Are Mercury 4-stroke outboards flat tappet?

USA_boater

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I am asking about a 2018 50hp but in general I'm sure others may want to know the answer and the caveats to their particular outboard.

If they are like I think they are, I am wondering why the OEM oil is "catalyst compatible" if many of their motors do not have a catalytic converter. Low valve spring pressures perhaps? I would think for longevity that they would have a catalyst and non-catalyst oil available just like the aftermarket does (sierra, west marine, etc.)?

Running 6k RPM on a non-roller motor with an SM or SN rated oil doesn't seem like the optimal thing to do. Can anyone explain the logic other than "don't question the Mercury engineers"...I think there are most certainly other influences on the OEM oil offerings & engine designs than just the engineers.
 

USA_boater

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Does Mercury make any outboards with catalysts? If so, I think therein lies the answer. Perhaps too much trouble or cost to create an oil for their motors without a catalytic converter but using a catalyst-compatible oil in a non-catalyst, flat tappet motor won't cause enough of an issue before the warranty expires? But for those who'd like to get as many full-horsepower hours out of their flat tappet outboard, it would be nice to have the manufacturer recommend a non-catalyst oil with a more flat-tappet friendly formulation?

I'm not arguing for what weight or brand here so this isn't a typical oil thread...I am asking if the OEM oil is SM or SN rated equivalent additive pkg, then why would anyone want to run it in a flat tappet motor when in other applications with flat tappets (tractors, generators, motorcycles, old Jeeps, etc.) it is well-known using catalyst-compatible oil could result in premature cam lobe wear. So why does Mercury essentially say its fine?
 

GA_Boater

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So this isn't another oil thread? Sure confused me with the SM and SN question.

The answer to the topic title is no.
 

USA_boater

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Well if you are confirming that the OHC 4-stroke uses some sort of roller rocker/lifter (or whatever OHC engines use), then the majority of my oil concerns are moot. It would make sense the optimal design would be roller, but of course a guy in the service department at the dealer the day I picked up my boat new told me it was flat tappet...he is the same guy who told me no need to break in the engine too though.
 

Scott Danforth

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Im not an expert, however the pic I saw showed the rocker arms riding on top of the cam lobes just like many of the overhead cam motors. however that was about 10 years ago.

BTW, the test group in Fond du Lac (and Florida) do not go easy on the motors.
 

racerone

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In today's world of precision / computer / robot controlled manufacturing is " break in " still as important as it was 80 years ago ????
 

GA_Boater

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Well if you are confirming that the OHC 4-stroke uses some sort of roller rocker/lifter (or whatever OHC engines use), then the majority of my oil concerns are moot. It would make sense the optimal design would be roller, but of course a guy in the service department at the dealer the day I picked up my boat new told me it was flat tappet...he is the same guy who told me no need to break in the engine too though.

No - I answered your question about flat tappets.

Might as well answer the roller tappet question too. No again.

Merc OHC motors don't have tappets or lifters.
 

USA_boater

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Okay well forgive me if I am using OHV terminology since I know more about that. The concern is the same though, is there some sort of roller contacting the cam lobes or not? If not, then I'd be concerned about wear if the oil was formulated to be catalyst-friendly.

To answer the guy's question on break-in, I used whatever oil the motor was pre-filled with (prob Merc 25w40 conventional). The dealer told me that despite Mercury removing their 20hr "break-in oil change" recommendation from the manual, that it would still be a good idea to do it. I agree and plan to change the oil at ~20hrs because regardless if they say you can go 100hrs on the break-in oil fill, I know it won't hurt a bit to be conservative about it. BREAK-IN is till required though so don't take the lack of the break-in oil change to mean no break-in procedure needs to be followed.

Finally, I came across a thread on another forum where a guy had done UOA on 50hrs in his 5.7L Mercruiser using the Quicksilver 25w40 syn-blend...the oil sheared to a 20wt! He said using DELO 15w40 oils UOA it only sheared to a 30wt...One of the claims to fame for the 25w40 OEM oil is that it isn't supposed to shear because it doesn't use viscosity index improves. That is alarming if the OEM shears worse than even a non-marine oil in a similar weight. comments?
 

USA_boater

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Well it was an "engine design" thread. But depending on engine design, it makes the oil choice more crucial :) I figured you'd prefer I mention that info in this thread then to start an oil thread for it LOL
 

dingbat

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You're way over thinking this.

It's a 50 HP motor that will spend 3/4 of it's life at half throttle or less. In 10 years, you'll be lucky to have 250 hours on it.

Fill it with the factory recommend oil and go boating...
 

USA_boater

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The fact it can only go ~35mph, I'm quite sure once fully broken in, I'll be running it wide open from spot to spot. I guess if you average idle speed and wide open you get half throttle LOL.
 
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