[:-]All the rod,pistons,top of pistons to wrist pin are the same.All of them can change out.The only head that is more differant is the 2 slot with comp releif cuts.The small case hits , but the large case none of them hit.
All rods are the same.The 3 rods that are differant are the same lenght.The WEIGHT are. Some are 66 grams,the others are 78 grams.For refrance- the 2 ring I beam style rod is 78 g. The other rod type with 2 rings is 68 g.The same rod with 1 ring are 68 or 78 g.
The crank throw is +/- 26.50 mm or 1.043 in. Small or large case.Didn't matter.

If the rods were NOT the same The "PARTS STORE" would have two rod type piston assemblys available.

I went parts hunting just this past Tuesday.I was asking around for pistons for these hoping to score some more 2 ring types.I did ask if the parts book showed 2 differant rod lenghts,and they didn't. ??? The last place I was at I was noticeing that there are Ryobi type(by the rear intake/exhast kind) motors with 28cc,30cc,31cc,33cc. ???
I did get me some 4 stroke 26.2 cc, but that is another project..Then he offered me a job,I seemed to have known more about them than he did.

To everybody. If you have a motor tore apart and can measure the parts, all the info would help.
I have looked at other engines that are set up like the Ryobi.There is several for r/c-airplane engines that are pumping out 2-3 +hp in the 8000+rpm range.To think that these engines can only do about 1.5 hp is wrong.

I have so many people say that covnersions are " to heavy, not worth it,cant make the same power,and so on" They are the out of the box kind.10 years ago the gas engines were expensive, and they still are.Now there are some less expensive ones out there,but if I or any one of you can make a hot running Ryobi that can work better and for less $$ with parts that you can get anywhere, thats the goal I have.I bought my JAGGs kit back in '03 and wanted to go EI with it was too expensive,but now aftermaket EI kits are 1/4 the price.To get the Ryobi running well for less than $80 ,thats what I want,not $250+.They all can hit the ground[] and they all sound the same when they do.