vegasphotoman
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How to:What I did to Diagnosis & Repair= Blown head gasket 3.0L Mercruiser 4 cylinder
a fairly common repair is a bad headgasket, I go through on this thread what I did to diagnose and repair the problem. hopefully this will give you a little insite into this reapir, I spent 6 hours total start to finish repairing it
Here are all of the 34 pictures
Heres a mercruiser service manual PDF format, thanks DON S for posting the original thread in the how to sections!
My engine is a 1990 Mercruiser 4cylinder 3.0L carburated (gm motor)
my motor Symptoms
The motor Started running weaker as the season wore on, top speed was slowing down more and more, and some excessive oil was coming out of the breather into the spark arrestor. Seemed like alot of air was coming out of the breather when the motor was running, some is normal, but this was quite a bit, no smoke coming out though, which was interesting.
I checked the plugs, bit oil fouled, not bad though, cleaned and reinstalled, no change, checked eng timing, it was off a bit, hmm...re timed it, 8 degrees BTDC. When I revved it to see if the timing advance was working ok, the timing didnt move stayed at 8 degrees (using timing light) timing was not advancing.
Pulled the distributor cap, found broken springs in the centrifugal advance, replaced the springs using aftermarket Holley advance spring kit
Re timed the motor, now the timing was advancing, but still ran lousy and SOUNDED like it was out of time still.
Pulled spark plugs, did compression check, Max compression which is 5 motor revolutions
#1 140lbs #2 40lbs #3 42lbs #4 142 lbs....
so the 2 center cylinders were way low....poss blown headgasket! Shared cylinders with low compression is almost ALWAYS a blown gasket. that explains the excess air coming out of the breather and lack of power
Teardown
Removed water hoses, removed the front u shaped water pump hose so the water would drain out below the level of the block deck, that way water doesnt get into the oil/cylinder area when you break the head loose.
Removed carb and wiring, moved throttle cable and shifter cable out to the side, removed exhuast elbow, removed valve cover
Checked valve rockers for excessive looseness, very little play in rockers so that was ok
Loosened all the rocker arms, rotated the rockers out of the way and removed the pushrods KEEP THEM IN ORDER I use a piece of cardboard with some holes poked in it to keep them in order (the world wont end if you mix em up, but its best to put the pushrods and rockers back in the original location due to wear patterns)
Here the rockers are roatated to the side for removing the pushrods and now I can see all the head bolts
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Remove the headbolts by de torqueing the head, that way you dont have a 90lb tight bold at one end and all the rest loose, could break a bolt or do some damge to the head. I loosened then starting at each end 1/2 turn loose, then working my way to the middle bolts working back and forth across the motor, once they are pretty loose go ahead and remove them completely
make sure all head bolts, hoses and wires are disconnected, its easy to miss the frt temp sensor wire, its kinda hidden under the tstat houseing.
I used a crows foot prybar to "pop" the head loose, if it is excessively stuck on there double check to make sure you havent missed removing a bolt or something.
Now that the head is popped loose, I hooked an engine hoist on using chain, the head with manifold is kinda heavy and In my situation it was a poss back breaker so I used the hoist.
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Head hoisted out and I could see the headgasket WAS blown, see pic
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Heres the Head surface
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the cylinders looked good, pistons good, no build up of carbon, the cyl walls didnt have a very big ridge.
Onto cleaning up the parts, looking for damage etc
Cleaning up the block surface and head surface using a side angle die grinder and 120grit scrubber pad available @ (snap on, HF, autozone)
Ive found using these does no damage to the iron block, unlike a metal scraper which can cause damage to the metal surfaces of the engine.
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my VIDEO on youtube of doing this here
once all clean onto checking head and block flatness
the mercruiser manual calls for .008 thousandths warpage over 6" as a max warpage acceptable. I used a straight edge flatness bar (I got mine from Snap on a long time ago) and flat feeler guage set,
Laid the bar out and pushed feelers under where the head gasket was blown, max feeler I could push through on the block on my engine was .003 GOOD TO GO
.jpg)
on the head I had a warpage of .006 GOOD ENOUGH no need to mill the head flat, if your head or block is past the specs .008 you need to have machine work done or replace the part, otherwise the headgasket will just blow out again.
I cleaned the head up using carb spray and compressed air,
didnt see any cracks in the head (look close!) , blew out the cylinder piston areas, make sure to blow out the areas around each piston well (dont want some foriegn material in the ring areas) I wiped it all down with a rag and carb spray, then oiled each cylinder wall with a clean rag and a little bit of fresh eng oil
See next post for the rest of the repair and assy
a fairly common repair is a bad headgasket, I go through on this thread what I did to diagnose and repair the problem. hopefully this will give you a little insite into this reapir, I spent 6 hours total start to finish repairing it
Here are all of the 34 pictures
Heres a mercruiser service manual PDF format, thanks DON S for posting the original thread in the how to sections!
My engine is a 1990 Mercruiser 4cylinder 3.0L carburated (gm motor)
my motor Symptoms
The motor Started running weaker as the season wore on, top speed was slowing down more and more, and some excessive oil was coming out of the breather into the spark arrestor. Seemed like alot of air was coming out of the breather when the motor was running, some is normal, but this was quite a bit, no smoke coming out though, which was interesting.
I checked the plugs, bit oil fouled, not bad though, cleaned and reinstalled, no change, checked eng timing, it was off a bit, hmm...re timed it, 8 degrees BTDC. When I revved it to see if the timing advance was working ok, the timing didnt move stayed at 8 degrees (using timing light) timing was not advancing.
Pulled the distributor cap, found broken springs in the centrifugal advance, replaced the springs using aftermarket Holley advance spring kit
Re timed the motor, now the timing was advancing, but still ran lousy and SOUNDED like it was out of time still.
Pulled spark plugs, did compression check, Max compression which is 5 motor revolutions
#1 140lbs #2 40lbs #3 42lbs #4 142 lbs....
so the 2 center cylinders were way low....poss blown headgasket! Shared cylinders with low compression is almost ALWAYS a blown gasket. that explains the excess air coming out of the breather and lack of power
Teardown
Removed water hoses, removed the front u shaped water pump hose so the water would drain out below the level of the block deck, that way water doesnt get into the oil/cylinder area when you break the head loose.
Removed carb and wiring, moved throttle cable and shifter cable out to the side, removed exhuast elbow, removed valve cover
Checked valve rockers for excessive looseness, very little play in rockers so that was ok
Loosened all the rocker arms, rotated the rockers out of the way and removed the pushrods KEEP THEM IN ORDER I use a piece of cardboard with some holes poked in it to keep them in order (the world wont end if you mix em up, but its best to put the pushrods and rockers back in the original location due to wear patterns)
Here the rockers are roatated to the side for removing the pushrods and now I can see all the head bolts
Remove the headbolts by de torqueing the head, that way you dont have a 90lb tight bold at one end and all the rest loose, could break a bolt or do some damge to the head. I loosened then starting at each end 1/2 turn loose, then working my way to the middle bolts working back and forth across the motor, once they are pretty loose go ahead and remove them completely
make sure all head bolts, hoses and wires are disconnected, its easy to miss the frt temp sensor wire, its kinda hidden under the tstat houseing.
I used a crows foot prybar to "pop" the head loose, if it is excessively stuck on there double check to make sure you havent missed removing a bolt or something.
Now that the head is popped loose, I hooked an engine hoist on using chain, the head with manifold is kinda heavy and In my situation it was a poss back breaker so I used the hoist.
Head hoisted out and I could see the headgasket WAS blown, see pic
Heres the Head surface
the cylinders looked good, pistons good, no build up of carbon, the cyl walls didnt have a very big ridge.
Onto cleaning up the parts, looking for damage etc
Cleaning up the block surface and head surface using a side angle die grinder and 120grit scrubber pad available @ (snap on, HF, autozone)
Ive found using these does no damage to the iron block, unlike a metal scraper which can cause damage to the metal surfaces of the engine.
my VIDEO on youtube of doing this here
once all clean onto checking head and block flatness
the mercruiser manual calls for .008 thousandths warpage over 6" as a max warpage acceptable. I used a straight edge flatness bar (I got mine from Snap on a long time ago) and flat feeler guage set,
Laid the bar out and pushed feelers under where the head gasket was blown, max feeler I could push through on the block on my engine was .003 GOOD TO GO
on the head I had a warpage of .006 GOOD ENOUGH no need to mill the head flat, if your head or block is past the specs .008 you need to have machine work done or replace the part, otherwise the headgasket will just blow out again.
I cleaned the head up using carb spray and compressed air,
didnt see any cracks in the head (look close!) , blew out the cylinder piston areas, make sure to blow out the areas around each piston well (dont want some foriegn material in the ring areas) I wiped it all down with a rag and carb spray, then oiled each cylinder wall with a clean rag and a little bit of fresh eng oil
See next post for the rest of the repair and assy
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