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Old 25-10-2013, 12:09   #1
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Top end rebuild or Re-power?

Ok guys here's my situation. I have a '73 Morgan OI 33 that I picked up a few years ago as a steal as the gentleman selling it was loosing his job. It has an older Yanmar 2GM20F that just gave out on me. I have no previous information on it. (year, hours, etc.) Upon inspection it appears that the exhaust elbow corroded to the point where it was allowing seawater to seep into the exhaust manifold and ultimately into the cylinders thru an open exhaust valve. The oil is full of water and the compression is shot. I have not pulled off the head yet, but at the moment I'm looking at the minimum of a top end rebuild, new heat exchanger, new exhaust manifold, and new exhaust elbow. Looking at the rockers and push-rods it appears that everything has some pretty significant surface rust from the moisture in the engine.

So in your opinion, should I be looking to go ahead with the new parts and the top end rebuild w/o knowing the condition of the corrosion in the crankcase? Or should I be looking at a new or rebuilt motor?

I love this boat and plan to keep it. Besides the motor it is fairly good condition. I still need to contact a Yanmar dealer, and hash out the cost difference between the two scenarios and the availability of a new/rebuilt motor.

Let me know your opinions. Thanks guys
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Old 25-10-2013, 13:56   #2
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Re: Top end rebuild or Re-power?

I have a 3gm30f and think it's a great little engine. The GM series is no longer in production, but I've found parts easy to locate and, from what I gather, it should remain that way for years to come. Yanmar parts sure are expensive though!!

Would you be doing the work yourself? That often seems like the tipping factor when deciding which route to take. Also, once you get head off and can actually size up the internals..

I'm not a mechanic, but that's my two cents. Best of luck.
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Old 25-10-2013, 14:09   #3
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Re: Top end rebuild or Re-power?

I will be doing all the removal and installation. I have none of the tooling or space to do the machining however. I do love the little 2gm. Yanmar makes a great motor and your definitely not wrong about the parts being pricey. I was looking at the new 3ym30's as a replacement if i end up having to go that route. I'm pulling the head off tomorrow morning and hoping the cylinders don't look to bad. :/
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Old 25-10-2013, 14:18   #4
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Re: Top end rebuild or Re-power?

With out knowing all of the details I would say it is a gamble. Obviously the most economical would be doing the heads. However some things to consider would be what happens if you spend all that money on the heads just to have a hidden problem in the bottom end creep up on you a year later and you need a new engine anyways.

Personally if I could swing the cost I would say go for a new or newer engine if nothing else for peace of mind that you wont always be worried if it is going to crap out on you from hidden damage

.....and new engines are pretty and shiny to look at.
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Old 25-10-2013, 14:31   #5
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Re: Top end rebuild or Re-power?

The rust may be just superficial and easily cleaned up. If the wear surfaces on the valve train aren't pitted or not pitted badly they may all be salvageable. Doing a top end rebuild is not that expensive as long as the head isn't cracked or very badly warped especially if you do the R&R yourself. A machine shop will do all the critical work on the head. It's basically just taking the head off and putting it back. No special tools except a torque wrench which you can rent and feeler gauges to set the valve lash.

The injectors should be sent off to a shop to be tested and rebuilt or replaced as necessary.

If the cylinders are scored/pitted, and the rings are shot, you'll have to pull the engine to get it machined. That adds more expense but should still be cheaper than replacing the engine with new. Once the head and transmission are off, you should be able to manhandle the 2GM short block. If you can't do it yourself, hire a young gorilla. If you don't go that route, a 'come along' on the boom would probably suffice to get the engine on the dock.

Failing all the above. Keep your eye out for a used 2GM20f. They seem to show up fairly regularly as those that believe horse power cures bad boat handling are stuffing in larger engines in place of the 2GM.

In the meantime, fill the engine with freshwater and pump out several times. Fill with fresh oil and turn the engine over with the starter to get it thoroughly circulated. Do another oil change and regularly turn the engine over with the starter to be sure oil is displacing any water.

Good luck with the project.
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Old 25-10-2013, 14:39   #6
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Re: Top end rebuild or Re-power?

In addition to the advise from the precious posts I would also take into account your wallet and plans for the boat.

Big wallet, just go for new. Of course, unless you are different than 99% of the CF members, unlimited budget probably isn't the norm.

Second, what cruising plans and how long will you keep the boat. If you plan to hold onto it for 10-20 years, go new. If you plan on a lot of motoring, up and down the ICW, trips to isolated islands, go new.
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Old 25-10-2013, 16:40   #7
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Re: Top end rebuild or Re-power?

Ya i live aboard on the ICW and try to do as much sailing as possible, but its quite a trek down to the inlet and the channel is pretty small in spaces. I definitely plan on keeping the boat for the foreseeable future, but the wallet isn't as thick as I would like it to be. I think the defining factor would be what the cylinders and rings look like tomorrow when i get the head off. I think if I have to pull the block out for any work I might just splurge for a new or rebuilt just so I have that peace of mind.
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Old 26-10-2013, 07:47   #8
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Re: Top end rebuild or Re-power?

See if Sailorchick 34 is available for a week or 2 in sunny Florida and needs to see the east coast. She does have the experience and the special tools to rebuild your engine. LOL
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Old 26-10-2013, 10:13   #9
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Re: Top end rebuild or Re-power?

All of the above advice, plus check the condition of the cam lobes. Cams are usually Nitrited(sp?) which is a surface hardening treatment. It doesnt take much rust to ruin that thin hard surface. You can clean the rust off and get the engine going again, and have a lobe go soft (wear out) in a few hundred hours. If the lobes show rust, check on the price of a replacement cam, or having yours sent to an overhauler for polish, and re-nitriting. This also applies to the lifter faces. None of this is real pricy, but you dont want to go to the expense of rings,bearings,valve job, and leave a weak link in the depths of the engine. Just my 2 cents worth. _____Grant.
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Old 26-10-2013, 10:28   #10
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Re: Top end rebuild or Re-power?

How much have you used it?
How well did the 2GM push your boat into a chop? seems a bit small to me. I'd much rather see a 3GM in that boat.
Minimum, I would rebuild the whole thing if not much is known about it. The older 2GM and 3GM's are famous for cracked pistons etc. You dont want to rebuild the top without knowing the bottom condition.
If you are going blue water, then I would replace with a Beta or something with more horsepower 25-30hp....
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Old 29-10-2013, 18:16   #11
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Re: Top end rebuild or Re-power?

You have saltwater in the crankcase where all the bearings are, plus could be a problem with cylinder wall corrosion, but maybe not. You just do not know until you get the engine apart, tested for cracks, measurement of all journals (surfaces bearings ride on) and micrometer readings for cylinder wall wear plus inspection of cam lobes, valves, pistons. Only after that will you know what it will cost. Your biggest problem will be finding a good machine shop. Look for someone that does large diesels. The amount of money for a rebuild on a big diesel means it has to be done right or guarantee work will run them out of business.
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Old 30-10-2013, 11:29   #12
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Re: Top end rebuild or Re-power?

That is exactly the reason I am looking at repowering it. By the time I get the motor out and the case split Im looking at the same cost or near the same cost of a rebuilt motor. Right now I have the head off and am planning to clean it all up, lap the valves, and clean up the cylinder walls. If i cant get decent compression and get it to fire I will be done with it and turn it in as a core for a new or rebuilt motor.
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Old 30-10-2013, 12:36   #13
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Re: Top end rebuild or Re-power?

Rebuilding is easier and less costly. I just rebuilt my 3gm30f this last july and august. Total cost for me was about $1200. $700 for parts. $270 for machining, which included boring out one cylinder, sleeving it and honeing the other two. I'm betting yours could be done for less

Piston and rings is about $125, 10 over piston and rings is $150 btw, rings alone are about $60 ish. Bearing are about $6 per set.

I also have the special tool 6" deep 36mm socket, that is needed to pull the inner nut of the crankshaft. Had it made for about $80.

Besides the special tool, I had a standard socket and wrench set, a few deep sockets, screwdrivers, feeler gauge and a torque wrench. But by no means did I have a lot of tools. I used a metal oil filter wrench as a ring compressor, that actually worked well too. The engine sat on fender boards in the cockpit with a plastic tarp on the deck under it.

Here's the link to my summer of discontent.

I was Bored so Pulled the Head on my Yanmar

I've over 55 hours on the new rebuilt and it works fine. Mine had no rust though.

I found a good machine shop, by talking to a few custom car guys. The machine shop had a big cat block and my dinky yanmar block. They did a great job too.
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Old 30-10-2013, 12:39   #14
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Re: Top end rebuild or Re-power?

SC, I don't have an engine to rebuild but I would be interested in that wench set.
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Old 30-10-2013, 12:49   #15
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Re: Top end rebuild or Re-power?

Quote:
Originally Posted by DeepFrz View Post
SC, I don't have an engine to rebuild but I would be interested in that wench set.
Alas my wench set is rather rare.

Sure wish my fingers could spell.
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