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Old 18-08-2016, 08:23   #1
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Repowering questions from newb

Hello all

My current set up is a pretty rusted out marinised Isuzu UM 3AB1, Velvet Drive 71 trans and a Walter RV10D Vdrive. Major problems are: exh manifold rusted thru to water jacket. Lots of bolts are so badly rusted that they break the heads off when I try to remove. Alternator is very suspect and so is the starter.

The trans is ok and Ive rebuilt the Vdrive with new bearings and seals.
I have a couple of questions about the rebuild but I'll put those in another post.

I can get a second hand 3AB1 in reasonable condition externally but it is not marinised. I would do a comp test at the minimum.

I can also get a nice nearly new turbocharged Kubota 1505 T but not marinised.

I understand the concept of the devil you know and stay with the 3AB1 as it will be a drop in replacement. (almost) However, I kinda like the idea of a new turboed engine.

The main questions I have are: How do I marry up the Kubota or another brand of engine with the velvet drive trans? What hardware is involved?

What are some considerations in using a dry exhaust manifold? There is plenty of clearance to the engine box on the exhaust side but I plan to wrap the manifold with exh tape. There is an existing exhaust blower in the engine bay which will help with heat.

Thanks very much in advance to a very helpful forum.

Cheers
Joe
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Old 18-08-2016, 23:57   #2
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Re: Repowering questions from newb

When removing rusted bolts, use an impact wrench. Usually the impact wrench will back out the bolt where twisting with a big wrench just takes the head off. You can rent one.
Turbos allow you to put more hp in a smaller block. But there are costs. When operating it creates higher exhaust gas temperatures. Especially when using above 80% of hp. EGTs cause greater wear of cylinder components - pistons, rings, sleeves, valves. Sometimes the higher cylinder temps cause cavitation on the water side and create pits. Without a special additive will ruin the engine. Turbo engines require overhaul twice as often as non- turbo versions. Turbos need rebuild or replacement more often that other engine accessories. And then more fuel. The highest hp turbo version of my mains use 3x the fuel.
I'd either rebuild the one you have or the 2nd hand one and miss all the trouble of fitting a different engine.
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Old 19-08-2016, 07:41   #3
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Re: Repowering questions from newb

Le--good post.
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Old 19-08-2016, 08:10   #4
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Re: Repowering questions from newb

If anything I AVOID turbo engines, just more to go wrong, and they are usually at the peak of the HP the manufacturer is trying to get out of a particular block. Those Isuzu diesels are nice engines too.
Given a choice I would take the lower HP out of a bigger block than the higher HP out of a smaller block. Everything is stressed less.


Just nit picky stuff though.
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Old 19-08-2016, 08:43   #5
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Re: Repowering questions from newb

I agree with the above posters.

I would stay away from non-factory installed marine turbos ( Seems like Everything is connected to, or changed when you install a turbo ).

I would rebuild the engine you have.
A non-marinised engine is cheaper than a marinised engine for a reason.

Generally more corrosion resistance but also different operating environment, so the components are sometimes subtly different.

Auto engines generally run hotter than marine engines. Different type oil for each.

And on and on.

Good luck with your repower whichever way you go.

Keep us posted on what you find and how it goes.

A rising tide raises all ships.
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Old 19-08-2016, 09:14   #6
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Re: Repowering questions from newb

[QUOTE=Lepke
I'd either rebuild the one you have or the 2nd hand one and miss all the trouble of fitting a different engine.[/QUOTE]

Excellent post Lepke. In addition I would also rebuild what you have. Been there done that and would stay with what you have. ReBuild your confidence back in the same motor.
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Old 19-08-2016, 10:11   #7
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Re: Repowering questions from newb

A few years ago I translated and edited "Replacing your boat's engine" by the Swedish boating writer Mickey Weston. It's readily available in the U. S. A, and I think it will help you a lot. Rebuilding an old engine is usually not worth it - parts are very expensive and once you're deep into the job, the next part you need may not be available, after you've already spent a small fortune. Even if you get it done, it's still an old engine. So I recommend buying a new engine. If you're in the USA, talk to Stan at Beta Marine - they offer adaptors that often obviate the need to rework the engine beds.
Don't throw your hard-earned earned money into the rat hole of an old engine
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Old 19-08-2016, 10:43   #8
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Re: Repowering questions from newb

Engines are rebuilt successfully all the time. Parts that should be replaced are known before hand, parts sourced, and costs determined. There can be fatal surprises like a cracked block or expensive ones like a cracked head. Fortunately, an engine that turns over without making ominous sounds and hasn't been seriously overheated will be a good candidate for a rebuild. With all the parts that should be replaced, a rebuild won't be cheap but way less than a new engine and cheaper to refit.
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Old 19-08-2016, 10:44   #9
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Re: Repowering questions from newb

To agree with most of the above. Why on earth would you want a turbo engine in a Bob Perry design?
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Old 19-08-2016, 18:21   #10
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Re: Repowering questions from newb

When I rebuilt my yanmar, I bought a standard rebuild kit, planed the heads and the block, and went to work. A couple of specialty tools later, ( and about a week, because it was my first diesel rebuild) and I had the sweetest sounding diesel I have ever heard. For about one third the cost of a good used. (or rebuilt by someone else)
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Old 21-08-2016, 08:25   #11
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Re: Repowering questions from newb

Thanks for all your comments.

I have decided to go with consensus and give the idea of turbos a miss.

I havent done much with this particular project due to other projects.

Your comments about how to marry up ANY suitable engine to the Velvet Drive would be greatly appreciated as that would allow me to consider other newer engines.

The Isuzu is getting a bit old and I think I might have trouble getting parts. After a quick canvass around the auto parts shops here, all I got was "bring in the old part so we can match it" which could end as a bit of a crap shoot if the parts arent available. A bit tough halfway through a rebuild...

Thanks a lot

Joe
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Old 21-08-2016, 08:27   #12
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Re: Repowering questions from newb

[QUOTE= Fortunately, an engine that turns over without making ominous sounds and hasn't been seriously overheated will be a good candidate for a rebuild. [/QUOTE]

How can one determine if a motor has/hasn't been overheated?

Cheers

Joe
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