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Outdrive Conversion

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ruckus3313

Regular Contributor
"I was interested in buying a

"I was interested in buying a new boat,however, it has a 350 mercruiser with alpha 1 drive. Can i convert that to a duo-prop outdrive. i know the engines are good and very common (5.7L 350 chevy) but would much prefer a VP DP outdrive. If not possible Im not buying the boat lol...thanks for the help"
 
"mmmmm.... just yesterday afte

"mmmmm.... just yesterday afternoon, my friend and I towed his neighbor with the same engine/drive setup. He'd broken something in the lower unit for the third time in two years.

That said... It depends on what you mean by "conversion" and how much work you are willing to do. 280 and 290 series DP drives will happily live behind a 350 MERC, however, you will need to source everything from the back of the engine thru to the props. The cutout in the transom for a 200 series drive is a larger hole than the MERCs. At one time a routing jig was available to enlarge the hole.

HOWEVER....350 CID engines have their breathing resricted if you run them thru 200 series lower units (MERC shop manual STIPULATES 4" minimum exhaust port for single exhaust, the VOLVO is less than 3" in effective diameter). I just converted my 5.7L MIE Merc to thru transom w/mufflers... got almost 500 RPMs more at WOT with the same prop. I also do not like the thru the leg water pickups and have converted every Volvo I/O powered boat I've owned to thru the hull pickup w/strainer with very good results. My current boat has an external wedge shaped strainer that seems to be totally trouble free (after 3 seasons)"
 
so it can be done i would just

so it can be done i would just have to replace everything flywheel back correct??? Also as far as exhaust that sounds like a
good idea!! Just run a thru hull instead of running through the out-drive and you can easily adapt exhaust diameter issues?? and as far as converting to a thru hull water pickup instead of leg pickup??got any pics showing me how it works and it ran??
 
"I'll ditto this idea of g

"I'll ditto this idea of going to the Volvo Penta Duo Prop drive.
I would, however, recommend a drive later than the 290 so that you can get away from the REV latch unit.
The DP C or later would be a good choice in my book.

In addition to everything from flywheel on back, you will need the smaller 153 tooth flywheel (and starter motor).
This can also use a standard AQ series Flywheel Cover w/ the fine spline Primary Drive Shaft.

Yes, transom cut out will be enlarged... no big deal.... it's just fine carpentry work with good layout.

Get rid of that dang Mercruier drive!
Easy drive bellows replacement, no thru prop exhaust, no more Shift Interrupt, no lower shift cable, no Dog Clutch gear engagement ..... only smooth cone clutch shifting from here on out!
Truly a win win!

. "
 
"Wow Ricardo! you just saved m

"Wow Ricardo! you just saved me alot of money and headaches. I was about to make a switch from my volvo setup to a merc. I have a '86 Bayliner 2560 with a 270 outdrive but no Motor. I still gotta find the original one that was in there. It had a AQ260A GM350 type. I can only find the expensive drop-ins, no used. I decided to convert an auto GM350 to marine. My winter project.Keeping my volvo setup!"
 
"James, the auto engine will u

"James, the auto engine will use the dreaded Dished Pistons..... very un-desirable for marine use.... especially when we get up to/around 24/25 feet and above.
Detonation is one of the gasoline marine engine's worst enemies. Dished pistons give detonation a good head start! Not good!

To do this correctly, you will want a Quench Effect piston/head combination. This can be achieved in several ways. (more on that unless "hell bent" on using the auto engine.... if so, I can't help you.)

It is always much more than marine head gaskets, brass freeze plugs, marine cam profile, dual plane intake manifold, etc. A marine engine's load is much greater than what a car/truck undergoes. We must build to accommodate this.

You will undoubtedly get feedback from the so called automotive- SLASH- marine cross-over guys who will tell you that the auto/truck engine with dished pistons will be just fine.
These guys typically do not routinely build these engines nor own, operate cruiser type boats.
They most likely have smaller hulls.
For this, it can work OK for them.
For YOU, I'd not do it!

You are only a few boat dollars away from building a properly built marine SBC using a quench style piston and proper cylinder head combination.
There are lots of piston choices available to acheive this. Large chamber heads/small chamber heads.... it can be done with proper piston selection!

In addition, we do not try to build High Horse Power into these for your type of usage in a 25 footer.
With the Volvo, performance can be additionally enhanced by installing the Duo Pro lower unit. (you mentioned this above)
This is the Best Bang for the Buck! IMO!

Good luck with which ever way you go! "
 
Thanks Robert!! That looks lik

Thanks Robert!! That looks like a good idea. Easy for winterizing too. So instead of that inlet hose being connected to the tube on the transom it takes it from the bottom hull of the boat
 
"Stern is the left hand side o

"Stern is the left hand side of pix. Note remnants of the zinc tabs on the back of the scoop. There are versions of that scoop where the inlet screen is removeable should one ever need to clean out the inlet.

Re: Winterizing...
Not only winterizing... but after a long run I flush the system ( I live in salt water).
All I have to do is shut off the 1/4 turn, hook up a short hose to the hose bib and stick the other end in a 5 gal pail with a hose running in it. Previous owner of boat did that every time he ran the boat and got 35 years out of a raw water cooled engine... When I bought the boat in 2004, it had the original engine... Boat built in 1969 and lived all its life in salt water.

Also info on thru transom exhaust coming.."
 
"Thru transom exhaust…

Merc

"Thru transom exhaust…

Mercruiser kit for Thru Transom Exhaust Outlets
- (3 in.).................843434A1 108
- (4 in.).................843426A1 108

Disconnect exhaust system after the elbows, run correct size exhaust line hose to thru transom kits.
Note, on some engines, if you run straight back you will interfere with some “stuff” on the 200s series drive
Some rerouting may be necessary. Note these kits include the all important shutters.

You can easily fabricate a plate to block off the hole thru the transom shield, or if you can find the part, Volvo actually made one.

The above will be noisy… some jurisdictions require mufflers… If yours does, let me know. There are several options.
Re:
Thru hull water pickup…
On my boat which has a deep V hull, the best place for the pickup was slightly to port of the hull’s centerline, just in front of the crankshaft pulley.

There are several options for the thru hull pickup. I would have been happier if my mechanic used, but he one with a non removeable screen.

External strainer P/N BUC00RSS650P (http://marineengineparts.com/shopsite_sc/store/html/page87.html)

Where and how to mount this, further down on writeup.
Thru hull…
http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/3157 8?&cid=chanintel&ci_src=14110944&ci_sku=31578

Use the one that is your correct size…. Probably 1 ¼ or 1 ½ “

Make a backing plate out of “starboard” and bond it to the inside of the hull with 5200 sealant.

Screw a shutoff directly on the end of the thru hull
http://www.marineparts.com/mpf/mpf460.aspx
I prefer the “Full port Apollo” types, again use correct size.
On the top end of the shut off install a bronze nipple (short pipe threaded both ends).
Onto the nipple, thread a bronze “T”. Face the “T” aft and install.
http://www.jamestowndistributors.com/userportal/search_subCategory.do?categoryNa me=Pipe%20Fittings&categoryId=612&refine=1&page=GRID

Again, use correct size for hose… Onto the barb connect marine water inlet hose… use wire lined as this is on the suction side. Route the hose in a big “U” aft and then to the raw water pump.

Onto the TOP of the bronze “T” fitting you can either install a bronze pipe plug or a bronze reducer. The reducer should be such that you can thread a bronze hose bib, i.e. connection for a garden hose. This is handy way to fresh water flush you system or to winterize it.

Mounting the wedge strainer. The front (narrow) edge of the wedge should face forward BUT it should be “toed in” towards the keel of the boat if you boat has a “V” hull aft. Water flow is NOT straight back but rather flows from the keel outward to the side and back at an angle. The strainer should face into the flow.

One of the mounts of the strainer should be a thru bolt so you can “bond” the strainer to ground. Likewise with the shutoff valve."
 
"Volvo designed a pretty decen

"Volvo designed a pretty decent water pick up system for these stern drives that picks cooler water up from under the surface enough to also aid in eliminating the possibility of floating debris.
My thoughts are, when we are given a choice between what Volvo gave us, and a thru hull, the Volvo system is going to be on my boat! (no offense, Robert!)
If you do the proper maintenance, these systems are Great!
If you wish to add the sea water strainer, by all means do so.

I don't want to be misunderstood here, the thru hull water pick-up works also.

And J.C.H., That drive that you link to is the later style Volvo Penta. With all of the flywheel-to-prop components, it would work for you.
I think that the AQ "C" or "C 1" series drives are a better choice but would require enlarging your transom cut-out!
Before discounting this, you'd need to educate yourself on the design differences and EASE of maintenance of the AQ series drives over that of the later Gimbal'd style drives.
No routine engine alignment, all steel drive coupler, easy drive bellows replacement, no thru prop exhaust..... just to mention a few!
(just my personal choice)

."
 
"Where I live and boat is a de

"Where I live and boat is a delightfull piece of water called..."Barnegat Bay". There are miles and miles of water that is only a foot or two deep and there are shifting (and often uncharted)sandbars all over the place. There is a saying here... If you haven't run aground in Barnegat Bay at least once this year, you haven't taken your boat out of its slip. It is rare to see a prop whose tips haven't been "polished" :).

Given that, thru hull water pickups improve my raw water pump impeller life drastically."
 
"In that particular case, I&#3

"In that particular case, I'd certainly agree, Robert!
I do not know how many of us other boaters have to deal with that scenario."
 
On the bright side.... the opp

On the bright side.... the opportunity to hit rocks (or anything hard) is limited to running into a jetty at one of the inlets.
 
"Rick,

I easily see the des

"Rick,

I easily see the design benefits of the Volvo over the Mercrusier all day long. And Im really hesitating on buying this boat JUST because of the Mercruiser. Almost easier to buy another REALLY nice boat with a V/P Duo Prop already installed!! I was just thinkin is all!! This boat with the Mercruiser is one beauitiful boat and was professionally surveyed.100% clean bill of health!!I can also aquire this boat real inexpensive!! I may still buy it and if I do you guys can guarentee that Im taking that Merc Alpha outdrive out and installing a V/P DP!!!Hope you guys can help if I do this.

Robert,

Thanks for your help on this project as I most likely will be doing this thru-hull exhaust if i buy this boat. A lot of work ahead of me but will be worth the efforts in the long run. I really look forward to this "swap" if the boat is bought."
 
"looking for a 20-24ft cuddy o

"looking for a 20-24ft cuddy or open bow with at least a 5.0L or bigger v8 thats in nice shape.



and of course with a Volvo
lol.gif
"
 
"Rick,

Could you give me a

"Rick,

Could you give me a link to where i could take a look at some pics on an "aq c" or a "c 1" outdrive please. that would be much appreciated !!"
 
and this engine alignment deal

and this engine alignment deal with the MERC's?? what the heck is all that about? Why do you have to align the engine with Merc but not these Volvo's??
 
"JC, Any of the drives using

"JC, Any of the drives using the Gimbal system (Mercruier or later Volvo Penta) require the routine/annual engine alignment.
The AQ series, however, does not use a Gimbal drive suspension system... so no alignment after initial installation."
 
"BTW, what are the consequence

"BTW, what are the consequences of not aligning the gimbal suspension system up correctly?? as Im aware my brother in laws 1979 18 ft open bow w/ merc 165 has had the outdrive off it seems like a 1/2 dozen times per year lol(because it always breaks) and never heard him mentioning"engine alignment""
 
"Most of the Gimbal'd syst

"Most of the Gimbal'd system engines use a rubber hubbed drive coupler. These early ones use aluminum splines in the coupler.
If out of alignment, the drive shaft will wear away at these splines, eventually ruining them..... hence the need for routine checking/setting of alignment.

The front engine mounts are raised Up/Down to adjust.

If a coupler goes bad from not addressing the alignment, the engine must come out for coupler replacement."
 
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