1998 Yamaha Vmax Ox66 200Hp Knock

[Lip 'em!]

I had posted a link to this video over on the yamaha parts forum but haven't gotten a response so far so I figured I'd pick my fellow BR members' brains.

During a recent fishing trip i spent 2-3hrs scanning and when I went to run to another spot my boat would not get on plane and the motor was bogging down. It would only get up around 3k rpms. I limped back to the dock and pulled the cowling and eyeballed and everything seemed to be okay. Pulled the sparkplugs and they were brand new and were fouled and a little dry for my taste. I put muffs on the motor and decided to run it at home and thats when I heard this knock..

It sounds like it is coming from the front of the powerhead instead of the back. It is a deep rumble and I even checked the lower unit to see if the sound could be traveling but it was fine. I did get a low oil alarm on my motor while idling so I checked the oil reservoir on the tank and it was full to the line and my remote resevoir was full as well. The alarm sounded again but I kept idling and it shut back off. What do you guys think could be the issue? Could the oil pump have gone out and starved the motor for oil, resulting in the knock? Heres the link to the video I put on youtube:

Thanks!!

[Al Wolbach]

I believe I would start with a compression test and I would not run it anymore. I do not hear well but that sounds serious to me. Crankshaft or rod serious and it will only get more serious($) by running it.

[Fishing Rhino]

Sounds ominous to me.

 

If you can get a grip on the flywheel, remove all the spark plugs, then rock the flywheel back and forth.  If you have slop in a journal, wrist pin, etc., you may hear and/or feel it.  If you don't, turn the flywheel ninety degrees and rock the flywheel again.  Still nothing, turn another ninety degrees and repeat.

 

This will not necessarily reveal the problem, but it may, and at least you won't tear the engine apart in the process.

 

I'll second the "do not run it".  All you'll do is increase the repair cost, or wreck the block if something breaks in the powerhead.

 

Your best bet is to get it to a reputable technician along with the video. 

[Lip 'em!]

I definitely wont run it anymore in its current condition and I will try the flywheel trick. I had a reputable mechanic check it out and he ran a compression test and surprisingly it showed good compression all around and all cylinders were close to the same reading. He said the knock sounds like a rod bearing to him and he immediately shut it down. Doesn't sound good guys thats what I figured. i guess I'm just trying to get a few more opinions because the truth hurts lol. Thanks guys

[Way2slow]

The bad part about a two stroke, once you hear the knocking, if it's a bearing, you can also say good-by to the rod and a crankshaft.  The bearings are so hard, if one does go, it takes the crankshaft and rod with it.   There is also only one person in the US I would trust to repair a two stroke crank, if he's still around.  (Which he was also the one Yamaha used for their factory rebuilt cranks) The way it has to be welded up, ground back to OEM specs and re-heat treated, they break about 95% of the time after a year or so from most peoples repair.

 

A few years ago, there was some guys having custom size bearings made and were just grinding and heat treating the cranks for some of the main bearing repairs, they may have gone into the rod bearings also

 

However, if you can't fix it yourself, it sounds like you can go ahead and kiss about four or five grand good-by.

 

Did a search and thought for a bit he was no longer around.  However when I looked at this companies email address, it's him, so I guess he's still going strong.  http://www.marinecrankshaftinc.com/outboard.html