hello, i purchased a used heli with ys f-91ac, does anyone have this particular engine? or know it very well, i have a few questions to ask you. thanks...

What is your questions , you can also ask the manufacture in the RCU engine manufacture section. http://rcuniverse.com/forumdisplay.php?s=&forumid=156

I have that engine, actually the ACH version which means air chamber heli version. What is your question?

Those engines had a sleeve and liner problem - would lose power after spool up and the RPM would just die out. Had to send it back to YS to get it fixed.

It is a very powerful engine - 4 stroke and lots of torque. Run it on Ys 20/20 fuel.

sharam, thanks for the reply, used heli ms60 i got it looks like the previous dropped the engine and crack the mounting housing for the air chamber, what it did was got a piece of aluminum and jb weld it on it looks cleanly done with no mounting holes, so obviously i have to modify to fit the air chamber, hate to buy another one or use a 61, but since being inside of the air chamber, wondering if the jb weld would desintegrad/melt in the throttle.

Sorry, but I don't know. I guess that the JB weld can become brittle after some time and break off. I would just start it and fly it and not worry about it. Perhaps you can get an experienced pilot to look over the machine before you fly it.

Repairing that engine may be more costly than getting a new 60 size anyway.

Good luck.