engine & prop advise

Discussion in 'Sterndrives' started by cattelona, Sep 27, 2010.

  1. cattelona
    Joined: Sep 2010
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    Location: chippenham uk

    cattelona Junior Member

    Hi, Friend has a problem he has had a 2.5 transit diesel engine fitted in his aprox 21ft crisscraft boat with a mercury leg not sure what prop, but the previous engine was a 250hp unit he has payed a marine engineer several thousand pounds to cary out this work but all this season he cannot get the thing on to plane engine overheats with black smoke wont go above 2k revs, I am new to boating but i think he has the wrong gear ratio or prop pitch for this lower powered unit he says the engineer changed the leg & prop but I haver watched him trying the boat many times , he has renewed every part on the engine as he thinks its not running ok , although it will rev to full revs and sounds a good engine to me , can anyone give advise? i believe there is a calculation to get correct pitch on a prop ?
     
  2. anthony goodson
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    anthony goodson Senior Member

    Speak to Mike Bellamy at Lancing Marine on 01273 410025 he will have the answer in his head ,but the older FSD engines had a very low service rating compared with what you have taken out, even the turbo version.
     
  3. gonzo
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    gonzo Senior Member

    The boat is underpowered. Also, the gear ratio is probably not correct. Several thousand pounds to install an engine is really high. Black smoke means the engine is overloaded.
     
  4. cattelona
    Joined: Sep 2010
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    cattelona Junior Member

    prop pitch

    Thanks Gonzo,
    this friend has had several engineers look at his boat tested fuel pump ,injectors,renewed heat exchangers as engine got hot trying to get on plane,renewed all the fuel lines, replaced breather pipe from tank,cleaned tank , fitted water separator extra fuel filter and much more, he got on the plane 28knots twice but calm sea no wind only 2 on board , i am no expert just starting out in boat world but i rebuilt a 1966 coronet 21 twin diesel stripped and rebuilt engines over last winter and have had a great summer on the sea, i have followed him choking on the smoke as he pushes the water along thottle full on getting no revs, I have found a site in states that gives the calculation for prop pitch etc but it did say that its pot luck & you need to try different props to get it right.
    cheers
    nick
     
  5. baeckmo
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    baeckmo Hydrodynamics

    What does the cooling system look like? Is there a freshwater cirquit and a heat exchanger, or is it direct sea-water cooled?
     
  6. anthony goodson
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    anthony goodson Senior Member

    Baeckmo ,if you remember ,its normally an all in one on these. Man/HE/Header tank combined.
     
  7. Bglad
    Joined: May 2010
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    Bglad Senior Member

    Does it make a difference if the motor box is open or closed? Are bearings in transom assembly good? Small displacement turbocharged diesels can have trouble generating enough horsepower before turbo kicks in to get up to speed. Sounds like it is overloaded or starving for air.
     
  8. baeckmo
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    baeckmo Hydrodynamics

    Yes, Anthony that should be the standard, but since the guy just says "Transit diesel", that mechanic might just as well have taken the shortcut...... As Gonzo pointed out, substituting 250 hp of something with a 2.5 l transit diesel means that someone probably did not know what he was doing.
     
  9. anthony goodson
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    anthony goodson Senior Member

    Yes ,point taken.
     
  10. cattelona
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    cattelona Junior Member

    wrong prop

    Thanks all for your help, engine runs perfectly when not in gear I have owned transits all my life worked on them a lot , his motor is good sounds great will run all day at revs and not get hot , as soon as he puts it in gear it wont get on plane revs stay at 2k and after a while gets hotter than normal the smoke is probably because he adjusted the fuel pump to inject more fuel but did not work, also engine sounds like its working under strain so it smokes { like me with 2 ton in my trany tipper does te same when I come to a hill but I can change down a gear } when he did get on the plane the engine revs went up to 3.5 k and 28 knots , i agree regarding the turbo he cant get revs which is needed to increase hp, I am pretty sure that if he were to take off all the weight in the boat and go out on his own on a good day he would be able to get on the plane , He is trying to get hold of a prop, will see him at the weekend will keep you all posted.
    cheers
    nick
     
  11. anthony goodson
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    anthony goodson Senior Member

    You haven't told us which version of the engine you have ,only that your friend has changed the heat exchanger, which implies that it was marinised prior to his aquisition .A standard turbo FSD made about 100bhp @4000rpm ,an intercooled one about 125bhp but there was a popular, made for the marine market ,intercooled version which claimed 140 bhp. Hope this might help with your prop selection. Your analogy with your tipper truck ,suggests you are on the right track and have an understanding of what is going on As regards the turbo a large diameter straight exhaust pipe exiting well above the waterline gives it the best chance , but Bglad is right, without the turbo you don't get the revs and without the revs you don't get the turbo. A finer pitch prop may let it all spool up . Your performance will still be sluggish compared to the original engine ,but perhaps it will make up for that in economy ,good luck
     
  12. cattelona
    Joined: Sep 2010
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    cattelona Junior Member

    prop size

    thanks Anthony for your reply, its a direct injection 2.5 itd , exhaust is underwater I did think this was a bit strange I couldnt listen to the sound which is usually a good indication that an engine is running ok and your point about this restricting the exhaust getting away probably doesnt help either,I met him at the weekend he had another mechanic there who said the fuel pump might be faulty so took it off I advised him to go to a couple of brothers I know in swindon {very experienced guys} and the pump is faulty so is now being repaired also i advised him to take injectors as well they were fine, but whilst chatting with him he said that the guys that originally converted the motor to deisel told him to change the prop but he said it went ok just took a long time to get on plane so never bothered that engine was wrecked in a couple of seasons this engine is another identical reconditioned replacement , seems to me that the recon may be less powerfull slightly which is why he has the problem , he is going to fit pump at weekend but also get a company he knows in pool to calculate & supply a correct prop , he said that as the prop made the boat faster he thought he was getting better economy , but he was making the engine work really hard he now understands that and when prop size is corrected he should have a good boat .
     
  13. anthony goodson
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    anthony goodson Senior Member

    Thanks for the update ,I still stick by my original post ,speak to Mike Bellamy he knows everything there is to know about this engine and prop selection . Take that exhaust and run it straight out of the transom above the waterline ,before you try it again ,the back pressure is inhibiting turbo spool up, just when you need it. Good luck and let us know how you get on.
     
  14. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If the engine blows black smoke it may also be overloaded. The injection pump puts more fuel, but the RPMs can't increase. It will create combustion chamber temperatures that are very high and damage the pistons and valves.
     

  15. cattelona
    Joined: Sep 2010
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    Location: chippenham uk

    cattelona Junior Member

    prop size

    hi thank you all for your help, my friend had his fuel pump & one injector repaired engine running well , he spoke to mike bellammy and he suggested he get the prop he has reduced in diameter{1/4 "} so he is taking it to a specialists in pool dorset to have it calculated and altered , boat should then run ok , he has now i think addressed all the minor problems which all together and with the wrong prop caused his old engine to fail , hopefully he will have a good season next year.
    many thanks
    nick
     
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