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Poor Compression in 1 cylinder

G

generallee

Member
Just wanted to double check th

Just wanted to double check the possible causes for one cylinder to lose compression and the other is perfect. I have 1982 25hp evinrude with 120psi in top cylinder and 60 on bottom. It was 120 in both and then i had a long trip out the other day and it died right by the trailer...and thats what i found. Upon inspection it appears on the head gasket a small chunk of it blew out right by the bottom cylinder...I have never seen this. Any ideas what would cause this? The only thing i could think was maybe a reed valve stuck and compression got to high? Or possible this is just a coincidence and i just need a new head gasket
 
"A sticking reed valve would n

"A sticking reed valve would not cause an increase in compression. You need to remove the cylinder head and inspect the gasket, cylinder and cylinder head for damage."
 
Yeah..i took it apart..I was j

Yeah..i took it apart..I was just thinking something else...The head gasket has the little metal ring around the cylinders and its got a little chunk that blew out..Must of taken a good amount of force to do that. Any idea what would cause that? The head looks decent..and so does the cylinder walls..
 
"Has the engine overheated in

"Has the engine overheated in the past? Overheating will cause the head and block to expand and compress the head gasket past it's normal thickness. After a while the gasket will blow because it is out of tolorence. I would check the sealing area of the block and the sealing area of the head for any damage, make sure the head is not warpped and install a new gasket and torque to spec. Run the engine until it warms up, let it cool and retorque to spec."
 
The head gasket sounds very ol

The head gasket sounds very old check the head for warpage and the block face anymore than .006 thou the surface would require machining. The head gasket blowing is not an uncomon problem.
 
"If no flaws exist at the seal

"If no flaws exist at the sealing surfaces of the crankcase or head, when installing the new head gasket, torque to factory specifications in the following sequence.

9...10
5....6
1....2
4....3
8....7"
 
"Alright I'll scrape the r

"Alright I'll scrape the remaineder of the old head gasket off tonight and check it over. Thanks for the bolt pattern Joe. That will help alot, I'm not sure if my book has that with the torque specs. The head gasket is coming tomorrow and I'll be sure to post a follow up if that was it. Thanks guys"
 
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