For Karla and others who need to know

[Frank Acampora]

This post is for those people who have no idea what is inside their Force engine. I have posted a couple of photos that I happen to have on hand. I invite others to post more photos to add to the collection.

The first photo is a three cylinder Force engine, veiwing from the open bypass side. This one happens to be a mid 90s 85 HP needing a rebuild. Four cylinder engines are the same mid leg and lower unit with one more cylinder added to the block. That is why the four cylinder engines only weigh about 25 pounds more than the three cylinder engines.

The second is showing the piston at bottom dead center with the exhaust ports open. Look closely at the bottom of the cylinder and you will be able to see a bypass port. Look at the top portion of the photo, exhaust side of the piston, and you will see why this engine is apart for rebuilding.

The third photo is of the pistons (generic) These happen to be from an older three ring engine. Newer ones have two rings each.

The fourth photo shows the Big ends of the piston rods connected to the crankshaft. Note the rollers in the uncapped rod.

Fifth photo shows a gear pak from an older two piece lower unit. Newer lower unit gear paks are similar with a few changes in how the reverse gear is carried and a longer prop shaft. While gears are cut differently, the drive dog clutch and method of engagement is the same.

Now: the two cycle engine operates by inducting fuel and air through a reed valve into the crankcase where the crankshaft is. This is accomplished by the bottom of the piston as it moves up to top dead center. As the piston moves down, it makes the volume of the crankcase smaller and the air/fuel is pumped through the bypass up into the cylinder. the piston again moves up and compresses the mixture and it is ignited by the sparkplug. This sequence happens once for each piston every revolution of the crankshaft.

The rotation of the crankshaft is transmitted to the lower unit pinion, here shown at the bottom of the photo, by the driveshaft. The pinion is constantly engaged with both the forward gear and reverse gear so both are constantly turning. When the drive dog clutch, here pushed backward into reverse by the thin shaft on the left, is pushed into one gear, that gear turns the clutch which you can see is splined to the prop shaft. The drive dog clutch turns the prop shaft. On the left side of the photo, forward gear is carried in a relatively massive tapered roller bearing. The prop shaft drive dog splines bear on the forward gear and thrust loads are absorbed by the roller bearing.

 

[Frank Acampora]

Re: For Karla and others who need to know

Here is a photo of a single exhaust one piece lower unit. You can clearly see the water intake (four slots) on the gearcase torpedo just ahead of the prop. Dual exhaust units do not have these, but rather, have six holes running up the leg above the torpedo.

And--an exploded view of an older fuel pump with all parts included. Note the position of the gasket on the base. Some newer pumps will not have the oil recirculation elbow shown here. This one was removed from the bypass cover for shipping purposes.

 

[Karla45]

Re: For Karla and others who need to know

Thanks Frank for all of your help. Pictures and explanations really help.

 

[jason32038]

Re: For Karla and others who need to know

Hey Frank what happened to the sleeve on the top cyl? Or is it just an illusion? Nice prop how does it perform and why did you decide to go with a 2 blade?

 

[Frank Acampora]

Re: For Karla and others who need to know

Because of the close-up, the bottom cylinder sleeve in the second photo is a bit blurred and the of light layer of white corrosion makes it appear that there is no water jacket around the cylinder. In the first photo, there is no piston in the top cylinder and the angle of the shot may make it appear that there is no sleeve either. While this engine did need rebuilding, it did not need reboring. A good honing with fine stones put the cylinder diameter at less than the .002 limit for wear or out of round and removed the mild rust and scratches. The nicks in the exhaust ports were not in a position to affect port timing. A decent set of standard 3.3125 diameter bore pistons was installed.

The prop is an old school solid hub Mercury racing prop from the days before stainless steel. Racing props were almost always two blades back then. Note the radical cup from the trailing edge right into the ear of the blade. I am "into" bronze, it has a beautiful blade shape, and I acquired it cheaply. I polished it for appearance at the ramp. Nothing looks better than a highly polished bronze prop. It is about 25 pitch and loads down the 140 to about 4000-4200 RPM on my 21 foot Manatee cuddy so I don't regularly use it. HOWEVER: Once that 140 is mounted on my little 15 foot Glastron GT 150 (James Bond boat) Then I will probably use that prop. I did need to use two thrust washers to correctly position the prop on the shaft AND there is also a standard spacer under the prop nut and washer.

Note that in that prop photo you can also see the old style anode which MUST be removed for some props (notably the Vortex) to fit. Since it is so high, it contacts the webs inside the prop hub.

Here is another photo which more clearly shows the drive dogs on the forward gear and the dog clutch. The second photo is the 140--an older late 70s distributor model--with the fuel filter I so frequently recommend installed between the carb covers. Yes, I practice what I preach! LOL.

 

[Frank Acampora]

Re: For Karla and others who need to know

Remember when I was explaining that the piston does double duty, sucking air through the reeds into the crankcase then compressing it? Well here are a couple of photos of the reeds. Reeds are named that because they are very much like the reeds in a woodwind instrument and indeed, sometimes when turning the engine over slow, you can hear them "honk".

Reeds are a set of reed petals mounted on a "V" block and act as a one way valve, letting air and fiel into the engine and preventing it from blowing back out through the carb.

The first photo is of a manifold and three "V" blocks from an older engine. This manifold has the older round tipped reed petals. You can count ten petals on each "V" block. The photo shows the engine side and the carb side of the manifold. NOTE that a multiple cylinder two cycle engine is in fact multiple separate single cylinder engines mounted in the same block and using the same crankshaft. Each cylinder is discrete and sealed from the others.

The second photo is of a new style reed block and manifold from a four cylinder engine. There are two on each engine. Each manifold and carb serves two cylinders. This reed block and the two "V" blocks are the newer square tipped reed petal assemblies. They are slightly more responsive and the "V" blocks are rubber coated for better sealing, however, these reed petals do tend to break more frequently than the old round tipped type. You can see eight petals on each "V" block. I have held one reed open for the photo with an allen wrench. These "V" blocks are the same for ALL three and four cylinder engines and can be interchanged from model to model and year to year, new and old style.

Because of the number of petals and the open area when the reeds open, it is possible for an engine to run, although quite poorly, with a couple of broken reed petals. It will, however be very difficult to start if it does start at all.

Because they are plastic and open easier, aftermarket reeds like Boyeson are supposed to make more power by allowing more air into the crankcase. The plastic will pass through the engine without doing damage if a reed petal breaks.

 

[Dustin099]

Re: For Karla and others who need to know

Frank, are you a mechanic by trade or just a DIYer? You seem to have an incredible knowledge of these old Force engines that baffles me.

 

[ljc1957]

Re: For Karla and others who need to know

Frank, I've done lots of external work on outboards but I had never torn into one. When I bought my 67 45hp parts motor, I decied I was going to open it up so I could fully understand how it worked. It was a real education and I was impressed at how simple it was. Maybe I'm wrong but it seems to me that if you keep these lubricated and don't let them overheat, they should last forever. Are they basically bullit proof?