Topic: Stripped threads in float bowl screw holes? (CB550K1)

[ilikepinkcrayons]

Hey Folks, this is my first post, so I thought I'd post something useful to set the tone right.

I managed to strip one of the threaded holes for the float bowls on my 1975 CB550K. It was just the first few threads, but enough that I couldn't tighten the screw enough to fully seal the bowl. I bought a M4x0.7 Helicoil kit from McMaster, along with a box of M4x0.7-12mm Allen head screws (I don't care much for Phillips head, and I'd like to replace the Phillips screws as they come up).

The factory screws were 10mm, but they don't go all the way through the flange, so I figured I'd be fine with 12mm long. As it turns out, that extra 2mm saved my butt. I couldn't drill out the hole without pulling the carb bank, and I just didn't want to do that. The extra 2mm was enough to get good purchase on the threads, and I'm able to crank down on those plenty tight. Don't go any longer than 12mm, as there is very little clearance between the end of the screw and other parts of the carburetor.

One word of warning: Carefully chase each hole with a screw to get all the paint and crud out before installing the bowls. My carb is painted black (i've never seen this before, and I'm fairly certain that wasn't something the previous owner did), and the last 2mm of each hole was filled with thick, black, sticky paint. The first time i installed the screws, they felt like they were tight. The second I turned on the petcock, fuel started dripping out. The paint made it feel like the screw was fully tightened, but that just wasn't the case. After chasing the holes, there was a nice positive feeling when the screw bottoms out on the flange.

I chose blue dyed zinc plated M4x0.7 - 12mm Round Headed Hex Drive screws from McMaster (https://www.mcmaster.com/#91352A123). The blue is so factories can tell the difference between zinc plated and stainless screws, but a pack of 50 was $3 cheaper than a 100 pack of plain zinc. I chose zinc because it is galvanically compatible with aluminum (see MIL-STD-889 for lots of good information on corrosion), where as stainless is not. If I were to do it again, I would choose socket head cap screws because they are easier to get started by hand.

I also cut 1 inch off the long end of my 2.5mm Allen key, which makes installation and removal a breeze.

Lastly, i replaced all my gaskets (that was the original purpose for all of this!) with the shaped o-rings from 4into1, which were very easy to keep in place! No need to fool around with axle grease or tape.

[Bankerdanny]

They don't need to be super tight, the bowls really aren't pressurized and the o-ring handles the sealing. Overtightened screws is part of the reason so many 500/550 carb's have stripped out screw heads.

[drumstyx]

I always read this stuff where people take bowls off without removing the bank -- how in the heck?!

To me it just makes sense to pull the rack if I'm doing anything but balancing. It's more effort to get in there in such a tight space.

[carnivorous chicken]

Z-shaped screwdrivers or small sockets will do the trick, and for me it's easier to pull a bowl on a mounted rack (with stock airbox) if it's just to blow out a jet or something. And for this stuff Philips heads work since they're not tightened down that much (and I haven't found the z-shaped screwdriver or small socket in JIS!).

[Bankerdanny]

I always read this stuff where people take bowls off without removing the bank -- how in the heck?!

To me it just makes sense to pull the rack if I'm doing anything but balancing. It's more effort to get in there in such a tight space.

You need to have a small enough screwdriver and work your way from the outside in, removing the floats as you go to make room for your hands.

I have a small reversible 1/4 in driver that I use with long #2 screw bits.

[jonda500]

No 550's came out with the carbs painted black. Leaking when the petcock is turned on is either from the fuel needle&seat valves or the fuel tee o rings. If it's leaking past the fuel valves and the float bowl gasket isn't sealing, it will then leak out there and run down the side of the bowl rather than out the overflow tube (which is a little higher than the top of the float bowl).
John
For removing the bowls without pulling the rack, I prefer the original screws and a little stubby phillips head with a finger under it to maintain pressure and the other hand to turn it.
I also need to install a couple more helicoils next time I remove the carbs, so for now I have two allen head screws in them which buys me some more time before they fully strip!

[ilikepinkcrayons]

Yep, there are certainly some merits to Philips head screwdrivers, and I'm in no way trying to sell that idea. Allen's are just my preference I guess.

I always read this stuff where people take bowls off without removing the bank -- how in the heck?!

+1 on the Z screwdriver. I've got huge hands and had no issue. But once I used a cut down 2.5mm Allen key, I'm so glad I switched them out.

The whole issue stared because I had fuel slowly leaking from one of my overflow tubes. I went in there to clean the float valves, but I had a tough time getting those old, cracked, and swollen o-rings back in. I threaded one of the screws in just a few turns to try to get the bowl on there with enough space to work the o-rings back in place with a screw driver, but it stripped out, causing the rest of the issues.

After allowing the o-ring to dry and shrink back down, it just didn't want to tighten without continuing to strip. Oh well, that's what you get for not doing it right the first time.

Moral of the story: if your float bowl o-rings are old or of unknown age, get some new ones and don't be a hack while putting them back in!