Replace or rebuild???

[Scudrunner]

I have the original Universal Atomic Diesel engine, model 5424 (Kubota DH1101) which can be a little cantankerous and a few seals are seeping a bit. I like a clean and a reliable engine. Should I rebuild this engine or buy a newer engine? I have a great Diesel mechanic where I live, who would probably rebuild it cheaper than a coastal marine mechanic... but is it worth it?

[WillieC]

This is apparently in an A25. It all depends. I know nothing about these engines, but diesel boat engines as a whole may be easily resurrected with a top end refresh, depending... Investigate any known issues with your particular engine as part of your decision making. Evidently, yours is still running so you and your mechanic can assess compression, oil pressure, general condition before ripping it apart. If your compression and oil pressure are good, your issues may simply be injectors and pump. Any leaks may be from the valve covers and failed bolt on parts gaskets or failing hoses and various loose fittings. Finding a compression tester for my old Volvo Penta inspired me to make my own adapter. A bit of a pain. The Armstrong compression test told me as much. If you can spin it easily by hand... Since yours is still running, be sure to test it when at least warm if not hot. Careful, make sure your fuel is "OFF". It would be quite a miracle to start the engine by hand, but you don't want to be wrapped up in it even if it backfires.

Now if seawater was poured into the crankcase and left to sit for twenty years that is another story. From your description yours sounds a lot like the Volvo Penta I was able to refresh, and a reminder that I should have paid closer attention to the main seals...ah well.

Is your engine sleeved so that you can replace cylinders and pistons at the same time? Can you get new valves, guides, and springs? Your diesel mechanic should have the skills and equipment to do a good valve job. I went as far as new rod bearings, head work as described above and of course all new gaskets and seals where disturbed. Throw in an injector pump appraisal and refresh, along with injector testing, boil out and pressure test your heat exchanger (this engine is not seawater cooled, I hope), new hoses, belts, and a serious paint job. The paint job is crucial so you can keep an eye on where any future trouble is brewing. The old VP was so corroded and oil saturated I couldn't tell what was bleeding and what was "patina".

The added benefit of keeping the old engine is you get to keep everything that was connected to it. This represents no small cost when doing a full engine swap. Make sure your mechanic replaces the oil soaked engine mounts and knows how to do alignment. There is a lot to do with the engine out, so be thinking ahead. Clean that pan, paint the bilge, replace hardened wiring, examine your grounds, send the starter out for a serious bench test, how is the alternator, regulator? Time for upgrade? Cam driven water pumps are fairly cheap, I went with spanking new. (I did not paint the pan directly under the engine. I figured a fiberglass tub that had soaked in oil and antifreeze for forty years would require prep beyond my interest. The thought of adding paint chips to that slurry led me to leave that pan alone.)

There are sad stories of rebuilds that do not perform as advertised. Read about them on the forum. I feel very fortunate with my success, but I have had that stinkin' VP torn apart three times to get it right. So much for the shade tree mechanic with too much time on his hands. However, ours is now running like a top with virtually no issues this season, well some issues but it's also pushing fifty years old. Close enough!

Long, boring story but I hope it gives you food for thought. We'd all love a shiny new 20K engine that never leaks, always starts and keeps the beer cold. But for one or two hundred hours per year? You are asking the right questions.

[DesertAlbin736]

Listen to to WillieC, he is the guy to talk to when it comes to rebuilding engines, lessons learned from school-of-hard-knocks experience as he said in his post. A big question to think about is whether it is fresh water cooled or raw water cooled? And if the latter was it primarily used in fresh water, lakes, rivers, etc, or in salt water? Your diesel mechanic, if he/she is honest and experienced, should be able to give you a good cost/benefit idea. Parts availability is one issue. How many hours/years will a rebuild add to the life of the engine is another. How long you intend to keep & use your boat is yet another. Repowering with a new engine is a serious chunk of change, money you'll never recover on selling the boat. I paid more than should have for our boat, but the 80s vintage Yanmar 3GM30F engine installed in the early 90s was worth it. Just the fact that it runs quiet will little to no vibration is a big help.

[Dieselram94]

Very, very good advice above. I would like to add another thought…how far out do you venture with your boat? If it’s a good distance from help, that is something else to consider as well as how mechanically inclined you are. I am very mechanically inclined but am seriously considering repowering my a25 with a new beta. I have a Perkins 4.108 now with what I consider low hours and it runs absolutely perfect. That being said the 4.108 is known to always have a leaking rear main seal and I’m not exactly happy with how it’s mounted. Although I have VASTLY improved that. When I got it and apparently since the motor was installed in 1993 it was never even centered in the boat. It’s dead on now but that took some modifications and lots of patience. It’s now at .002 runout on the flange. My wife is terrified of boats and I really don’t want to scare her if the Perkins s quits in the water. We will see what I end up doing

[Ambler27FC]

Dieselram94 has an excellent point. I did re-power and it was because of the type of boating I wanted to do.

I was lucky to have a neighbor who used to be diesel mechanic and help me tear apart and rebuild many of the sub-systems - a great experience. But Some parts were harder to find (or impossible - with custom work-arounds) and took up to 4 weeks for delivery. No problem for day trips, but anchoring in the middle of nowhere was a real concern. My engine was perhaps overly complex and I could see a lot of failure points - just lost trust. The electrical system in particular had too many relays, a floating ground design, and suspect wiring. Dropping anchor in a swamp and just knowing what was going to happen in the morning has been a game changer.

If I were doing day trips I would have kept a perfectly serviceable engine. Leaking gaskets are easily replaced.

[Scudrunner]

So if I did spring for a new motor, what would you recommend?

[WillieC]

I’ll start with the obvious.

Brand new in a crate Beta 38 if you have the deluxe hull.

Now if used… I’d rebuild the used engine I already have.

[Ambler27FC]

I would recommend Beta too if going new. Very simple engine, easy maintenance, and good customer service. But can’t say I’ve surveyed the in the last few years.

[Scudrunner]

I’ll start with the obvious.

Brand new in a crate Beta 38 if you have the deluxe hull.

Now if used… I’d rebuild the used engine I already have.

I don't have the Deluxe hull. I was thinking new not a rebuilt if I go that route.

[Burton]

Yanmars are great engines too, but we have experienced HORRIBLE dealer customer service. I tried multiple dealers in trying to buy things like fuel filters, motor mounts, fan belts, throttle shut off solenoid. Finally resorted to multiple sellers to get these. The distributor was great getting me a manual, but lots a luck with the dealers! If I had to repower I would look very seriously at the dealers and parts availability.

[WillieC]

You could probably dial back the HP with the early hull. Maybe 24 HP or so. What say you, early owners?

Make sure you keep it clean and simple. Naturally aspirated, mechanical fuel injection, and up to Tier 3 requirements. Just my opinion. I like the Beta option for easy and cheap(er) parts, so I hear.

[WillieC]

So where are you boating, as Ambler pondered? Trying to look at a map with lousy interweb connection. Looks like the Platte runs through it. Navigable? It’s been a while since I’ve seen the USA in my Chevrolet. I’ve been surprised by the size of the Missouri.

Just curious.

[dkirsop]

Given all the electronics that now are common on most boats you likely need to have a 60 to 80 amp alternator. The single belt drive on my 21HP engine is challenged with this load. The 24 HP will be o.k. power wise but a dual belt drive for the alternator would be a worthwhile upgrade.

[DesertAlbin736]

Given all the electronics that now are common on most boats you likely need to have a 60 to 80 amp alternator. The single belt drive on my 21HP engine is challenged with this load. The 24 HP will be o.k. power wise but a dual belt drive for the alternator would be a worthwhile upgrade.

FWIW I have a 100 amp alternator from Mark Grasser DC Solutions. Have no trouble with it, but on the other hand my house loads are minimal. Only changed out the OEM 35 amp Hitachi because I couldn't keep its internal 14 V regulator from overriding the the external "smart" regulator programmed for AGM batteries.

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Still working on my fuel tank inspection hatches project. Tank is out in my workshop. Found some very stiff 10 gauge 8" X 8" plates that I'm cutting & drilling along with sheets of 1/8" Buna-N rubber gasket material. Pictures are still in my phone, so none to post here.

[dkirsop]

Your belt looks like it might be larger than the 10mm belt on my AD21.