as I am finishing up the install of wiring to support my generator, I have noticed that the ground leads from the fuse panel and shore cord to the chassis are no longer connected.. the screw holding the two clamps has broken off. somewhere on the inside of the chassis rail is the black water tank, as the drain pipe is right there and so is the release handle. can I use a self tapping screw, or will I need to drill a pilot hole?I have some short self tapping screws from when we did the metal roof on the shop. I think they are 1 inch.to drop the lower cover in this area I would have to remove the retainers for the gas pipe, and take off a section about 10 ft long!.

I asssssume the broken or missing screw is on the chassis frame rail?If yes, that frame rail might prove to be a little to thick for a self tapping screw to work well.Be sure whatever part of the frame you tap into to hold the ground wires that that frame member is not a separate piece of the frame which is riveted to the main frame rail. The ground wire must be connected directly to frame material: that is either the original large frame or a cross member that has been welded to the frame.I picked up the habit of tapping holes in a frame rail with SAE threads from a tap I only use SAE thread bolts when connecting anything to a frame. Put an external tooth lock washer under the ground terminals then use the SAE bolt on top of that. then gob atop the bolt and the wire terminals or use undercoating spray.Voice recognition works great if your vocabulary consists solely of "Hwang chow wah kee shan a day kong may fang toy". It sure as hell doesn't work worth ten cents with Inguish.

Yes a self tapping screw will work just fine. The frame is soft steel !!

MEXICOWANDERER wrote:I asssssume the broken or missing screw is on the chassis frame rail?If yes, that frame rail might prove to be a little to thick for a self tapping screw to work well.Be sure whatever part of the frame you tap into to hold the ground wires that that frame member is not a separate piece of the frame which is riveted to the main frame rail. The ground wire must be connected directly to frame material: that is either the original large frame or a cross member that has been welded to the frame.I picked up the habit of tapping holes in a frame rail with SAE threads from a tap I only use SAE thread bolts when connecting anything to a frame. Put an external tooth lock washer under the ground terminals then use the SAE bolt on top of that. then gob atop the bolt and the wire terminals or use undercoating spray.Voice recognition works great if your vocabulary consists solely of "Hwang chow wah kee shan a day kong may fang toy". It sure as hell doesn't work worth ten cents with Inguish.correct, the broken screw was into the main chassis rail. I have tap & die sets so can use one of those.. just wondering how much clearance I have on the other side of the chassis rail for drill and tap.

Jayco used ST screws with drill point tips. I've found them through the chassis of our Ford E450. Once IN, they break off at any attempt to back OUT. They must have spun them in with an air tool going about a million RPM. I'd drill and tap as noted above. Make a stop for the drill bit that allows it to just get through the chassis rail material.

I used the tip of the self tapping screw to make the starter hole, then my battery drill to open it up just enough, then tightened with ratchet wrench.Done

electrical chassis ground screw broken | Good Sam Community

Almot
Explorer III
Mar 24, 2015
Sorry, dumb me. No soy mechanico. One thing I know - if you run a tapping screw into the hole to make it threaded, no "bolt" will fit into these threads. Not well, anyway. I would imagine forcing some B-thread screw in there, but a 1/4x28 screw?
westend
Explorer
Mar 24, 2015
Almot wrote:
OK, with water tank I see now the need for depth control.

Back to the bolts - how do you drive a 1/4x28 bolt like This in a newly drilled hole in black steel that didn't have any screw in it before?
I can answer that one. You run a tap into the hole to make it threaded. The bolt and lock washer will then hold the ground lugs when turned into the tapped hole.

It was probably too obvious to Mex since he discussed the "three drill" sequence of establishing correct hole diameter.
Almot
Explorer III
Mar 24, 2015
OK, with water tank I see now the need for depth control.

Back to the bolts - how do you drive a 1/4x28 bolt like This in a newly drilled hole in black steel that didn't have any screw in it before?
MEXICOWANDERER
Explorer
Mar 23, 2015
"somewhere on the inside of the chassis rail is the black water tank, as the drain pipe is right there and so is the release handle."

Depth control seems to be an issue here...a plunging drill bit would be disastrous.

28 threads per inch in thinner material has a much better chance than 20 threads per inch to not strip threads. Self tapping screws have caused me far too much grief except for things like roofing and siding.

When things are very thin I use fine thread nutserts. I also tin the frame itself with lead-free solder and a pencil torch. Good technicians are lazy technicians who despise having to go back and re-do work even if it's ten years old :)
Almot
Explorer III
Mar 23, 2015
MEXICOWANDERER wrote:
A 1/4" X 28 SAE bolt will be fine. Take your time with the hole. Three drills in steps. Pilot, mid, then finish. Use a magic marker on the two remaining drills. Paint the depth using the pilot hole drill as a gauge.

Could you be less cryptic? :)

I think you are talking about bolt in a very thick metal where it doesn't come out on the other side, otherwise why worrying about proper depth? RV frames are - usually - not that thick.

Also, you keep on saying "bolt". But I don't see you mentioning any "nut" with this "bolt". Did you mean a bolt that cuts its own thread, like type B?
j-d
Explorer II
Mar 23, 2015
Sounds like you've got that ground restored with a new screw and probably a lock washer. Good on YOU! Bet things work better now, too.
MEXICOWANDERER
Explorer
Mar 23, 2015
A 1/4" X 28 SAE bolt will be fine. Take your time with the hole. Three drills in steps. Pilot, mid, then finish. Use a magic marker on the two remaining drills. Paint the depth using the pilot hole drill as a gauge.
sdetweil
Explorer
Mar 23, 2015
john&bet wrote:
Another thought would be to extend the wires to a spot where you don't have to worry about hitting anything on the back side. Then you can drill a hole and use a good bolt and nut.

yeh, can't get to the other side without a lot of work to drop the belly panel. On this side of the unit the belly panel is pinched between the chassis rail and the propane black pipe, which doesn't move.
wa8yxm
Explorer III
Mar 23, 2015
You can use any type of screw or bolt you like but... You mentioned the nearness of the black tank

MAKE 200% sure you do not puncture said tank!!!!!

(Check and DOUBLE check where the thing will go)
john_bet
Explorer II
Mar 23, 2015
Another thought would be to extend the wires to a spot where you don't have to worry about hitting anything on the back side. Then you can drill a hole and use a good bolt and nut.