Chainsaw not going - PLEASE help

[Al Smith]

On that note,I will elaborate.I have seen several old outboards,with broken top rings.The remedy,clean the cylinder,move the bottom to the top,run 'er til she blows.The dang things would run for years,believe it or not.Oh,before you ask,what caused the ring to break on the boat motor.Ideling[trooling],with a 25 hp Evenrude,at 16 to 1 oil to gas ratio.{carbon built up around the ports,my fathers engine,been there done that]

 

[Bill G]

On that note,I will elaborate.I have seen several old outboards,with broken top rings.The remedy,clean the cylinder,move the bottom to the top,run 'er til she blows.The dang things would run for years,believe it or not.Oh,before you ask,what caused the ring to break on the boat motor.Ideling[trooling],with a 25 hp Evenrude,at 16 to 1 oil to gas ratio.{carbon built up around the ports,my fathers engine,been there done that]

Al,

There are still a large selection of old outboards here. My father had a 1957 18HP Evinrude that as far as I know he bought new. It was used every trapping season since he bought it up until he became too old too trap. I do not think the engine was every touched. Over the years he accumulated more and more outboards. There are still quite a few in his shed. I remember my cousin dropping off his 1956 18HP Evinrude that would not run. When dad got it fixed Raymond said to just keep it. The motor is still here too as well as several others Raymond could not get running. I had a 50HP V-4 Evinrude. That was one heavy motor but ran great.

Bill

 

[Al Smith]

True story Bill:I have several outboards,made in the late 50's,or 60's,that run like a charm The deal on the outboards is the fact that they have great cooling.These old relics,most likely.will make it to the next century.It is my opinion that the air cooled are killed ,by allowing the fins,etc,to be clogged with gunk,thus no air,ala,no cooling.As far as saw motors go,compressed air air,properly applied,saves the saw engine,in the long run.

 

[Lawn Masters]

Has anyone thought about putting a piece of spark arrestor screen around the cylinder to prevent the crap from getting in to begin with? it'll allow air to flow through but not dirt, so you've got a plus there. I'm sure theres a reason this hasnt been tried before, but I dont know the reason.

 

[Bill G]

Al.


I still remember how clean those engines looked when you pulled the hood on them. What you said is very true, they were water cooled and ran in very clean air. Dad used a 55 gal drum to test out motors but when you put the throttle to them the water was gone. When dad wasn't around that was great fun. I would say that over the last 50 years there have only been two outbards that left here. One was stolen off the boat and one was sold with a Texas Maid.

Bill

 

[pallis]

I'll have to remember this in case I ever have a two ring saw with a broken ring. With my luck I'm sure it will happen.

 

[Al Smith]

Not to get away from the ring issue,but heat,or the inability to disperse of it,most likely is the biggest engine killer.In the case of saw engines,or other types that use the fan blast as a primary cooling component it is important to have a clear path for the air.Some of the engine builders comments on the fact that modified exhausts run cooler,has a lot of merit.In the case of kart engines,they had a stream of 60 mph air passing around them while in a race,and they were set up a tad looser than saw engines.They,of course ,did't have a very long life.One of the old kart tricks was to use paint remover to take the engines down to bare metal.It was felt,at the time,that this would give better cooling,I really don't know.Back on the rings.In the late 60's there was a guy that ran funny cars at Kettlersville drag strip.He had a Henry J with a 427 Chevy.The dang thing only ran the top ring,no oil ring at all.He was unbeatable,but was banned from running because of the amount of oil that contraption blew all over the track.It was kind of like fogging for mosquitoes

 

[lostone]

OK, mechs correct me if I'm wrong here please, this is where I try to correct myself and understand piston ported. He said that it felt as if compression was coming back through the carb, at this time I say ok yes but only a small amount, this would be caused by it being piston ported and as the piston comes down on the stroke it is pressurizing the crank case but just a small amount comes back up the intake port until the piston skirt covers it up, is this correct? so this would be the pressure coming out the carb that he is talking about? I'm trying to get a better understanding of the two stroke and it never entered my mind until tonight, I was thinking way to simple on the 2 stroke design and not thinking of the piston skirt.

 

[Lawn Masters]

I think you're thinking like I am, not totally sure, but generally, your thinking would make sense. piston ported engines use the piston as you said to block the intake port on the downstroke which pressurizes the crankcase, then it opens on the cylinder compression stroke, unlike a reed valve, which utilizes the vacuum created during the compression stroke to suck in more air through the reeds, and uses that same air, when on the downstroke to close the reeds sealing the case. I hope this paints a fairly clear picture for you. if not, well, I did my best.

 

[lostone]

I found this link on piston ported engine and it described it well for me to understand how it works, I was thinking way to simple and wasn't taking into consideration for the piston skirt sealing the intake from the crankcase, and using transfer ports to send the fuel/air mix into the cylinder, this has given me allot better understanding of the piston ported design, I have always seen the models of the reed valve design before which didn't give me an understanding of how the piston ported design worked, its a good thing the 028WB is torn down as it gave me a cylinder to look into and see and understand as well after seeing the diagram.

 

[Al Smith]

You might want to take a look at Macdizzy,or Mc dizzy.This guy has an excellent website,discussing 2 cycle engines.You might also take a look at piston design.A good many piston ported engines use"windows" in the piston as part of the porting design.The famous Mac 125 ,while being a reed valve engine,uses a piston design that has one skirt of the piston shorter than the other.This semi slipper design allows the engine to operate like it has a racing "cam",so to speak.Once a person can grasp the fact that the intake stroke occurs at the same time as the compression stroke,it becomes quite clear how it works.

 

[Molecule]

I'm also wondering whether the intake airflow might have enough velocity, so as to also have a *momentum all its own. That is that, it's not a purely mechanical question, of where in the stroke the piston skirt begins to "open" the intake port relative to a static view of crankcase pressures. The momentum of the incoming pulse from the carb might have to be considered also. The question is where in the stroke, is enough "back-pressure" pressure in the crankcase exposed, by the lifting of the piston skirt, to overcome the forward momentum of the incoming pulse of charge organized by the prior stroke. My suspicion is that even though the piston skirt might mechanically open the intake port while the static crankcase compression is higher than the static pressure in the carb, the momentum of the next incoming pulse might be strong enough to keep the carb from getting backwashed.

 

[lostone]

Thanks Al, that page has a ton of info on it.