Snapdragon 747 new engine

[malcolm]

I currently have a Snapdragon 747 (1980) with its original Mk7 Dolphin two stroke petrol engine which is now giving problems with overheating so I am contemplating replacing it with either a Beta or Nanni 14 twin cylinder diesel engine. I have come across a secondhand but still boxed and unused Nanni 14 complete with gearbox, instruments and wiring with an asking price of £3,000. My question is has anyone made a change like this to their Snapdragon? The engine mounts on the new engine would seem to be 380mm at centres whereas the existing bearers which would appear to be part of the original construction of the boat are about 250mm centres. Presumably the engine mounts can be changed but the crank case and flywheel housing which are lower than the mountings would foul the bearers. How do you get over this? Major surgery? If anyone has already overcome these problems I would value their input.

I have already asked the association but without success so far, so felt I would approach a wider knowledge pool.

Any help would be appreciated.

MVT

 

[davidbfox]

Welcome. If you post your location someone local might be able to show you their installation.

It is worth persevering with the class association. Have you joined? £10 for a year! The technical guru is a man called Mike Shepherd who responds to phone messages but does not, so far as I am aware, use email. He knows his stuff. I think there is an article about reengining on the members technical pages.

The forum on the association website is a recent innovation with not much traffic.

Almost every Snapdragon has had the original engine replaced, so someone will know the answer. Mine has a Yanmar YSM, installed after five years and unchanged since. I can't see evidence of changed bearers, but chunks of the fibreglass between the engine and the cabin have been removed. In principle I would assume you can chop out old bearers and glass new ones in, but I don't envy you the challenge of working out heights and alignments.

Please post news of your progress.

Dave

 

[malcolm]

Hi Dave,

Thank you for getting back to me. I am in fact a member and my 747 was originally owned by Mike Shepherd when it was new. If it is going to be really difficult I will persist in the Dolphin although I am not keen on petrol in the marine environment. Perhaps it would be a good idea to talk to MIke Shepherd as you suggest.
I am located in Bosham in Chichester Harbour so if there is anyone local with a Snappy 747 or 24 that has already changed their engine I would be very pleased of a chat.
Malcolm

 

[carl_harker]

Welcome to come and look at our 747 we have an old Yanmar yse8 fitted. Situated in the yard at Emsworth while we slowly refurb her.

 

[l'escargot]

I think you may be looking at major surgery. I used to have a Snapdragon with a Yanmar YS engine and the bearers were spaced to suit. I suspect that the bearers were built in according to the engine the builders were intending to fit.

They were built by a number of yards and some were home finished so there is a range of original equipment.

 

[Lakesailor]

Malcolm. Is your user name really your email address?

That is not a very good plan. Security wise.
If you PM the Admin they are able to change your username to something more anonymous.

 

[duncanmack]

I think you may be looking at major surgery. I used to have a Snapdragon with a Yanmar YS engine and the bearers were spaced to suit. I suspect that the bearers were built in according to the engine the builders were intending to fit.

They were built by a number of yards and some were home finished so there is a range of original equipment.

And it now has a Vetus 16hp in it. It was major surgery.
You're very welcome to look at it Malcolm, but it's in Morbihan.

 

[MoodySabre]

We put a Beta 10 in our Snappie 26. It was a whole new world compared to the petrol ****heap that was there before. A 13hp would have been better. The advantage of a Beta is that provide mountings to fit the engine beds. Comes at a cost of course.

The only problem was that the engine was a bit taller and so I had to modify the step to fit. No big deal but check height and whether the filters etc will be accessible.

 

[Tranona]

You will almost certainly have to cut away all or part of the existing bearers to clear the crankcase and sump. The Dolphin is exceptionally narrow because it has no sump, whereas most older engines are wider than the Nanni. The fixed point is the prop shaft coupling so you have to build your bearers to suit that. You may be able to retain part of the original and use this as a base from a steel framework to suit the Nanni mounts, or it may be better to take the old ones out and glass in new bearers. Not a particularly difficult job and it will help if you mock up a 3 dimensional template of the new engine using the installation drawings supplied. The Nanni would be a good choice as it is the most compact of all the small diesels, but it is taller than the Dolphin. You will almost certainly need to replace the propeller and probably the shaft as well as controls and exhaust.

 

[l'escargot]

And it now has a Vetus 16hp in it. It was major surgery.
You're very welcome to look at it Malcolm, but it's in Morbihan.

Hope she's still serving you well Duncan - would be great to see some pictures

 

[lavantian]

Hi I have a 747 and it was fitted with a Yanmar YSE8, it was the worst engine I have aver come across, rated 8hp @ 3200rpm, but here on the river Tamar the boat would go backwards against the flood tide. I removed it and fitted a home built Beta 20, in fact it was not a Kubota D722 but a D662 base engine this gives me 18.5 bhp @ 3600 rpm. It is silky smooth being a 3 cylinder engine and has enough power to push the hull over it hull speed to 7 plus knots, it was a we bit of a squeeze to get in but has more room around it that he old Yanmar unit did. I was lucky to get a brand new D622 from a plant company that was going bust for just £600, the conversion cost me about £2000 in total but I now have a reliable quiet engine that will even run a calorifier A engine that would fit in no problems would be a Beta/Kubota Z482 this is a twin cylinder engine very light and can be set to 13.8hp @3800 rpm or 10hp@300 rpm I have built three of these engines and they are a delight to work on and install. IF you like some photo's I will try and up load them or email me at monza6c@gmail.com. Len.

 

[lavantian]

The only difference between the Beta 10 and 13, apart from the sump pump out is the injection pump stop that is set to let the engine run up to 3600 under load, the maximum unload speed is 3800 rpm. I have converted lots of Kubota engines. for use in boats, even a couple of Z482 engines with raw water cooling instead of close circuit with a manicooler.
Len.

 

[lavantian]

I further note on my 3 cylinder conversion I used a shallow alloy sump that gave me more ( a Beta Part) I had to cut the engine bearers down and also the front cross member, easy with a angle grinder, I then bonded/glasses and bolted 3/8 steel plate along the bearers so I had a flat base to sit the engine mounts on, I used the same 1" prop but had to replace the prop with a right handed prop. The Nanni 14 is a Kubota Z482 same as the Beta 14/10hp, so you could get a shallow sump from Beta or I maybe able to help. I think I may have a steel sump fo a Z482 that you could get modified. My 662 is the same width and height as the Nanni or Beta 14 just about 4 " longer. Len
Len.

 

[lavantian]

Len again the width of the sump on the Z483 Nanni/Bets is 137 mm the width between the mount centres of the Beta is 370, on my installation made new narrower steel mounts for the front of the engine and also the gearbox and the flexible mounts are NOT in the centre of my bearers but of to the outer edge, the bearers are 3/8" x 2 1/2" wide, they are also angled down from the front to the back. to keep the flexible mount short as possible as recommended by Beta. In all I did not think it was a very had job to do. I did a similar job on a Tomahawk 25 again using long steel bearers, it make lining up the engine gearbox to the prop very easy... Len.