Forums Archive Index > Outdoor Power Equipment > OHC 2 cycle?
Date: 27 Nov 2006 8:49 pm
Went to my local OPE shop today to pick up some small stuff, when I noticed a small cylinder head that had the exhaust valve head broken off the stem. Lady said her workers put straight fuel in it instead of gas/oil. HUH? I said thats a 4 cycle engine, NO gas/oil mix needed! Well, it WAS a 2 cycle and with overhead valves no less! I had never seen one before, this one was on a Shindaiwa blower. Pretty neat, apparently no more reed valves in order to clean up emissions. Problem was the valve didn't seize, the head broke off & it beat up the seat. Everything else was ok - I inspected it myself.
Question for for 'Lint & Shoveller - would straight gas cause this to happen?
Marty
Date: 27 Nov 2006 10:06 pm
Marty,
It is really a 4 stroke engine, but uses mixed gas. It doesn't have an oil sump like a 4 cycle, but draws the mixed fuel into its sealed crankcase like a two stroke and pushes it past the valve train to lubricate the lower end and the valve train, before the fuel charge goes into the combustion cylinder.
It still has reed valves: on the intake and where the charge leaves the bottom crankcase to go out to the valves and intake.
Date: 28 Nov 2006 5:00 pm
Hi Guys!
Marty- We have been using 4 stroke engines as you describe which burn oil added to the fuel mix in Radio Controlled Models for at least the last 15 years. The advantage is they are very quiet and will swing larger props.Lots of torque developed at low RPM. They will self destruct if you don't use a two stroke type fuel mix.
Marc
Date: 29 Nov 2006 6:47 pm
Highwind wrote:
Marty,
It is really a 4 stroke engine, but uses mixed gas. It doesn't have an oil sump like a 4 cycle, but draws the mixed fuel into its sealed crankcase like a two stroke and pushes it past the valve train to lubricate the lower end and the valve train, before the fuel charge goes into the combustion cylinder.
It still has reed valves: on the intake and where the charge leaves the bottom crankcase to go out to the valves and intake.
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I have a FS-90R which Stihl calls a 4-Mix. Does this manufacturer use the same lubrication method as you described in the Shindaiwa and does it also use reed valves?
I believe this model is fairly new so I am not sure if you have seen one of these engines disassembled yet.
Date: 29 Nov 2006 7:23 pm
Thanks for the enlightenment guys! I ALWAYS SAY that I NEVER know it all...
Marty
Date: 30 Nov 2006 12:12 pm
newjerseybt wrote:
I have a FS-90R which Stihl calls a 4-Mix. Does this manufacturer use the same lubrication method as you described in the Shindaiwa and does it also use reed valves?
I believe this model is fairly new so I am not sure if you have seen one of these engines disassembled yet.
Haven't seen much on the Stihl. It will use the same method of pumping the oil/gas mix around the the crank and valves. I would suspect that it has some form of reed valves since that would be the simplest way of directing fuel from the carb to the crankcase, and from there to the combustion chamber.