Stihl air filter question

[smokechase II]

Regarding the felt covered pre-filters that are common for Stihl 044/440 and similar saws.

(They Stihl filters have three layers;
1) Inner large foam that prevents gas back flow,
2) Larger rigid, usually paper element primary filter,
3) The outer felt pre-filter with sewn elastic stretch connector.)

Does anyone have enough experience to say that this outer felt should be automatically discarded because it if clogs it can disrupt the air flow enough to "suck the piston" or do damage to the carb side of the piston? This despite the intellicarbs ability to alter gas flow to match the air coming in.

Here is an example of an aftermarket filter that is similar to Stihl's from the Baileys catalog:

http://store.baileys-online.com/cgi-bin/baileys/1945

Thanks for any help.

 

[Hired Gun]

I can tell you this, I just took apart a 460 that belongs to my renter (The saw was seized up tight). He is a logger, and only use's Stihl 460's. He runs them hard, gets paid by the thousand ft, does not open the mufflers or mod the carbs to be adjustable. On average he burns up 4-5 saws a year. Anyhow I am putting a Baileys big bore 460 P&C on this one for him. Back to your question. He runs the filters with the pre-filter on them and I am sure they don't get much cleaning, just the ocassional bang on the tailgate to knock the bigger material off. The piston that came out of this 460 had all the scoring on the exhaust side. The carb side looked very good. This is the first 460 that I am rebuilding for him. I did see the piston and cylinder that came out of the his last 460 that grenaded, and that piston was also scored in the same spot, on the exhaust side. Don't know if any of this helps, just my observations.

 

[Justsaws]

Does anyone have enough experience to say that this outer felt should be automatically discarded because it if clogs it can disrupt the air flow enough to "suck the piston" or do damage to the carb side of the piston?

None of the 066s or other larger Stihls that I have been scavenging parts from using Stihls filter system have had any damage on the intake side. Usually bearing damage or exhaust side piston scoring typically resulting from overheating and to many RPMs. I do not think that their system if properly maintained would cause the problems you are referring to.

I have not used the system from Bailey's. I use Stihl H. D. filter systems on the larger Stihls. No problems yet. I did use an after market "high flow" foam system that came on a Husky and was not pleased with the maintenance for it. It worked great for about 2 tanks, then needed to be throughly cleaned.
I do not know which brand it was. I no longer own it.

 

[Lakeside53]

A clogged prefilter will just give you with a rich mix at higher power, and if dirty enough, limit your high end performance. It's not going to hurt the piston. The "intellicarb function only works within a reasonable but limited range. After that, it just works like any other carb with a dirty filter.

The prefilter is there so you don't clog up the main filter. The "sponge" is only installed in earlier saws that do not have the extended defector for carb spit back.

Clean the prefilters regularly (carry a couple oi spares) and your main filter will last for years. Just throw them in the washing machine with your jeans.

The main filter is not "paper" - it's a woven "fleece" of polyester, a least it is in the Stihl system.

.

 

[smokechase II]

Thanks guys

I had a couple loggers feed me a line and was pretty sure they are the typical let's get all the performance we can out of this tank of gas types.
NW loggers are famous for breaking saws. You would probably have to go to a third world country to do worse than we do.

I carry a small Tupperware container that holds a 044 filter set up and keeps it clean. It also works well as a washer in the field. I found that I could clean two filters pretty well with judicious use of a quart of water on the fireline at the end of a shift.

The Madsens site has a nice little explanation on filter cleanliness that backs what you're saying here.

Thanks again