Yamaha OX66 EFI vibrates and rattles

[aquadj]

I have a 1998 250 hp Yamaha OX66 EFI motor with about 800 hours. I've been hearing a slight noise that I haven't been able to pinpoint until today when it got much louder and started vibrating. According to my mechanic something let loose with the driveshaft or damper that will require him to almost completly disassemble the motor. I'm expecting his estimate in a day or so and I'm wondering what I should expect and if I should be considering a new motor.

[jb123]

while running, at idle ?? did you inspect the lower unit, do a compression test, any horns go off ??

Please let us know the diagnosis.

[aquadj]

Prior to it getting loud and vibrating, the only indication there was a problem was it was louder than my other motor (twins on boat). They both run at 5200 rpms with no concerns. After the noise and vibration I couldn't run any faster than 1600 rpms without it really making a chatter. I have all gear motion, haven't hit anything, and had the lower units rebuilt (pumps and gaskets) about 150 hour ago. The mechanic said he would check the compression before he started any repair.

[jb123]

well after the comp check he or you could isolate the SOUND by running without the lower unit/driveshaft in place, just hookup a garden hose hose to the water tube.

[slim]

its a possiblity that the harmonic balancer nut worked loose and the balancer fell off the bottom of the crank. this could be a cheap fix or could be expensive depending on the damage.

[aquadj]

I just received the preliminary report from my mechanic. Compression in the top 4 cylinders was 115 and the bottom 2 was 105. When he disassembled part of the motor he found the main bearing let loose on the bottom of the motor and rattled around in the power head and damaged the fuel pump along with other stuff. He's now searching further to see if this power head is worth fixing, or if it should be replaced. He also mentioned the possibility of a complete new motor which worries me since this is one of a pair. Any comments?

[IFish4Tuna]

Bummer.

I've got the same engines. My thought if one shits the bed, is to replace them both with a single 300. Better on fuel, and who really gives a crap about top end speed.

Ed

[jb123]

i had to deal with a powerhead issue when the season started...shredded #2 and blew holes in case and intake on my starboard. rebuild was 3.5k - 4k...new was 4100 from boats.net....you do the math,i chose new.

[aquadj]

I had a conversation with the mechanic who gave me my options. As I understand it he can attempt to rebuild this motor, but there is the risk that metal fragments are in the motor and will cause damage down the road. The alternative would be a new power head, oil pump, fuel pumps, oil filters/strainers, and some misc. parts for about $8,000.00 compared with a liitle more than 1/2 that for the rebuild. I'm not capable to do this work myself so I'm relying on a reliable mechanic and his advise. Any comments on wether the new vs. rebuild is worth the cost?

[jb123]

the new powerhead ,intake and base gaskets and misc labor shouldnt run you over 5k. i put mine back together but had a tech check it out when i was done.
what is wrong with your oil pump ? and what oil filters...in the tank??
did he ever say why he thought the cylinder let go?
i searched hi n low, found the best price here on boats.net , NEW not rebuilt( factory warranty)and if youre outta state you pay no sales tax.

[ October 06, 2006, 06:24 PM: Message edited by: jb123 ]

[jb123]

i see 2 prices here, 38XX and 4150, which i paid, probably carb and efi. again, for me it was a no brainer, 4k for a rebuild or 4150 for new.

[aquadj]

His quote goes something like this...about $6,000 for parts and 16 hrs. labor at $95.00 per, plus tax is about $7500.00. I added a couple of bucks for misc. stuff. His parts are obviuosly list.
The oil filter stuff is in the tank and the reason for the pump is because he's not sure if that didn't have something to do with the problem. When I saw the damage to the power head, I saw the harmonic balancer worn from wobbling and the main bearings and cup in pieces. I grabbed the crank at the bearing and it had some movement - I'm not sure if it was normal or loose. He's willing to rebiuld but he's not willing to gaurantee it.

[slim]

you want my opinion? if he is a mechanic and he says he can get all the metal fragments out, he must not be that good or he is trying to pull one over on you. like jb said, you should be able to get this done for much cheaper.

[aquadj]

Thanks everyone for all the suggestions.
I met with the mechanic and owner today who made my decision pretty simple. After pulling the heads and seeing some metal fragments in the cylnders, I decided to replace the power head.