TOPIC: 8 Cyl. Merc.

Ok I am sitting here bored trying to think of a project that will carry me over the winter. Since I really don't have the room to do another boat I was looking at my old Mark 55 sitting in the corner. Beside it is a mark 55 block. So dont laugh yet. Kinda got to thinking, would it be possible to stack these 2 motors into one. I know there would be a little bit of a problem setting up the timing to run the 2 mags just right. Making an adaptor to join the 2 blocks would not be too hard. As for the throttle cable you could make it like the old bikes or just make an rod setup to join the 2 carb throttle rods together. As for the lower end I believe they should handle the power ok. I am not looking to make this a really over complicated motor, just a simple one. Just was wondering if anyone out there has ever thought about it. Not really looking for a million tech issues why it won't work, just some easy to figure ideas to make it work. I have joined engines from a 3 HP briggs together all the way up to 2 350 chevys. So why not 2 4 cyl mercs.I think that this may be a really interesting idea. please let me know what you think, Skip.

Build the ultimate dock buster
make one run forward and the other reverse

The kicker is I was thinking along the dockbuster idea.

OK Skip, I have the lower unit for your project, the old mark 78, I can disguise it somehow in a box so the wife won't know what it is. You'll need a wrap also.
Cal

Ya can side by side them too..(Merc twin V6 blocks, single L/U..the "Wizard")..but that thought a REAL TALL STACK 8C?

I WANT ONE!Damn, do the exhaust right, and a sound, well be ..a.."WTF is THAT!"

Here ya go.."Mark55's on a single D Quicky tower" .

The only way to do it without lots and lots of mods is the second pic Robby posted. Mount them beside each other and gear drive them to your drive shaft.

Problem with stacking them is many. Cooling water and exhaust dump wild out the bottom of these motors. How would you controll that ? Would also be hard to build a coupler to the top of the drive shaft. You could attach to the flywheel, but it would surely spin a key almost instantly.

If you want to cut the blocks and weld them togther that would be awesome. timing two mags together should be possible if they were fixed to each other somehow.

The first stack 6 was made by welding smaller motors together at the mercury factory.
Conrad

Would be easier to adapt an 8-cylinder automotive distributor to it...

Could you get it to fire each revolution for the 2 stroke?

Skip, If you want an impressive straight 8 how about adapting a car motor with an oil sump on the lower end and run a pipe to the upper end for a continuous flush. All other problems would be solved using the auto add-ons. You will still need a lower unit which I have and a wrap which I also have half of
Cal

Well skip as long as you,re bored why not a HOP12?? Thats a horizontally opposed 12 cyl using two inline 6 blocks and one crank. Using the old style rods, discard the bottom of the end cap and bolt two pistons together around a common throw. Stuff all 12 into the opposing blocks and bolt the sucker together. Everything else is external plumbing

Well, thanks for all the imput on the 8cyl tower. I was thinking of the side by side idea before but that is just too fat for me.I can live with a fat50 but not a fat merc. The stacking idea is coming along slowly. I have been busy measureing and drawing up a couple of different adaptors to bolt the motors together. One idea has an adaptor that encloses the fly wheel on the lower motor and keeps the dist on the side of the block so you will be running 2 dist. on this engine. An adaptor would be made to connect the 2 cranks together. The other idea is use just one fly wheel on the top block, and have an adaptor to bolt the 2 blocks together with a coupler between the cranks. I would have to design a dist that would fire properly. I contacted a place that makes custom dist. and they said as long as I give them the firing order they can build me one that will be electronic. And it will not cost me an arm and a leg. The exhaust will be different to say the least. Maybe 2 sets of headers or something that connects the upper exhaust to the lower one. It will be interesting. As for using a straight 8 block from a car, I have not found one yet that is short enough or light enough to be useful. Plus way too many things to change for the oiling and cooling systems on them.The only way I could do it would be to buy a junk inline 4 , 4 stroke and start from there. I fully xpect to spend alot of the winter just working on drawings and trying different things from molds just to see if all of this will fit together. I don't just want to start hacking away on a couple of motors just to end up having a pile of scrap metal. That and a pissed off wife. So keep the ideas coming , good bad or otherwise. I am sure with all the members here this may well be a doable project. Thanks, Skip.

Skip, when you are working out the distributor don't forget the wasted spark concept. Since you are working with a 2 stroke for every cyl at tdc there will be one at bdc. You can fire 2 plugs at a time. Might simplify your design.

On a "making spark"

"Would be easier to adapt an 8-cylinder automotive distributor to it..."

And...

"Could you get it to fire each revolution for the 2 stroke?"

Think using a Marine 8 cyl Dissy, running belt drive, one to one, instead 1/2 speed, should be easy set up. Also a straight 8 4stoke would be a iron block, all the extra weight valve train, etc, too heavy..(and a 8cyl 2 stoke noise?...be too cool!)

Daveswaves wrote:

Skip, when you are working out the distributor don't forget the wasted spark concept. Since you are working with a 2 stroke for every cyl at tdc there will be one at bdc. You can fire 2 plugs at a time. Might simplify your design.

Thats possibility too....Harleys been doing that decades.

I though of it in 1957. Do it!