Low compression #2&4

gtfireftr

Member
Oct 9, 2014
292
Westport MA
Boat Info
1997 Sea Ray Sundancer 290
Engines
Twin 4.3 liter w/Alpha Drives
1998 290 DA, twin 4.3's..... Changed engines in 2017, both have about 100hrs since... I felt I had an issue, but I thought the bottom may have been dirty from not using very much in the past few weeks..... Went to start port motor and she would not fire... I figured flooded.... Went back the next day with a set of plugs and my compression gauge....... results are as follows...
#1 150, #3 148, #5 150
#2 90, #4 30, #6 150.....
I am hoping I have a blown head gasket...... Any direction is appreciated.....

TIA
 
1998 290 DA, twin 4.3's..... Changed engines in 2017, both have about 100hrs since... I felt I had an issue, but I thought the bottom may have been dirty from not using very much in the past few weeks..... Went to start port motor and she would not fire... I figured flooded.... Went back the next day with a set of plugs and my compression gauge....... results are as follows...
#1 150, #3 148, #5 150
#2 90, #4 30, #6 150.....
I am hoping I have a blown head gasket...... Any direction is appreciated.....

TIA
Do a leak down test, tuliped valves would be my guess.
I had a similar issue this spring and it was the valves. If the you lug the engine it will build cylinder temperature and the valves will pull up into the seats and lose compression. I was shocked when it happened to me because I don’t hot rod my boat. But I think my boat was over propped for the load of stuff on our boat.
 
Do a leak down test, tuliped valves would be my guess.
I had a similar issue this spring and it was the valves. If the you lug the engine it will build cylinder temperature and the valves will pull up into the seats and lose compression. I was shocked when it happened to me because I don’t hot rod my boat. But I think my boat was over propped for the load of stuff on our boat.


Thanks for your reply..... I am just trying to figure out why it would be 2 cyl's adjacent to each other....Well if it's not head gasket I guess the next best would be that.....
 
Thanks for your reply..... I am just trying to figure out why it would be 2 cyl's adjacent to each other....Well if it's not head gasket I guess the next best would be that.....

I'd pull the head and get a look at it. I had something similar when our motor went but I ran it for a few extra minutes and it burned a nice hole in the block between the two cylinders, forcing a full rebuild.
 
Are you raw water or fresh water cooled ?Did you check your oil did the level increase? Are you losing any antifreeze? How were the plugs when you pulled them out? Were they wet with gas, oil, antifreeze/water This is usually tell tale signs with a blown head gasket
 
Are you raw water or fresh water cooled ?Did you check your oil did the level increase? Are you losing any antifreeze? How were the plugs when you pulled them out? Were they wet with gas, oil, antifreeze/water This is usually tell tale signs with a blown head gasket
Raw water cooled....oil level is good, no increase...... plugs were wet....
 
I would be stunned if its not a head gasket. But that begs the question....why? On a motor with only 100 hours.
 
I agree..... crazy stuff....
With wet plugs I might look at the exhaust flapper valves. If raw water were able to get in the cylinder it would increase compression. That additional compression would have to go somewhere and the head gasket would be the line of least resistance.
 
Well how are you going to be certain there isn't water sitting on bare metal parts?
 
What Scoflaw said....do not let it sit until spring. If there is water where it’s not supposed to be you’re giving it 5-6 months to make things worse.
 

Forum statistics

Threads
112,945
Messages
1,422,741
Members
60,928
Latest member
rkaleda
Back
Top