Rod Bearing

"I recently purchased a 1977 C

"I recently purchased a 1977 Crestliner with a 4 cylinder engine I/O, closed cooling system and Mercruiser outdrive. I purchased on consignment and had a marine dealer check it out for me. He stated that it sounds like a small knock from one rod bearing but he wasn't sure, and he went on to tell me that I should put heavier oil in and it probably would run for many years without needing repair. The price was right on the boat so I bought in anyway, assuming that with this vintage the motor may need rebuilt in the near future anyway. Any thoughts on assessing this problem and how do you know when a rebuild is necessary? I am sure that with the current economy, most local dealers would sing up that it needs rebuilt and try and scare me into never putting in the water."

"If it has good oil pressure a

"If it has good oil pressure and its not making too much noise, you may be able to use the boat. If it truely has a rod knock, it isn't going to last. Keep an eye on oil pressure, temp and listen to the knock to see if it gets worse.

But if it is a rod knock and you use it and it fails, you may end up with an un-rebuildable core... i.e. damaged pistons, cylinderwalls, crank, block, etc."

when it goes BANG you need a r

when it goes BANG you need a rebuild.

Right! But after it goes bang.

Right! But after it goes bang... you may not have much to rebuild.

"Would taking the oil filter i

"Would taking the oil filter in for an oil analysis help with figuring out if there is a problem and what it might be? If the oil was changed at winterizing, how much does it need to run in the spring before an oil sample can determine anything?"

"Tom, usually a rod knock can

"Tom, usually a rod knock can be isolated to a certain cylinder by pulling each spark plug wire off one at a time. If you have a bad bearing, the noise will lessen or quit, when you pull the plug wire on that cylinder. When the plug fires on that cylinder, thats when the noise is the loudest."