Need Ideas NO COMPRESSION
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Need Ideas NO COMPRESSION
I have a 400Mod compression runs like this: 1-120 2-80 3-90 4-120 5-0 6-80 7-90 8-120. The previous owner says he replace the head gaskets (wondering) and he thinks it's the intake manifold gaskets and that I should redo those taking special care of the crossover gaskets connecting the manifold gaskets. I haven't heard of intake manifold gasket issues causing low or no compression in a cylinder. Any ideas?
More Turbo
Joined: Aug 2008
Posts: 531
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From: LaGrange
Hello,
__1'st thing you need to do is pull the valve covers.
Then check to see what the prob' is for #no.5 cyl.
Could be something like a stuck valve, loose rocker arm,
bent push rod, burnt valve, or just stuck/gummed up rings.
If you need to dig deeper, check to
see if the pushrods are plugged up.
Or if you have any crushed/broken lifters.
__1'st thing you need to do is pull the valve covers.
Then check to see what the prob' is for #no.5 cyl.
Could be something like a stuck valve, loose rocker arm,
bent push rod, burnt valve, or just stuck/gummed up rings.
If you need to dig deeper, check to
see if the pushrods are plugged up.
Or if you have any crushed/broken lifters.
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ok all sound like great ideas. it'll be a a couple weeks before i can do that extensive work. I forgot to mention. It sounds great, no missing no oil on spark plug the only symptom I have is oil being pushed out the pcv/breather cap. No "sucking exhaust" or "back flow".
More Turbo
Joined: Aug 2008
Posts: 531
Likes: 4
From: LaGrange
__could be due to just a overloaded/really dirty
stock valve cover oil bath/filter element.
This element is usally made into the valve cover
it's intended design is to condense/cool oil,
so it will drain back onto the valvetrain.
Not get sucked into the intake to get burned off.
Once these get so dirty, they become insufficient
or just plain quit working entirely.
When you pull your covers off, check this part out.
You may be surprized how bad some of these are.
Later.
Cargo Master
Joined: Sep 2003
Posts: 2,110
Likes: 32
From: southwest pa
only two places your compression could be going. either out through the rings, or out through the valves. your valves are either not getting a good seal or your rings are shot. i dont see where the intake manifold could be affecting compression. im going to place my bets on the valves. something was either done wrong and is causing them to stay open, or the heads need rebuilt.
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Lead Driver
Joined: Nov 2000
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From: Albuquerque
Could be the timing chain/gears. Also make sure you are doing the comp. test correctly. Pull all the plugs, pull the coil wire and prop the carb all the way open, crank over at least four times. Sometimes you can squirt a little oil in the cylinders and try the test again. If the numbers rise the rings are bad.
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Elder User
Joined: Feb 2008
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From: Davison, Mi.
0 is unusual.
Seems like more than bad valve seats, bad rings or a blown head gasket.
Intake cycle malfunctions (burnt valve, wiped lobe, leaky intake) usually drop compression pressure. But usually not to zero. Some exhaust cycle malfunctions (wiped lobe) actually RAISE the compression pressure. Some drop it (burnt valve)
My guess is a burnt valve or a hole in the piston. My instincts tell me a hole in the piston.
Zero compression is as unhealthy as it gets.
Or a ReaLLY bad valve seat.
Seems like more than bad valve seats, bad rings or a blown head gasket.
Intake cycle malfunctions (burnt valve, wiped lobe, leaky intake) usually drop compression pressure. But usually not to zero. Some exhaust cycle malfunctions (wiped lobe) actually RAISE the compression pressure. Some drop it (burnt valve)
My guess is a burnt valve or a hole in the piston. My instincts tell me a hole in the piston.
Zero compression is as unhealthy as it gets.
Or a ReaLLY bad valve seat.
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Ok I preformed another compression test with new spark plugs. Results were identical (or very very close) there is also no missing evident, no oil on the spark plugs (incl. cyl. 5) only symptom is excessive blow by. I learned that the eng has also a high volume oil pump installed. It did also pop a exhaust plug on the back of the right bank cyl head so I will be fixing that shortly. I will remove the head to do it so I can kill two birds with one stone.
Senior User
Joined: Jan 2003
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From: beaufort
Listen highboy, do a dry and wet comppression test on #5 see if squirting some oil in #5 helps compression at all if not remove valve cover make sure you have cam action (valves go up and down just like the ones next to it). If you do remove cylinder head look for broken piston thats what ussually causes lots of blow by dont just look for hole in middle of piston look all around the edges they will burn there. sometimes that burnt piston will be very subtle. By the way if that motor doesnt have any compression on #five it is missing. hope this helps, chuck