Go Back  Offshoreonly.com > Technical > General Q & A
Low Hour 383 valve seats dropped, why? >

Low Hour 383 valve seats dropped, why?

Notices

Low Hour 383 valve seats dropped, why?

Old 08-15-2022, 09:05 AM
  #1  
Registered
Thread Starter
 
Join Date: Mar 2019
Posts: 120
Received 34 Likes on 26 Posts
Default Low Hour 383 valve seats dropped, why?

Summer 2021 one of the two Mercruiser 383s in my dad's boat had a water pump fail, and it got a little hot.
Water pump replaced and no issue since.
3 weeks ago the exhaust valve seats dropped into cylinder 6 and 8 simultaneously at IDLE speed.
After tear down both pistons wrecked, both cylinder walls cracked (I am assuming this was a result of wedging the piston in the bore trying to compress a valve seat, happened to me before)
The engine had only 200 hours on it. Mercury was no help, out of warranty.

What caused this? Has anyone else had this happen? Is it related to overheating over a year ago?

Follow up question, got the engine swapped in one day, and the new engine is identical to the old, but it has higher fuel consumption according to the Garmin than the engine on the other side (18gal/hr vs 16.5gal/hr at cruise), any normal reason that might be? Previously both engines were nearly identical on fuel consumption.
LakeHuronPower is offline  
Old 08-15-2022, 04:24 PM
  #2  
Registered
 
Join Date: Feb 2013
Posts: 1,095
Received 188 Likes on 110 Posts
Default

I would look for crack/s in the heads in the valve seat boss area. That would explain them falling out. Maybe do a Dye penetrant inspection on the suspect area?.
zz28zz is offline  
Old 08-15-2022, 08:16 PM
  #3  
Registered
 
Join Date: Oct 2005
Location: Waldorf, Md
Posts: 801
Received 93 Likes on 56 Posts
Default

Were the engines re-manufactured or new ? I don't remember what heads are on those but I didn't think they had exhaust seats from the factory. I have only seen a couple over the years so i might be wrong.

As far as the fuel consumption goes are you sure the "new" engine is identical ? Maybe bored .030 though I wouldnt think that would make that big of a difference in fuel use.
BillK is offline  
Old 08-15-2022, 10:52 PM
  #4  
Registered
 
Join Date: Jun 2011
Posts: 1,130
Received 77 Likes on 57 Posts
Default

Originally Posted by LakeHuronPower View Post
Summer 2021 one of the two Mercruiser 383s in my dad's boat had a water pump fail, and it got a little hot.
Water pump replaced and no issue since.
3 weeks ago the exhaust valve seats dropped into cylinder 6 and 8 simultaneously at IDLE speed.
After tear down both pistons wrecked, both cylinder walls cracked (I am assuming this was a result of wedging the piston in the bore trying to compress a valve seat, happened to me before)
The engine had only 200 hours on it. Mercury was no help, out of warranty.

What caused this? Has anyone else had this happen? Is it related to overheating over a year ago?

Follow up question, got the engine swapped in one day, and the new engine is identical to the old, but it has higher fuel consumption according to the Garmin than the engine on the other side (18gal/hr vs 16.5gal/hr at cruise), any normal reason that might be? Previously both engines were nearly identical on fuel consumption.
I had a exhaust valve seat drop, but about 720 hours on the motor. (Merc 350 Mag EFI/MP) Happened at lower rpm. Cause was an injector that leaned out, detonation ensued, knock sensor retarded timing and heated up the exhaust valve seat. It finally had enough and took the engine with it.
Trash is offline  
Old 08-16-2022, 10:41 AM
  #5  
Registered
Thread Starter
 
Join Date: Mar 2019
Posts: 120
Received 34 Likes on 26 Posts
Default

From what I understand the 383s from Mercruiser are remanned 377s, bored 40 over.
No cracks are visible in the head, but what is weird was the simultaneous dropping of 2 valve seats.
Checking the injectors is a good idea, but since it happened at idle I wouldn't think leaning out a cylinder at idle would do much other than make it miss.
LakeHuronPower is offline  
The following users liked this post:
SB (08-16-2022)
Old 08-16-2022, 06:20 PM
  #6  
Registered
 
Join Date: Oct 2005
Location: Waldorf, Md
Posts: 801
Received 93 Likes on 56 Posts
Default

Originally Posted by LakeHuronPower View Post
Checking the injectors is a good idea, but since it happened at idle I wouldn't think leaning out a cylinder at idle would do much other than make it miss.
Its still a very good idea. The seat might have come loose earlier and was just waiting to fall out. Slowing to an idle changes the temperatures in the head so you never know. And I have seen exhaust gas temps go way up at idle if the tune isnt correct. Especially if there is not enough timing.
If the injectors have a lot of hours on them I would probably replace them.
BillK is offline  
The following users liked this post:
SB (08-19-2022)
Old 08-16-2022, 07:02 PM
  #7  
Registered
 
Join Date: Jun 2011
Posts: 1,130
Received 77 Likes on 57 Posts
Default

Originally Posted by LakeHuronPower View Post
From what I understand the 383s from Mercruiser are remanned 377s, bored 40 over.
No cracks are visible in the head, but what is weird was the simultaneous dropping of 2 valve seats.
Checking the injectors is a good idea, but since it happened at idle I wouldn't think leaning out a cylinder at idle would do much other than make it miss.
If the injectors are clogged or flowing poorly then the lean damage occurs at higher power settings, but then the damage is done and they can fall out at any time, including idle. You are assuming they are only lean at idle, but that is not the case.
Trash is offline  
Old 08-19-2022, 10:16 AM
  #8  
Registered
iTrader: (2)
 
Join Date: Oct 2012
Location: dfw texas
Posts: 1,327
Likes: 0
Received 2 Likes on 1 Post
Default

Seen some seats crack on the 906 hd heads with the inconel exhaust seats ,and lots of tuliped intakes and a few lost valve heads on the 062's,often accompanied by water inrusion from a bad manifold , throttle chop ,engine stall at speed ect .would make sure water pressure ok on your replacement engine for peace of mind
airjunky is offline  

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 On
Pingbacks are On
Refbacks are On


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.