Rod Knock

[Seafury]

I have a 1988 Johnson 40HP on my Boston Whaler I have a rod knock at low rpm's. Any suggestions. I s it worth fixing?<br /><br />Chris

 

[Capt DHD]

Re: Rod Knock

Chris:<br />If you do have a bad bearing/rod, better sooner then later, definatly worth rebuilding. Rebuild complete with recon crank, bearings, pistons rings,water pump, the works, should still be able to be done for $1500-$1600 max. New over $4000. <br />You make the call, wait and let it blow through the side of the case and your decision will be made for you.<br />Who diaginosed the knock?<br />Good Luck<br />Rob

 

[Seafury]

Re: Rod Knock

CAPT.DHD,<br /><br />Thanks for responding. I have owned the Boston Whaler about 4 MO. The 40 HP Johnson has a oil injector pump on it. I have always kept the right amount of oil in it. I just have a feeling it may have let me down. I have not taken it to a mechanic. I just heard a knock at low RPM's. It just sounds like a rod. I changed the fuel. I added new oil to the new fuel. Changed the spark plugs with new one's. Still knocks.<br /><br />Chris

 

[Capt DHD]

Re: Rod Knock

Hello Chris:<br />Checking for a rod bearing is not to tough. <br />Remove you spark plugs, turn the flywheel clockwise untill the #1 (top) piston is at the top of its stroke, continue to rotate the flywheel untill it begins it's downward movement. While holding the flywheel from turning with one hand, and using a screwdriver with your other hand, lightly, push on the dome of the piston. If you have a small amount of movemet thats probibly normal, but if you get a good clunk, you should have someone check it more closely. Repeat with Cylinder # 2.<br />What are you using for fuel? I would recommend at least an 89 octane. The burn in the combustion chamber is more easily controled by the engine. Higher octane fuels are less likely to develop hot spots on the piston domes or cylinder walls. These hot spots can lead to premature firing of the fuel charge, leading to a noise you are describing.<br />Unless you see a leak from your Vro pump dont worry to much about it. The pump seems to get a bad wrap, what we see most is water in the oil tank. Water in the oil + 10 Minutes run time = scuffed cylinder. The pump didn't stop pumping, just pumped the wrong stuff. That **** pump. (Get a fuel restriction) My pump is over oiling, my engine is real smokey! That **** pump. See what I mean. I could go on. Don't get spooked into not using the oil injection system it really does work well. <br />I hope your noise is easily corrected.<br />Good Luck, Rob

 

[Seafury]

Re: Rod Knock

Bob,<br /><br />Thanks for your help. I will check out the motor. I have a tank of hight test fuel running right know.<br /><br />Chris

 

[Seafury]

Re: Rod Knock

I let a mechanic listen to it today. He said it has piston slap....Bad wrist pin. Motor has to be rebuilt. I did a compression check and got 150lbs on both cylenders. I am thinking about running it till this winter then rebuilding it.<br /><br />Chris

 

[Capt DHD]

Re: Rod Knock

Chris;<br />Very good, glad you idenfied your problem, I hope your repairs work out well. Have a good boating season.<br />Good Luck, Rob

 

[Seafury]

Re: Rod Knock

Do you think I could take in on a new 4 stroke?<br /><br />Chris

 

[nicko]

Re: Rod Knock

Save your money. Buy a Honda 4 Stroke with cash. Donate the old motor to charity. You will get a much better deal, Trust me. It will make a world of difference if you can stand the spending the bucks. The Honda will give you twice the economy and will last 3 times as long. If you have to get it rebuilt get a new powerhead. It just aint worth the aggravation.

 

[corm]

Re: Rod Knock

Nico,<br />If you work for Honda, help the guy with the<br />alternator wire problem.<br />...thank you...corm

 

[Seafury]

Re: Rod Knock

Originally posted by corm:<br />Nico,<br />If you work for Honda, help the guy with the<br />alternator wire problem.<br />...thank you...corm

<br />How much for a new power head? I don't feel like puting out 5k for a honda.

 

[Capt DHD]

Re: Rod Knock

Hi Chris:<br />A new powerhead from OMC is big bucks. Have the one you own rebuilt by a experienced dealer if you don't feel confident enough to do it yourself. This way you will know what you have paid for. <br />If you order in a rebuilt from one of the advertized guy's you never know what you will get. Not saying they are all bad, we just have had mixed results in the past, to many bad, we won't use them. <br />If you have your existing head done, you have the chance to meet the person doing the work. You'll know you have a matched crankcase, OEM pistons & bearings ETC...If there is a problem you have a face to talk to, not a blank phoneline.<br />My shop will rebuild between 60-70 Powerheads a year, all brands, we take alot of pride in what we do, I know there are alot of shops like ours out there. <br />Avg rebuild on a running 40-50Hp engine, $1000.-$1200. Find an experienced shop who you feel comfortable with, use OEM parts, and your chances of ending up with a good result is much higher. You don't need a new Honda yet. Just my opinion.<br />Good Luck, Rob