Sport jet 120 exhaust gas in water jacket

[Craighimself]

200 Dollar rib jet boat.

Rebuilt engine using Force 120 outboard block and new/used Ldrive manifold

Runs great, except cannot get water to flow through water jacket. Pressured up with exhaust gas and naturally overheats quite quickly.

Not so bad on the hose but in the water I cant get it to flow, I imagine I have an exhaust to waterjacket leak.

BUT:

the force block has an opening at the bottom where it mounts to the mounting bracket for the Ldrive, the sport jet block did not. I imagined the gasket would seal this off.

the head is in less than perfect shape but there is no visible leaks across the gasket when I remove the head.

I haven't checked the exhaust manifold gasket yet But I cant see the backpressure from this manifold overcoming the water pressure.

ill try to get a nice video up

 

[Craighimself]

Re: Sport jet 120 exhaust gas in water jacket

http://www.youtube.com/watch?v=vs1rEMoj4iw



http://youtu.be/vs1rEMoj4iw


links to the video.

 

[Craighimself]

Re: Sport jet 120 exhaust gas in water jacket

Just machined the head and re torqued with new gasket, more of the same, is it possible that the powerhead mount on top of the jet is leaking by into the water passage, it seems like there wouldn't be a lot of pressure there as its open ended out the elbow.

I guess since im the only one on this thread Ill try checking that out next.

 

[Grub54891]

Re: Sport jet 120 exhaust gas in water jacket

I really don't know what the problem could be but,I don't lie the look's of the head.I've used jb weld in pits like that with success but no guarantees. Hope ya figure it out!

 

[Craighimself]

Re: Sport jet 120 exhaust gas in water jacket

Is there anyone out there who can explain how water moves through the cooling system on these sport jets.

The pump cover has a hole that raw water is supposed to pressure up through into the powerhead.

Is this attached to anything below the cover to something? Or is that area of the pump somehow pressurized? It seems like exhaust flows out through there and it only contains the l drive housing and the shaft to the pump.

I don't understand how water would pressurize enough in this area to circulate through the powerhead.

Someone please help the service manual is no help.

 

[Craighimself]

Re: Sport jet 120 exhaust gas in water jacket





My Original Exhaust elbow had a fitting in the side for a raw water intake, The old elbow was fused to the block so I had to get a new one, I found this force elbow cheap, no inlet in the side for water intake, I had to make my own hole in the block and thread in a 3.4" fitting to pump some seawater.




I believed that somehow this hole on the plate fed raw water to the powerhead through the tiny 1/8" hole on the bottom of the block, After close examination of the cooling system I have come to know that that is merely a drain hole. I really struggled on this thing having the cooling system backwards, now that it cools itself properly it runs tip top.

 

[H20Rat]

Re: Sport jet 120 exhaust gas in water jacket

Is there anyone out there who can explain how water moves through the cooling system on these sport jets.

The pump cover has a hole that raw water is supposed to pressure up through into the powerhead.

Is this attached to anything below the cover to something? Or is that area of the pump somehow pressurized? It seems like exhaust flows out through there and it only contains the l drive housing and the shaft to the pump.

The pump housing has some holes right after the impeller, so when the engine is turning, that area is pressurized and sends water up the hole that you are seeing where the engine mounts to the housing.