Merc Engine Question

[beauhill]

I have an old 1978 18' Mark Twain with a GM 230 I-6 engine in it. The motor is going bad and I was wondering if I had any other options motor wise. Mainly I was looking if it is possible to swap in a 4.3L Chevy? The stern drive is the original in the boat. Is it possible to do this, mainly will it bolt right up to the drive or not? Any help would be appreciated.

 

[Don S]

Re: Merc Engine Question

Nope, it's not a direct bolt in. The shaft on the drive (that goes into the coupling) will have to be changed to the shorter one, the exhaust Y will have to be changed to one for a V6, along with motor mounts for the side mounts on the V6 instead of the front mount on the IL6.

 

[beauhill]

Re: Merc Engine Question

Any idea where I could pick up that shaft? Is it a pretty easy to replace the shaft? I am very mechanically inclined when it comes to cars, but pretty new to boats. I figured that I would have to change the motor mounts, and I was thinking of a exhaust system that goes through the transom to bypass the y pipe.

 

[DHPMARINE]

Re: Merc Engine Question

is saving the I6 engine an option?Seems that would be the easiest/most economical.<br /><br />DHP

 

[ziggy]

Re: Merc Engine Question

i've never done a engine swap before. so i am just ranting on here. i guess first is a question. what's the goal for you beauhill? more HP, newer style engine to work on? or just to get it running again since your old motor is wore out. why not rebuild what ya have? or maybe donS can answer a question if more HP is wanted. at a quick glance of the CLYMER's book. looks like the 230,50 and 92 all have the same bore. different stokes though. and a different cam also. also other slight toloance differences from one version to the other. maybe ya could get more hp by rebuilding it as the bigger version on what you have. i don't know about the 230, but i've heard nothing but good things about the quality of a chevy 250. not a real buildupable motor, but is very good for durability. just wondering. <br />also saw a whole engine (165hp)on ebay the other day for a k note or roundabouts. <br />just seems to me it would be easier to work with what you have than to modify motor mounts, driveshaft lengths, etc. straighten me out on my notions dons and others. <br />ps, forgot about ya wanting to do the pipes out the back. read about that here on iboats, from what i read that will make yer boat sound poorly. + no gain in performance. also, there is some more mods to do.

 

[Bondo]

Re: Merc Engine Question

Ayuh,...... Ziggy brings up Many Good Points....<br />And,.. He's Right.... A Free Breathing V6 sounds More like a Piper Cub,.. Than a Hot Rod Boat......<br /><br />A 250cid motor out of a pickup truck is the Easiest Repair/Replacement.......<br />As long as the Accessories on Your Present motor are usable........<br /><br />Going to a V-motor is Very Doable, But the Little Pc.s needed will Eat your Budget......<br />Unless you can find a running "Donor" boat......<br /><br /><br />Don,........I Thought that the Inline motors used the 8" shaft,+ the V-motors used the 9" shaft ??<br />And,... While I've got your attention,... I know the Rear motor mounts on a Pre-Alpha are about 15"s apart,+ the Alpha 1s are about 9" apart,... <br /><br />Do you know how far apart the mounts are on a Bravo transom plate ????? Thanks...

 

[Don S]

Re: Merc Engine Question

You can get the shaft from any Merc dealer, local or online. It's item #14 at the link below. <br /><br />I sure hope you are aware that parts of the fuel and ignition system must be "Marine grade" parts and not automotive so you don't blow yourself (and Others) up.<br />Also, what engine are you planning on putting in the boat? Is it a full Mercruiser engine or are you going to try to start making an automotive V6 fit the boat. If that is what you are going to do, things are going to get expensive real quick.<br /><br /> http://dougrussell.com/partscatalog/collections/index.cfm?fuseaction=collectdetails&colid=04

 

[Bondo]

Re: Merc Engine Question

The shaft on the drive (that goes into the coupling) will have to be changed to the shorter one,

I Think You've got that Backwards...........<br /><br />He's Got the Short Shaft......<br /><br />He'll Need the Long Shaft for a V-Motor...........

 

[Don S]

Re: Merc Engine Question

Yep, got it backwards.<br /><br />

 

[beauhill]

Re: Merc Engine Question

My goal was a little more horsepower, and for me it is much easier to get my hands on a 4.3L than a 230, 250 or 292. I can usually pick up a 4.3L for next to nothing, but I am having trouble finding a reasonable I6. More than likely I would go with an automotive engine adding a marine cam and using marine accesories. After hearing what would need to be done to adapt a 4.3 in it sounds more economical to just find a I6. Thanks for the help.

 

[beauhill]

Re: Merc Engine Question

Also do you guys know anywhere to pick up a marine rebuild kit for I6 motors? Thanks

 

[Silvertip]

Re: Merc Engine Question

If, in your search for an engine, try for the 292. It was only available in trucks, has a very long stroke so it is a torquey engine and about 30 cubic inches bigger than the 4.3. It would be a bolt-in replacement. I would look at some truck salvage yards. The engine should be fairly inexpensive as they haven't been used for a few years now.

 

[Bondo]

Re: Merc Engine Question

Also do you guys know anywhere to pick up a marine rebuild kit for I6 motors? Thanks

1 Good way is to find a MachineShop you're comfortable with,+ Buy from them.........<br />They're more apt to give you breaks on machine time, because they're making a few nickles on the parts......