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Lack of Performance Low Compression

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cavalosjr

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I have a compression problem w

I have a compression problem with cylinder #6 on a 2000 Volvo Penta GSi engine. The compression is quite low @ 35 psi as compared to the other cylinders (all approx. 180 psi). There are only 240 hours on the engine. How do I determine if this is a top end issue or bottom end issue? Thanks for your help.
 
"Most likely a mushroom valve.

"Most likely a mushroom valve.
Either do a leak-down test (compressed air into the combustion chamber through the spark plug hole, or more easy:
Take off the valvecover, turn the engine until 6 is in TDC.
Loosen the rocker arm nuts.
If valve-stems are of different hights when off-loaded, valve problem."
 
"Charlie, you will have to do

"Charlie, you will have to do a wet compression test (at a minimum) to determine what's up w/ #6. Others with more experience will almost certainly weigh in here soon, but here's a start. Wet test involves putting a little (amount anybody? I used 3 squirts from my small oil can.) clean motor oil in the suspect cylinder(s) through the spark plug hole before hooking up the compression gauge and bumping the motor over a few times as in a regular (dry) test. (don't forget ALL spark plugs out, coil/ignition disconnected.) The oil added in the cyl. acts as a sealer for the piston rings and temporarily corrects some or all of the compression loss potentially caused by bad/worn rings. This takes the rings temporarily off the list of potential compression loss causes. If #6 compression does not improve dramatically when tested wet then it is probably not rings. Suspect a valve problem. If #6 compression comes up dramatically on the wet test then it is likely a rings problem because making the old/bad rings act temporarily like new/good rings solved the compression loss problem. El Pescador will likely answer up here for you and suggest a "leak down test" too (or instead) which I am not that familiar with. I am interested to see his reply/description of it.

Good luck!"
 
"A compression test doesn'

"A compression test doesn't tell me squat. I don't even do them anymore. Leak it down and you'll know exactly whats wrong with the cylinder. A person doesn't want to know if the compression is bad, they want to know what's wrong with their engine."
 
Whatever methode and test You

Whatever methode and test You do I guess the head must down anyway. Then You'll have the answer.
 
"I gotta add to morten........

"I gotta add to morten.......... Sounds like a valve issue. You can do the wet test, but with that low compression, and hours, sounds like a valve.
That is also a cylinder that can starve for oil. so be sure you have good oil pressure.
More than likely a valve...."
 
"Charlie, follow their guidanc

"Charlie, follow their guidance but I have the same engine, same year and with 600+ hours my #6 exhaust valve was mushroomed with #4 just behind. Engine never ran hot nor over heated. Replaced both heads last winter and now I add Valvetec gas additive at each fill. Lots of discussion around ethanol and run lean conditions. My theory is knock sensor should be replaced frequently so the ECU keeps the timing dead on."
 
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