OMC Swap to Mercruiser

[rrumba]

Looking for some technical adivse / information. I have another thread in the restoration section for the boat i am working on.

I have a 1967 20ft IMP Aztec with a OMC TU-15S, 200HP 300CID Buick engine and stringer drive. I am replacing the stringers, transom and floor. originally i was going to tear apart the engine to do a thorough check but have not been able to find the headset or lower end gasket set and the fact that all power plant items are 44 years old and obsolete has guided me to the unfortunate decision to swap to a readily available power plant from a donor boat like a merc. So i am going to sell the electric shift outdrive, intermediate housing, parts and motor to help offset the cost of the donor, hopefully they will sell. :facepalm:

My questions:
1. Is my transom going to be able to support the new sterndrive unit once i rebuild it to a 2" - 2 1/4" width with extra knee braces and glassing into the sides of the hull? currently the transom does not extend to the top of the cap. see picture at bottom.
2. where can i find information for the placement of the engine support pads for the engine mounts, distance from the transom, height and how they should be constructed?
3. what size engine would be best, 4.3, 5.0, 5.7? i was looking at a 5.7 but not sure if that would be best for the hull.
4. Is a transom drilling fixture absolutely necessary, would i be better off having a shop do it, will a cut out from the donor boat work?

Any assitance would be GREATLY appreciated so i do not make any mistakes as i get closer to the transom replacement.


this shows the transom

Rebuild thread with other pictures
http://forums.iboats.com/showthread.php?t=487195

 

[HT32BSX115]

Re: OMC Swap to Mercruiser

1. Is my transom going to be able to support the new sterndrive unit once i rebuild it to a 2" - 2 1/4" width with extra knee braces and glassing into the sides of the hull? currently the transom does not extend to the top of the cap. see picture at bottom.

Howdy,

It should be. If you're making it strong enough by meeting the minimum thickness requirements, and adding support.

2. where can i find information for the placement of the engine support pads for the engine mounts, distance from the transom, height and how they should be constructed?

You need to get a Mercruiser installation manual.....Someone should along shortly with a link that should get you to a place to download it.

3. what size engine would be best, 4.3, 5.0, 5.7? i was looking at a 5.7 but not sure if that would be best for the hull.

If that's a 20' boat, I would want a MINIMUM 5.7L engine.

4. Is a transom drilling fixture absolutely necessary, would i be better off having a shop do it, will a cut out from the donor boat work?

While you could probably do it without a drilling fixture, I would consider having a shop do it if I couldn't find one........getting it right is worth a little extra money. (just make sure they do it right!!)


Regards,


Rick

 

[Bondo]

Re: OMC Swap to Mercruiser

Ayuh,... #4,... I usually use the fiberglass piece from the donor boat to lay out the cut-out, then do the deed by hand, No fixture...

If ya get it wrong, refill the holes, 'n try again...

 

[04fxdwgi]

Re: OMC Swap to Mercruiser

I have the drive installation manual, but it's a 3 meg PDF. Here is a link to it http://www.boatfix.com/merc/Install/gas/86017211.pdf

The OMC to Mercruiser conversion docs are readily available on the net, as I HAD them when I was considering a fix-r-upper w/ a bad OMC on it. Pretty much if you are converting OMC Cobra to Merc, it is just about a bolt in swap, using existing cut out. If the old OMC is a King Cobra, you are SOL unless you want to fill in and re-cut the transom cutout

 

[Bondo]

Re: OMC Swap to Mercruiser

I have the drive installation manual, but it's a 3 meg PDF. Here is a link to it http://www.boatfix.com/merc/Install/gas/86017211.pdf

The OMC to Mercruiser conversion docs are readily available on the net, as I HAD them when I was considering a fix-r-upper w/ a bad OMC on it. Pretty much if you are converting OMC Cobra to Merc, it is just about a bolt in swap, using existing cut out. If the old OMC is a King Cobra, you are SOL unless you want to fill in and re-cut the transom cutout

Ayuh,... He's doin' a Stringer drive to Merc...

Nothing bolt-in about it....

 

[04fxdwgi]

Re: OMC Swap to Mercruiser

Ayuh,... He's doin' a Stringer drive to Merc...

Nothing bolt-in about it....

OOPs... my bad. Just saw "OMC" and didn't notice the "stringer drive". Whole different animal. Break out the Sawzall and drill.

 

[HT32BSX115]

Re: OMC Swap to Mercruiser

OOPs... my bad. Just saw "OMC" and didn't notice the "stringer drive". Whole different animal. Break out the Sawzall and drill.

If the old OMC is a King Cobra, you are SOL unless you want to fill in and re-cut the transom cutout

Yeah........I did a "King Cobra" to Merc Bravo and it was an essentially "Bolt-in" swap.....

 

[rrumba]

Re: OMC Swap to Mercruiser

Yeah i kind of figured i would have to fill in that HUGE gaping hole in the transom and that was on the to do list as it is soft and seperating, so it is a good time to do so.

I have the drive installation manual, but it's a 3 meg PDF. Here is a link to it http://www.boatfix.com/merc/Install/gas/86017211.pdf

Thank you much for the link. that will help to figure out the mount for the outdrive.

Any information on the engine mounts? That link did not seem to cover the placement for the engin mounts from the transom, unless i just missed that part.

While you could probably do it without a drilling fixture, I would consider having a shop do it if I couldn't find one........getting it right is worth a little extra money. (just make sure they do it right!!)

I am leaning toward this way myself

Ayuh,... #4,... I usually use the fiberglass piece from the donor boat to lay out the cut-out, then do the deed by hand, No fixture...

If ya get it wrong, refill the holes, 'n try again...

This i might practice with the donor boat. Can't hurt anything and i should have several shots at it as well to make sure i can get it right, or it will have to go in.


I have been trying to find information on the net for the engine swap and have not been able to find anythign about the enigne landing pads for the mounts. might have to look at someone else's boat to get the measurements.

With a 5.7L, should i look for a bravo drive or an alpha1 gen2, or just an alpha1?

 

[rrumba]

Re: OMC Swap to Mercruiser

forgot to ask........

do you think the transom will be able to support the outdrive even though it does not extend up to the cap?

 

[rrumba]

Re: OMC Swap to Mercruiser

hmmmm.......

just noticed, someone moved it into the restoration section. Sorry if i had posted it in the wrong place, thought it belonged in the engine section. i have another thread on here for the restoration i am doing on the boat, should these be combined or this one deleted?

again, sorry for that

 

[HT32BSX115]

Re: OMC Swap to Mercruiser

hmmmm.......

just noticed, someone moved it into the restoration section. Sorry if i had posted it in the wrong place, thought it belonged in the engine section. i have another thread on here for the restoration i am doing on the boat, should these be combined or this one deleted?

again, sorry for that

The biggest reason for moving it is that it gets it closer to the people that are in to resto "stuff" so it's a good thing when it gets moved!

do you think the transom will be able to support the outdrive even though it does not extend up to the cap?

I don't think it's a "Big" problem....... Since you're going to replace the transom, You can make some changes to it that will stiffen it up including putting a sort of "top-cap" on it that could be screwed into the top to give you a little more structural integrity.

With a 5.7L, should i look for a bravo drive or an alpha1 gen2, or just an alpha1?

You could in reality do any of the above.......

I think it would be cheaper to do an Alpha. AND since you;re going to do some resto-work I would probably get a new SEI Alpha II type drive to get the warranty. Just make sure you get the right gimbal mount. (there's a LOT of them on ebay, new and used)

 

[rrumba]

Re: OMC Swap to Mercruiser

thanks for the advice will have to look into them.

 

[oops!]

Re: OMC Swap to Mercruiser

good choice on the swap.

you will have no worries about your new transom........just make sure you are at the 2- 2 1/4 thickness......dont go over with the thickness because the transom plate will not have long enough studs to go thru and the new drive shaft will not be in the coupler far enough thus causing vibration issues.

every thing you need to know is in the link in my sig......detailes and pics.
you can get a t plate jig.....but any paper template will work.
don s knows where to download instructions and a printable template.

do not be afraid.......you CAN do this.
just be precice in your measurements.

once the x dimension is calculated..(crank shaft centerline).....the mount height is easy to figgure. also you will have 2 inches of tolerance on the isolator pins. so motor mount height is not too much of a factor.

one newer trick......is an aluminum L bracket or angle iron with a 4 inch lip.....this is bolted to the side of the stringer and the isolator goes on top of the channel.

in the thread in my sig......is a guy called rob j.
this is a good buddy of mine that used this system......he has a link in his sig with pics of that mounting system.

cheers
oops

 

[rrumba]

Re: OMC Swap to Mercruiser

every thing you need to know is in the link in my sig......detailes and pics.
you can get a t plate jig.....but any paper template will work.
don s knows where to download instructions and a printable template.

thanks Oops, i will have to see if i can get Don Ss' attention for a paper template. I did see the jig that Frisco used and that seems like it should work quite well for the holes as well.

one newer trick......is an aluminum L bracket or angle iron with a 4 inch lip.....this is bolted to the side of the stringer and the isolator goes on top of the channel.

in the thread in my sig......is a guy called rob j.
this is a good buddy of mine that used this system......he has a link in his sig with pics of that mounting system.

I have searched quite a few of his posts and could not find anything in his sig for it. I will try a search for it with his user name.

Now i guess i can put this thread to sleep for a little bit until i get to that point, which hopefully will be within the next week.

I still have to post some pictures up for the engine area that i have partially removed in my other thread.

Oops, if you have a minute could you look at my other one regarding my layup schedule and let me know if there are any suggestions for changes? I would greatly appreciate itf. and if anyone else would as well that would be GREAT! I have some changes that i will be making to it tonight.

 

[Bondo]

Re: OMC Swap to Mercruiser

and have not been able to find anythign about the enigne landing pads for the mounts. might have to look at someone else's boat to get the measurements.

Ayuh,.... Rebuild, 'n locate the transom plate...
Hang the motor on the rear motor mounts...
Align the motor(hangin' on a chainfalls) with yer alignment bar,...
Then meassure, 'n build up the front mounts to match what ya found,...
Install the motor, 'n realign....

 

[rrumba]

Re: OMC Swap to Mercruiser

Ayuh,.... Rebuild, 'n locate the transom plate...
Hang the motor on the rear motor mounts...
Align the motor(hangin' on a chainfalls) with yer alignment bar,...
Then meassure, 'n build up the front mounts to match what ya found,...
Install the motor, 'n realign....

thanks for the input Bond-O


It sounds so easy reading everyone's response. I can't wait to get to that point, that has been one point that has been stressing me on how to accomplish as i have not been able ot find much on the engine swap. It seems that most swaps that are posted are from a cobra or smaller merc to a different merc and very difficult to find a stringer conversion.

thanks,
Roger

 

[wire knot]

Re: OMC Swap to Mercruiser

I did one, OMC - Volvo penta. Last year. I was a virgin before.

http://forums.iboats.com/showthread.php?t=455808

My motor mounts were fabbed to sandwich the stringer and raise aprox 2 inches.
I went from a high profile omc, doesn't matter what ya got now. fill the hole.
get the template, measure ,measure , measure. Cut her up.

If you keep a thread going with lots of pics and updates, the gurus on IBOATS will help you.

 

[rrumba]

Re: OMC Swap to Mercruiser

Wire Knot, nice job and what a power package......

what type of plywood was that? I am looking at using the Auraco to redo the stringers and transom with and have read about all types of plywood being used from plain exterior grade, sheating, pressure treated that has sat to dry out, fir, birch, no one really said anything about pine though but to me it seems like it would be a little weak. Anyone have any suggestions?

I like the idea of the plate you used, but stainless plate isn't that cheap and i do not have the welder for that. guess i will have to have pay someone to do that part.



I guess i should dump my other thread and just keep this one going instead. I will repost my pics and work so far in this thread and see about getting one of the mods to delete my other one. i'll get that done tonight. I have a planned layup schedule that i would like some advice on as well and will get that posted up.

 

[jasoutside]

Re: OMC Swap to Mercruiser

Eh Roger!

Just thought I'd swing through and say howdy!

I am about half way through the OMC Stringer Drive to Merc 4.3 V6 transplant myself. Though, I'm working on aluminum vs. glass. So some differences, some similarities. There may be some value in swinging through my thread to see how I worked the transom and cutout, might be helpful to you.

At this point I am just about ready to start installing the new driveline, maybe within a week or so.

Anyway, just thought I'd say hey what's up!

Have fun man

 

[rrumba]

Re: OMC Swap to Mercruiser

Hey jasoutside.........

thanks for the visit and information

Funny thing is I have been reading your post off and on but only got up to page 5 so far. I will definitley be checking the rest of it out as well. Will keep your mom in our prayers also.

The only thing that i can see having an issue with what you are doing is that white stuff you get up there nothing good can come from that stuff, good thing the sun is out now. i am originally from hawaii so i will never get used to that white stuff......