Cracked block?? Mercruiser 120

[bugzy_1]

Hey all,
It's been a while since I posted. Im back.
I have a 1979 120 Merc. (153CID).I have restored the boat after getting the motor running good on the ear muffs, but when I put her on the water not only did I find a hole in the oil pan it was leaking oil the color of chocolate milk. we got here back and I drained the (oil all milky brown)out. After reading several post on the subject Ive come to the conclusion that the block may be cracked. I did a compression check (150psi across the board).
So Ive pulled the motor,dropped the pan ,pulled the push rod coverand the manifold. I havent been able to find a visible crack.I pressurized the water jacket and can not here any "hiss".I did find some deposits that look like rust sediment in one side of the intake port.If the manifold is leaking water into the intake, could this put enough water into the crankcase to turn the oil? The motor appears to be in great shape inside, no signs of wear. Have not pulled the head yet but plan to if all else checks out.
Any insight anybody?
Any reliable way to check for block cracks? (when the motor is out). Thanks for any help!

 

[Bondo]

Re: Cracked block?? Mercruiser 120

I did find some deposits that look like rust sediment in one side of the intake port.If the manifold is leaking water into the intake, could this put enough water into the crankcase to turn the oil?

Ayuh,... It would have to pass the piston rings,... Your's sound pretty tight at 150psi...

No crack or rust along the block, inside it's drain hole,..??
How about along the bottom of the cylinder bores, same side of the block,..??
Could also be the head,...

The lack of the Hiss has me baffled....
Will it hold 15psi,..?? for how long,..??

 

[bugzy_1]

Re: Cracked block?? Mercruiser 120

It did hold over25psi for some time but my plug was leaking so I couldn't do a leak down test. Goin to fix that and try again w/ soapy water and a better plug. Need to rotate crank n check cyl. walls.
Do U think a head gasket could be the prob?
I aggree the water would have to get past the p.rings.
Thanks for ur quick response!

 

[bugzy_1]

Re: Cracked block?? Mercruiser 120

ARRRGGH! After moving the pistons and further examination I found this (a crack that runs from the top of the rear main bearing housing up the block and into the cyl. wall). Pic is kinda hard to see look close.
I found that blue light, ie. LED flashlight, really shows the imperfections.
Well guess its time for a block. Figures, this is the best time of year in Tx. to be on the water!
Thanks for your help Bond-o

 

[Bondo]

Re: Cracked block?? Mercruiser 120

Ayuh,... I see it... Find a 3.0l runner, or buy a 3.0l long block....

Both the money, 'n the bolt holes are the Same.....

 

[bugzy_1]

Re: Cracked block?? Mercruiser 120

Thanks Bond-o
That sounds like a good idea! Is that a 181CID? do all the other parts match up as well? manifold,carb,ect?
Ill do some research!

 

[Fishermark]

Re: Cracked block?? Mercruiser 120

I second the 3 liter. MUCH better than the old 120s. I had a boat that went from a 3 liter (140) down to a 120. HUGE difference! You'll be happy with the result.

 

[nearpar]

Re: Cracked block?? Mercruiser 120

I have the same problem, milky oil, good compression. I want to start the repair but I don't know if I should take the exhaust manifold off first and look at that for cracks or ? any help would be great....

 

[Bondo]

Re: Cracked block?? Mercruiser 120

I have the same problem, milky oil, good compression. I want to start the repair but I don't know if I should take the exhaust manifold off first and look at that for cracks or ? any help would be great....

Ayuh,.... Startin' yer own thread explainin' Yer problem will be a Good start....

Insteada Hy-jackin' this antique...