Repower Young Brothers 35

port side patriot

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2003 Young Brothers 35
Last weekend we washed out a cylinder on our 3126B 450 hp cat (only 3400 hours). Now I am forced to make the repower/rebuild/remanufacture decision. I am set on the c7.1. I have my own opinions on liter to HP ratio on these engines and understand the risks involved with going to high HP and small block. but frankly its all I have the space for and with the bridge we need HP to get her going. obviously looking at getting re power done ASAP with the season in full swing here in cape may.
obtaining one of these engines has been difficult, like everything else. It looks as though I can get one in 24v and avoid the 14 week wait time for one of these engine from the UK in 12v. doesn't seem overly complicated to go the 24 volt route and seems better to use less amps and more voltage to start the engine and run all the electronic crap that comes with it.

main question is what are the complications with going to 24v on the engine and would it be abnormal to have the engine at 24 volts and the rest of the boat at 12 volts? I.E. haulers, teaser reels, electronics, bilge pumps, lights etc would all still be 12volt system. I would imagine running a secondary auxiliary alternator at 12 volts would be the best way to keep the house charged up.

In addition does anyone have any experience going from 3126B, 3126 or c7 to C7.1?


This entire thing has been a complete slap in the face since I maintain the boat to the highest level and was not expecting to experience such a catastrophic failure this early in the life of the engine. All I can say is glad it happened at the end of the canyon trip and not the middle especially with my charter guests on board!!

thank you for anyone's input always good info and advice on here.
 

port side patriot

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Sounds like you’re set on a Cat, but have you considered the Cummins 6.7L 480hp? I’ve installed a number of Cummins QSB’s, they are a very nice package in my opinion, and may be more readily available than the Cat.
I looked into all engines and on the Dollars and cents side of the re power cat seems to be the front runner. with the boat already set up with cat controls, exhaust and the mounts able to be reused it is more economical to stick with cat. also more service options in our area for cat, direct company technicians that is. Cummins would be my second choice if I had to change manufactures
 

xbskt

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Sorry for your loss.
I looked into the 7.1 to replace a C7 in my Northern Bay. The more I looked the less I liked.
It has been a while but if I recall Cat doesn't make the engine?
Have you checked to see about hanging a second alternator on the Cat? Probably doable but from the factory?
In the end it was expensive for the HP class and unproven with not a lot of familiarity in the Cat service world so I went with Yanmar.
In my research not a lot of people were too impressed but you may have better luck and your CAT service may be top notch.
As I said, it has been a while so maybe it turned out to be the best engine ever.
What Powerdro says makes a lot of sense. The 6.7 480 is a great motor but I can't comment on size comparison.
I would be interested to compare the size of these three.

Cat 7.1 450hp (?)

Cummins 6.7 480hp

Yanmar 6LF530

Whatever you do.
Good luck.
 

bluezone

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If it’s just one cylinder fix it. New liner if needed and piston and rings. Done in a weekend and consider a Re power over the winter if needed.
 

port side patriot

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I am exploring all options. looks like more love on the forum for cummins power than back here at home. its good to get different perspectives. I will continue to post on the route we go. Any suggestions are always welcome. Summer season is toast, if I take my time and do the Job right. so I have some time to make a smart decision and still be able to get going before the blackfish season starts in mid November.
 

xbskt

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I am exploring all options. looks like more love on the forum for cummins power than back here at home. its good to get different perspectives. I will continue to post on the route we go. Any suggestions are always welcome. Summer season is toast, if I take my time and do the Job right. so I have some time to make a smart decision and still be able to get going before the blackfish season starts in mid November.
Bluezone makes a real good point. Is your existing motor not fixable if only one cylinder is involved?
Get the injectors tuned up.
While you have the head off have look at the other cylinders and start planning for the future.
Maybe give you a season or two to plan a repower properly.
 

F/V KRISTA MARIE

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I would pass on the CAT and the Cummins in the 480 configuration. I would without a doubt buy the Yanmar 6LF530. This is from my experience with all three in question.
 

cb34

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I would pass on the CAT and the Cummins in the 480 configuration. I would without a doubt buy the Yanmar 6LF530. This is from my experience with all three in question.
What did you have the 480 Cummins in ?
 

port side patriot

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So our repower project is underway. I elected to go with the C7.1 in 500hp to replace the 3126B 450 HP. The project is going slow but its moving along. Parts and labor have been overall the biggest struggle. I am listing some notes and struggles I have had during the project to aid anyone that is looking to do this project so they know what some of the "unknowns" could be.
some interesting things about the project
-needed to make a new mixer and riser/elbow, originally thought I could use the old one ( was only 2 years old ) with a new flange welded on to match up to the turbo however while CAT calls for a 6" all reputable marine exhaust companies recommended I upgrade to an 8" bc this engine is a "heavy breather" and the 6" compromises performance. fortunately the boat has 8" exhaust from the surge tube to the transom or this would be an upgrade that would have to be made for anyone considering the repower combination.
-the 24v to 12v conversion was fairly easy and inexpensive once we found the location of the relays that needed to be replaced (kit to convert included starter, alternator, glow plugs, relays and 115v block heater)
-new engine is going to be mounted with soundown isolators which should improve vibrations and overall noise of engine.
-C7.1 has turbo moved about 2" further off the Center line from the original 3126B we had thus making the elbow for exhaust very tight on our engine box (definitely something anyone considering this repower combo should take into account).
-Fuel lines are almost plug and play if there is enough slack. I elected to replace all of them while boat is undergoing project.
- The cooling water intake is perpendicular to the crankshaft of the engine so it is oriented in a different direction than the 3126B was. the engine is not in the boat yet but for our setup an elbow or Long sweep of the 2" hose will need to be used to make the connection.
-we rebuilt our twin disc gear box to save some money on the project but ensure the old workhorse was in top shape for the new power plant.
I hope this helps anyone that finds themself in a similar situation

******
I do have a 3126B with 3800 hours for sale for parts or rebuild. If you know anyone please send them my way. most of the parts on the engine are new. #6 cylinder is down. cylinder wall is scored and experiences extensive blow by. I also have many spare parts available for the old engine.
 

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