Which Engine??
 

I know this question has been asked before. Just hoping to get some new info.

Which Ryobi engines are best to convert (new ,old, what models etc.) , same question with for Homelite..

Also, anyone know what other name brands use these engines.

Thanks

RE: Which Engine??
 

Stick with the older in both cases. The newer Ryobis have some slots in the cylinder that cost some power. We think they are for smog purposes. The newest Ryobis also have a different crankcase design that is harder to convert. Also, an older engine is more likely to have a carb with both high and low adjustments. Many of the newer engines, thanks to the "all knowing" EPA aren't fully user adjustable.

AV8TOR

RE: Which Engine??
 

How old of Ryobi would be a good one? What year did the changes take place?

I found a Yard Machines ZR725R anyone know how good this would to convert, I think it is a 2005 or 2006 model.. I can't seem to find any info on what engine is in it...

Thanks

RE: Which Engine??
 

Here is a 25cc Homelite engine. http://www.cumminstools.com/browse.cfm/4,770,0.htm

RE: Which Engine??
 

The current Ryobi engines in the Bolen weedeaters are the best of them all, dual rings, no slots, the new style exhaust port, they even made a little larger relief in the crankcase so the transfer ports match the cylinder better. Lowes had them for $64.95 the last time I looked. You'll have to machine the "shroud" off the front of the crankcase though, it doesn't bolt on like the older style motors.

RE: Which Engine??
 

Do any of the Sears Craftsman have Ryobi engines? Would this model have a Ryobi in it ?

http://cgi.ebay.com/Craftsman-32cc-G...QQcmdZViewItem

RE: Which Engine??
 

My Guess is the slots help reduce compression for more easy starts. Capt,n

RE: Which Engine??
 

I'm thinking "Exhaust Gas Recirculation". If they wanted to lower the compression for easier starts, they could have done so by lowering the static compression ratio, or by adding a compression release. The former would have been just as easy to "tool for" as the slots.

AV8TOR

RE: Which Engine??
 

How is this "Recirculation" performed? Like from where to where does the gas,es get recirculated? Thanks Capt,n[X(]

RE: Which Engine??
 

The two slots extend upwards from the exhaust port like "pseudo" transfer ports. I think that sends a small amount of exhaust gases into the combustion area acting like exhaust gas recirculation. As you probably know, this is used on car engines to lower the combustion temperature to avoid the formation of oxides of nitrogen, a component in smog.

AV8TOR

RE: Which Engine??
 

How is hot exhaust gases going to lower temps in the engine we are talking about...a Ryobi? Capt,n

RE: Which Engine??
 

Exhaust gases contaminate the fresh mixture, which then doesn't burn as hot. I looked it up in Wikipedia so that I could give you a source other than myself. Here it is:

Quote:
EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. Intermixing the incoming air with recirculated exhaust gas dilutes the mix with inert gas, lowering the adiabatic flame temperature and (in diesel engines) reducing the amount of excess oxygen. The exhaust gas also increases the specific heat capacity of the mix lowering the peak combustion temperature. Because NOx formation progresses much faster at high temperatures, EGR serves to limit the generation of NOx. NOx is primarily formed when a mix of nitrogen and oxygen is subjected to high temperatures.

EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR is also omitted at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle.
End quote

AV8TOR

RE: Which Engine??
 

Is this for 4 cycle engines or does this also appy for 2 cycle engines? Remember the 2 cycle engines fire every time around...the 4 cycle has lot more time between power strokes. Capt,n