wheelsmithy (Joe-with-an-L)
wheelsmithy (Joe-with-an-L) PowerDork
7/26/22 3:14 p.m.

I thought I might be able to give someone back the ten minutes I wasted today in confusion. I'm sure plenty here already knew the following, but I didn't.

The patient:

Symptoms: 2 stroke leaf blower is extremely hard to start. Pulls the cord out of your hand like it's out of time, but that's not possible on a two stroke, right?

After finding a valve cover, watching the tiny rocker arms move Very fast as I turned it over, its seems the valves are out of adjustment, which can cause the "locking up" feeling I got when pulling it over. 

Turns out, this is a newer, friendlier smoker. The valves let it run cleaner, since they can be more precisely timed (compared to side ports, reed valves, etc. Downside: I'd call them extremely sensitive to valve adjustment. 

The more you know...

gearheadE30
gearheadE30 Dork
7/26/22 3:30 p.m.

Aren't those actually 4 stroke, just using mixture bypass to lubricate with the oil-fuel mix?

Noddaz
Noddaz PowerDork
7/26/22 3:33 p.m.

The cam and crank turn in 1:1 time?  Interesting.  But maybe not.  Note:  I am not sure these are for the engine in question.  I will climb back in my hole now.

Crank illustration

Cam illustration

 

wheelsmithy (Joe-with-an-L)
wheelsmithy (Joe-with-an-L) PowerDork
7/26/22 3:44 p.m.

In reply to gearheadE30 :

Nope, No crankcase oil. Premix apparently lubes the bottom end.

In response to Noddaz. Yep, as far as I can tell. The valves were actuating fast per crank rev to mu highly calibrated duh-o-meter

wheelsmithy (Joe-with-an-L)
wheelsmithy (Joe-with-an-L) PowerDork
7/26/22 3:46 p.m.

In reply to Noddaz :

That appears to be the engine in question. Very similar architecture at any rate. I can't see the cam, but those gears look like 2:1. Maybe there are two cam lobes for each valve.

buzzboy
buzzboy SuperDork
7/26/22 5:11 p.m.

I've got a Stihl like that. They call it a "4mix" which I've always assumed to be a 4 stroke that runs on mix. Mine's been dead reliable for 17 years.

gearheadE30
gearheadE30 Dork
7/27/22 11:22 a.m.

Yep that "4mix" engine is the one I was thinking of. Runs cleaner than a 2 stroke without the lube system angularity issues of most 4 strokes in yard equipment. Always weird filling a 4 stroke with mixed gas, but I have had good luck with the ones I have used.

Noddaz
Noddaz PowerDork
7/27/22 3:28 p.m.

In reply to wheelsmithy (Joe-with-an-L) :

I think the cam sprocket IS the cam.  Notice the two followers to the right of the cam sprocket.

wheelsmithy (Joe-with-an-L)
wheelsmithy (Joe-with-an-L) PowerDork
7/27/22 5:08 p.m.

In reply to Noddaz :

I did. My best guess was that that gear had lobeson the far side thatwe can't see. Two intake, and two exhaust, 108 degrees from omeanother to account for that gear (I ASSume) being twice the size of the drive gear. 

Again, I'm no rocket surgeon, but it seemed like those valver were opening and closing really fast (2X???) per crank revoloution as I pulled it over. 

To buzzboy: That may be true, but I can find no crankcase oil, which I ASSume makes it a two stroke. Weird.

81cpcamaro
81cpcamaro SuperDork
7/27/22 6:59 p.m.

It is a 4-stroke, just without crankcase oil, as the fuel mix goes through the crankcase on the way to the intake valve.  That way no worrying about keeping the engine level and keeping oil in the sump.

2-stroke Diesels have crankcase oil like a 4-stroke, so crankcase oil isn't a good determining factor.

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