1986 Mercruiser 140 Blown Head Gasket?

[pvovk]

A couple months ago after acquiring this boat (1986 Winner Escape 17'), I took compression readings on all four cylinders after warming up the engine. #1-130, #2-118, #3-115, #4-70 (all in psi). After squirting some oil into the #4 cylinder, it went up to 90 psi. Motor has not idled very well since I got it. Now is worse. Checked compression today: #1-130, #2-110, #3-110, #4-25 (squirting oil into cylinder did not improve reading). I have not performed a leak-down test yet. No water in oil and oil still looks good (changed it when I got the boat in March with Quicksilver part synthetic 25W-40). No oil usage after ~10+ hrs of running. Seems to use a lot of gas. 140F thermostat (new in April) and runs at 165F max, but never at 140F. Plugs look good except the #4 not as clean as the others and slightly sooty but not oil soaked. Runs very good above 1200 or so RPMs, but doesn't seems to lack power. I have not run it above 3200 RPM. I am ready to remove the head, and am hoping it's a bad head gasket and/or valve issues.

Any thoughts or recommendations?

Will I cause more damage to the block or head if I continue to run it?

 

[alldodge]

Number 4 is sooted because of low compression. Running hot means you have a restriction in the water pathways, impeller issue, or head gasket.

Have you found any water in number 4?

More damage to keep running, probably. Pull the head and hope its a valve or head gasket. Note what the cylinder wall looks like.

 

[Swimforshore]

Compression reading seem low across the board when you take a reading make sure the throttle plate is wide open that'll make them go up about 25-50 psi 70psi should be a dead hole misfire engine would, always run like crap. If it's a blown head gasket usually you overheat bad and the spark plug/cylinder and piston too will be very clean. That said problems create more problems so I would get it fixed before heading back out

 

[pvovk]

Thanks for the replies. I did forget to open the throttle when taking compression measurements yesterday.
I replaced the impeller soon after getting the boat and before using it.
I did take it out yesterday (risking further damage) but it was worth it to spend a beautiful evening with my oldest son and his GF tubing, etc.
Before going out, I set the timing as it was way off due to installing a Pertronix and not being able to use my timing light with it (just didn't work) and then re-installing the points while on vacation (and not having a timing light with me) due to the Pertronix cutting out after a while (they said due to a voltage issue in the boat), but I haven't been able to resolve. No issues with the points.
Ran great yesterday except for rough idle (kept it

 

[Swimforshore]

Really sounding like a valve issue may try using a top end engine cleaner to clean some carbon off the valves in combination w/ fuel treatment. Injecting a mist of water into the intake at about 2500 rpm or transmission fluid works well. Use half a quart or so just don't add so fast that you hydro lock the engine

 

[pvovk]

Thanks for the suggestion as I had not thought of that.

I misted and then slowly poured (a bit at at time) a 1/2 qt of distilled water, then half a can of SeaFoam. No difference at idle (shakes the boat quite a bit), but I do think (hope) it's in the valves. The vacuum did seem to stabilize at the higher RPMs, but still very rough at idle with fluctuating vacuum. I didn't re-check the compression though. Not sure if running it hard would help or hurt. Try it again with transmission fluid (or Mystery Oil as I have a quart)?

Maybe just need to pull the head but I first need to find a machine shop without a backlog (the one I've used before on an auto engine has a 2 month backlog). Do you recommend the Mercury head gasket or Fel-Pro marine (I ordered a Mercury one from the local marine dealer last week)?

Starts first time every time, by the way and I did a bunch of maintenance when I got it: new plugs, new exhaust flapper, new plug wires, new dist. cap, new t-stat and hoses, rebuilt the carb (had torn accelerator pump piston rubber and was flooding-did not have spring needle), greased outdrive u-jounts, new impleller, replaced gear oil (of course), new prop, emptied both fuel tanks and replaced with non-ethanol premium and a can of SeaFoam, cleaned all electrical connections, new oil and filter, cleaned distributor advance springs and assembly, new drive belt cleaned out the anti-siphon valves, added a fuel-water separator and new fuel line to fuel pump, both new fuel filters (pump and carb).

 

[Swimforshore]

Bouncing vacuum gauge is a good indicator of valve issue. I'm not real hopefull the the tranny fluid will do the trick. With the tranny fluid make sure the engine is up to temp and slowly poor it in then back it down to idle and stall the engine let it sit for a couple hours then fire it up and clean it out expect smoke. That use to be part of a standard car tune up in the 70s, but it's probably too far gone.
I always prefer OE parts even if I have to pay a little more. Felpro makes a quality product, but make sure it's marine grade

 

[bruceb58]

Do a cylinder leak down test.

Quit messing around with the snake oil suggestions.

Based on the cylinder leak down test you can decide what your next course of action is.

 

[nola mike]

^^^^^

Compression of 25 is bad. 70 is bad. You had poor but more consistent readings across the other cylinders; #4 is clearly an outlier. bruceb58 , would a leak down test even help? I can't think of anything that wouldn't need the head to come off, and once off would guess that the cause would obvious with that low compression...

 

[Bondo]

would a leak down test even help? I can't think of anything that wouldn't need the head to come off, and once off would guess that the cause would obvious with that low compression...

Ayuh,.... It'll tell ya whether it's the rings, or the valves,...

Bad rings are pretty hard to see, with the head off,...

Doin' a head rebuild, 'n not doin' the bad rings also won't help, but will hammer the bad rings worse,....

 

[bruceb58]

Ayuh,.... It'll tell ya whether it's the rings, or the valves,...

Bad rings are pretty hard to see, with the head off,...

Doin' a head rebuild, 'n not doin' the bad rings also won't help, but will hammer the bad rings worse,....

That's exactly why I was recommending the leak down test.

 

[Swimforshore]

I think we better go back to the beginning. From my understanding, you have an engine with a rough idle, but performs well once off idle. Based on your spark plug inspection your misfiring cylinder is #4 which is confirmed by compression readings. So the compression test can't be qualified as accurate due to the throttle not being wide open, so it needs to be done again. With the throttle closed, it restricts air into the engine causing low numbers and also allows the carb to dump fuel and wash down the cylinder walls causing low numbers.

I do agree before any tear down a CLT test should be performed to determine where the problem is. A head job can be done in the boat rings or Pistons are a no go. Remember we are dealing with a carburated engine that is not spraying high pressure fuel directly at the valves which acts as a cleaner. Carburated engines are carbon producing monsters that sticks all the places you don't want it to, so introducing a cleaning agent into the intake is well worth the half hour of time you spend even if doesn't fix it. The ports and valves will be better for it. The Carbon problems take longer to show up in marine engines due to them only seeing seasonal use and probably mostly on weekends.

Sorry for the rant but if you can avoid major tear down for at least the rest of the season that's a good thing in my book. Not saying that will happen but it's worth a shotI'll qualify myself by saying my mechanical experience comes from being ASE master certified with Advanced engine drivability diagnosis cert(L1). Not certified at all in boats, just maintain the 1 I have and help people adrift on the lake

 

[pvovk]

I performed a leak down test tonight (first time for me so hopefully, I did it correctly). Cyl 1=30%, 2=88%, 3=90%, 4=88% (the higher % is worse). When doing #1 some air heard coming out of #2, When doing #2, lots of air out of #3 and #4. When doing #3 lots of air out of #2. When doing #4 air out of #3. That is, after the leak down, I increased the pressure to hear where the air was coming from. I did not hear or feel air coming out of the dipstick tube or carb. ever. Maybe I should have put the other 3 plugs in to check ring or valve loss though since it seems as though the head gasket is so bad (?) it would mask anything else (I guess I still could as I haven't removed the head yet). Each cylinder was at TDC and I did them all a second time just to be sure.

I then started the head removal process. After 1.5 hrs., got the manifold off (only have the valve cover on down to remove tomorrow as all other stuff has been removed). The intake valves have a lot of carbon on the stem end closer to the valve. I found out today that the local machine shop the marine dealer uses can look at it in two days, so hopefully, I can get it to them Wednesday and have an answer by Friday or Monday at the latest. I should also be able to see the condition of the head gasket when I remove the head.

Thanks so much for all of your responses. It helped me to finally take action instead of wondering what to do next.

 

[pvovk]

Whoops! Never mind about the putting in 3 plugs (valves won't all be closed in the other cylinders). But what about doing it after removing the pushrods? Would that help show if there was also a ring issue?

 

[bruceb58]

A properly tuned carb will have identical carbon build up on valves as fuel injection. BTW, I always thought the cert is called The Advanced Engine Performance Specialist. I have friends that have that particular certification.

Hopefully, you don't suggest doing these carbon removal tricks on modern engines with O2 sensors and cat convertors.

I agree it would be good to do the compression test again but if the throttle was affecting cylinder #4, it would be affecting all the cylinders. #4 is FAR below the numbers of the other cylinders. This could be caused by many issues including bad valves or rings. Since it is #4, that is the cylinder that gets affected most by leaking manifold/riser issues. A cylinder leak down test would indicate if it was exhaust or intake valves. Obviously if it was an exhaust valve, no snake oil is going to help that.

 

[bruceb58]

I performed a leak down test tonight (first time for me so hopefully, I did it correctly). Cyl 1=30%, 2=88%, 3=90%, 4=88% (the higher % is worse). When doing #1 some air heard coming out of #2, When doing #2, lots of air out of #3 and #4. When doing #3 lots of air out of #2. When doing #4 air out of #3.

Did you rotate the engine on every cylinder so it was at the top of its compression stroke? Doesn't sound like it.

You really jumped the gun taking the head off. You will have no idea if its valves or not.

 

[pvovk]

I have not removed the head yet, just the manifold and everything else to be able to remove the head. This morning, I removed the rocker arm cover and made certain I was at TDC compression on #1 (I think I was also on TDC compression on all the others last night as I was watching the distributor rotor position).

All except the #2 exhaust rocker arm and associated pushrods are loose (when #1 is at TDC compression). That is, doesn't that mean the valve should be fully closed? The #4 in/ex were both looser that the rest. Seems to me the valve lash needs re-set, but I don't think that affects the ability of the valve to close if there is freeplay in the pushrod and rocker arm (but I could be wrong).

When injecting air into each cylinder (~20 psi, #1 at TDC compression), I observed lots of air coming out of the following:
#1 exhaust, #2 exhaust, #3 exhaust, #4 exhaust (assuming that's the furthest to the rear as it was hard to tell). Per the Seloc manual, I think the following valves should all be closed in this instance (GM engine): #1 in & ex, #2 in, #3 ex, #4 in. and I would not expect to feel much air coming out of those ports, correct? Since all of these had free play in the rocker arm and pushrod (all ex. #2 ex), does that means these valves were fully closed?

Is there anything else I should test? Doesn't this mean that the valves are not sealing?

Please excuse me if I am confused or misunderstanding something. I really do appreciate all the replies to this.

 

[alldodge]

Hearing air come out of all the exhaust valves at once would not happen, probably just sounding like that. These are bad numbers, only one which is sealing at all is number one

Cyl 1=30%, 2=88%, 3=90%, 4=88%

Check your pushrods, and while there should be play, your looking for any kind of up and down movement for play. The twisting is not much in the play area, but if there was any real pressure from the cam, you should not be able to twist it

With the valve cover and manifold off it should be easy to make sure valves are closed

 

[pvovk]

I also felt a lot of air coming out of those ports. So much that I couldn't cover with my hand without the air pushing through with strong pressure.

 

[fishrdan]

Only test the cylinder that has it's piston is at the top of it's compression stroke.

With cyl #1 at TDC of it's "compression stroke", no air should come out of the intake and exhaust valves for cyl #1.
With cyl #2 at TDC of it's "compression stroke", no air should come out of the intake and exhaust valves for cyl #2.
With cyl #3 at TDC of it's "compression stroke", no air should come out of the intake and exhaust valves for cyl #3.
With cyl #4 at TDC of it's "compression stroke", no air should come out of the intake and exhaust valves for cyl #4.