STIHL MS500i

[dodge man]

Two stroke don’t have valves was the reason he had a question on it.

 

[Skeans1]

In the 2nd summer of using our Stihl KM 131R it wasn't starting all that well any more so I brought it back our dealership. A tune up kit and valve adjustment brought it back to two pull starting. This is what our dealer said he did to it.

Some of the Stihl stuff actually does have a valve in it, to my knowledge none of the saws do other then pole saws.

 

[dodge man]

I have a Stihl poke saw and they were trying to tell me it was a 4 stroke but yet still a two stroke. I never did follow up to figure out what that meant.

 

[sd455dan]

Right I saw the 26 year old Farm Boss quote and knew it was a 2 stroke, as for spin trims several are 4 strokes like Husky/Honda

Wonder if the Stihl 4 mix are like the Honda units-

Worked on and tuned up a Husky model had 2 problems
hard start and wouldn't stay running very well- then if it died would not restart due to virtually no compression
Valves needed adjustment (way to tight) and the fuel line they used was constricted from the rubber seal the line passes thru expanding or the line collapsing.

Those little 4 strokes are really nice smooth running and torquey when everything is working right.
I think they are an engine that needs oil level and oil changes looked after for sure.

 

[dodge man]

I just read up on my saw, a Stihl HT 101. Stihl calls it a 4 mix. It does have valves and is a 4 stroke but there is no crank case. You still mix gas and oil and it diverts a little of it to the lower end for lubrication. In other words Arly wasn’t crazy when he said they adjusted valves on his.

 

[ericm979]

The 4mix is a four stroke, with overhead valves. Suck squeeze bang blow. Part of the fuel/air mixture gets sucked into the head under the valve cover and travels down to the bottom end to lubricate the crank bearings and piston. This page has an animation that shows it: 4-MIX engine: Lightweight with good lugging power | STIHL
Theoretically the 4mix could be operated in any orientation like a two-stroke. They don't seem to rev very high though. All the ones I hear in leaf blowers and string trimmers are droning on at what sounds like 5-6k rpm. In racing motorcycles, modern four strokes rev out farther than the same size two strokes. Maybe the plastic cam or the amount of piston lubrication limits peak rpm.

Stihl uses to trumpet the 4mix when it came out but now they try to hide which engine is in what implement. But they don't use the 4mix in any saws, those are all two strokes. Maybe because the power curve and max rpm is not suitable for saws.

 

[ArlyA]

Stihl was trying to make a cleaner running engine, which is OK, whatever. Nonetheless, this Stihl KM 131R has buckets of power and we can operate a 4 string head running .155 springs with ease. Using a saw head does not require any power, compared to strings.

Patiently waiting for the 170 head to come out.

 

[dodge man]

I corrected my post, I don’t know why I said a 4 mix is a 2 stroke, it is a 4. I looked at the owners manuals for my leaf blower and weed eater, they are both 2 strokes.

 

[ArlyA]

Right I saw the 26 year old Farm Boss quote and knew it was a 2 stroke, as for spin trims several are 4 strokes like Husky/Honda

Wonder if the Stihl 4 mix are like the Honda units-

Worked on and tuned up a Husky model had 2 problems
hard start and wouldn't stay running very well- then if it died would not restart due to virtually no compression
Valves needed adjustment (way to tight) and the fuel line they used was constricted from the rubber seal the line passes thru expanding or the line collapsing.

Not like Hondu's at all.