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  1. #1
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    Nov 2019
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    Default Merc 305 to Volvo 350 swap

    Hey everyone, Im Jack, new to the boating scene. So Im going to ahve a ton of questions but here is the background. Got suckered into a '79 Searay 22.5 footer for free. The 305 in it was cracked and the manifolds shot (someone didnt winterize). So before doing anything costing money, I took off the outdrive (what came before the Alpha one? has the eyehook on it), seems to rotate just fine, before I took it off I put it in forward drive and it would lock into place one way and ratchet freely the other. Put it in reverse and it same thing just opposite direction. Neutral just let it free wheel. Im going to assume that this is all good and that the outdrive is fine. So after taking it off I took off all the wires, hoses, etc, and still need to pull the engine out of the compartment. In the meantime I was able to get my hands on a rebuilt Volvo 350 for $500 that was hooked up to a paragon transmission prior to rebuilding. The thermostat housing on it shows a casting date of 12/1984 (please tell me thats a date and not some serial number?!) Im looking to keep the outdrive and put in the Volvo. Now I havent been able to lift the old 305 out yet to look at how exactly the outdrives shaft slid into it, but im really hoping all I should have to do mechanical wise is to swap out the flywheel and clutch plate? Any hints, thoughts or have I gone insane? Oh on top of all that, I am also thinking that I will have to put a new prop on it to deal with going from a 305 to 350. Correct?

  2. #2
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    Nov 2019
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    Norfolk VA
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    Default Re: Merc 305 to Volvo 350 swap

    Update to this, so a bit more searching, The Volvo is an AQ260 (no letter designation) and the serial number is CU4071 . Attachment 22314

    The Transom has this (52??55)Attachment 22315 and the gimble has this (5225(3?)22) Attachment 22316
    and the outdrive has this (5245551)Attachment 22317Attachment 22318
    Last edited by Jdadali; 11-25-2019 at 07:58 PM.

  3. #3
    Join Date
    May 2010
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    DC Burbs/Maryland Eastern Shore
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    Default Re: Merc 305 to Volvo 350 swap

    Ha ha ha as you see getting a boat for free is a giant money pit. I would just swap everything over (new gaskets as needed) and see what happens. I'm sure Post Count Rick will chime in with the usual quench-effect piston treatise and a bunch of other off the wall tish.
    You really want to be sure the hull is in good shape structurally (no rotten engine beds, bad transom etc) before putting effort into this project
    Practicing the ancient art of ren-ching

  4. #4
    Join Date
    Nov 2019
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    Norfolk VA
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    Default Re: Merc 305 to Volvo 350 swap

    Haha I hear ya. Ive brought back some other much smaller boats with outboards on them. Ive already started to rip out carpeting, trim, and marking areas for fiberglass reinforcement. Nothing major yet and ive poked around the engine bay. Good thing im also a good woodworker and jack of all trades. Im a bit worried about mating the two together, just need to get the other engine lifted out before i rip that apart and see about swapping flywheels. Curious though, Cant find a year for the AQ260, but since it doesnt have an A or B on it im guessing early 80's and the flywheel is 13" not 14" so maybe I got really lucky and the bellhousing should swap over?

  5. #5
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    Default Re: Merc 305 to Volvo 350 swap

    yeh should
    Practicing the ancient art of ren-ching

  6. #6
    Join Date
    Jun 2006
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    Spotswood, NJ, USA
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    Default Re: Merc 305 to Volvo 350 swap

    remove the drive BEFORE removing the motor. ask how if your not sure how

  7. #7

    Default Re: Merc 305 to Volvo 350 swap

    Strip it down to the long block and swap all the merc components over. Advice to check stringers and transom condition before you get in too deep is sound advice

  8. #8
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
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    5,886

    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Dieter View Post
    Strip it down to the long block and swap all the merc components over. Advice to check stringers and transom condition before you get in too deep is sound advice
    Ayuh,...... Completely Agree,...... Swap the long blocks,......

    Don't even try to swap the bobtail motors,.....
    Any Grease is Better,... Than No grease at All....

  9. #9
    Join Date
    Nov 2019
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    Norfolk VA
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    Default Re: Merc 305 to Volvo 350 swap

    Im on boss! Already too the outdrive off. Planning on swapping out the coupler and flywheel IF they will match up. otherwise back to square one. From the looks of it the Volvo used a raw water pump on the front of the engine instead of in the outdrive? Should I just remove it or should I remove the impeller in the Merc outdrive, or should I just use them both? Oh and the stringers under the engine will def get a good look once actually lift the engine out.

  10. #10
    Join Date
    Mar 2009
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    Portland, Oregon,
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    11,508

    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Jdadali View Post
    Hey everyone, Im Jack, new to the boating scene. So Im going to ahve a ton of questions but here is the background. Got suckered into a '79 Searay 22.5 footer for free. The 305 in it was cracked and the manifolds shot (someone didnt winterize). So before doing anything costing money, I took off the outdrive (what came before the Alpha one? has the eyehook on it), seems to rotate just fine, before I took it off I put it in forward drive and it would lock into place one way and ratchet freely the other. Put it in reverse and it same thing just opposite direction. Neutral just let it free wheel. Im going to assume that this is all good and that the outdrive is fine. So after taking it off I took off all the wires, hoses, etc, and still need to pull the engine out of the compartment. In the meantime I was able to get my hands on a rebuilt Volvo 350 for $500 that was hooked up to a paragon transmission prior to rebuilding. The thermostat housing on it shows a casting date of 12/1984 (please tell me thats a date and not some serial number?!) Im looking to keep the outdrive and put in the Volvo. Now I havent been able to lift the old 305 out yet to look at how exactly the outdrives shaft slid into it, but im really hoping all I should have to do mechanical wise is to swap out the flywheel and clutch plate? Any hints, thoughts or have I gone insane?
    Oh on top of all that, I am also thinking that I will have to put a new prop on it to deal with going from a 305 to 350. Correct?
    When up and running, you will want to perform what's called a WOT RPM test. This test will let you know if the drive reduction and the prop are correct or not.
    The prop that you now have may work.

    Quote Originally Posted by o2batsea View Post
    ............... I'm sure Post Count Rick will chime in with the usual quench-effect piston treatise and a bunch of other off the wall tish.
    Note that Jdadali picked up a "rebuilt Volvo 350 for $500".
    If this engine is good, there's no need to tear into it and make any changes!


    Quote Originally Posted by Jdadali View Post
    .......just need to get the other engine lifted out before i rip that apart and see about swapping flywheels. Curious though, Cant find a year for the AQ260, but since it doesnt have an A or B on it im guessing early 80's and the flywheel is 13" not 14" so maybe I got really lucky and the bellhousing should swap over?
    All of the early Volvo Penta AQ series GM SBCs used the 153 tooth ring gear flywheel.
    Merc typically used the 168 tooth ring gear flywheel.
    If both engines were pre-1986, the crankshaft flange will be the same.
    If by change the Volvo is post-1986, then the flange will require the flywheel with the smaller center bolt pattern, which also means that the Merc drive coupler will need to be a match.

    Side note:
    The 153 tooth requires the starter motor with the straight across bolt pattern.
    The 168 tooth requires the starter motor with the staggered bolt pattern.

    Either way, you'll do better with one of today's HTGR/PMGR starter motors.

    Quote Originally Posted by Jdadali View Post
    Im on boss! Already too the outdrive off. Planning on swapping out the coupler and flywheel IF they will match up. otherwise back to square one. From the looks of it the Volvo used a raw water pump on the front of the engine instead of in the outdrive?
    That is correct! All Volvo Pentas use an engine located seawater pump.

    Should I just remove it or should I remove the impeller in the Merc outdrive, or should I just use them both?
    The Merc Alpha requires the OEM drive located seawater path for upper gear unit cooling.
    If you use the Volvo Penta seawater pump (with a thru-hull pickup), you will need to leave the Merc pump active, and perhaps allow that seawater to go over-board.

    By the way, IMO, the crankshaft seawater pump is a much better system!

    Oh and the stringers under the engine will def get a good look once actually lift the engine out.
    Good call!




    .
    Last edited by RicardoMarine; 11-26-2019 at 09:00 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  11. #11

    Default Re: Merc 305 to Volvo 350 swap

    Just a thought might be worth running the 350 on the ground as is before stripping it down check compression oil pressure and look for evidence of water intrusion into oil before swapping components and is stalling into boat

  12. #12
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    Sep 2003
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    New Tripoli, PA, USA!
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    16,419

    Default Re: Merc 305 to Volvo 350 swap

    ALWAYS run a motor "on the ground" before going to all the work of installing it.

    Jeff

  13. #13
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    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Dieter View Post
    Just a thought might be worth running the 350 on the ground as is before stripping it down check compression oil pressure and look for evidence of water intrusion into oil before swapping components and is stalling into boat
    Great idea.... and I couldn't agree with you more.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  14. #14
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    Nov 2019
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    Norfolk VA
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    Default Re: Merc 305 to Volvo 350 swap

    Just want to say thank you to everyone! Sorry its been a bit, I finally got around to ripping out the old engine and sure enough, just gotta swap out some components and it should be good to go! Ill be putting it in closer to the spring, just working on the hull and other components. Click image for larger version. 

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  15. #15

    Default Re: Merc 305 to Volvo 350 swap

    Nice gibbet.

  16. #16
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    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Jdadali View Post
    Just want to say thank you to everyone! Sorry its been a bit, I finally got around to ripping out the old engine and sure enough, just gotta swap out some components and it should be good to go! Ill be putting it in closer to the spring, just working on the hull and other components. Click image for larger version. 

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ID:	22361
    On the merc outdrive, the pump has to remain. it cools the drive. You can remove the water hose in the TA and let it pump outside the boat. Put a thru hull for the Crank pump, with an eel grass strainer on the bottom, no strainer in the boat.

    You need to hook water to the drive and the engine if flushing on the hose.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  17. #17
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    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Docksidemarineservices View Post
    On the merc outdrive, the pump has to remain. it cools the drive. You can remove the water hose in the TA and let it pump outside the boat. Put a thru hull for the Crank pump, with an eel grass strainer on the bottom, no strainer in the boat.

    You need to hook water to the drive and the engine if flushing on the hose.
    So I have been debating that. Not too sure about punching a hole into the hull for that...Best placement? Best method? Or just removing the seawater pump and using the drives...

  18. #18
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    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Jdadali View Post
    So I have been debating that. Not too sure about punching a hole into the hull for that...Best placement? Best method? Or just removing the seawater pump and using the drives...
    I would just use the drive pump. Shop a newer drive also, get rid of that preload pin drive. They are cheap enough used. You need a 1.50:1 drive for that 350.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  19. #19
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    Default Re: Merc 305 to Volvo 350 swap

    Thanks Chris. Ill get into that whenever I get around to it. Just found a section of the engine bay rotted out....Thankfully its not on the keel or transom. Gonna have to do deck replacement.

  20. #20
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    Default Re: Merc 305 to Volvo 350 swap

    Quote Originally Posted by Jdadali View Post
    Thanks Chris. Ill get into that whenever I get around to it. Just found a section of the engine bay rotted out....Thankfully its not on the keel or transom. Gonna have to do deck replacement.
    Stop. Haul this to the landfill and go find a boat that's not a basket case. Unless you are REALLY HAPPY doing fiberglass work you'll be way ahead of the game by not putting money into this project. I'll bet you a dollar that the transom is rotten too.
    Practicing the ancient art of ren-ching

  21. #21
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    Default Re: Merc 305 to Volvo 350 swap

    Sadly, I agree. This is can be a nightmare--and I'm a fiberglass guy. Lots of good boats with bad drive systems out there.

    Jeff

  22. #22
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    Default Re: Merc 305 to Volvo 350 swap

    ...Lots of good boats with bad drive systems out there.
    Yeh in Tidewater there are gazillions. Since it's very military there, you get boats that have had many many owners over the years as people move in and out of the area. You really have to know what to look for or else you end up with a toad like the OP has on his hands.

    On the bright side you (OP) probably have a relatively good engine now, so that's a plus!
    Practicing the ancient art of ren-ching

  23. #23
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    Nov 2019
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    Default Re: Merc 305 to Volvo 350 swap

    Last update on the project. O2BatSea owes me a buck. Transom was actually dry. Drilled about 4 holes in different areas. The rest of the stringers....rotted to hell. So total investment - $500 engine, $20 bilge pump. eh...now im off to find another project. But like you said, at least i got a good engine!

  24. #24
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    Default Re: Merc 305 to Volvo 350 swap

    I thought about it, then I thought about how I like actually having a life and not having my wife yell at me.

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