Insight in diesel Luhrs 28 re-power

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

  1. Luh28
    Joined: Jul 2021
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    Location: Michigan

    Luh28 Junior 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
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    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
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    Location: Michigan

    Luh28 Junior 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
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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
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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
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    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
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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
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    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
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    Location: Michigan

    Luh28 Junior 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...
     
  11. 7228sedan
    Joined: Nov 2009
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    Location: New Jersey USA

    7228sedan Senior Member

    I just sold my 72 28 Luhrs Sedan right before the Covid craziness... I had looked into a diesel re power when I ultimately rebuilt the 454 that was installed prior to my purchasing. The biggest limitations I found were the height of the deck to bilge, the shaft angle needed complicated things. Unless you plan on raising the deck considerably, or a raised hatch, fitting a 5.9 cummins would be tight if not impossible. I was also looking at the 240HP Yanmar 4cyl due to their power to weight ratio. Not sure I ever looked into the height measurements on it though. With the fresh 454 in standard Mercruiser 340HP trim, 1.5:1 Velvet drive, and a heavily cupped 3 blade 16x16. I'll have to dig up the actual performance numbers but she topped off at around 23-24 knots, cruised at 15-16 knots at 28oo RPM burning around 10GPH. You'll need the 300 HP Cummins at least, appropriate gear ratio to turn a bigger prop 2.5inch shaft, etc to take advantage of the power. I wish you luck, and happy to provide any additional details if you'd like. it's all on here somewhere :)
     
  12. Luh28
    Joined: Jul 2021
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    Location: Michigan

    Luh28 Junior Member

    This is great. Thats exactly the info I've been looking for. It's been tough to find performance specs for this old of a boat, esp. seeing as its wood on the topside, not many left. I'm running into the same issues: Deck clearance, shaft angle, and prop dia. hull. clearance for a lower RPM diesel engine. I created scale CAD drawings of my hull so I'm able to drop in the mfg. drawings and scale them to see how they fit. I have some flexibility as I'm rebuilding the deck but I can't raise it too much without messing with the entry door into the cabin. I noticed later fiberglass models had wells in the cockpit deck to enter the cabin, not sure I want to do that. Also seems that new V-drives that are integral with gear are taller than the separate Walter model that I have. Opinions on integral vs. divorced v-drives? The new 700lb Merc. V6 TDI diesel looks interesting, higher RPM and fits, but at 275HP not sure if that's enough. It's definitely a recreational grade engine. Won't last like the indestructible Perkins, but, clean, quiet, light, and over 200% more power. Not sure why, but local diesel shops advise is to steer clear of 4 cylinder for my boat, something about pulsing / vibration / idling in gear problems? Any feedback, ideas about that? Thanks again for the info!
     
  13. 7228sedan
    Joined: Nov 2009
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    Location: New Jersey USA

    7228sedan Senior Member

    Odd that your has the wood superstructure. Mine was all glass, with that step down from the cockpit companionway into the salon. With the original tired 454, I needed a lot of trim tab to plane. The fresh motor ran out like a dream. The Merc V6 is the 2.8L I think. You probably want to take the torque curve into consideration as well as the HP. The torque is what will get the larger wheel going at the low RPM's. That motor is based off of the VW/Audi diesel from what I understand. more of a light duty motor, agree. Not sure why folks would tell you to shy away from 4cly. The modern 4cly diesels such as the yanmars are quite popular. the 240HOP variety from a few years back was a common upgrade for a 454 powered boat. I knew a captain that re powered a 31 Bertram from 454's to the 240's faster and MUCH better range/economy. My Father has a 4-53 Detroit in his 68 Chris Craft... that motor doesn't even vibrate much.
     
  14. 7228sedan
    Joined: Nov 2009
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    Location: New Jersey USA

    7228sedan Senior Member

    20190806_190847.jpg 20190806_190904.jpg
     

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  15. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Good to see another builder resurrecting one of these early seventies boats.

    If you're rebuilding engine stringers you'll need a way to locate the new stringers in a big, open three dimensional space. Before I began removing soft engine stringers I constructed a jig that provided me with the exact location where the old engine beds were located.

    Planning on using the existing shaft log? I did, as I didn't want to reinvent the wheel so to speak. This past year I installed a new Walter V-drive. Put in a new RV-26D to replace an obsolete RV-20D. The new drive was an inch or so longer and slightly greater in height. So I had to move the engine back a bit for clearance between it and the bulkhead that was rebuilt to better support the aft cabin wall. This slight shifting in position caused the engine to be positioned slightly lower in the boat due to the shaft angle. It also moved the prop shaft back, which effected clearance between the tail
    end of the shaft and the rudder and also effected my ability to get the propeller onto the shaft with the rudder in place.

    The only real good that came of all this was that I increased my hull to propeller tip distance which enabled me to install a much more efficient propeller.

    I only mention these things to point out that there are lot's of things to consider. At the end of the day it all worked out but it was close in a couple of aspects. I came close to having the oil pan resting on the inside of the hull.

    BTW, good to see 7228sedan still around! Hope all is well with you and your family.

    Keep posting about your project and best of luck to you.

    MIA
     
    Last edited: Nov 16, 2021
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