1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all 6

[shawpdx1]

I run the motor no white smoke from exhaust ( btw i run it in a big tank not ears) I looked at the back of the motor while running to see if the water jacket by plugs were leaking i see nothing, the compression is 135 psi on all 6 cylinders including # 3 the suspicious cylinder were the light white smoke is coming out after running it when i pull the plugs. its not alot of smoke but enough to draw my attention but defiantly i would assume it to be water somehow get around the cylinder the #3 plug does not look washed out it has normal looking it has the normal left over mix on it, i did notice were the the o ring around the head is is a little milky white seems odd to have good compression if water is entering a cylinder any suggestions on were to look would be great. thanks

 

[aussieflash]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Check your compression again when engine is hot?running temp.I doubt its water unless very minor.You would thinks white smoke will blow out while running and plugs would be steam cleaned.

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

i did check compression at operating temp ran it for 10 minutes doesn't over heat that white smoke worries me no doubt. none of the other 5 do this btw its very light but it rolls up out of cylinder text book white smoke as water intrusion would look like id hate to ruin power head if its a simple gasket btw this motor has not seen salt water

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

im going ti need to run it again today little worried about knocking out that cylinder if it is water. the exhaust cover is nice and cool the gasket looks to be ok from outside edges as well as the back cover were the plugs go into powerhead. id rather be safe then sorry. any suggestions on how to trouble shoot before i go tearing into the powerhead would be great

 

[CharlieB]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Use a penlight or something so you can see the top of #3 piston, compare it to the others.

If water is getting in the piston dome should be clean or have a clean area that the other pistons do not.

If it is clean, the most like source of water is a failing water cover gasket. The exhaust cover is actually two cover and two gaskets. The divider plate separates the exhaust chest from the water cooling passages, the exhaust outer cover is the other half of the cooling chamber.

Be VERY careful when removing exhaust cover bolts, they have been in there a long time and have a nasty habit of seizing and breaking if you just put a wrench on and turn. They must be carefully coaxed to come out. Often a small 1/4 air wrench, turned down, will vibrate the bolt and help break loose the corrosion locking the threads. If/when the bolt does turn even just a little bit, STOP, turn it back IN then out again, making small increases in the amount of travel each direction, otherwise they often totally seize and twist off.

Remember these are small 1/4-20 bolts, actually a screw with a bolt head, it doesn't take but a few lbs force to twist off. Tightening torque is measured in inches, not lbs.

 

[Chris1956]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

The only reliable way to detect water in the cylinders is by inspecting the spark plug. If it looks real clean, you have water intrusion. I doubt you would see any white smoke (steam) if you run the motor in a tank of water. I also doubt you would see residual steam after removing the spark plug.

BTW- water intrusion will not affect compression, at least not until something is damaged.

Can you water test the motor and see if it makes full power? Then inspect the spark plugs, and post back results.

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

The only reliable way to detect water in the cylinders is by inspecting the spark plug. If it looks real clean, you have water intrusion. I doubt you would see any white smoke (steam) if you run the motor in a tank of water. I also doubt you would see residual steam after removing the spark plug.

BTW- water intrusion will not affect compression, at least not until something is damaged.

Can you water test the motor and see if it makes full power? Then inspect the spark plugs, and post back results.

Thanks Charlie and Chris,
I ran it again today for about 20 minutes. Yes #3 top of pistion is washed, the rest have typical carbon on them ( black top of piston.)
@ Charlie are you saying you think it could be the exaust side or the back cover were plugs go in? Which one would u pull and is there any obvious sign thats the issue? If I could up load a pic I have a great pics of the cylinder that has top of pistion washed its pretty obvious.

Thanks Ted

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

I started pulling exaust bolts they all seem to come out easy I guess I got lucky I still have the lower ones in cowling area to get to I wonder if this has been done before how do you upload pics ?
Its pretty obvious i think I read that other post on dude with that mariner .. these are the lower 3 cylinders the cleanest one is cylinder in question but the other looks like its cleaning up to should I shoot some Wd40 down the cylinder to get some oil in there while im repairing this

 

[CharlieB]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

.......................... how do you upload pics ?

Those icons on to of the reply box, hold your curser on the third one from the right, it should indicate 'Incert Picture' click and browse to where-ever you save your pics.

When re-installing the exhaust be sure surfaces are clean and dry, install gaskets dry or if you insist on using sealant apply it absolutely as thin as possible and allow it to DRY before assembly. Wet sealant can allow gaskets to squeeze out like a tiddly-wink and tear, causing a new leak.

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Yeah Ill install it dry Charlie. Are the parts available I wonder for this older 150HP merc 1974 -77 im guessing ill have to pull the serial # Im hoping I see a obvious tear or hole in that plate . This is a nice motor would like to save it !!

 

[CharlieB]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Have your model and serial #'s handy and look up the part #'s at Merc parts. Once you have the factory part # you can look anywhere for comparable parts.

The #1 web site for genuine Mercury Mercruiser engines, parts and propellers

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all




Thanks Charlie I got serial # sitting in front of me. I have 1 bolt left below this shift guide in above pic I pulled 2 bolts to the block seems like its riding on a pin or something any trick to get this out of my way? I got all of the bolts out easy none of them broke off Guess I got lucky.

Thanks Ted

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

anyone? anyone? ive searched my manual and old threads i cant find any info its loose but feels like its on a pin off the block??

 

[mercurymang]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Have you disconnected the throttle linkage?

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

No I have all the cables off as you can see in pic .. were do you disconnect the Throttle linkage at? Im 1 bolt from pulling this exaust cover and this guide is holding me up

 

[Chris1956]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

It will be a lot easier if you pull the powerhead off the midsection. You do not absolutely have to pull the powerhead, but it will make life a lot easier. Look for holes in the exhaust baffle plate, and the inner exhaust cover. The bolts on the inner exhaust cover are epoxied in, and are real hard not to break.

Shift guide has 3 bolts, if I remember correctly.

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all



I dont see anything looks good to me......could the inner gasket on the baffel leak this look like new to new

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all



These 2 pictures are down by what looks like a water jacket from the back of block could the gasket of failed there? is that normal to have water back there....maybe ?just a failed gasket


bummed maybe a crack in powers head? were else would a guy look


Any other sugeestions would be great. Id hate to trash this motor

 

[CharlieB]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Excellent focus, just a bit too close to get any perspective.

Water passes between the plate and the cover, it is hard to tell but I see two blacken spots on your very last picture, is that oil smeared from handling or gasket failure?

The 'cocoa' smear proves water contamination, the source should be high or near high enough to spray to the top of the smear.

 

[shawpdx1]

Re: 1976 150hp merc has white smoke coming out of #3 cylinder i have 135 comp on all

Yeah those iPhones have good cameras on them. i tried to load full view of baffle & that back side of motor to much site would not let me load it.

All i can think is that the gasket failed , Cheap enough to give it a try,

Should I buy new bolts? when tightening im guessing i should start center and criss cross ? work my way up to 70 " pounds?