94 Sea Rayder 175 conver. Cavitation Proble. Need help...

corstrat

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Jul 4, 2011
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Four years ago I picked up a deal on a 94 Sea Rayder which recently had a Merc 175 installed. Boat has run great with zero problems until Sunday. I had me and three on board on a brackish bayou. We pulled up to shore where the water was shallow for a pit stop. While it appeared to be kicking some muddy water when leaving, no real friction.

As soon as I gunned it, I realized I had no acceleration. Only a few knots idle speed. The motor seemed to be just fine making normal revs. After a one hour two mile trip to the boat slip and trailering the boat, I noticed a couple of clam shells stuck in the intake grate.

Yesterday I took the grate off and looked closely at the impeller. Everything appeared to be clean and tight. No noticeable dings on the impeller or ring. Driveshaft was tight. I then looked in through the nozzle from the rear. Also all looked clean.

I don't know much about the pump in this boat so I asked a neighbor who also did know much, but was more mechanically inclined. He suggested that since this was a direct drive, the only logic that it would run at idle speed, but no faster no matter how much power, that perhaps there was some sort of "shear pin or key" installed to protect the engine/impeller that snapped thus allowing a safe "return to shore" mode.

I have read most of the relative posts here and also searched the net to see if I could find any confirmation of such a shear pin but have not yet found any reference to it,or any other suggestions to solve my problem. Any help or advice here would be greatly appreciated.

(I have also posted this under the Sea Ray Forum, but have gotten no responses)
 

kend301

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Re: 94 Sea Rayder 175 conver. Cavitation Proble. Need help...

You got a case of the clams , anything stuck to the intake grate restricting water flow will your speed . I have the same problem with pine needles in the grate in my area , just clean the grate and you will be fine.
 

corstrat

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Re: 94 Sea Rayder 175 conver. Cavitation Proble. Need help...

kend301-Thanks for the response. When I pulled the boat out of the water, there was only two small clam shells lodged in the grate and none inside the grate. I can't imagine that it restricted more then maybe 5% of the intake. Do you really think that this alone could have caused a total loss of acceleration past maybe two or three knots, even at full RMP's? When your pine needles were plugging the grate did it take away all of your acceleration, or just slow it down relative to how much needles you sucked up?

I have subsequently taken off the nozzle (but not before twisting off one of the four bolts. The perils of Locktight) everything from the back also looks clean and tight.

I assume by your not commenting, that you are not aware of any type of "break off" bolt or key as I addressed that is purposely put on the shaft to protect the engine.

Is there anyway short of pulling the whole pump to see if the driveshaft may have come loose. Or do you think it is possible that the shaft that connects the engine to the pump may have some problems?

I bought the repair manual and taking out the pump, particularly without the two dozen special tools it seems to call for, is a chore I would rather not attempt until all other possibilities are addressed.
 

kend301

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Re: 94 Sea Rayder 175 conver. Cavitation Proble. Need help...

Easy test , these are direct drives , only gears in the drive box , Pull the spark plugs have a friend rotate the motor by HAND as you hold the driveshaft by hand and see if it turns without stopping as he turns the motor . if it seems to skip you may have broken a gear if it turns for the full motor rotation then it is fine. DO NOT DO THIS TEST WITH THE STARTER TURNING THE MOTOR OR WITH THE PLUGS IN !!!!! If it started with your hand in there you would loose it !!
Yes it killed all speed for the boat got perhaps 2-5 mph , engine just screaming and bow in the air.
My guess is that you had more in there that cleared out as you went in or perhaps came off while driving home .
 
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corstrat

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Re: 94 Sea Rayder 175 conver. Cavitation Proble. Need help...

Thanks, I will try what you suggested in the next day or two.
 

kend301

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Re: 94 Sea Rayder 175 conver. Cavitation Proble. Need help...

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