Too much compression

[PogoInTheWoods]

You are a bunch of thread hijackers. Talk about whatever I am good with it. I just enjoy reading what you guys have to say.

I finally checked the cord to see how it filled the spool and I could maybe add one more turn of cord. Probably not worth doing.

It finally warmed up to about 50 degrees today and I got the saw out to see if I could start it. I used one of the suggested techniques of gently pulling the saw until it was at the top of compression stroke and then ripping the cord. This technique along with the warmer weather seemed to make starting the saw more do able. I got the saw cranked with about 5 pulls and the saw was spinning over well when pulled.

Thanks for all the help. I now think that I maybe be able to crank this saw with very little trouble.

May wanna check your exhaust port/muffler for carbon buildup, mud wasp nests, or anything else obstructing the exhaust air flow....which would otherwise pretty much make it seem like the saw had compression out the ass....unless perhaps the crankcase is full of oil or mix or something else somehow displacing everything.

Ya sure it has the correct piston in it?

Now where'd I put my beer and popcorn...not to mention the four pages worth of wasted brain cells I'll never get back?

 

[CR888]

but the faster the crank turns the easier the engine turns over. pull the rope slow its not easy. there is a lot more going on here than big gear and little gear.
acceleration, speed, and inertia, and momentum have a lot more to do with starting an engine than gearing. and if you think you have an advantage with the coiled up rope. you would lose it after the rope is a foot out and it would get harder to turn. and the simple physics everyone is talking about may apply to turning a coffe grinder, but not starting and engine. look up inertia, acceleration,momentum,and speed. a lot of close minded people on here.

SORRY WRONG! don't take that personaly but you do not quite get it.

 

[mountainlake]

I'd add that one more turn but make sure when the rope is all the way out none is left on the spool and it's not the end of the spring,, If you have too much rope and the spring comes to the end of it's travel it will break. steve

 

[half_full]

heck, remove seventy forty thirty two turns to make it start when the wind blows.

Some times threads are educational. Sometimes they are entertaining...

 

[half_full]

heck, remove seventy forty thirty two turns to make it start when the wind blows.

Some times threads are educational. Sometimes they are entertaining...

 

[066blaster]

SORRY WRONG! don't take that personaly but you do not quite get it.

I'm not gonna argue any more about this . All I know is I have had several big four stroke engines that pull over 10 times easier with shorter ropes. It doesn't make alot of sense to me either when I think about it but it's true. I never replace the ropes because they pullover and start so easy they never break again. And my dad's 68 and he can actually pull them over after their shortened. I tried it on a saw and it didn't work as good because of the compression. There has got to be someone out there who has experienced this too. I would say part of it is your loosing alot of leverage as your pulling so much rope off the pulley and I mean muscle leverage not mechanical leverage. But whatever . I'm not a scientist.

SORRY WRONG! don't take that personaly but you do not quite get it.

 

[PogoInTheWoods]

The fact of the matter is that mechanical advantage is in the best favor of the operator starting a saw when the most rope is correctly wrapped around the recoil pulley.

A well serviced and maintained saw should only need the first or second revolution of the flywheel to achieve ignition after following appropriate choking/starting procedures anyway...regardless of whether it's being started by a rope pulley with one wrap or fifteen.

Some methods are just easier to apply to the situation than others....for good reason.

Otherwise the pulleys would be a lot smaller and the ropes a lot shorter.

My outstanding and exemplary effort has concluded here. Nothing more to see or learn.

As you were.

 

[Stihl 041S]

I'm not gonna argue any more about this . All I know is I have had several big four stroke engines that pull over 10 times easier with shorter ropes. It doesn't make alot of sense to me either when I think about it but it's true. I never replace the ropes because they pullover and start so easy they never break again. And my dad's 68 and he can actually pull them over after their shortened. I tried it on a saw and it didn't work as good because of the compression. There has got to be someone out there who has experienced this too. I would say part of it is your loosing alot of leverage as your pulling so much rope off the pulley and I mean muscle leverage not mechanical leverage. But whatever . I'm not a scientist.

Muscle leverage IS mechanical advantage.
Your answers of "10 times easier" is like answering a question with "because". Pretty worthless.
Maybe your big Ol low compression motors have to get spinning faster.
But if your theory is right......put half a wrap on your starter and give it a spin.

 

[Marshy]

You can get a good look at a T-bone steak by sticking your head up a bulls @ss but wouldnt you rather take the butchers word for it?

 

[066blaster]

I did try it on my 290. I will say the first foot of rope was harder than the last foot with the stock rope. Then I shortened it down to about 14 inches total. It had the initial resistance like before and then pulled easy. I would have to try it on a saw with a decompression valve to really draw an conclusions. It maybe a person's arm has more strength when not fully retracted . And again most of what I have said is based on big four strokes. Just thought I would try it on a saw

 

[Stihl 041S]

The Laws of Physics are no longer relivent.

Abandon all Hope.

 

[Marshy]

*Shakes head, Palms Face*

 

[066blaster]

Muscle leverage IS mechanical advantage.
Your answers of "10 times easier" is like answering a question with "because". Pretty worthless.
Maybe your big Ol low compression motors have to get spinning faster.
But if your theory is right......put half a wrap on your starter and give it a spin.

And your arm has the same strength through its entire range of motion?

 

[066blaster]

Ok I will draw a conclusion. With less rope coiled on the pulley you spin the crank more times and faster per inch of rope . This coupled with the fact it is occurring in the strongest range of motion in your arm . The engine starts quicker while creating less fatigue on your arm. With more rope coiled you must pull faster and harder to achieve the same rpm's and use a larger range of motion of your arm.

 

[Marshy]

Just for chits and grins, lets break this down a little and talk about it. I think your starting to come round... (dont take this the wrong way, I am not attacking you just friendly banter, I think your reaction so far has been good natured about the whole matter so kudos).

Ok I will draw a conclusion. With less rope coiled on the pulley you spin the crank more times and faster per inch of rope ....

Fact, I agree. Verses a larger pulley and same draw speed (arm speed), yes.

... This coupled with the fact it is occurring in the strongest range of motion in your arm ...

Irevelant, ignore your body and your arm strength. The only provable fact is the mechanics of the saw and the laws of leverage created by the size of the recoil pulley and how the leverage is increased when the size of the pulley increases. Those things will dictate how much force from your arm is required to provide to start the engine.

The engine starts quicker while creating less fatigue on your arm...

Irevelant again. Everyones point is the engine wont start or turnover a complete rev if you cannot exert enough force to overcome the compression of the fuel/air charge. Take arm fatique out of the equation because you wont get a full rev out of the crank without necessary torque from the recoil pulley.

With more rope coiled you must pull faster and harder to achieve the same rpm's and use a larger range of motion of your arm....

No, you increased the diameter of the pulley therefore there is less torque required from your arm to overcome the compression. Likely you will end up compensating and pulling it over faster because it is easier to turn over not because you need/goal is to maintain a certain RPM for starting. Your only going to pull as hard/fast as you need to start the saw. If you had a saw that could be started by a 5 yr old then you'd probably pull it over like a 5 yr old... generally not the case though.

Again, were not adding 5 miles of rope and just because you added rope doesnt mean you have to use the entire length of it to start the engine. If the diameter of a recoil is 3 inches and you added one more turn of rope on top of it, the diameter would increase to 3.5 (2 x 1/4" rope diameter). The circumfrance increases by almost 1-5/8 inches but you also increase your leverage by 16.7%! (0.25/1.5 x 100 = 16.7%) Thats a huge amount. Cant argue with more leverage, it always wins.

 

[mountainlake]

Ok I will draw a conclusion. With less rope coiled on the pulley you spin the crank more times and faster per inch of rope . This coupled with the fact it is occurring in the strongest range of motion in your arm . The engine starts quicker while creating less fatigue on your arm. With more rope coiled you must pull faster and harder to achieve the same rpm's and use a larger range of motion of your arm.

On any saw the first compression cycle will be the hardest and that where you need mechanical advantage, once it get turning it will be easy. Keep in mind even with a long rope you spin the saw just as fast as you get to the end of the rope. Try this, take a hard to pull saw and pull it over real slow as the rope get farther out (shorter rope ) it will get harder and harder to pull over . Steve

 

[7oaks]

Thought I'd post this detail pic from a Contra poster I have showing the rope pulley. Thought it might help understand what is being discussed.

 

[Little Al]

I

 

[Little Al]

I`m confused[ quote when weather is cold the oil is thick & makes it hard to pull over] Surely the only oil involved in 2T chainsaw start up is the oil mixed with the gas, as the oil pump for chain lube doesn`t come into it,at pull over speed, & the minute amount of oil in modern mixes ie. 40/50 to 1 being mixed in the gas I would have thought had no bearing on the difficulty in pulling the motor over, can some one please explain to me if I`m on the wrong path, Thanks.

 

[tmessenger]

The ratio is constantly variable more leverage initially and as the rope unwinds more speed. So initial leverage to get the engine spinning and more acceleration as the pull progresses, maybe the guys that designed these systems know what they are doing after all.