Chainsaw Repair

066 stock OEM (late) jug.

attempt to increase torque value by 40%.

can this be done without adding aluminum? 

link to dyno graph of stock 1998 066 saw:  http://www.dlg-test.de/pbdocs/4713.pdf

attached is a text file that shows the results of what i found.

this includes digging into the chamber and dropping the jug as modifications.

edit: note on the text file, the correct connecting rod length is 68mm.  (not 64 mm).  deleted and reattached the correction.  (this was a two fingered typing error trying to write this up).

regards
-joe

(had to link the graph because it was to large, sorry).

Stroking the two piece stihl cranks is a pain, but stroking and a smaller bore would be a good start. Using some epoxy to "tighten" up the transfers and perhaps drop them a few degrees.  re-cut the squish for optimum squish velocity at target rpm.  Increase compression, and use higher velocity intake/carb tract along with timing advance if the Motor will take it. small sprocket too. Who has a small engine dyno ? Be a cool project! Adam'

its just bench racing for me adam.  like the ideas.  lots of work for too little gains for me.

don't know if a stroker crank would work with the same cylinder, without maybe needing a custom made piston and stroker plate or welding material onto the case.  possibly putting a longer rod with the stock stroke crank, with stroker plate under the cylinder might be another idea to get the piston up.

the only other 54mm piston option i have seen requires a 13mm wrist pin, and has a shorter pin height.  would not be a direct trade.

the only other physical measurements i have to compare the late oem jug to, would be an older 56mm big bore aftermarket jug.  the timings and port time-areas are slightly different than the stock jug. have not taken the time to do this yet.  will get around to it and post some results, to see if it is any better.

regards
-joe

385 piston fits. You just use the piston rod bearing for that piston. 288 piston fits also. You can also put a 056 piston with the factory dome in for more compression. Lots of options. The 385 piston requires a spacer under the cylinder.

thanks gatekeeper.  will root around for the piston info of those, and work them out.

regards
-joe

do to my poor typing skills...re-check the first post. did not affect the calculations only the write up.
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did the same bench racing 066 knockoff 56mm big bore kit.

similar gain was attempted, with worse results, is attached.
same sqush band cut and cylinder dropped in this one as well.

was thinking about doing one modification at a time, so folks could see what ech step actually does or doesn't do.

next try will be playing with the transfers, to reduce blow down on both the stock and knockoff jugs.

after that.....  will plug in some frankenstein pistons, stroker plates, etc.  if i can find dimensional info i need on them.

regards
-joe