No Load Question

[scottr]

Wiithout a bar/ chain and "sprocket".

Hey Fish, it was in this old thread. http://www.arboristsite.com/showthread.php?t=13837&highlight=clutch

 

[Slamm]

Before I started using 100LL AV gas, I would just dump the gas into the jug with a large funnel, then start the saw and clamp it in a vise (at home/shop) or put the chainbrake on and let it sit on the ground (when logging) and idle until it died while I did something else.

I have never had any problems with that.

If you are just idling it, it shouldn't matter if the bar/chain is on it, but I wouldn't go reving it much to get it to finish the gas.

As to the running out of gas while cutting issue. After awhile of cutting you can get a pretty good feel for how much wood you can cut with certain favorite saw, but if I fail to refuel before it starts to run out, I will try to hit the kill switch before it dies on its own completely, not for safety of the engine, but because if you use all of the gas up in the carburator then it is harder to start again after you refill it, so I try to kill it as soon as I think it will die.

Sam

 

[Justsaws]

Justsaws,
From the time my main saw shows any sign of being out of gas to being out of gas and not running in my experience is like a second or three maybe, at the most, on a straight level cut. Are you really saying that instantly hitting the kill switch vs. waiting the second or two really significantly reduces the saws useful life?

Usually the saw bogs and wont cut or run without gas anyways so it's self limiting isn't it? If it has gas sufficient to run it's lubed, if it isn't getting gas and lube it isn't running? Am I mistaken in thinking that way?

Typically I notice the saws running out of gas with much more time between when they start acting differently and are actually out of fuel. The fuel lubricates and cools the P/C so it is a good idea to allow that function to happen after the saw has been put under a sustained load.

The self governing function that you are referring to is as good for the saw as running the saw with a carburetor that is set to lean.

I would not recommend that a saw be shut off during a long sustained load because it has not had any time to cool down and can bake off the lubrication from the P/C resulting in glazing and carbon build up, heat transfer, particulate scuffing, etc..

For storage it seems to be generally recommended that if you store the saw for longer than 3 months empty fuel from tank, start saw and let it idle until it stops. If you are really picky, you would still need to choke it and pull it over quite a few times to get most of the fuel cleared from the carb and lines.

Personally I would not let my saw idle until it stops but rather shut it off when it begins to sound as though it is going to stall.

Also in terms of reducing a saws useful life it depends on how many actual hours of run time a person wants to get out of the saw. Most saw owners will not run a saw enough to warrant a new set of rings before they destroy their saw with some other type of preventable damage.

Most saws seem to handle a wide variety of operating and maintenance variables long enough to keep most owners happy. The difference between what many do and what others do is really only visible when the known hours of actual use and the reason for failure are known. There are the obvious exceptions that have the tell tale signs of improper use etched in and baked on to the piston and cylinder.

A good looking well used piston will have enough skirt left to reuse with little to no scuff marks, heat printing or baked on crap and the used rings will be less than half the proper thickness and still flexing as they should. I do not see many of those as most simply accumulate damage until the piston starts scuffing or fry an engine through carelessness.

I am editing to add that the new generation of chainsaws seem to be much more suseptible to heat damage than the older non-strato saws. I would imagine that for most switching from the the previous generation of non-strat it will not be much of an issue but for those making the jump from the antique to strats it could and seems to an issue. Dogging and bogging seems to be a real issue with the strats.

Also in terms of saw life, understand that the operator having the saw on site is not the same as the operator running the saw on site and most will highly exaggerate both numbers unless they are after warranty work and then the saw was only run for five minutes using the sharpest chain, best fuel and the appropriate branded mix oil, even if it is 2 years old.

 

[isaaccarlson]

If my saw does start to run out of gas in a cut

I pull it out and let it idle for the few seconds it has left so the P/C can cool at least a little. Even if it is a little lean it is at a very low rpm and it is better IMO than baking the engine. I also refill it as quickly as safely possible so I can get it going again and lube/cool it. But yes, I try to fill up before I run out.

 

[nanuk]

all good info on running saw out of fuel

lots of food for thought.

but the OP was asking about WOT with NO B&C.

Bearing, from what I've read on them, are rated for about 22k rpm... so I doubt that's an issue, but the torque on them and the engine as a whole is the limiting factor, I would guess.

the heavier the components, the more weight/torque on the parts. and there is a limit as to what the machine can handle. the piston/rod/crank are not in balance, so you are asking a lot of the bearings and housings to withstand the stress of the hammering effect of super high speed. Now, it you could get heavier rated bearings, and reinforce the case...

Isn't that why 4 cycle race engines get "Balanced" and Blueprinted?

so... perhaps a little 32cc 017 can take a WOT no load of say 18k without problems, but a weighty 088 at that rpm needs load to damp vibrations to save the engine, cause the vibrational torque could cause metal fatigue or catastrophic failure.

:dunno:

 

[Justsaws]

lots of food for thought.

but the OP was asking about WOT with NO B&C.

Bearing, from what I've read on them, are rated for about 22k rpm... so I doubt that's an issue, but the torque on them and the engine as a whole is the limiting factor, I would guess.

the heavier the components, the more weight/torque on the parts. and there is a limit as to what the machine can handle. the piston/rod/crank are not in balance, so you are asking a lot of the bearings and housings to withstand the stress of the hammering effect of super high speed. Now, it you could get heavier rated bearings, and reinforce the case...

Isn't that why 4 cycle race engines get "Balanced" and Blueprinted?

so... perhaps a little 32cc 017 can take a WOT no load of say 18k without problems, but a weighty 088 at that rpm needs load to damp vibrations to save the engine, cause the vibrational torque could cause metal fatigue or catastrophic failure.

:dunno:

The golden rule referring to WOT with no load came in to existence back when many saws were un limited or had "sloppy" governors, machine tolerances in some were huge and the bearings/seals in some that were close enough for hand grenades and horse shoes. Some of those saws would literally spin themselves a part to the point of severe damage.

I would still not be comfortable recommending that anyone stand around and WOT with no load their saws for any sustained length of time but few newer stock models will rev out far past their safe operating RPMs. Beyond that it is a matter of tuning for lube and cooling. In regards to newer limited models I do not see many pistons that suffered the damage typically associated with being over reved that did not have a long history of other abusive issues or low quality control parts manufacturing.