Engine repower with newer engine or just rebuild?

T

Twinbrook

Member
Apr 7, 2014
33
Middle River, Md
Boat Info
1998 Sundancer 370
Engines
twin merc 7.4 MPI''s
I realize the Merc 7.4 MPI 454 is no longer made and Merc does not have re manufactured blocks available anymore. Lost the starboard engine at the end of the 2018 boating season. Having the engine taken out and sent to a local machine shop for a tear down to see what the problem is (stopped and once restarted something was hitting, lost the number 3 cylinder after doing a compression check - marina did all that).

Has anyone had a retrofit/repower on a 370DA with the 7.4MPI? Just looking to see what my options are at this point.
 
Is the engine Fresh or Raw water cooled? If raw water cooled I would not consider rebuilding the existing engine. If FWC rebuilding properly would be the preferred method as long as it is done properly. That way the boat is kept original and won't affect market value. BTW does the boat have the upgraded water lift mufflers? If you still have the log style mufflers you should make the upgrade no matter what engine repair or replacement you do.
 
GM marine longblocks are available brand new from several suppliers.
I bought 2 from https://www.1800runsnew.com/new-base-engines/ when I repowered.

Nothing wrong with rebuilding but, I like knowing it’s brand new from the factory, instead of relying on the talents of an individual.
 
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I trust the boating community's
Air O'Nautical said:
GM marine longblocks are available brand new from several suppliers.
I bought 2 from https://www.1800runsnew.com/new-base-engines/ when I repowered.

Nothing wrong with rebuilding but, I like knowing it’s brand new from the factory, instead of relying on the talents of an individual.
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Thanks for the reply for some reason the marina (cert Merc Techs) seem to think that because Merc does not have rebuilts to buy from them anymore a rebuild is the only option.
 
Last Dollar said:
Check with Jasper Engines. My son's boat had a new Jasper Engine when he bought the boat and it has held up great. Several seasons and hundreds of hours now and no problems.
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Is that a new engine or a rebuild factor spec? The marina my boat is at for this engine work says they don't have luck with rebuilds? I don't get that however they have a machine shop that they send engine to to have them rebuilt. The machine shop apparently builds high end racing engines and marine rebuilds.

Does GM still make that engine block? Anyone?
 
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https://www.gmpowertrain.com/marine.html

In 2013, I replaced both of my 1995 Gen V engines with GM Marine Gen VI long blocks.
The Long-blocks were factory cast new and all internals were factory assembled in 2013.
I needed to add the OEM bolt on accessories like intake, exhaust, charging, cooling etc...everything was a direct fit for me.
The new motors spin smooth like turbines....

Possibly your Mercruiser mechanic can’t source anything other than a Mercruiser product?
I also didn’t trust a rebuild from anyone so, a new long block and me building it up as a Mercruiser was my choice.
 
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Base engine long blocks can be ha for around $3500-$4000 if you search online. Many of the places shown are pretty pricey.
 
Update. Marina sent the engine to the local machine shop they deal with and I've list several cylinders, as I expected from a compression test done about 2 months before the engine stopped. The rebuild is $6,000 with new heads and the the marine said that there is about 8-9 hours to drop it back in, test and do some other things like replace exhaust components so my total bill will be about $10,000 when all is said and done. Does this sound directionally correct to anyone? I really don't have a choice and we are keeping this boat for another 10 years at least because it's in excellent condition, no accidents and we just love it. Signed - "new to having an engine rebuild.
 
Sounds about right, at this point you can only hope they are good at what they do.
 
Twinbrook said:
Update. Marina sent the engine to the local machine shop they deal with and I've list several cylinders, as I expected from a compression test done about 2 months before the engine stopped. The rebuild is $6,000 with new heads and the the marine said that there is about 8-9 hours to drop it back in, test and do some other things like replace exhaust components so my total bill will be about $10,000 when all is said and done. Does this sound directionally correct to anyone? I really don't have a choice and we are keeping this boat for another 10 years at least because it's in excellent condition, no accidents and we just love it. Signed - "new to having an engine rebuild.
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I would be asking them to break in the engine at there place or the marina before putting it back in the boat.
 
Thanks scoflaw and Rusted Nut. The engine shop is going to get the engine running and break it in from what I was told but will verify. I'm not sure what that entails though. The rebuild shop is a hot rod and marine engine build shop as that's all they do. They just rebuild so the engine will go back to the marina to get installed as they only work on engines so the marine may handle the break in if needed but I will clarify on Monday when I actually talk to the marina mechanic. http://www.jbsautomachine.com/
 
Twinbrook said:
Thanks scoflaw and Rusted Nut. The engine shop is going to get the engine running and break it in from what I was told but will verify. I'm not sure what that entails though. The rebuild shop is a hot rod and marine engine build shop as that's all they do. They just rebuild so the engine will go back to the marina to get installed as they only work on engines so the marine may handle the break in if needed but I will clarify on Monday when I actually talk to the marina mechanic. http://www.jbsautomachine.com/
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Good luck sounds like you’re on the right track I had mine done by a race shop as well make sure you get Dyno sheets for your engines and if you have the opportunity to be there and videotape it that would be great I did that and it was a wonderful experience they also ran the engine broke it in put it through its paces so by the time I got it back to the marina it was drop in and go
 
can anyone tell me how to "break in" a rebuilt engine? Someone told me years ago that engines get broken in over about 10 hours but I'm not sure what that means.

Also, the starboard engine it the one I lost to my surprise because it had been the port engine that needed to work harder to sync the engines to the tune of burning 25% more fuel. injectors removed and sent out for cleaning, spec'ed fine etc. So I've decided to have the port engine rebuilt at the same time and be done with it and since they are 1998 engines that are original to the boat - surly the port would crap out as soon as the boating season would start. Would also help on resale I think if they were done at the same time.
 
From a marine rebuilder: (FYI the last line says change the oil every 30 hours. Maybe for the second change. I think 50 hrs is more reasonable)

Engine Break-In Procedure
Running the Break-In Procedure during the first 10 hours of operation will:
  1. Improve overall engine performance.
  2. Extend the life of your engine.
  3. Prevent excessive oil consumption.
The Engine Break-In Procedure
1. Preparing for Engine Break-In Procedure:
  • Keep your engine in neutral.
  • Start your engine.
  • Run your engine for 5 minutes.
  • Keep an eye on your Oil and Temperature gauges.
  • Time your engine with a Timing Lamp to factory specifications.
  • Continue running your engine for 45 minutes at 1500 rpm.
  • Make sure your Oil and Temperature readings are OK.
  • Note: this preparation can be done with your boat outside of the water. Make sure the water supply is hooked up correctly!
2. Engine Break-In Procedure: The 10 Hour Sea Trial
  • Safely run the engine with the boat in the water.
  • Shift into gear.
  • Advance the throttle above 1500 rpm.
  • Vary the throttle every 15 minutes.
  • Do NOT exceed 3/4 throttle during the first 10 hours.
  • Check your exhaust manifolds and risers for any water leakage.
  • Check for oil leaks around your engine.
3. After the First 10 Hours:
  • Change your Oil and Filter.
  • Do NOT operate at full throttle until engine reaches normal operating temperatures.
  • Take your engine to full throttle for 30 seconds.
  • Take note of your full throttle rpm.
  • We highly recommend operating your engine at 300 rpm under your full throttle rpm or less
  • Running your motor at 300 rpm under full throttle rpm or less will help avoid damages due to improper fuel/air mixture.
  • Avoid full throttle acceleration from IDLE speed.
  • Remember to change your Oil and Filter after the first 10 hours of operation and every 30 hours thereafter.
Enjoy the Water!
 
me personally id trust my engine builder over some guy on an assembly line. BUT i also have a VERY good engine builder who builds race motors for me.
 
MarinePower out of La (not L.A.) has several gm based repower options. My 1979 Searay 310 sv was repowered with Marine Powers Sportpac 5.7 / 350 in '03 or so. pretty big upgrade as the newer motors are multiport injection and closed cooling system They have great customer service and parts availability
 
Wyocoyote said:
MarinePower out of La (not L.A.) has several gm based repower options. My 1979 Searay 310 sv was repowered with Marine Powers Sportpac 5.7 / 350 in '03 or so. pretty big upgrade as the newer motors are multiport injection and closed cooling system They have great customer service and parts availability
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I started following the Facebook page of the shop that's doing the rebuild and they were featuring it on their page (big smile).
 
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