i cannot figure it out!!!

[cedarjunki]

theres already too many threads on this but im loosing my mind!
first off im not an ameature here but not a professional either...
father bought a used 1975 120 merc from a boat repair shop... in a sc 18ss to replace his 1970 140 thats been noisy for too long and blew a head gasket last season...or so i thought anyway.
we took his word that it did run. he said he got it from a marina in vt., its been sitting a couple years but there was a complete tune up done along with the carb being totally rebuilt just prior to the previous owner blowing out the lower unit... it was winterized and parked.

now i cleaned the motor up slapped it in using a manifold that is only 5 years old and the carb off of the 140. fired up on the muffs and it ran great, until i shut it off..it didnt spit sputter or anything...but it didnt want too star back up so i pulled the plugs...#4 was full of water. figured head gasket. took head off and gasket looked good, no sign of leakage. put a new gasket and (different) head on. still the same way! fired up and ran great till shut off again. #4 is pulling water in when its shut down.
i figured maybe the manifold blew instead of the gasket last season so i drilled out a steel plate bolted it on the manifold clamped the garden hose to the water inlet and its holding pressure. now im really confused. the well pump is set at 55 pounds. a previous manifold was tested good at 35 pounds years ago so now im confused how im getting water in the manifold.
water is being pulled in #4, but not filling the crankcase.
any thoughts???? im losing my hair fast enough i cant take it anymore!

when i take the manifold back off the exhaust cavity is full of water but #4 is getting most of it maybe due to the angle of the engine.

 

[Juniinc]

Re: i cannot figure it out!!!

riser

 

[chriscraft31]

Re: i cannot figure it out!!!

The exhaust manifold could be creating a siphon when you shut it off, that would be caused by a rusty riser/manifold. Could have a cracket head or block too.

 

[cedarjunki]

Re: i cannot figure it out!!!

i forgot to mention that the two core plugs were steel and very rusty. i blew through them when the pressure got close..
if the block was crack wouldnt it be dumping water in the crankase and not the manifold?
2 different heads, same symptom.
manifold was tested (diy) but held enough pressure to expand the hose i used to clamp the garden hose to.
i thought it may have been a bad seal on the brand new riser gasket so i tried hight temp gasket maker as well. the riser itself looks ok nowhere near as bad as the rest i have.

 

[cedarjunki]

Re: i cannot figure it out!!!

a compression test also showed 137-140 on all cylinders..

what am i missing?
the block shouldnt be cracked seeing how the core plugs were so rusty they disinegrated when hit with the washer...

2 different heads same results...

manifold held water pressure without any leaking for almost 45 minutes.....

sorry for ranting ....thinking out loud..

 

[chriscraft31]

Re: i cannot figure it out!!!

if the manifold is mixing water and exhaust before it goes over the riser, when the motor is running it all goes out the exhaust. When you kill the engine... thats when it can siphon back in.

 

[Howard Sterndrive]

Re: i cannot figure it out!!!

reassemble everything with a new head gasket and pressure test the cooling system

 

[floater180]

Re: i cannot figure it out!!!

Check the connection between the riser and manifold. There might be some pitting on the metal thats causing water to go in. Try filing both bown a bit so it shows how flat is the connection between the riser and manifold. Good luck

 

[cedarjunki]

Re: i cannot figure it out!!!

riser

nailed it!!!

Have you tested the intake manifold for water leaks?

yes previously stated!

reassemble everything with a new head gasket and pressure test the cooling system

a new head gasket was used with the second head with same results as stated!

Check the connection between the riser and manifold. There might be some pitting on the metal thats causing water to go in. Try filing both bown a bit so it shows how flat is the connection between the riser and manifold. Good luck

that was my thought too, thats why i assembled it with gasket silicone just to try but didnt help.




ends up the riser is either cracked or rusted through just above the flange face. i took it off , flipped it over, slowly poured water in the exhaust chamber till full...it started filling the water chamber after about two inches of water was poured in.....
thanks guys!!! much appreciated!! i spoke with a machine shop here that tests the manifolds, explained how i tested mine and he said that it was more than exceptable! he only tests them with 40 pounds of pressure. the life of his bussiness he has only had one situation that it what a bad riser. first riser ive seen go bad. never expected it!

now i just gotta get one...the boat repair shop i got the boat from has a crapload of risers but there the newer style that dump sideways and a 120 riser is smaller. figures since i have an extra one

thanks again everyone who chimed in...maybe going to work and getting away from it is a good thing once in a while :/

 

[Juniinc]

Re: i cannot figure it out!!!

most likely rusted through,,,
I'm just glad U figured it out!

 

[chriscraft31]

Re: i cannot figure it out!!!

With patience I find a lot of stuff on ebay or craigslist for cheap. Osco makes a lot of cheap aftermerket manifolds & risers for most marine applications.