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90 hp 4-stroke jumps timing chain

D

dranes

New member
2008 90 4-stroke keeps jumping out of time. Locks up motor. Everything looks good inside. 2009 model. I'm sussprcting low oil pressure. Any ideas?
 
Thanks for the response. I replaced the timing chain. Everything looks good, but it still jumps off time. There is a tensioner that rides on the chain. Pressure is applied to the tensioner lever by hydraulic (oil) pressure. I'm wondering if low oil pressure could cause the tensioner to be too loose, and if this is a common problem. On another post I saw reference to a Mercury service bulletin regarding bad oil pumps.
 
guyjg said:
Is the tensioner worn or the spring weak?
Click to expand...

The tensioner is a lever that rides on the chain. It is forced against the chain by oil pressure acting on a plunger-like part about 3/4 inch diameter (very similar to a hydraulic valve lifter). Oil pressure extends the plunger, shoving the lever against the timing chain and tensioning it (I think). All the parts, sprockets, lever, plunger, cam bearings show no appreciable wear. I have read on another thread that 3 examples of this engine have experienced very premature oil pump failures, so it makes me suspect that as the cause. Another clue is that one journal of the crankshaft showed some blue coloring, possibly indicating it had overheated (due maybe to low oil pressure). This is a rental boat so I do not have personal experience of how the engine acted as it failed. I live on Grand Lake in Oklahoma, and my mechanic has contacted a few of his technical buddies at other repair shops. Two of them are dealing with the same problem: Mercury outboards jumping out of time with no apparent reason. He has also contacted Mercury techs with no results. I told him today to order a new oil pump and try that. So far, the chain has jumped and the motor locked (from idle) so we surprisingly did not break anything (yet). Thanks for your interest and your help.
 
The tensioner is a lever that rides on the chain. It is forced against the chain by oil pressure acting on a plunger-like part about 3/4 inch diameter (very similar to a hydraulic valve lifter). Oil pressure extends the plunger, shoving the lever against the timing chain and tensioning it
Click to expand...
What a piss-poor system!
 
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