What were the specs on the 650 MDG motor put in several Spectres. That seemed like a solid combo for a boat.

mercury sold the sc900 as a poker run engine,id say that would be called an endurance marine engine.i believe the sc850 and sc1075 were also solid roller equipped.mercury marine never claimed 300 hours on any of the high performance engines as far as i know.the sc850&sc1075 are both dry sump oiled.the three engines listed are no longer sold by mercury but imo they are great engines.

You have all winter to figure out a way to get the valve covers off. I'm in the same boat. Have the same exhaust and the same valve covers. I'm not spending $1000 on valve covers that leak oil so I can adjust valves. Mine will be adjusted every Monday with the exhaust on and the same valve covers that have been on the boat. But then again I'm not the type of person that can be told I can't do something. I will prove you wrong every time. Being able to access the valve train is a minor obstacle to be overcome.

What about a spacer between the ex manifold and head? Would something like that work?

Absolutely. I'm going to make a wedge. Then I will machine the exhaust ports on the heads so the width doesn't change. That's my plan if I can't get away with a 1/8-1/4" spacer. I don't think it will take much. I can get the bolts out of the valve cover. The cover will not make it over the rocker arms and clear the manifold...

I really think solid vs hydraulic, is like ford vs chevy. Some guys swear by them, some guys hate them. Historically, when someone thinks "solid roller" , they think of a cam that slams the valves open, and slams them shut. When they think of hydraulic, they think of a cam that opens the valves nice and easy, and sets them down nice and easy. Both appllications can be made, to open the valves in a similar manner. Hydraulics can slam stuff around too.

Theoretically, a hydraulic lifter plunger, should , when filled with oil, have no give. If they did, and you tried opening an exhaust valve against over 1000psi of cylinder pressure, plus seat pressure, the valvetrain would look like a kid jumping on a pogo stick. Instability is what breaks lifter axles, pounds out valve seats, busts rockers, etc.

I think the #1 reason, hydraulic lifters have been in play in most oem applications, is simply the self adjusting feature , and noise . Nobody wants a new grocery getter than has a noisy valvetrain at startup, or wants to have to adjust valves on their minivan. For decades, any serious performance engine, had to run solids, because the hydraulic tappets just couldn't keep up with higher engine speeds and power outputs. The lifters have come a long way, and nowdays , guys are turning some serious RPM with a hydraulic. Hyd cams, are also getting more and more aggressive as well, to compliment the lifters. A racy hydraulic stick, isn't going to be more reliable than a similar racy solid stick. And an easy hydraulic, isn't going to be more reliable than an easy solid. All things being equal.

For Tim's engine, I don't think I would move to a solid. Any solid that is going to give a noticeable performance increase, is also going to probably be a hard lobe . If I was Tim, I would be looking for a cam that is easy on parts, this isn't a competition engine build. A well designed, and well spec'd hydraulic roller, coupled to good lifters, proper spring setup, geometry, etc, should have no reason going the distance. Stay away from the unorthodox cam lobe designs. Focus on duration that suits the combo, a triple check your assembly and machine work, and go boating. jmo.

Icdeppl dan had to use some spacers on his gen 3 manifolds. One set he purchased, had the manifold flange milled down if i remember. They wouldnt clear his setup with the spring oilers if i remember right. Maybe he could explain better.

A lot of times we even put spacers on stuff that clears just to make it that much easier to access the valvetrain...

Why would you want to add more maintenance to your boat? Leave it Hydraulic , Solid Lifters are for High RPM ( above 7000 ) they also Induce high frequency harmonics into the valvetrain . They are loud , they need to be adjusted Hot , they are a pain in the ass . Yes people use them , stud girdles , shaft rockers , big pushrods etc ,etc , but why ? Good Hydraulic rollers are unbeatable in these kind of applications . Its kind of like riding a Hardtail chop compared to a Softail Bagger for your valvetrain. You wont notice any improvement in performance with comparable cam profiles , just noise and maintenance on the solids. They chatter like a hog eatin hickory nuts when they are running , it will scare the **** out of you the first time you fire it up with the solids it makes so much noise .

The old style big tube headers needed 1/2 inch spacers to adapt the bolt pattern. CMI even still carries them for that application.