Clean air

[Woodchuckels]

Have a Jonsered 535 that I bought new probably 15 to 20 years ago. Have always noticed fine saw dust in the intake prior to the carb after cutting. Has been like this from day one. Checked air cleaner and looks ok and see no problems around the air cleaner housing. Have even put tape around the edges of the air cleaner when snapped together. This saw has cut alot of wood and still runs good. Has anyone experenced this. I realize that I am getting some wood dust in the motor, but it hasn't seemed to affected it's performance.

 

[BobL]

If there is one thing I feel I can comment on, it's dust, having studied it on an off over the last 35 years as part of my day job. Almost every dust making activity makes a lot of dust we cannot see. Clear air can still have thousand to millions of particles per cubic ft of particles >0.3 microns and millions to tens of millions per cubic ft <0.3 microns. Humans can only see dust greater than about 5 microns so the vast majority of dust in air we simply do not see.

All wood related activities generate dust. Just sitting there exposed wood generates dust, let alone cutting it, even when it is green.

Operators who think they have completely excluded dust from their engine internals are kidding themselves as all CS air filters, including the high performance varieties simply cannot filter out dust below about 1 micron in size. The smaller the dust is the more gaseous like it behaves. Like air it passes straight through air filters and into the engine where, if it is wood dust, it combusts and is expelled along with the exhaust. Like any combustion engine saws can tolerate some dust, the question is, how much can they tolerate?

Heating too much sawdust inside an engine converts some wood to carbon which together with unburnt resins and tars gunks everything up.

Of greater concern is when fine dust that passes straight through filters and aggregates and accumulates in the carby fuel where it can foul orifii and needles and starve a saw of fuel. Usually this manifests it self as a stuttering or completely non-functional saw but occasionally it can allow the saw to run, just and causes the saw to run too lean and it can cause engine overheating.

Obviously keeping as much dust as possible out of your engine is the way to go but no filter will ever keep all dust out so don't sweat the small stuff and regularly clean your carby to minimize the chances of the worst thing happening.

 

[Woodchuckels]

If there is one thing I feel I can comment on, it's dust, having studied it on an off over the last 35 years as part of my day job. Almost every dust making activity makes a lot of dust we cannot see. Clear air can still have thousand to millions of particles per cubic ft of particles >0.3 microns and millions to tens of millions per cubic ft <0.3 microns. Humans can only see dust greater than about 5 microns so the vast majority of dust in air we simply do not see.

All wood related activities generate dust. Just sitting there exposed wood generates dust, let alone cutting it, even when it is green.

Operators who think they have completely excluded dust from their engine internals are kidding themselves as all CS air filters, including the high performance varieties simply cannot filter out dust below about 1 micron in size. The smaller the dust is the more gaseous like it behaves. Like air it passes straight through air filters and into the engine where, if it is wood dust, it combusts and is expelled along with the exhaust. Like any combustion engine saws can tolerate some dust, the question is, how much can they tolerate?

Heating too much sawdust inside an engine converts some wood to carbon which together with unburnt resins and tars gunks everything up.

Of greater concern is when fine dust that passes straight through filters and aggregates and accumulates in the carby fuel where it can foul orifii and needles and starve a saw of fuel. Usually this manifests it self as a stuttering or completely non-functional saw but occasionally it can allow the saw to run, just and causes the saw to run too lean and it can cause engine overheating.

Obviously keeping as much dust as possible out of your engine is the way to go but no filter will ever keep all dust out so don't sweat the small stuff and regularly clean your carby to minimize the chances of the worst thing happening.

Thanks for the reply Bobl. All these years it has not seemed to affected the engine. Was just curious if anyone else had seen this.
Thanks again.

 

[pwoller]

I noticed the same thing on my 2100 that I mill with. Always seems to be a light coating of saw dust in the throat of the carb, doesnt seem to bother the saw much though.

 

[MCW]

Bob's reply was spot on and don't think modern saws are any better at filtering dust than your old Jonsered - all of this air injection mumbo jumbo only applies to larger particles and woodchips that carry more mass. Smaller dust particles tend to become worse with air injected saws. Although the newer HD2 filters from Stihl and the Dolmar HD filters do a better job than most, I still have to oil my Husky 390XP filters and my 3120XP filters. Dry hardwood dust gets through them easily. If you do think too much dust is getting through then a liberal squirt of filter oil will help but your filters will block up faster.

 

[BobL]

Apologies to those that already know this stuff here is a simplified diagram about what happens.


Starting with a clean filter, effectively all the big particles get stopped at the surface of the filter.
The medium sides ones ricochet off the filter fibres and some make it through while others lodge inbetween filter fibres
The fine particles are carried though the same way that air is and most avoid collisions with fibres because the ride the air stream which flows thought the filter like water through a grating.
Adding oil coats the fibres so that particles that collide with the fibres have a better chance of sticking to or between the fibres but of course before that happens they have to collide with the fibres and only some very fine particles ever do this.