omc engine switch

[prblygnasnk]

Hi, I have bought a 24' Starcraft cheiftain aluminum boat.It's partly iboats fault. While it was love at first sight,I didn't decide until after reading threads of restorations by SPRINTST,WRFALPACAS,NORTHBEACH,and BOB VT,some how I got hooked. My question for this forum is...my boat has a 120 hp 4 cylinder OMC with a cracted block. I have been offered a 165 hp 6 cylinder OMC. Can the cheiftain handle the extra hp ? Would I have to put extra bracing in ,or just move the mount ? The sterndrives look the same, would they be geared the same ,or would I have to switch them too?

Any help is appreciated thanks.

 

[wire2]

Re: omc engine switch

What year? It's the last 2 digits of the VIN, usually on the outside of the transom, right side.
If it pre-'85, it's a stringer 400 drive, with 2:1 gear ratio.
If post-'85, it's a Cobra, still 2:1 outdrive.
An I6 (or V6) is usually ~1.6:1. You will need to change the outdrive if it's a stringer.
As for the extra power, a 24 ft boat can easily handle it. Lots of 24 footers have V8's.

 

[prblygnasnk]

Re: omc engine switch

Thanks for the info,as I thought the drives were the same,wishful I guess
both boats and motors are inline and 1977 with stringers
the 6 is longer than the space , I'd have to cut the floor and make a new dog house
I've also found a rebuilt 140hp omc straight 4 without a drive.I'd have to use my 120hp drive. It cost more for less and no trailer or parts boat to resell as with the 6
140hp = easy install +$900
165hp = refit,exchange drives time&labour $ free if able to sell extra trailer & 120 drive
how many wknds of labour are we talking? any guide info available,tricks? or DON'T DOS? any special tools needed? is 25hp worth the labour?
My Wife is going to name the boat GROUNDS4DIVORCE if it ends up living in the yard and shop in peices. I have to decide soon and get the one I choose winterized.
Thanks again

 

[reavesga]

Re: omc engine switch

I would go with the 140 HP conversion. Easy to do, easy to install, will work with the stringer with no issue. I have a 140 in a Crestliner Cuddy, similiar to the Chieftan, and the 140 gets the job done nicely. Now, if you are going to go through all of this effort, you might want to switch out to a Mercruiser drive instead of the stringer due to parts and support. I just did this conversion. 3 months of weekends and evenings steadily working on it. Started second weekend in August. Water tested it last weekend.



http://forums.iboats.com/showthread.php?t=436500

 

[prblygnasnk]

Re: omc engine switch

nice boat ,I read your thread on the conversion, nice work. but 12 weekends and I don't have a Mercruiser, switching one stringer for another (that looks the same), no measuring, I think would still be easier. if I do go for the 140hp then as for the stringer if it aint broke... Other than a 14' 40 evinrude,this is my first "real" boat I/O is all new to me. (why are they called stringers?)

 

[wire2]

Re: omc engine switch

..... (why are they called stringers?)

The entire engine and outdrive is mounted on/supported only by the boat's stringers. There's no thrust to the transom like with a Merc.

 

[prblygnasnk]

Re: omc engine switch

Oh...I get it ,that explains the bigger hole and rubber seal.So would the transom have to be beefed up and braced to switch to a merc? (maybe down the road )
thanks Dale

 

[prblygnasnk]

Re: omc engine switch

Well I bought the parts boat motor and trailer,a 1977 20' fiberglass Starcraft 165 inline 6 omc,great deal half what I was quoted for just the motor.The problem is it's too good. It's intact perfectly good usable as is (now winterized).I think I'll just run it next year and get a feel for the I/O. In the meantime (after Christmas) I'll watch for a drop in motor for the Cheiftain.
I'd add pictures, is there instructions as to how?
thanks Dale

 

[Bluestream]

Re: omc engine switch

The entire engine and outdrive is mounted on/supported only by the boat's stringers. There's no thrust to the transom like with a Merc.

As I recall that is what OMC used as their main selling feature of the Stringer drive in their brochures. All force goes dirctly to the stronger stringers and not the weaker transom...

 

[prblygnasnk]

Re: omc engine switch

As I recall that is what OMC used as their main selling feature of the Stringer drive in their brochures. All force goes dirctly to the stronger stringers and not the weaker transom...

thanks ,it sounds good to me. I just hope it functions properly as is(once I put a motor to it). If not, then I'll look deeper into modifying/updating vs replacing.
these are my projects (collection)

 

[wire2]

Re: omc engine switch

As I recall that is what OMC used as their main selling feature of the Stringer drive in their brochures. All force goes dirctly to the stronger stringers and not the weaker transom...

That, and the ability to make a U turn in the boat's length.

 

[prblygnasnk]

Re: omc engine switch

time to update the good deal I got on the 20' fg 165 omc was wasted. I had it winterized by a professional, or so I thought . I now have 2 boats with cracked blocks. It messed up my holidays to say the least, What a sick feeling.
Putting that behind me , I found and bought a motor for the cheiftan. It's a 120HP OMC duel carb, exactly the same as the one I took out, minus the crack. The boat still needs cosmetic work ,but for this year I just want to get the motor in and adjusted,and try it out.
I also want to learn the best way to winterize it myself , any sugestions ?

 

[Gettinther]

Re: omc engine switch

time to update the good deal I got on the 20' fg 165 omc was wasted. I had it winterized by a professional, or so I thought . I now have 2 boats with cracked blocks. It messed up my holidays to say the least, What a sick feeling.
Putting that behind me , I found and bought a motor for the cheiftan. It's a 120HP OMC duel carb, exactly the same as the one I took out, minus the crack. The boat still needs cosmetic work ,but for this year I just want to get the motor in and adjusted,and try it out.
I also want to learn the best way to winterize it myself , any sugestions ?

Your almost my neighbour
Look here for a beginning
http://forums.iboats.com/showthread.php?t=468655