90 hp 4 stroke questions

O

oteps

Senior Member
04 merc 90 hp 4 stroke. When do the valves need adjusted? Timing belt replacement? Im helping a friend out getting it ready for spring. its on a pontoon boat. It gets ran a lot on the Susquehanna river.
 
At 10 years old I would do the belt if it was mine. I believe they reccomend adjusting the valves at 250 hours, and doing the belt at 500 hours.
 
I rarely see anyone adjust the valves, it s a PITA to do. I've checked them for people from time to time and rarely find them out of spec, If you decide to check them, make sure you do a strong decarb treatment before you check them. My friends that run the harbor taxi checked theirs every 1000 hours,they kept the same timing belt on till Yamaha offered to pay to have the belts changed at 5000 h ours, they wanted the old belts back. Those engines were sold at 8700 hours
 
Thanks, I will probably do a belt. I have to fix the lower unit first. The seal went out and it froze over winter.
 
No cracks in lower unit, but has a bearing carrier that was pushed out when it froze. I had a friend weld the tabs that broke, replaced o ring and seals, plus impeller. Ran it in muffs, hopefully put it in water soon. The o ring was torn letting water in.
 
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