Bolts and vibes and red loctite

Steel/Aluminum with Heat/Vibration = Loose studs every time.

The fix would be two fold. One install the correct size heli-coil. Next install studs into the heli-coils using Loctite 2620 (it will handle 640 degrees continuous Vs 450 for the common 266/272 versions)

Or if you don't want to do that. Cross drill the bolt heads, torque them down and install safety wire so they cannot loosen.

Can you drill & lock wire?

Serrated washers under them?

Make up a shim lock tab to go under the bolts & bend up to lock the heads?

if they'd fit, and you can get some, try nord-lock washers. they are magic under the right conditions.

I solved similar problem with chainsaw carburator by using stronger thread compound with higher working temperature. I'm not certain which one was the important feature, but it helped.

Another possible solution is Belleville washers under the screws. The screws may be stretching or the cylinder/plate is crushing under the thermal cycling.

Jon

Can you replace the bolts with custom length studs that can bottom out in the holes to get them tight enough not to back out?

MikeB

Can you cross-drill the heads of the screws, and then use safety wire to keep them from turning with the vibration? (It helps to have the special safety-wire pliers to twist each run from one screw to the next to do a neat and tight job.)

Enjoy, DoN.

Aw, I'm sorry. ;)

Drill the bolts for safety wire and wahr them suckers in there, Snag. The mounting angle evidently prevents the bolt head from securing properly against the carb body.

I'm surprised that you are having the screws come loose even though you are using Loctite. I have never had a bolt or screw loosen when using Loctite properly. Are you sure that the screw and tapped hole were totally free from any oil? The regular red Loctite will withstand

400 degrees F without loosening and I would be surprised if that area of the cylinder gets that hot. But it may indeed get that hot. I have used locking Heli-Coil inserts where Loctite was not appropriate. They will not let the screw come loose from vibration, in my experience. Eric

Eric, you're used to straight screw on flat surfaces. This is a case of a screw head contacting an angled surface. Ideally, they should have counterbored the carb flange at a flat angle to the head, but it sounds as if they didn't.

Use a "locking plate" - just a small sheet of sheet metal, drilled for the bolt, and a tab bent up to one or more flats on the bolt, and another tab or more bent back over the flange. IMOSSIBLE for them to vibrate loose - or the classic aircraft approach - safety wire through drilled bolt heads.

Nope , it's properly counterbored . Someone upthread I think nailed it , it's a combination of differential expansion and vibrations . I'm thinking I'll use some antiseize on the threads , then use green wicking loctite to lock the bolt head to the flange of the angle plate - these are like #8 or10 screws with a torx head , no room to drill and lockwire . This has been a pretty good saw , had it for several yeatrs . But it apparently wasn't intended for heavy usage like I've been using it . That's OK though , I'll get it repaired and hold it as a backup .

Perhaps the reason they didn't is that there is to much carb hanging over the flange. But why they didn't change the mold is left up to the imagination. Maybe they have a deal with some of the repair stations out there, sending them more business for a cut of the profits, the cads.

An excellent thought, IF there's enough room in the counterbore for it. Or perhaps he could slot the top of the flange, taking off some of the counterbore meat at the outside to allow a single tab?

I can guarantee it would only loosen once for me!!