Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 08-07-2010, 19:01   #1
Registered User
Olorin's Avatar

Join Date: Aug 2009
Location: On the Boat
Boat: Fortuna, Island Spirit 400, 40ft. Catamaran - S/V One White Tree
Posts: 107
Advice on Sick 3GM30

I purchased a sailing catamaran with two Yanmar 3GM30s.

The starboard engine has around 3000 hours on it and has a 55 Amp alternator. This engine runs quietly and well.

The port one is hooked to the hot water tank and a Balmar 120 Amp alternator and has around 3300 hours. I would expect the additional hours were at idle making hot water and/or 12 volts. This one sounds very bangy at less than 2000 rpm and will eventually stall out if it is reving at 1200. It does drive the boat well at high revs.

A number of mechanics have suggested that I have it rebuilt. If this were a gas engine, one might think that it is varnished up and a light honing of the cylinders and light regrinding of the valves might everything OK.

What the wise thing to do? replace it with new? or reconditioned? or do the rebuild? etc.

I hope to cross oceans in this thing.

thanks in advance,


"And all I ask is a merry yarn from a laughing fellow-rover
And quiet sleep and a sweet dream when the long trick's over."
John Masefield
Olorin is offline   Reply With Quote
Old 08-07-2010, 19:26   #2
Registered User

Join Date: Dec 2007
Location: Brisbane
Boat: deboated
Posts: 672
Going on what you have written check tappets not likely to be main problem but is always overlooked and takes not much time and next to no money. I would then have a good Diesel injection guy check, compression + pump timing + have the injectors tested and at the very least serviced. I would not run the engine much until you have had these items checked as damage may be done to a serviceable engine that only needed some external repairs. 3000 hours is not much if the engines were looked after so run slowly. The not wanting to run under 2000rpm makes me feel that the fuel system or valves could possibly be the real culprit.

meyermm is offline   Reply With Quote
Old 08-07-2010, 19:47   #3
Senior Cruiser
Roy M's Avatar

Cruisers Forum Supporter

Join Date: Feb 2007
Location: Southwestern Yacht Club, San Diego, CA
Boat: Searunner 40 trimaran, WILDERNESS
Posts: 2,926
Images: 4
Pull the exhaust elbows off and examine them carefully for blockage.
Roy M is online now   Reply With Quote
Old 08-07-2010, 20:26   #4
Boracay's Avatar

Cruisers Forum Supporter

Join Date: Feb 2004
Location: Pelican Bay, Great Sandy National Park
Boat: Steel Roberts Offshore 44
Posts: 5,175
Images: 18
How much money and time do you have?

You boat looks to be 6 or 7 years old. Boats 25 years old have similar engines that run well, as does your starboard engine.

For mine it's a question of time and money. If the money is no problem, and you're short of time have the engine pulled, sell it on Whatever and have a new one installed. End of problem.

If you have plenty of time and no money I'd suggest assuming that the bores had glazed and act accordingly.

There have been suggestions that changing to a straight mineral oil and running the engine hard is the way to go. Other on this Forum will know way more than me.

The worst course of action in terms of both time and money is to chase unknown faults at umpteen dollars an hour and expensive parts with a mechanic. I'd suggest do it yourself or don't do it. It might be expensive lessons but by the time you've got the problem sorted you could be as good as some mechanics. A nice way to go cruising.

There is, after all, the starboard engine if the port goes kaput.

Do keep in mind that my advice is worth exactly what you're paying for it.
Rust never sleeps
Boracay Blog.
Boracay is offline   Reply With Quote
Old 08-07-2010, 20:42   #5
Moderator Emeritus
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
Before investing in a very expensive rebuild I would do some basic maintenance. If the banging doesn't get worse at higher speed it is not very likely that something is coming loose inside the engine. A bad bearing would be very apparent.

Low RPM performance issues can be related to timing. You say its "bangy" and won't idle well. Bangy is a had thing to troubleshoot over the internet. Here are some things I would do.

- Adjust the valves on both engines. Probably hasn't been done in like forever. Valve clearance will affect performance, especially at idle. At low rpm excessive clearance can be heard as a mechanically "clackety-clackety" noise kinda like gears not meshed properly.
- Check the exhaust mixer - How many of those extra 300 hours were at low power where carbon build up could be worse.
- set the suspect engine in neutral to the rpm where the "bangy" is prevalent. Set the other engine to the same rpm. Examine both engines visually. Is the suspect engine shaking on its mounts? - Maybe new mounts are in order.
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 08-07-2010, 22:36   #6
Registered User

Join Date: Dec 2007
Location: Brisbane
Boat: deboated
Posts: 672
While I would check (clean) the exhaust elbows as a matter of service blocked exhausts usually effect an engine as the RPM increases and have lesser of an effect at idle, usually!
meyermm is offline   Reply With Quote
Old 09-07-2010, 02:19   #7
Registered User

Join Date: Oct 2009
Location: australia
Posts: 433
Try changing the injectors over you may surprised,cheap and easy too.
shakey doug is offline   Reply With Quote
Old 09-07-2010, 06:44   #8
Registered User

Join Date: Dec 2008
Location: Oriental, NC
Boat: Mainship Pilot 34
Posts: 1,429
I had the same problem in my cat with two 3gm30fs. Having two engines focusses attention on the lesser one. In my case the stbd engine was hard to start and clattered exactly as you describe.

Replacing the injectors solved the problem.

djmarchand is offline   Reply With Quote
Old 25-07-2010, 00:15   #9
Registered User

Join Date: Jun 2010
Posts: 11
Pulling and sending in an oil sample will tell you if there are and expensive problems that break things and make holes it the block, about $75 now. also run the engine to the rough RPM and crack the fitting for each of the injectors indivigually, there should be a noticable change when you have the line cracked. If no change you have a bad injector, injectors can be bad but still workable, send in for check and rebuild.
diesels can be hard to set the pump timing without a very good mechanical background.

cowboy is offline   Reply With Quote

3gm, 3gm30, yanmar

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Sea Sickness and Stugeron 42AFJ Seamanship & Boat Handling 36 05-09-2013 14:05
Can Dogs Get Sea Sick ? vintageray Families, Kids and Pets Afloat 38 29-09-2010 08:58
I'm Sick of Bad Boat Ads ! sww914 Off Topic Forum 30 05-07-2010 05:48
Sea Sick Cat Kai Nui Families, Kids and Pets Afloat 6 14-04-2007 20:28

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 11:10.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.