnet]

When I installed a new engine and beds into a boat, I made an alignment frame based on the dimension drawings of the engine as GILow has suggested. This frame included engine mount positions, engine outer dimensions (to make sure the engine wouldn't foul anything in the engine compartment) and included holes to allow a string line to be used to align the position with the stern tube (i.e. shaft). On the last point, I ended up printing some "targets" on a printer that were placed on this frame and at the entry and exit of the stern tube. the stern tube and rear frame targets had a small pinhole in the centre and this allowed a laser beam to be passed through these pinholes and then it was an easy matter to align the frame up with the stern tube very precisely. Once marked out and measurements made, the engine literally fell into place and the amount of shaft alignment required was next to nothing. Of course the secret to this method is to ensure your alignment frame is an accurate representation of the actual engine but it's well worth it as it's far easier to manipulate and work around a wooden frame then a great massive lump of iron!

[GILow]

“Alignment frame”. I knew there had to be a name for it. [emoji846]

Didn’t think of using lasers though... darn.

[Reefmagnet]

Lol. It's my own term, but it fits the bill...


Dragged out some photos of the project for reference

[GILow]

Very tidy. And the second last one looks like some kind of mad scientist experiment that results in the moon exploding.

My “alignment frame” was made from bits of 90 x 35 MPG10 and plywood offcuts. Alignment was the Mark I eyeball with a generous application of she’ll-be-right optimism.

Got the engine in place and used about 60% of the available adjustment on the rear engine mounts, and 20% on the front set, so it was closer than I’d have liked (50% on each would have been nicer) but still in tolerance.

[GILow]

Originally Posted by Wotname

Don't forget you will need to change the prop.
The YSM12 uses a left hand prop while the 2YM15 is right hand.

Or do what some silly bugger had done in a boat dad looked at recently...

They’d swapped the gear linkages and run in reverse. Dad said the gearbox sounded like a bandsaw.

[GILow]

Originally Posted by Wotname

The YSM12 uses a left hand prop while the 2YM15 is right hand.

Actually... how do you KNOW all this engine stuff? Seriously, it’s like a dedicated engine Wikipedia down there in your corner of Tassie.

[malbert73]

Originally Posted by GILow

I have just done something similar, replacing my 420 kg 96 HP Nissan with a much smaller 50 HP Beta, all on my own. Big job, but very satisfying.

Simplest thing to do is make a quick timber mock up of the new engine that gives you the location of the feet and the drive coupling. Use this to figure out the modifications, if required, for the engine bed. And to check things like the location of the cooling water feed etc.

In my case, the model quickly showed that I’d have to replace the factory supplied rear engine mounts of the Beta (an easy job) if I were to have any hope of it fitting. This may well be what will work best for you with the narrower engine.

I used the model to get the engine beds just right then plonked in the new engine.

As noted, the alignment procedure is well described online.

Hi GILow, how do you like the new Beta? You get to use it before lockdown or do you have to be content running it in your slip? I got to deliver my boat to and from another yard where my mast was being re-rigged. After 240 hours I still like hearing my beta 50 purr.

[GILow]

Originally Posted by malbert73

Hi GILow, how do you like the new Beta? You get to use it before lockdown or do you have to be content running it in your slip? I got to deliver my boat to and from another yard where my mast was being re-rigged. After 240 hours I still like hearing my beta 50 purr.

I am loving it. We are still able to sail around out in the Gulf St Vincent, so it is getting plenty of use. It now has 2.4 hours of run time. Only 47.6 hours till the first oil change. [emoji846]

[Jim Cate]

Originally Posted by GILow

Actually... how do you KNOW all this engine stuff? Seriously, it’s like a dedicated engine Wikipedia down there in your corner of Tassie.

Aww, Matt... Wottie just makes up all that stuff outa the blue. Don't believe a word he says! You know how Tasmanian immigrants are. But horses... well, just ask him about horses, he'll set ya right.

(For those ab out to report this post... just a joke amongst friends, festering away under lockdown))

Jim

[Wotname]

Originally Posted by Jim Cate

Aww, Matt... Wottie just makes up all that stuff outa the blue. Don't believe a word he says! You know how Tasmanian immigrants are. But horses... well, just ask him about horses, he'll set ya right.

(For those ab out to report this post... just a joke amongst friends, festering away under lockdown))

Jim

Guilty as charged - Jim's got me clocked - and it's a fair cop. ()

But hay, it makes horses fat and that is the sum total of my equine knowledge. Wait... I forgot, they are an expensive pastime - don't ask me how I know..

But as to Matt's question - how does ANYONE know stuff?

I have always assumed they read (accredited data like manuals) and remember; do stuff and remember what went wrong and what worked.

In my case, I done a lot of stuff that went wrong, read a lot and remembered of it.

For the OP, the first questions for any engine swap must include "What can I reuse?" e.g. is the shaft strong enough for the new engine and is the prop suitable?

In his circumstance, it would be reasonable to assume if the shaft was suitable for 12 hp, it will be OK for 15 hp. However older small Yanmars used left hand props while newer ones use right hand props. I have had both and this is something I remembered

[mvweebles]

Originally Posted by GILow

Or do what some silly bugger had done in a boat dad looked at recently...

They’d swapped the gear linkages and run in reverse. Dad said the gearbox sounded like a bandsaw.

Some gears (transmissions) are designed to do just this. Twin engine power boats have counter rotating props - stbd engine has a RH prop, port has a LH prop. Either the crankshaft reverses direction or the transmission does. Years ago, Detroit Diesel made left and right engines - mirror images of one another. These days it's all done via the gear.