Insight in diesel Luhrs 28 re-power

Discussion in 'Diesel Engines' started by Luh28, Jul 27, 2021.

  1. Luh28
    Joined: Jul 2021
    Posts: 3
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    Location: Michigan

    Luh28 New Member

    I have a 1972 28’ Luhrs flybridge Sedan that I just finished rebuilding the cabin. I’ve now moved aft and tore out the cockpit deck and considering my options on re-powering.

    Current Powertrain is a single normally aspirated Perkins 6-354 (120HP@2800), 1:1 Velvet drive, 1.54:1 Walter V Drive, 1.25” shaft at appx. 12 degree angle with a 4 blade 17” prop. The V drive got frozen so it’s needs to be replaced. These boats typically had 250HP gas when new but in the early seventies with the gas shortage Luhrs dropped in these Perkins. (The old v8 unused engine ways are still there) This all results in the boat being fairly tilted to the stern and at 5 tons, unable to get up on a plane.

    Seems Yanmar, Cummins, VW/Merc and FTP are some options that fit within the limited height I have. Currently the Perkins can’t get her to plane and seems most happy @ 2100 rpm - 8.5 kts. The payoff for pushing it seems to only give you a knot or two and burning oil. The 28 Luhrs is 23' 4" at waterline and is 11’ wide on deck and 9’ at the WL. (wide walk around deck) At stern 3.5’ of bottom is flat and then it has a 15 degree deadrise. The hull is 1” thick woven FRP. The 4x4 engine ways have rot and will be replaced. The cockpit rebuilding I’m doing allows some flexibility for engine fitting. Pretty new to this but fully aware of all the complexities involved (powertrain needs to be optimized for engine/hull) Wondering if anyone is familiar with this hull and recommendations / experience on re-powering one. I'm assuming Luhrs used the same shaft on the 250hp gas but was wondering if there is a way of identifying its make up, SS 304, Aquamet, etc... as I will have to make sure the shaft can handle the power upgrade.

    Thanks!
     
  2. KeithO
    Joined: Jul 2019
    Posts: 325
    Likes: 66, Points: 28
    Location: Michigan

    KeithO Senior Member

    Perhaps a Cummins 5.9 with around 200hp ? Would ditching the V drive and moving the engine forward to more centralize the approximately 1200lb motor be feasible ? The gas engines seemed to be around 200hp from some google research I did. If you get a 12 valve engine with the P7100 mechanical pump you would have a very reliable engine that you could maintain yourself.
     
  3. Luh28
    Joined: Jul 2021
    Posts: 3
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    Location: Michigan

    Luh28 New Member

    Thanks! No room to move forward, that would put it in the salon. The existing Perkins is definitely reliable, most of any I've owned, sitting for 19 years and it starts immediately with original fuel! (conditioned and filtered). Surveyor that inspected the boat at purchase said it would outlast me.
     
  4. missinginaction
    Joined: Aug 2007
    Posts: 1,055
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    Location: New York

    missinginaction Senior Member

    Are you sure you want to stay with diesel? You'll lighten the boat up with a single gas engine (GM 5.7?) which may get you a lot closer to the planing that you desire. Those old Luhrs/Silverton hulls were certainly solid. I own a 73, fully restored and am just now getting ready to do some test runs after changing out older v-drive and repropping.

    I'm thinking you have a Walter RV-20D in there (the one that froze). You will find that the RV-20D is no longer made and the smallest you'll get from Walter is an RV-26. This will set you back about $3,200 with a new shaft coupling and the splined adapter that attaches to the Velvet Drive, assuming this is the set up you have.

    Pearl profile.jpg They called this a 25.5 Sportster. A little smaller than what you have.

    MIA
     
  5. comfisherman
    Joined: Apr 2009
    Posts: 169
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    Location: Alaska

    comfisherman Senior Member

    Only caveat to a p7100 configured cummins is price. While an awesome package they are shockingly expensive in marine trim and not exactly a bargin even for the diy marinizer.

    That's a thick solid hull, modern diesels are awesome but they are not cheap. A reman 5.9 with suitable iv configured zf gear would likely clear 30k with a panel and still need the small nickel and dime bits that add up in a hurry.
     
  6. KeithO
    Joined: Jul 2019
    Posts: 325
    Likes: 66, Points: 28
    Location: Michigan

    KeithO Senior Member

    I just bought a 2001 Cummins 5.9 truck engine that I am going to rebuild. Its the 24V and by default has the VP-44 rotary pump. I paid $1500 for the engine. I bought a 12V timing cover with the P7100 timing gear to convert the engine to the P pump. $350. A rebuilt P pump starts at $800 and goes up. Just 1 wire needed for the fuel shut off solenoid. I will tear down the engine and determine whether any parts need machining, on condition. If the head is cracked that could be expensive. If it is the version with integral seats, I may need to get new seats fitted and then replace guides at the same time. There are potentially a lot of valve which may need to be replaced. I have a good shop to work with locally who is reasonable and does good work, just very busy....
    There are generic marinizing parts available for the engine. One can blast the engine and paint with 2 part zinc rich primer and follow that with a 2 part epoxy overcoat. It would certainly help with external corrosion. If one is expecting someone else to provide a turnkey solution, yes it will be expensive from any source. If one is willing to do a substantial amount of work and sourcing yourself one can save a ton of money.
     
  7. comfisherman
    Joined: Apr 2009
    Posts: 169
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    Location: Alaska

    comfisherman Senior Member

    Huh.

    The reman cummins were in the low 20s.

    My last p pump rebuild was 900 for a good core, almost a half decade ago. Maybe regionally it'd a lot cheaper.

    Wet manifolds run in the several thousands then water jacket turbos, bellhousing adapters, heat exchangers etc... that's on a block with and unknown level of wear on internals. Marine loadings can be a bit harsher than over the road. A high mileage truck may rock on but be a bit lacking plowing water. Might work, but an inframe right after an install would be a bummer.
     
  8. KeithO
    Joined: Jul 2019
    Posts: 325
    Likes: 66, Points: 28
    Location: Michigan

    KeithO Senior Member

    Brand new 6BT engines can be had on ebay for $8500 after which marinizing parts need to be added.
     

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  9. Luh28
    Joined: Jul 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: Michigan

    Luh28 New Member

    I'm putting together a spreadsheet with all the options, including gas. Would like to stay diesel, but it may not pan out. Expecting to pay up to 30k for one that has a warranty, after a couple of years of restoration would hate to inherit someone else's engine problems. Including a Cummins 6BT recon as an option, but would have to add a 4K core to it. The FTP option is less and doesn't need a core. Current Walter V Drive is a RV30. Walter quoted @ 4k for a new one. The years this boat was in the marina I got 2 letters from people that wanted to buy it, low profile with wide walk arounds and diesel seem to be rare in the 28' range. Would like to keep that marketability, but at what cost? I don't mind loosing on my woodworking labor, which is the majority of the refurb cost, if I re-power with a new higher hp diesel, I would like to get that cost back.

    Just discovered a new variable with my past performance. Within a year after purchase, a blade broke off the prop in crappy conditions (welcome to boating!) got a good samaritan tow to port and had the spare that came with the boat put on. My original and spare both have 17 RH 16 stamped on them but the original measures 17" dia. and the current spare 16". I remember being able to do 10.5 kts way back but never since. Prop calculators say I should have a 17-13?! Was I originally propped wrong and its worse now? Tempting to drop back in ol reliable (replace manifold, corroded injector pipes and v-drive) BUT - when I ran it in the 2600 rpm range for a 5 hr cruise I went through 2 quarts of oil, after talking with the local Perkins rep he said don't worry drop the rpms down and you'll be fine. He was correct, 2400 and minimal oil loss, BUT, is that normal? The cockpit of my boat is stripped down to a clean hull with a shaft, I have a once in boat-life opportunity to an easy swap.

    Anouther thing I'm bumping into is the distance from the hull to prop. Seems this was optimized for gas, currently there's only 2.2" clearance with a 16" prop and with a diesels lower rpm range, optimum props seem to run bigger dia. And there's this nagging question of if the 1 1/4" shaft alloy, can it take added HP?

    Thanks for all the feedback!
     

  10. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    There are lots of good used Cummins B motors on the market.
    Shop carefully, try to get a motor that’s still in a boat running if possible.
    If it starts right up from stone cold, puts out minimal smoke, and is not overpropped, I’d not hesitate to buy.
    The Luhrs will need considerable hp to get up on plane, it’s a heavy hull, don’t expect a 210 to do it, look for 330-375.
    Yes, you’ll need more room for a bigger diameter propeller, so might as well put in a beefier shaft too.
    There Perkins will make a nice mooring anchor...
     
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