Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-12-2013, 19:12   #1
Registered User
 
svstrider's Avatar

Join Date: Apr 2003
Location: back on Gold Coast after sailing north to Thailand then east to Pacific via Irian Jaya, PNG & Solomons
Boat: Tennant 47ft Catamaran
Posts: 310
Decompression required to start 3GM30 Yanmar

If it has been more than 24 hours since the engine started, It will not start unless I decompress the 3 cylinders and then flick the levers. I have changed the fuel filters )both primary & secondary) but without benefit. There are no fuel line leaks that I can see. Any ideas??
__________________

__________________
Paul & Kaspar de Wonda Dog
S/V "Pelican V"
"Trust not a living soul and step warily around the dead"
svstrider is offline   Reply With Quote
Old 25-12-2013, 19:28   #2
Senior Cruiser
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 7,930
Re: Decompression required to start 3GM30 Yanmar

The starter may not be able to turn the engine over fast enough to get good compression. Could be caused by weak battery, bad battery connections, starter malfunctioning (dirty), starter brushes worn, solenoid contacts burned. Those are some places I would look.
__________________

__________________
The Blue Dot Campaign. This Changes Everything.
DeepFrz is offline   Reply With Quote
Old 25-12-2013, 19:48   #3
Moderator
 
sailorchic34's Avatar

Cruisers Forum Supporter

Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 4,815
Re: Decompression required to start 3GM30 Yanmar

So next time you have the engine running, pull each decompression lever one at a time and see if there is a difference between cylinders. If there is no change or not much of a change on one cylinder, that cylinder has in issue, Rings, injector or valves. Then next time you start the engine just decompress the one BAD cylinder.

If all are good each cylinder will sound like the next. Then

I found that if one cylinder has bad compression, it will prevent the engine from starting. Could also be a bad injector or miss adjusted valves.

Mine in the end was broken rings . From discussions here, there was a bad batch of yanmar 3gm30's from the early 90's that tended to break piston lands at relatively low hours. Mine did at 1100 hours. With luck yours will be a bad injector or valves needing adjusting. Also check for leaks in the fuel system.
__________________
sailorchic34 is offline   Reply With Quote
Old 25-12-2013, 19:51   #4
Registered User

Join Date: Oct 2009
Location: australia
Posts: 467
Re: Decompression required to start 3GM30 Yanmar

Did the engine turn over prior to decompressing it ?. If it did was it at normal cranking speed?.
__________________
shakey doug is offline   Reply With Quote
Old 25-12-2013, 20:21   #5
Registered User
 
svstrider's Avatar

Join Date: Apr 2003
Location: back on Gold Coast after sailing north to Thailand then east to Pacific via Irian Jaya, PNG & Solomons
Boat: Tennant 47ft Catamaran
Posts: 310
Re: Decompression required to start 3GM30 Yanmar

Quote:
Originally Posted by DeepFrz View Post
The starter may not be able to turn the engine over fast enough to get good compression. Could be caused by weak battery, bad battery connections, starter malfunctioning (dirty), starter brushes worn, solenoid contacts burned. Those are some places I would look.
Thanks Friz, I will check these things. However I have been crossing both starter batteries (cat with 2 engines) but will check starter connections. Starter will be a problem as am in Sabah.
thanks
__________________
Paul & Kaspar de Wonda Dog
S/V "Pelican V"
"Trust not a living soul and step warily around the dead"
svstrider is offline   Reply With Quote
Old 25-12-2013, 20:22   #6
Registered User
 
svstrider's Avatar

Join Date: Apr 2003
Location: back on Gold Coast after sailing north to Thailand then east to Pacific via Irian Jaya, PNG & Solomons
Boat: Tennant 47ft Catamaran
Posts: 310
Re: Decompression required to start 3GM30 Yanmar

Quote:
Originally Posted by shakey doug View Post
Did the engine turn over prior to decompressing it ?. If it did was it at normal cranking speed?.
Yes turned over andf cranking speed was normal.
__________________
Paul & Kaspar de Wonda Dog
S/V "Pelican V"
"Trust not a living soul and step warily around the dead"
svstrider is offline   Reply With Quote
Old 25-12-2013, 20:43   #7
Senior Cruiser
 
Starbuck's Avatar

Cruisers Forum Supporter

Join Date: May 2005
Location: Long Beach, CA
Posts: 827
Re: Decompression required to start 3GM30 Yanmar

If you have been starting on "both" batteries, try each separately. You may find you have a weak battery. If so, combining them will cause the good battery to discharge into the weak one, and you then are trying to start the engine with what is essentially a big (combined), weak battery without enough juice to crank to detonation.

Happened to me.
__________________

__________________
s/y Elizabeth Catalina 34 MkII
"Man must have just enough faith in himself to have adventures, and just enough doubt of himself to enjoy them." G. K. Chesterfield
Starbuck is offline   Reply With Quote
Reply

Tags
3gm, 3gm30, compression, 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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 17:09.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.