Mercury 90hp 4 stroke burning oil

[13lokei]

I have a 200 mercury 90 hp 4 stroke and its burning oil at start up. The compression on all 4 cyls are 150. The oil burning is like a 2 stroke for about the first 2 or 3 minutes of start up, then it clears up. The new plugs on number 2 and 3 are solid black and oil covered in only 2 hours of run time. Maybe Valve seals? Some advice before I sdart would be good, Thanks

 

[marb123]

Re: Mercury 90hp 4 stroke burning oil

To test the valve stem seal you need a vacuum gauge hook it up to a vacuum on the intake manifold let the engine idle if the needle fluctuates you either have a valve that is not seating right or a worn valve seal/guide to change valve seal you might not haveto pull the head off just need enough clearance to put the spring compressor tool and you will need a leak down tester just put the piston on tdc of compression stroke and pressurize the cylinder so it holds the valve in place and compress the spring to remove the keepers once u do that you can remove the spring to get access to valve stem seal hope this helps

 

[13lokei]

Re: Mercury 90hp 4 stroke burning oil

I will follow your advice and get back with you. Thanks