Diesel Convertion

[Duster]

Does anyone have first hand experiance of exchanging the V8 petrol mercruiser engine for a V8 GM diesel of the type advertised by Samuri Convertions?
Are they;- sucessfull , dificult to do (for a reasonably competant mechanic ), did the added wieght cause any handling problems? Or have you a better suggestion where space is limited?
The boat concerned would be a 24 foot sports cruiser.
Waterside access to petrol (or lack of it !) is a greater problem for us than the actual cost of fuel.
Thanks Mike

 

[Guest]

Would it not be cheaper to move next to somewhere WITH petrol, forward planning is a great thing /forums/images/icons/wink.gif

 

[hlb]

Save the heart ache. Flog it and buy a diesel.

<font color=blue> Haydn

 

[Guest]

I have a pair of GM 6.5'diesels in my boat, although I bought them new (as long motors from peninsular in the US) and did all the marinizing etc, they're 325hp, but It's a lot of work and agro.
My previous boat had a single 6.5 ex automotive which I rebuilt and marinized (from samurai) It ended up exellent and remarkably fuel efficient,(after undescribable probs!) but the max you can expect is about 220hp with the higher compression automotive version(earlier models didn't have piston cooling either), and that's if you get the right pump and injectors for turbocharging!

What are the petrol V8's?

Have you looked at the supercharged version from sweden?...easier swap!

 

[Duster]

Hello John,
The existing engine is a 5L Mercruiser.
I am sure that 160 to 200 bhp would be quite adeqate as the boat weighs less that 3 tons.and I only require it to plane comfortably at around 20 knots plus 25 flat out.I am not confidant that the Lancing 2.5L Ford would be enough.
I do not want to swap the boat as I like it.This model was never offered with diesel option and there is very little similar available used ,with diesel of a reasonable power.
What sort of problems did you encounter and were Samuri helpfull? Did the added weight cause any problems?
I have not seen the other engine you mention, do they have a web site?
Regards Mike

 

[Guest]

Mike, If your running a 5.0L I suspect you have an alpha 1 drive, It's very questionable whether the Alpha will take the torque of the 6.5GM, even normaly aspirated! I personaly wouldn't use one. On the other hand, if you have a Bravo then it will be fine, In N/A form the motor will make 160-170hp ish, drive plate and bell housing from petrol will fit, as will front engine mounting feet (same pattern as petrol, so no need to alter engine bearers in boat, just get softer mounts from R&D or you'll lose your teeth!) Stay wide awake when dealing with Justin at Samurai, he's a lovely guy....but, well, just stay awake! my first engine from him had to be replaced as when it arrived it was totaly f****d, cracked heads, knackered piston the works! not quite as described, I went down there and picked one out myself, still needed work but, but was workable. Swedish crowd do N/A 170hp and supercharged up to 410hp(I'm currently fitting a 410hp in a B-28 Batboat) thier web address is "www.marinediesel.nu" hope this is of help to you

Regards Jon Fuller

 

[terryw]

If space is tight have a look at the 4 cylinder Yanmar engines which are available in 3 power ratings of 150hp, 190hp and 240hp, and are designed to be used with the Bravo outdrives.

 

[spannerman]

You definitely won't be able to use an Alpha drive with 6.5 diesel, I know we sell it with the new 1.7 112hp but that doesn't have the torque of the engine you are looking at, also there are problems with gear chatter at idle speed with the Alpha. So it will have to be a Bravo I or II drive, also you will have to work out the gear ratio and prop size.

 

[tico]

send me a PM and i'll tell you all about diesel conversions with the Lancing 2.5T.
PS Mike now does the Puma engine and claims 150 hp and its lighter

Been there, done that, got the oily T shirt

 

[Guest]

Spannerman,
Bravo also sufferes with awful drive chatter at idle (only when in neutral of course)
Mercruiser use a thing they call a two stage coupler in place of the regular drive plate on the 6 cyl VM motor, it's got a very soft cush drive to elliminate the chatter, but takes up when the load goes on! but it costs about £2500, not nice!
my drives have been chattering away at idle, and I've covered 3000 miles now, doesn't seem to get any worse, or cause any problems but it does sound horrid!

JF

 

[Duster]

Thanks have sent you a PM
Regards Mike

 

[spannerman]

Yes thats true, this is because if you measure the idle speed on a diesel with an oscilloscope over several milliseconds you can see that because of the high compression ratio in a diesel the engine slows down as each cylinder comes up to its comp stroke then accelerates as it fires. This causes the gears to be Driven then go onto Overun as each cylinder fires. Thus causing the characteristic gear chatter, this can be alleviated by raising the idle speed slightly so it smooths out, but not so much as it goes in gear witha thud. This won't work with an Alpha drive because its a crash box unlike the Bravo which has a cone clutch. and explains why it never happens witha petrol engine as they idle far more smoothly.

 

[Guest]

It's nice to find someone who understands this stuff, as I've explained this problem to many people, almost word for word as you just have, and more often than not, just get a blank face looking back at me!
I have managed to reduce the chatter on mine a little by advancing the timing just a smidge, although the engine becomes slightly noisier, the duration of the "deceleration" part of the chatter cycle is reduced, it's surprising how much difference it made!
The bit I find strange is, Mercruiser make the two stage coupler to cure the chatter on the VM 6 cyl so that 6 cyl motor obviously suffers from it, but the yanmar has only the rubber doughnut like a petrol motor (or mine for that matter) but the yanmar Isn't that bad in the chatter department. there are sugestions however, that the 4.2 yanmar has a "harmonic" disagreement with the bravo which results in the common failures they've had (not just the torque, which makes sense to me as my motors are more torquey than the yanmar with no probs ,mine are not X's)
A pal of mine had untold trouble finding the reason his Hurth 630A's kept failing on his raceboat, worked 5.7's circa 350hp driving through surface drives with big props, after each failure it was such a mess it was hard to do a post mortem, turned out it was the reverse (uningaged) clutch assy being shaken to bits by the harmonics coming back up the shaft from the surface props! these fragments then caused the demise of the rest of the box(had already tried removing one reverse clutch plate to increase freewheel) did away with reverse on that motor, never another hint of trouble