Marinizing automotive diesel engine and transmission.

Discussion in 'DIY Marinizing' started by DennisRB, Apr 14, 2010.

  1. DennisRB
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    DennisRB Senior Member

    The prices for genuine marine diesel engines are pretty huge. Specially over 50hp. But you can get engines over 50hp easily from an old hilux or similar for dirt cheap. What would be required in getting a motor like this to run a yacht? Would the transmission that comes with the engine have any useful ratios for a yacht? Would the reverse ratio be right enough to develop the right prop speed for maneuvering? Would a heat exchanger cooling system be mandatory?

    Thanks Dennis.
     
  2. CDK
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    CDK retired engineer

    There are lots of related threads in this section.
    You can use the (marinized) engine but not a manual transmission.

    Before you decide, check the availability of a water cooled exhaust manifold.
     
  3. DennisRB
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    DennisRB Senior Member

    Would the auto transmission be OK? I was thinking of getting rid of the torque converter. That way I would have a few forward gears and reverse. I wonder if reverse would be too far undergeared? But I guess it would be fine since usually reversely is for slow speed maneuvering. Could I just make a steam pipe log exhaust manifold and make my own box around it go run water through?
     
  4. CDK
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    CDK retired engineer

    Using the automatic transmission is not impossible, but there is an important issue: thrust forces. Marine gearboxes have a thrust bearing, your gearbox has none, so you have to add that externally. For a 50 hp engine it should be able to take up at least 5000 N. in two directions.

    Common gear ratios for 50 hp are between 1.8 and 2.2 in both directions. Higher and lower ratios are possible as long as you can find the matching prop.

    The manifold in the car is the hottest part of the engine, it needs air from the fan and/or vehicle velocity to remain at an acceptable temperature. In a boat such air speeds are not available so it overheats, cracks or heats up the engine bay and intake air, thus reducing engine output.
     
  5. DennisRB
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    DennisRB Senior Member

    Thanks. More on this thrust bearing. What is it and why is it there? What is the difference to a drive shaft in a car and a drive shaft in a boat and how and why would the forces be so different? I would have thought that a drive shaft going to a live axle rear end in a car would have much more movement than in a yacht where the drive shaft is fixed in one position in the hull relative to the engine. What am I overlooking here? Is the thrust bearing there to counter the force of the drive shaft being driven toward the transmission by the prop? If so I guess you could put something on the shaft itself before the transmission?

    Also, how does a turboed marine engine cool its manifold? Is the turbine housing also externally cooled with water? I am sure I could make a steam pipe manifold that would never crack, but the heat would be terrible in the engine bay so water cooling would be highly desirable.
     
  6. CDK
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    CDK retired engineer

    The axle in a car is held by springs or reaction bars, the splined drive shaft allows for compression of silent blocs and engine movement.
    The prop shaft in a boat takes up all the thrust and transmits that to the transmission and engine, trying to move them towards the bow.
    A marine gearbox has a set of axial bearings or large tapered roller bearings to cope with that. With an automotive transmission, the prop shaft needs a similar bearing between two collars on the shaft, held in place by a frame, firmly attached to the hull.

    For turbo charged diesels, read the thread about VW TD engines, this forum.
     
  7. FAST FRED
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    FAST FRED Senior Member

    Before contemplating any conversion go on most any marine diesel engine sites and note that there are at least 4 ratings for every engine.

    One is for very short periods of time , like 60 seconds to get a big wallowing tub up on the plane.

    The smallest will be the 24/7/365 work boat rating.

    The difference in the ratings may be 3-1 , or a 75% reduction to keep it operating.

    The power ratings for auto and light truck engines is the first , instant , not continuous .

    Beware of advertised "HP".

    FF
     
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  8. DennisRB
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    DennisRB Senior Member

    Thanks guys. I will take note. The way I was looking as it was automotive engines can be sourced cheaply with much higher outputs than I would ever need, so I would be running them at well below their rated power anyway, but the extra power would come in handy in emergencies.

    Does anyone have any more info on drive shaft mounted thrust bearings?
     
  9. CDK
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    CDK retired engineer

  10. gonzo
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    gonzo Senior Member

    If you compare a marinized engine with the cost of fabricating and modifying a car engine, you'll se that it is cheaper. You are reinventing the wheel. If you are planning on using an old beat up engine, a used marine engine is way cheaper, easier and will be much better modified than what you can do.
     
  11. Frosty

    Frosty Previous Member

    Totnes ha ha ha.

    Yeah but look at the fun you have doing it.

    Ive put all sorts in boats --its the best fun ever. The best years of my life.

    making stuff and pytting it in the river on a summers day.Ive used a washing machine pump to cool the wet exhaust injection.
     
  12. hinemoa
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    hinemoa hinemoa

    much to the same question really, so the prop in forward gear would want to push the in to the gearbox right? and opesite in reverse?? so all the bearing block would do is stop the shaft wondering in or out??
    and im in the same block as this, if a car auto trans was used and obviously cooled thru its manufactured way and torque convertor removed, and not in commmercial use , with this i mean the odd weekend venture thru the year maybe 50-100hrs yearly, would it cope?? as a final drive, as in 3rd gear or some 4th gear(top gear) is 1 to 1 isnt it?
    the reason i ask this as im setting up similiar and i dont know what ration etc i need so i thought with a auto out of car i would have several different ration options to play with?

    really interested in this and i know that marine etc blah blah is better, but the costs are so horendous to set up for a weekend play boat
     
  13. CDK
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    CDK retired engineer

    Hinemoa, I guess you are looking for a cheap way to power your 16 m. catamaran.

    A marinized diesel engine with a locked auto trans is feasible. You need a bit more drive train length but that should be no problem in your case.
    Install a thrust bearing block near the end of the prop shaft and connect the engine by means of a short universal shaft (http://www.glenwoodmarine.net/Catalog/TORQUE TUBE AND GUARDS.pdf).

    That allows for small alignment errors and flexible engine mounts so there is less hull vibration.
    The thrust bearing you can buy as a unit or construct it from two tapered roller bearings; the important thing is that it is firmly attached to the hull so axial loads are not transmitted to the gearbox which has no provisions to cope with that.

    Include a small oil cooler for the transmission and lock that in 3rd so the prop shaft turns not faster than 2000 rpm at full speed. The prop dia. can be 13" or 14" then. Ask other forum members to estimate the pitch and blade number you need, that's not my field.
     
  14. anthony goodson
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    anthony goodson Senior Member

    Dennis RB
    You already have experience of a marinised car engine .From your previous postings your Roberts Spray 36 ,has a perkins prima installed. This was primarily an automotive engine ,used extensively by British Leyland {bless em } in the UK .There was also a turbo version of this ,on which piston cooling oil jets were added and the CR was slightly lowered. Volvo marinized this {well almost} too.
     

  15. FAST FRED
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    FAST FRED Senior Member

    While it might be a challenge marinizing a diesel is really cheap IF you can use the work boat system of dry stack and keel cooling.

    Personally I would purchase a used ,,rebuilt Twin Disc marine tranny as most trucks use SAE mounting standards on their bell housing.

    Google "Boats and Harbors" a marine sales paper for a source.

    The cost and maint of a thrust bearing would be eliminated (its built in) and the entire package would be shorter and far lighter , as suits a multihull , where weight is a huge NO NO.

    FF
     
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