Opening the Ryobi 790r trimmer

[motoman]

After 10 trouble free years trusty, powerful trimmer friend began to make a little noise and loose some RPM. Opened the darling and entered into an new adventure. I f anyone is interested I located some parts places online, got burned by one, defeated a "no tamper" screw and ruined a perfectly good clutch. Also I have an "A28/A31 Engines service manual" from MTD which I have found of relativelly little value, but full of torque specs. I will share pieces of this if any one needs. The engine in my 790r is A34 and I can not find any factory service data.

The problem I discovered after cutting off the clutch cover is .015" deflection of the drive shaft allowing the flywheel magnet to contact the ignition coil pickup. One spec I will use from the manual is the max of .015" clearance for the fly to coil. Maybe I can squeeze some more hours out of this loyal tool. Incidentally the manual has "Ryobi idc, and RYAN" printed on the cover. :dance1:

 

[Mini Motors]

Yeah, Ryan, IDC,and Ryobi are all the same. Exactly what specs are you looking for?

 

[motoman]

Mini, I was hoping to find a deflection spec for the shaft which would suggest whether to go in further and replace the outer (?sealed?) bearing. Yesterday I used the .015" specified in the older manual for the coil to flywheel clearance, but that caused the interference I heard. I opened the gap to .025" and it seems to have eliminated the contact (static test by hand). The shaft deflects .013" at midpoint with a dial indicator. Will the coil respond with spark at .025?"

Also I am still puzzled at the hold-down screw which secures the clutch cover to the shaft. I found that I could not use a T-20 torx despite "factory help" via phone. I cut and peeled off the cover which ruined a $29 part to find what looks like a "no tamper" screw head. The torx part had been drilled out and only a straight slot (screw driver) blade slot remained. But a screw driver with wide enough blade will not enter the square drive tube to loosen the cover. Throw away society ? Thanks :mur:

 

[Mini Motors]

I didn't have the option of Torx on mine. But I do have a large collection of screwdrivers, and got lucky. You might try grinding one down where it is at it's widest part, so that nothing is wider than blade and the shaft.

Sorry, but I don't have that spec. But it seems like you have it worked out.

 

[motoman]

Mini, I also have a lot of screwdrivers. The square dirive tube width corner-to-corner is not enough to let a wide enough blade down onto the screw head. Either the square tube must be squeezed into a parallelogram or some kind of trick spring-out screw driver head is required. Or you are supposed to throw the trimmer away. Thanks anyway. I'll let you know if I get running.