Twin V6 to single diesel conversion

[burt2]

I am in the process of buying a CARVER 27’ Mid Cabin which has 2 X King Cobra V6’s on Mercruiser legs (not going) I have a few years experience in fibre glass and carbon fibre laminating and 3 years of small boat rigging, so I’m pretty confident in altering the transom, but I have never played with stern drives before. A quick look around has showed me the Volvo gear is better than Mercruiser but at a price, so im not fussed if I don’t have the best but diesel is important.

The two engines have had salt water running straight through them and even though they have done only 400 hours they haven’t been started in 5 years so I think they are stuffed. The legs appear ok but are only Alpha I legs so they are not really suitable for a diesel engine, of course I want to do it as cheaply as possible but at the same time I want to make it as functional and as safe as possible. I think I will just get rid of both engines and legs and try to get a little money for them to go towards a Volvo diesel and duo prop leg but or something similar.

A few Questions; are DUO props much better, are Mercruiser cheaper to repair, where can I find good info and learn how to set up ratio and prop size and I’ve also thought of putting two small diesels onto to Alpha ones

Any suggestions/advice would be great; the boat is a mess so I got the whole year to think about motors and configurations

Thank,
Glenn

[cyclops]

Supposedly Volvo's are only for twin engined, new Mfg. built boats. $$$$ Volvo is now American auto company owned. Should be almost up to US auto quality by now. Ford or GM owns Volvo. Any difference? :o

[cyclops]

I would do a online, Michagan Wheel inboard prop selection form fillout , on their web site. You can juggle the engine power and torque and speeds till you get your speed desired. Cheap enough. Free.

[drs3317]

burt2,
What are you going for,...similar performance with the diesels or strictly functional with the best fuel economy?

I have thought of the idea of repowering with twin very small diesels for the economy but would loose any possibsble speed performance. Haven't decided if I'm ready to give up the speed and move like a trawler yet.

[cyclops]

1 engine is always cheaper than 2. Forever. "The reliability of 2 engines is reduced by the # of times the owner plays with or adjusts them. " Quote is from Cyclops. :)

[burt2]

I'm not interested in going huge speeds so economy is the go I think between 165-200 hp diesel engine would be fine, a single engine is also preferred. I would like to cruise around 20kt.
2 small diesels would let me use the alpha I stern legs which would be an easy install but 2 engines would not be as simple to maintain and would be expensive to buy.

Cyclops what’s that web site you were talking about got a link?

Thanks

[gonzo]

Volvo is Swedish. Ford bought the automotive division only. Volvos are fine for single engine application. If you want economy, fixing those engines may be cheaper. Even two V6 rebuilt or new units would be cheaper than a diesel conversion. The Alpha drives can handle a diesel. There is no difference as long as the torque rating is not exceeded.

[cyclops]

Can you hitch a ride on a similar sized and powered boat? It would nail down in a hurry, which way to go. If you dock in a windy and strong current area go with the 2 engines. Get another job for the gas. It has dropped about a $ per gallon also. Twin engines make docking a pleasure. Go for the twins. 1 rebuilt running engine, beats 1 dead new one, offshore.

[burt2]

ok ive found 2 x nissan 4cyl Turbo Diesels 135hp each for $8000 NZD ($5500USD) marinised and ready to go on Alpha I, thinking of giving them ago. By the way Petrol/Gas is about $1.45 per litre here vs $0.95 per litre for diesel ($5.48NZD per gallon/$3.7678USD per gallon for petrol/gas vs $3.591NZD per Gallon/$2.46USD per Gallon for Diesel)

[cyclops]

Twins ALWAYS sound great when a little off synch. Singles sound, alone?

[burt2]

Now I feel silly, just been to look at the boat and noticed that the legs are in fact OMC (not what I was told). Can any tell me where I can find out more about these legs, spec ETC

Engines King Cobra 4.3L V6
Legs are cobra with the model number 985685

[cyclops]

2 Diesels as planned and 2 very good quality rebuilt stern drives of your choice. Enjoy.

[gonzo]

What year is it? OMC and Volvo had a joint venture for some years, and those Cobra drives are actually Volvo SX. Can you post some photos?

[burt2]

The legs and boat are both 1989 ill take some pictures tomorrow hopefully, they appear in good order and have 400 hours on them, but the boat was imported from Japan and the doesn't look like any maintenance or servicing has been done. They go in and out of gear still, but I can’t test them because the engines are seized up.

[burt2]

Sorry took so long here is a few pics of the legs

[gonzo]

That's and OMC Cobra drive. The name Cobra covers a lot of models so it's confusing. With 4.3 engines the gear ratio is about 1.65:1 . With lower revving diesels you would need a lower ratio; probably around 1.20:1. It would depend on the RPM rating.

[cyclops]

Burt. I am sorry I did not see your request for Michigan Wheel Corporations web site. Old brain.-------It is www.miwheel.com---------It should be very accurate for a cruiser boat. That is their bread and butter line of prop sizes and shapes. Do the prop selector forms with the present engines and drives. Then the other guy who posted his results. Then start entering what engines and drives you would like to get cruise speed and gpm. Then if nothing still looks good give them a call at the ----outboard & sterndrive division. ------Better yet E Mail at----- info@miwheel.com--------I spent$ 60 on Tech. Assist., But the props were so close to perfection. :)

[burt2]

Thanks guys, well still so many paths to take and I have been thinking about buying a new stern leg (bravo 2). I don't mind playing with old gear as im not rich but the engine and stern drive is the most important part of the boat.

Also I have been offered a 6.2 Star Power V8 turbo diesel for a good price and it comes with a stern drive to suit, although the prop looks wrong as it was off a 40' semi-displacement launch. 6.2 Star Power is just a Chevy right? Looks like one.

I’m doing this boat with my father and we both decided that we want a single engine, we will put it on a poll mooring down a tidal river we don’t need to manoeuvre round tight mariners.

I would still like to find out more about the cobra drives so I know exactly what I got.

[drs3317]

The 6.2 is a chevy diesel motor. It was known for cracking heads. They usually crack from the water jacket to the exhaust valves. That said, I had a 1985 Suburban with the 6.2 and it actually was a very effecient motor. Mine cracked the heads at about 120,000 miles. I replaced the heads and run the truck to almost 500,000 miles before it was totaled by a drug dealer being chased by the police. The factory never used turbochargers on the 6.2 but after market turbos are available.

[marshmat]

My grandfather's been running a Cobra drive almost identical to yours, with a 4.3L V6, on his boat for 18 years. I am aware of exactly one major incident, when it threw a bearing and seized a shaft last year (we suspect this was the mechanic's fault, not OMC's). That was kind of scary, but not dangerous and was quick to fix.
Check the gearcase oil (dipstick's on the top of the upper unit, it's the large flathead screw in the middle of the top panel of the upper unit housing, if I recall correctly). If it's low, or contaminated, your drives have probably been poorly maintained. If the oil's full and clean, and everything else checks out OK, I'd think the drives would be good for some time yet. But if you're repowering anyway, it's probably best to follow Cyclops' advice and go for new rebuilt drives. I'm kind of leery of going to a single from twins, but if you're confident that you can safely rebuild the transom, the Starpower unit could work.

[burt2]

I can’t find anything bad about the marine 6.2 and it would fit nicely (might have to cut into and reinforce the two center stringers) also comes with the above stern leg, does any body know this leg apparently it’s a really strong commercial leg.

Changing from twin to single won’t be a big deal I have done plenty of laminating like this; also I will over engineers it to be safe (might laminate a new stringer in).

[MAD JAX]

Interesting Thread...I'm in the throes of doing this of late, just need to install some Stringers.

Please reply as to the out-come of this project, Thanx!