Return to the home page...

Go Back   Moyer Marine Atomic 4 Community - Home of the Afourians > Discussion Topics > Troubleshooting

Thread Tools Display Modes
  #1   IP:
Old 04-17-2010, 02:42 AM
Charles Taylor's Avatar
Charles Taylor Charles Taylor is offline
Senior Member
Join Date: Sep 2007
Posts: 17
Thanks: 0
Thanked 0 Times in 0 Posts
Knocking / Runs Rough

Over the last few weeks, I have been pulling the valves and replacing their springs because of a sticking exhaust valve in #2 cylinder. I finished up last Sunday and the engine was running fine.

Today I went to clean up the boat and see if the engine was still running well. It was running fine while I warmed it up so that I could change the oil.

One of Murphy's Laws must have taken effect. After nothing more than changing the oil, the engine developed a pronounced knock and ran rough.

I tried adjusting the timing, checking the fuel filters and squirting MMO into the cylinders. I noticed no change.

I did notice that choking the engine has no effect at idle. The knocking decreases at higher RPM. There is no smoke. I also noticed that the manifold stays rather cool to the touch and the temperature gauge is in the normal range.

What could cause this problem that only chose to manifest itself after an oil change?


Charles Taylor
Reply With Quote
  #2   IP:
Old 04-17-2010, 08:16 AM
Don Moyer's Avatar
Don Moyer Don Moyer is offline
Join Date: Oct 2004
Posts: 2,811
Thanks: 0
Thanked 183 Times in 124 Posts

Assuming that your oil pressure is normal after the change, I don't believe your rough running has anything to do with the oil change. My first guess is that you bumped something during the oil change that is affecting the secondary ignition system on one or two of your cylinders.

When an Atomic 4 runs on only two cylinders it will emit a knocking sound and deliver considerably less heat to the manifold (addressing your other symptom).

Reply With Quote
  #3   IP:
Old 04-17-2010, 12:40 PM
Qben's Avatar
Qben Qben is offline
Senior Member
Join Date: Mar 2010
Location: Anacortes, WA
Posts: 74
Thanks: 0
Thanked 0 Times in 0 Posts
I had the exact symptoms you describe when my engine was firing on only 2cylinders (due to water in them though). Try removing spark plug wires one at a time to isolate which cylinders are affected (the engine will immediately die if you remove the wire from a firing cylinder when only 2 of them are firing). You can probably also tell by feeling the plug wire boots where they attach to the plugs. The ones over the firing cylinders will be much hotter than the ones over the non-firing cylinders. After you isolate the cylinders that are not firing, you can start troubleshooting, by switching plug wires and plugs around (or replacing with new). Also check your distributer cap for cracks or blemished surfaces on the affected contacts (underneath).

You should also probably check cylinder compression and torque on your head nuts. Since you recently had the head off, this could also be a leak at the head gasket.

Qben Oliver
Reply With Quote

Thread Tools
Display Modes

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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Runs rough under load Fuel System 12 06-30-2009 11:29 AM
engine runs rough then dies after 20min run time ray mizell Electrical 9 08-20-2008 06:47 PM
Runs rough under load jwhite1245 Troubleshooting 1 02-21-2007 12:36 PM
Atomic 4 runs but VERY rough cfritzsche Troubleshooting 6 02-26-2006 06:19 PM
Runs rough under load... flyinelvis Troubleshooting 2 03-24-2005 06:07 PM

All times are GMT -4. The time now is 07:33 PM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

Universal® is a registered trademark of Westerbeke Corporation

Copyright © 2004-2024 Moyer Marine Inc.

All Rights Reserved