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Northeaster 02-26-2008 02:06 PM

Rebuild 2GM vs repower with 2YM15 or 2YM20
Hi Folks,

My mechanic brother is about to check out my 25 year-old (raw water cooled) Yanmar 2GM. The engine was smoking a bit at high RPMs / High load, but otherwise worked well. I did have an issue where the raw water flow stopped a couple of times, but when I pulled off the water hose on the exhaust elbow, there was a poof of dry air, then the water flow came back right a way, and worked fine after that. May be an intermittent failing water pump??

Anyway, he will do a compression test, possibly an oil analysis, and check the head (valves, valve seats, etc.) If all check out OK, He will replace gaskets, and I may still spend about $500-1000 for new engine mounts, and a rebuild (or gasket kit) on a 25 year old engine - that has been raw water cooled, in salt water, for 25 years.

I don't have extra cash!! But, I can get a new 2YM15 for $5800 + tax. or a new 3YM20 for $6900.

Any advice would be appreciated! If my engine does not test well (compression, oil analysis, or look at water jacket, etc), do you think it would be wise to replace with an engine of approx same HP (2 YM15), or, as they say most boats are underpowered, and we have strong tides in the area (35 ft tides, on the Bay of Fundy) - Should I consider the 21 HP (3YM20).
I assume that I would have to look at re-propping, or at least re-pitching, if I went with more power. I have an old fixed 3 blade prop, on my current 13HP (2GM)
The boat is a 1978 Seafarer 30 (book disp 8600lbs, crane said it weighed 10,000, with gear onboard)
- A new 3YM20 is only 38lbs heavier than a new 2YM15!
- I do plan on keeping the boat for the next few years, at least.
- My water heater would be much more efficient with a fresh water cooled engine

PBzeer 02-26-2008 02:53 PM

Shaft length might also be an issue with a new engine. I would think if the boat isn't in your long term plans, I would think rebuild first.

JohnRPollard 02-26-2008 04:14 PM

Will your brother be pulling the engine to do this work? Or doing it in place?

If he's taking it out regardless, and you plan to keep the boat for more than a few years, I would swap it for a new engine if you can afford it.

That's a good price on the Yanmar 3YM20. But definitely compare it to the Betamarine BD722 (3 cylinder 20 hp), which has some nice features that the Yanmar lacks.

You could probably get some money for the 2GM, and even more if you rebuilt it...

Northeaster 02-26-2008 06:24 PM

The engine is already out, as I wanted to check / replace the aging diesel tank, and clean up / repaint the engine compartment.
As the engine did work OK in general, and started immediately each time, it will probably last a few more years. My main comcern is putting cash into rebuilding (if necessary) a block that has been raw (salt) water cooled for 25 years.
My brother can:
a: Just clean it up, so I can put it in the freshly painted engine compartment.
b: try to do a compression test, although he will have to borrow the tools, ask someone to help, as his auto engine compression tools won't fit the diesel injector holes.
c: take an oil sample in for analysis, but it has been sitting for a couple months - would the oil sample be a true picture, as particles may settle out.
d: remove the head, so he can see the piston/ ring tops, valves, seals, and maybe see more of the block water jacket, to see if there are major corrosion issues.

If he can check some of the above, and put it back together for a couple hundred bucks ( I need new engine mounts, approx $200 as well), then I will put it back in.

However, I think that if anything major need replacing, I would opt t oput my cash into a new engine, instead of one that old.

I would also like to know what the normal changes would be, in going form a 13hp engine, to a 21hp new one. Would that normally require a larger prop, different pitch, etc.
The 3YM20 is a couple inches longer, but I have room to push the shaft / prop towards the stern a couple inches. As well, I know a retired prop guy, who could probably shorten / rekey the shaft, if necessary.

JohnRPollard 02-26-2008 07:18 PM

If you have gone to all the trouble of pulling the engine, you really should do more than "just clean it up". At a minimum, I'd have your brother do b,c, and d while it's out. Otherwise you may be re-installing an engine with little life left in it, or not, but you just won't know.

With a larger engine, I would expect that you'd need to re-prop (size and pitch). If you do go that route, this would probably be a good time to replace the shaft rather than re-use the old one.

If space is tight, the Beta equivalent is about 1.5 inches shorter and 1 inch narrower than the Yanmar.

I would suggest you peruse some of the re-powering threads here on Sailnet. There's usually quite a bit more to it than simply swapping the engines out....

Faster 02-26-2008 07:37 PM

As someone mentioned already, shaft length may need to be changed, is the engine mount footprint the same? are there clearance issues on the "new" engine (height, width, accessories, access?) Going from Yanmar to Yanmar I'd hope most of these would be minimal, but if changing brands it can amount to a lot of work/money/both.

Sometimes even the angle of the engine beds needs to be altered.

I think you're right to be concerned about 25 years of RWC and its effects on the waterjackets... But realize the cost of the repower is always more than the cost of the engine itself.

Best of luck in your decision.

Northeaster 02-26-2008 08:02 PM

I have definitely read alot of the repower threads. I realize that in many cases, when changing between different manufactures / models, there is often alot of extra work in adding / modifying the engine beds, etc.

In my case, if I change to the newer 2YM15, the current engine mount placement matches that of the new engine. Also, alot of the other measurements are similar, would not require a shorter shaft, and probably not any prop change - as the current 2GM is 13hP, and so is the new 2YM15.
So it would be an "easy" repower. I also have full access to crawl under the cokpit, to run the new wiring.

But, if I am going to repower, It may be worth the extra $1100 engine cost, as well as a new / used prop / shaft, to get the added HP of the new 3YM20.
Even this new engine matches the current engine beds, in width, and the front mounts are in the correct position. I would have to move the rear mounts back 3", but as I have good access, that is not a bad job.

I will have to check on the recommended exhaust hose size, with the larger 3YM20!!

John Pollard - I talked to my brother tonight, and he is going to take an oil sample for analysis, and pull the head, and oil pan off to have a look.

Faster - If I need a new shaft, I would have to get one. However, if it just needs to be shorter, my retired "prop guy" friend can likely mofify the currnet one to work fine. I may have to eat the cost of a new / used prop, but maybe nothing fancy for a year or two.

Northeaster 02-26-2008 10:30 PM

John Pollard- Any idea of a price on the Beta Marine BD722?

Also, you mentioned advantages over Yanmar. Can you be more specific?

JohnRPollard 02-27-2008 08:58 AM


I got a price of $6800 for the BD722 when I inquired with Beta a month or two ago. That's not a whole lot less than your Yanmar 3YM20 price. But you'd have to study the specs to see what the respective prices include. For instance, the Beta price includes a new transmission, motor mounts, control panel, a PTO, etc.

Off the top of my head, some differences that I recall are that the Betas have built-in oil change pumps, shallow sump options, and glow plugs. Also, the Beta raw water pump is cam driven off the engine, so there is only a single belt (for the alternator and fresh water pump).

Another consideration is that the Betas are based on the ubiquitous Kubota tractor engines, so the replacement parts tend to be cheaper and more readily available than Yanmar.

Northeaster 02-27-2008 09:09 AM

John - Thanks for the info!

I am waiting for a call, form the Beta dealer in Maine, to get a price, just in case. I believe the Yanmar comes with all of the needed parts, as well, but I will double check. The price on the 3YM20 was about the same as your Beta quote!!($6900 in Nova Scotia, and in Maine, as the dollar is about even)

As far as installation, with both the Yanmar 3YM20 and the Beta BD722, I could use my existing engine bed / front mount positions, and would have move my rear mounts back 2-3".

I have decided to only repower if we find problems with the old 2GM, which will require putting more than a few hundred bucks into it!

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