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2 questions
1) in a number of posts people talk about a certain motor being a "looper". What is a looper and is it good or bad?
2) I recently tried a 9.9 kicker on my v20. but when I went to the stern to start it (non-electric kicker) water came in the floor drain. I read in a post that water coming in the boat like that can be corrected w/check-valves between the floor and hull. I can't, however, seem to find a find info or pics of these "check valves". Could someone please give me some addnl info of these. Thanks, Jim |
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A looper is a type of engine where the pistons and ports are arrainged in a certain way so as to better scavange the exhaust gases from the combustion chamber. THEFERMANATOR or Spareparts can probably explain it much better than I can
As to the floor drains, if you do a search in these forums you'll find many topics on that subject. Just search under drains, scuppers, and floor drains. :head: |
TWO STROKE DEFINED
The two-stroke engine completes its power cycle in only one crankshaft revolution with two strokes of the piston. There are no valves, camshafts, springs chains, etc. so the engine is much less complex and lighter. Instead of valves There are a series of strategically located transfer ports - intake and exhaust, cut into the sides of the cylinder wall. The ports are on opposite sides of the cylinder. The transfer ports are opened and closed by the up and down movement of the piston. To accomplish a complete power cycle both sides of the piston are used; consequently several events occur simultaneously during each stroke. They are: Up Stroke - Intake and Compression: On the up stroke the top side of the piston is compressing an air/fuel mixture in the cylinder. At the same time the BOTTOM side of the piston pulls another fresh charge of air/fuel mixture into the crankcase thru a one way valve called a reed valve. Near the top of the stroke the compressed air/fuel above the piston is ignited by the spark plug and begins to burn. The rapidly burning fuel expands and begins forcing the piston down. Down Stroke - Power and Exhaust On the down"power"stroke the piston is forced towards the crankcase reducing its volume and creating a positive pressure. As it continues downward travel it starts first to uncover the exhaust ports. Exhaust gas begins to rush out of the cylinder. Then the intake ports are uncovered. The fresh air/fuel charge in the crankcase is forced into the cylinder and continues to push the remaining exhaust gases out. The 2 stroke process of purging exhaust gases from the cylinder and filling it with a fresh air/fuel charge is called scavenging. Two stroke engines use 2 different scavenging methods, cross-scavenging and loop scavenging. Both differing designs have particular advantages. TWO STROKE CROSS-FLOW two stroke cross-scavenged engines can be identified by the irregular shape of the top of the piston called a deflector. This deflector directs the incoming air/fuel up, towards the top of the cylinder. This creates a wall or column of fresh mix that sweeps across the cylinder towards the exhaust ports. As the column advances it pushes the spent exhaust gases out of the exhaust ports. See Picture Below Hope this makes since to all and helps all. TWO STROKE LOOPER Pistons in loop scavenged engines are generally near flat. They do not rely on deflectors to aim the fuel/air mix, rather they have shaped intake ports and combustion chambers to control the scavenging of the cylinder. Several intake ports are aimed upwards and arranged such that their combined streams flow upward and then LOOP down toward the exhaust ports. Cross-Flow engines are better performing at idle and low speed. All older motors of any horsepower are of this design. Until the late 60's it was not economical to try to produce this design in quantity at a reasonable cost. Looper engines, although having poorer idling characteristics are more fuel efficient and perform better at higher RPM's than crossflow as they have lighter pistons. This lowers the strain on the connecting rods, bearings and crankshaft. OMC created the first US production looper in 1968 with the 3 cylinder 55HP. |
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http://i3.photobucket.com/albums/y90...n/DSCN1300.jpg CHECK VALVES: http://www.westmarine.com/webapp/wcs...classNum=50649 The valves shown in Smoke's post above are considered "scupper" valves...the link here is the one I was talking about...it is installed internally in the hose that connects the outter thru hull fitting to the inside thru DECK (drain)fitting...as the outter thru hull fitting goes out the side of the boat, I don't think a "scupper" fitting would be a good idea...although they would be fine to run out the transom of the boat... |
Thanks for the info. What type of drainsdo you think work best on the v20 1) inline vs the scupper type 2) if scupper type, which style (ping pong ball v. flap) 3) can you use both of these values at the same time. (an inline between hull and floor and a scupper on the outside of hull)?
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Any of the above will work. the in-lines are nice but do have a disadvantage of being harder to access and clean out if fowled.... the ping pong and flapper style are a little more work to install (screws and 5200) but are accessible without contorting yourself.
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i would suggest if you go with the in-line style that you also install a screen or grate over the deck drain.
Another thing to consider being in the north, make sure that it is installed such that it can't hold water and freeze |
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P.S. If you DO find an in-line valve that works right in that existing hose, PLEASE post where you got it.. Thanks! |
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