mercury 120 sport jet, Blown up?

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paulford8

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Today I was given (yes free) a 1997 rinker rocket with a 120hp mercury sport jet. I have been told this maybe a force engine..... the owners burned two starters before taking it to a dealer. Dealer says water is in one of the cylinders and that the block is likely cracked. <br /><br />If the block is cracked can I repair it? OR could I use any year 120 sport jet bock in this? I have found reman/rebuilt for around 2K but not 97's. ALso Any good place to find a used sport jet motor? <br /><br />I now have on ebay a 57 thompson with a great running 40hp.... Looking like I am a moron selling the good looking, good running boat and keeping the broken down one!!
 
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paulford8

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Re: mercury 120 sport jet, Blown up?

I know this is the outboard question but moderator JB locked my question in the inboard section.... and I need help figuring this out!!
 
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Zamboni

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Re: mercury 120 sport jet, Blown up?

The sportjet is a hybrid, closer to an outboard than inboard so you'll get more help here. Merc used the force head on these engines, its self draining so doubt its cracked block...dl the shop manual and start by looking at the head gasket.<br />I'm looking for a reman/rebuilt 175hp sportjet/pump, 90hp doesn't cut it in 16'...let me know if you see any in your (net) travels-Russel Marine has none.
 
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JB

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Re: mercury 120 sport jet, Blown up?

Paul has complained about his duplicate post being locked. This is where his post belongs, so I will leave it here.
 
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funpilot

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Re: mercury 120 sport jet, Blown up?

I agree that the cylinder head gasket is likely the problem, or else a striped out cylinder head bolt thread. The other possibility is that a submerged jet boat (from throwing it into reverse and diving into the subsequent bow wave) can sometimes overwhelm the height of the jet pump, letting the engine submerge slightly in the water. If that happens you need to pump out the hull enough to get the water level to below the power head, and then run the engine until it steams off the possible moisture contamination. This usually shows up in cylinder four and possibly three.<br /><br />I believe almost any 120 hp force block would serve your purpose (but I too doubt the block is cracked) and any Sport Jet 120 hp power head would bolt up to the jet pump, but Force engines will not bolt up to the jet pump because the splines on the crank shaft are different between a Sport Jet and a Force engine.<br /><br />The primary difference from the Sport Jet in 1997 should be the electronics are more refined, but a Sport Jet from 1995 can be made to run well.<br /><br />good luck<br /><br />fp
 
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paulford8

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Re: mercury 120 sport jet, Blown up?

The people said they took it to a boat mechanic, he took the head off. Shouldnt the guy been able to tell if the head gasket was blown?<br /><br />The people that had it left it out with the head off.... the cyclinder walls are rusted and it looks pretty bad.... I guess I cant complain because they gave me the boat but.... why the heck did they do it??
 
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funpilot

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Re: mercury 120 sport jet, Blown up?

Ok, email me separately. I'll show you pictures of a really really bad sport jet engine with internal rust and the whole nine yards. That engine today (well, not today because it snowed here, but just wait until May 15) takes me across the lake at 44 mph. <br /><br />The engine is a snap to take out of the boat, and a snap to tear down. Once you get it that far, you can have the cylinder head and block checked checked. From there you can buy some pistons, bearings and maybe rods and have the block machined for the pistons you buy. The rest is just reassembly. If the block is bad, a used force block isn't hard to get, the important thing is the crank in this case.<br /><br />funpilot15 at hotmail.com... put the @ sign in for at<br /><br />take care,<br />fp
 
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paulford8

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Re: mercury 120 sport jet, Blown up?

Thanks for all the help sailors!! I am going to dive into it this weekend. I just wish I could find a manual! Everyone I find only goes to 1995 sport jets. I am sure it is similar but I would like to find the one for my year!!
 
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stevenp63

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I'm going thought the same problem what did you do I'm thinking of converting the engine it's just Engine and Jet
 
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