HELP mechanic wanting to do rebuild

[mikey'smoneypit]

hi, i just boat a 18.5 ft wahoo with a 1996 115 Johnson ocean runner. the boat ran great when we took it on its water test. how ever when i took it out today it was running fine under 3,000 rpm's. as soon as we took it over 4,500 rpm's the steady motor alarm went off. i immediately backed the motor down to idle. the alarm stopped going off after 30 seconds. we idled it back to the dock. after doing research on hear it seems like it could be the temp or fuel restriction alarm. heres where i need help fast. i dropped the boat off at a mechanic and he ran a compression check and 3 cylinders are at 130 and the 4th at 95. i know its low. he immediately said the motor needs a complete rebuild. i asked did you find out why the alarm went off and he said he will find out more once he tears the motor down. i don't have the money for a complete rebuild. that still did not answer my question on why the alarm went off. it could be as simple as a fuel related issue.
even though the compression is low on the 4th cylinder this motor starts right up. idles and runs like a brand new motor as long as your under 4,000 rpm's. what should i do??? how long could this motor run with the compression being low on cylinder 4??? i just boat this for the summer for me and my two boys and don't really want to pay 2,000 or more for a rebuild, but i don't want to blow the motor up. sorry for the long post. please help.
thanks,mike

 

[narmstrong26]

Re: HELP mechanic wanting to do rebuild

Chances are that its going to have to be rebuilt. I don't know the ocean runner series well but I believe its just a V4 Crossflow power head. Before allowing him to tear it down I personally would check the head gaskets myself. Its not very hard to get the heads off and if your looking at a rebuild anyway get them open and take a look yourself. Look at the head gasket for heat damage that could be causing leakage. Check the cylinder walls for scoring and the heads for any signs of impact of metal. I had a manifold plate break up on my humpback from overheating and it put a large chunk of metal through no.4 piston. I don't know how handy you are but the rebuild isn't bad. Machine work included I spent about 1000 rebuilding mine myself. If you go that route contact Lee at TriState marine (847) 526-6211 for the rebuild kit he is a good bit cheaper then others out there and offers great service.

 

[Dhadley]

Re: HELP mechanic wanting to do rebuild

The motor you describe is a 60 degree looper, not a crossflow. If it were mine I'd do a decarb with BRP's Engine Tune and concentrate on the low cylinder. We just did one with similar numbers and the low cylinder came up just fine. Even if it doesn't work you haven't lost anything except about 9 bucks on Tuner.

If it was an overheat the motor would have went into SLOW (rpm reduction) and the alarm would not have shut off so quickly. Kinda sounds like a fuel restriction. I assume the mechanic has explained this to you so you can know the difference.

You didn't say the motor locked up or stalled so I'd think we have a good shot at getting some compression back. Especially if your top rpm is 5500 or less.

 

[boobie]

Re: HELP mechanic wanting to do rebuild

Your mtr didn't have a fuel restriction device built into it. That was only on the V-6's so it's not that. Defineatly try the BRP engine tuner for your compression prob before going back to that ( mechanic??). Follow the directions on the can exactly for best results. As far as the horn going off, OMC did have some bad ones in that era.