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  1. #1
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    225 2.5 Promax Build. Starting with a new 2015 block - tell me your secrets!

    Hello,
    I toasted #2 cylinder on my '97 promax... its at 50 PSI and the rest are at 130 PSI ...time for a rebuild. I've searched all I can on the subject... I know it's been talked about a zillion times but most of the post I find are about 10 years old and there may be better info out there. This is a lake motor that will be used for everything from waterskiing to all out WOT runs, it needs to be reliable. A little extra grunt wouldn't be bad either.

    I'm starting out with a brand new 2015 block from Mercury Racing.

    Here's what I've got so far:
    - Injectors just cleaned by Bruacto this spring
    - Heads just measured and confirmed to be cut to 35cc
    - Timing set to 25°C @ WOT
    - Oil injection and ignition black boxes are long gone

    Here's my additional plans:
    - Steel Caged Bearings
    - All new gaskets, seals, thermostats


    Here are my questions:
    1) I'm going with 6 new cast pistons and are going to contact John Marles to have them top pinned. (Jay Smith I've read your posts and have got the message) What brand should I use? (I'm not made of money)

    2) What else should I be doing to build this thing right?

    Thanks,
    Dave.
    1989 21' Skater - twin 2.5s
    1986 Cougar 21MTR, 15" 300XS - sold
    2002 TUFF 21 (#0.1), 300xs - sold
    1986 Valero YT, 225 Promax - sold
    1987 Viper, 140 cross flow - sold

  2. #2
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    I'm not an engine builder or mechanic but have a fair amount of knowledge with 225 Promax's!

    ~#1 for me is to find out and confirm what toasted #2, this is very important!
    ~Vertex or ProV pistons from ProMarine would be my choice. Unfortunately Vertex are out of stock at the moment. If you are not spinning it high ProV is a good choice.
    ~I would back the timing down some 23,24.
    ~Rebuild the pulse pump on the motor.
    ~Open, check and clean the VST epecially the filter on the pump.
    ~Make sure you run high test fuel with 35cc heads. The fuel quality today is not the greatest.
    ~~Some new electrics like switch boxes, trigger and stator are always a good thing but IMPO not totally necessary if the stuff you have came from a running motor and is in good working order.

    I think you have everything else covered.

  3. #3
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    Listen to Tux he is our best customer when it comes to buying Pro Max blocks. He might have the record

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  5. #4
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    Quote Originally Posted by vnemous View Post
    Listen to Tux he is our best customer when it comes to buying Pro Max blocks. He might have the record
    Well that doesn't sound good! Tux am I correct in assuming that you've learned these things the hard/expensive way?

    Good comments on the fuel system - I will proceed as advised. I'm trying to decide between ProMarine and Wiseco for the pistons; Mother Mercury is big $$. (And from what I gather they're made be Wiseco anyways) Most of the electronics were replaced about two years ago when I got the motor (stator, voltage regulators, maybe the trigger), on the boat side everything is new including the main wiring harness to the motor. The plug wires are new this year from Bob's Machine Shop.

    I have not taken the motor apart any, other than pulling the heads. It mildly overheated a few times over the past few summers so perhaps it finally lost a ring locator pin (the damage kinda looks like it). The gas was 91 octane and not from a marina.
    1989 21' Skater - twin 2.5s
    1986 Cougar 21MTR, 15" 300XS - sold
    2002 TUFF 21 (#0.1), 300xs - sold
    1986 Valero YT, 225 Promax - sold
    1987 Viper, 140 cross flow - sold

  6. #5
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    Alot of people have great results with vertex pistons ....racers spin em 9k....lake motor= no worriesDid #2 injector fail flow test?What was cause of #2 melt downEdit..sorry I was a Lil late on this one.....if I was building one and vertex wasn't available. ....I would run the pro v piston over wiesco..jmo
    Last edited by texasvector; 09-08-2015 at 02:38 PM.
    81' HYDROSTREAM VECTOR / slightly Modified 200
    before and after:http://www.screamandfly.com/showthre...inished!/page3

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  8. #6
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    Another vote for the Vertex pistons and toast the the whole VST set up and run a bosch pump with a fuel pressure regulator. Cleaner and more reliable system.
    Allison XB02, 22ft Tritoon 225 4 stroke, two seadoo sparks

    Past rides 2001 STV EURO, Allison Grandsport, STV RiverRocket, STV Euro, STV ProComp, Hydrostream V-King
    RIP RPM RACING
    RIP GTS1

  9. #7
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    Quote Originally Posted by Fullthrottleguy View Post
    Well that doesn't sound good! Tux am I correct in assuming that you've learned these things the hard/expensive way?


    No, that means he keeps buying them, building them and selling them plus the two he runs on his Rally Sport.

  10. #8
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    No Wisecos for me in a steel sleeve block. Sure, it can be successfully done but your machinist better be well versed in proper sizing/tolerance for them!
    Like I previously mentioned Vertex is my first choice with Prov's close at hand, they are both coated which help while break-in! For me cast in steel blocks, this is just my personal preference!
    Like texasvector mentioned they have been tested more then once above 9000rpms, so that works for me not to mention the amount I have had put in motors with great success.

    Vnemous is absolutely correct about buying new blocks, heck they just ask where is this one going.... and this is because I found that it has been cheaper to do so on certain situations and for no other reason!
    If I can save a block I have no problem having my builders/machinist do so! They are actually inexpensive to repair as longs as they do do not window!

    225PM's is the only motor I bother with because I strongly feel they put out a great amount of power for the weight ratio.
    Hope this info helped you and post away if you have any other questions or concerns!
    There many other members here extremely familiar with the 225PM which will provide you with some good info.

    Tony

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  12. #9
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    I would recommend you look at WSM pistons. They are not widely used because they are a little more $ and not as widely available as the Vertex and Pro (I have used tons of these pistons with no complaints). BUT, I think the quality of the WSM piston is much better (coated piston with a high quality alloy) and most important in the Promax, they use the 1.5mm ring (like the factory stock piston), the others do not, they only come with 2 mm rings. I built a "new" Promax last year, and except for TDR reeds and WSM pistons, its factory (without the oil injection obviously), including the heads. The motor runs fantastic and pushes my Allison Grandsport to mid 90s. I plan to build another one this winter. I am going to take the promax I built last year and with the help of local ace Lee at Sanderson Marine, going to set it up with a Brucato SVS and PCU. I plan to have Lee dyno the powerhead stock as is first then we will install the SVS and Lee will tune the brucato system and then do another series of dyno runs to determine what the real gain is....kinda an experiment. I'm with Tony...No wisecos for me either...
    Go Time
    2003XS GS 225 Promax/ 260 / 280
    26 Regulator twin 250 EFI

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  14. #10
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    Thanks GT,
    I just called and they apparently make them to OEM specs, (side pinned and OEM weight), standard and oversized bores with 1.5mm rings. Retail they are $110.00 each. Vs. ($126.00 each for Vertex), ($109.95 for the ProV) and ($128 for Wiseco) from Pro Marine.
    1989 21' Skater - twin 2.5s
    1986 Cougar 21MTR, 15" 300XS - sold
    2002 TUFF 21 (#0.1), 300xs - sold
    1986 Valero YT, 225 Promax - sold
    1987 Viper, 140 cross flow - sold

  15. #11
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    I run WSM pistons in my promax since this year and have no complaints. Dave from AIM outboards builds them with those for the reasons stated above. i'm pretty shure shane runs them also since the beginning of the year. 1mm head gaskets and shaved heads give me 138psi in every hole.

  16. #12
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    WSM pistons.

    Quote Originally Posted by mistah_max View Post
    I run WSM pistons in my promax since this year and have no complaints. Dave from AIM outboards builds them with those for the reasons stated above. i'm pretty shure shane runs them also since the beginning of the year. 1mm head gaskets and shaved heads give me 138psi in every hole.
    Hey Max,
    What was the reasoning behind going with this brand?
    Did you guys get them top pinned?
    1989 21' Skater - twin 2.5s
    1986 Cougar 21MTR, 15" 300XS - sold
    2002 TUFF 21 (#0.1), 300xs - sold
    1986 Valero YT, 225 Promax - sold
    1987 Viper, 140 cross flow - sold

  17. #13
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    Quote Originally Posted by Fullthrottleguy View Post
    Hey Max,
    What was the reasoning behind going with this brand?
    Did you guys get them top pinned?
    mainly it was for the 1.5mm rings. dave told me they are dirt cheap to replace if I ever needed to. we left them side pinned because of money issues since I wasnt planning on putting fresh pistons at this time. re-ringing what I had would of cost me almost as much as those pistons.
    the reason for tearing it down was the unknown hrs on the engine and it had plastic cage bearings in it
    Dave may have explained me other advantages of going wsm but I cant remember.

  18. #14
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    Anyone have any complaints with WSM's? Can anyone else confirm they are built with a high quality alloy? I have heard that Vertex to quite well (9000rpm from a few racers), so WSM would seem to be an incredible deal if they are even better than vertex. You could essentially re-do an entire engine just for the price of the nic rings!

  19. #15
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    Call Chris Carson in Key Largo he's probably use more of those pistons than anybody.
    Go Time
    2003XS GS 225 Promax/ 260 / 280
    26 Regulator twin 250 EFI

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