MS 440 - Stripped shroud thread repair options, please.

[Philip Wheelock]

While doing normal maintenance and checking screw tightness, I discovered that the threaded boss in the crankcase that anchors the clutch side of the shroud was stripped. See attached diagram of shroud, showing M5-16 screw location. Used blue Loctite to reinstall screw for now.

The attachment boss is not big; has anyone had success in installing a 5mm helicoil in this location to make a more permanent repair? Other options - rely on Loctite and don't take off the shroud if possible, even to clean cylinder fins, or leave the screw out and don't worry about it? Or find a master welder who can TIG weld, drill and tap a new thread in the magnesium?

Any success stories and suggestions appreciated.

 

[splitpost]

retap to a larger size

 

[Patrick62]

Not much to work with

The heli coil would be the best option, drillin and tapping for it is gonna be pretty tough.
I agree with the previous reply, but with a twist. Abandon staying metric. tap it out to the closest size of bolt, metric of sae. Use a button head and run it.

 

[w8ye]

I've probably put in a dozen 5mm X .7 Helicoils in Huskies. I never had any trouble with them. I bought the initial set at the NAPA store.

I also have used Timeserts in Huskies.

EDIT: It is 5MM x .8

 

[Philip Wheelock]

Thanks for the replies...

Thanks. I think I've got a couple of good options. The Helicoil catalog shows an M5x0.8; with a minimum boss dia. of 2X the nom. bolt size. The actual boss dia. is 10mm so this should work. I'd rather have a stainless steel insert than retap the magnesium if possible. No room for error, though.

I'm sure this isn't the only MS440 requiring this type of repair. Other designs probably minimize this issue, especially at the shroud attachments. My ms260pro has a simpler and fairly bulletproof shroud connection by comparison.

 

[CedarRock]

Why improve it when there are all these 'field engineers' that can make it better than new? All threaded holes in aluminum and magnesium should have HeliCoils in them. If the screw gets just a little loose the vibration strips the threads. That's why its a good practice to tighten all screws once in a while.

 

[Philip Wheelock]

...All threaded holes in aluminum and magnesium should have HeliCoils in them. If the screw gets just a little loose the vibration strips the threads. That's why its a good practice to tighten all screws once in a while.

Wisdom in that. I'm on the MS440 learning curve. The saw is new to me within the past month and has miles on it. It hasn't shown many quirks in terms of maintenance, but this is one of them.

 

[Fish]

Some of the older stihls came from the factory with helicoils, they are a good repair. Avoid all of the overdrilling, as it is kind of a one way street optionwise.

 

[nmurph]

I would not helicoil it at this point. It is not stripped bc of vibration but bc of over-tightening. You will remove more meat installing a helicoil than tapping it to an M6. Just retap it to the next size up and be done with it.

 

[Jacob J.]

I would not helicoil it at this point. It is not stripped bc of vibration but bc of over-tightening. You will remove more meat installing a helicoil than tapping it to an M6. Just retap it to the next size up and be done with it.

The problem with that is those brass inserts in the top cover keep you from using an oversize screw. So you'd have to knock the brass insert out and that's not desirable because the plastic itself won't hold up to being crushed by the screw. I've put many 5mm helicoils in those top cover mounts and they work just fine and hold for the life of the saw.

 

[nmurph]

I'm headed back to my hole for a while!!

 

[Philip Wheelock]

Thanks for the responses...

Asked the dealer about a helicoil repair for the thread and he said easy breezy and asked if it was the clutch side shroud attachment. Seems that's the one that tends to let go. Stainless steel thread = better than new. :smile: